Device for relieving pain and / or delivering sedation

Abstract

This invention relates to a device (1) for relieving pain and / or delivering sedation, such as through the administration of a sedative, analgesic or anaesthetic substance in a breathable form The device (1) can be configured to deliver a predetermined volume the substance in a single delivery event, the predetermined volume having an upper limit calculated based on a parameters of a single inhalation event. The predetermined volume may be determined and / or delivered based on a monitored breathing characteristic of a user. One or more exhalation filters (50), providing a total filter capacity matching a predetermined volume of substance in a reservoir (322), may be provided.

Description

[0001] DEVICE FOR RELIEVING PAIN AND / OR DELIVERING SEDATION

[0002] This invention relates to a device for relieving pain and / or delivering sedation. In particular, this invention relates to a device for relieving pain and / or delivering sedation through the administration of a sedative, analgesic or anaesthetic.

[0003] The use of sedation, rather than general anaesthesia, is beneficial for patients, clinicians and healthcare organisations. It has been shown to result in a lower incidence of postoperative cognitive dysfunction, shorter hospital stays, and a reduced environmental impact (Anaesthesia and Perioperative Medicine Getting It Right First Time Programme National Specialty Report (2021)). However, sedation remains underutilised as an alternative to general anaesthesia, possibly due to patients’ and clinicians’ concerns about safety and intraoperative awareness and recall (Chatman N, Sutherland JR, van derZwan R, Abraham N. A survey of patient understanding and expectations of sedation / anaesthesia for colonoscopy. Anaesth Intensive).

[0004] Sedation also has utility outside the hospital and surgical setting. GP surgeries often perform minor procedures such as mole removal and IUD insertion which cause pain and / or discomfort for the patient, but for which there are currently limited options for effective pain relief. Outside the clinical setting, acute situations such as sports injuries or injuries resulting from accidents can lead to severe pain, for which significant pain relief may not be available until the patient has been removed to a clinical setting. In scenarios such as these, a reliable, portable, means of delivering safe, effective analgesia or sedation in situ would be hugely beneficial. Furthermore, many medical and surgical procedures currently conducted under general anaesthetic could be carried out in an outpatient setting given a suitable sedation approach. This would provide significant operational efficiency improvement and better utilise operating theatre resource.

[0005] Effective sedation is a balancing act between awareness and anaesthesia. If too little sedation is given, patients may continue to experience discomfort and be able to recall intraoperative events. On the other hand, if too much sedation is given patients may become fully anaesthetised and require airway, respiratory or cardiovascular support. Sedation can be delivered with intravenous or inhalational drugs and the drug doses can be controlled by clinicians or by the patients themselves, with clinician-delivered intravenous sedation being the most common.

[0006] However, there are benefits associated with patient-controlled sedation / analgesia, including minimisation of drug doses and improved patient satisfaction (Sheahan CG, Mathews DM. Monitoring and delivery of sedation. Br J Anaesth. Dec 2014;113 Suppl 2:ii37-47. doi:10. 1093 / bja / aeu378). Likewise, inhalational drugs offer advantages over intravenous delivery, including less inter-individual dose response variability and faster recovery (Sahinovic MM, Struys M, Absalom AR. Clinical Pharmacokinetics and Pharmacodynamics of Propofol. Clin Pharmacokinet. Dec 2018;57(12):1539-1558. doi:10. 1007 / s40262-018-0672-3 ; Ibrahim AE, Ghoneim MM, Kharasch ED, et al. Speed of recovery and side-effect profile of sevoflurane sedation compared with midazolam. Anesthesiology. Jan 2001 ;94(1):87-94. doi:10. 1097 / 00000542-200101000-00018). However, potentially due to concerns about safe dosages, suitable administration apparatus and an increased risk of disinhibition-excitation, patient-controlled and inhalational delivery have not been widely adopted.

[0007] It is possible to provide control of a medicament delivery rate for inhalation, for example based on breathing rate of a user. For example, a control system could adjust the volumetric flow of a volatile liquid onto or into an evaporation or wicking medium to ensure that a suitable amount of medicament is available for evaporation and subsequent inhalation by a user. Control of this type helps to maintain a consistent inhaled dose per breath as / when a breathing rate increases or decreases, by increasing or decreasing the delivery rate to compensate. Some control systems also provide a form of user intervention, where an operator is able to increase a flow rate to increase the dose if required, and / or to provide an additional bolus of medicament on demand.

[0008] Control systems as described above can, however, result in an undesirable buildup of excess medicament in / on the medium. User intervention, if not properly managed, can easily lead to a delivery of surplus medicament which will quickly build up on / in the medium. For this reason, highly skilled operators are typically required to ensure safe and proper use of a system. A similar undesirable buildup of medicament can also easily occur in the event of any lag in an automated control system adjusting flow when a breathing rate drops from a high rate during use.

[0009] The first of these problems can be mitigated by effectively limiting the maximum possible delivery rate, but the second scenario could still easily result in a sudden build-up of medicament.

[0010] Any such build-up is problematic for the next inhalation, and potentially also for subsequent inhalations. In extreme cases, the medium becomes completely saturated leading to pooling and possible inhalation of the liquid medicament rather than the vapour as intended. Even where this is avoided, for example by ensuring that the medium has a sufficiently large capacity to retain significant excess medicament, there remains a risk of overdose or at least of uncontrolled and unknown dose sizes being inhaled.

[0011] These problems are particularly pronounced in a closed system, such as a breathing mask, where there is little or no possibility of free evaporation of the surplus medicament before the next breath is taken.

[0012] It would clearly be beneficial if a system were provided that mitigated or overcame some or all of the above problems.

[0013] According to the present invention there is provided a device for relieving pain and / or delivering sedation, the device comprising a patient delivery interface with an evaporation medium for receiving a volatile substance for inhalation, a delivery system for delivering the volatile substance to the evaporation medium and a control system for controlling delivery of the volatile substance by the delivery system, wherein the control system is configured to deliver a predetermined volume of volatile substance in a single delivery event, the predetermined volume having an upper limit calculated as that which can be completely vaporised from the evaporation medium and inhaled by a user in a single inhalation event.

[0014] It should be understood that the predetermined volume will not typically be a fixed / unchanging volume. The volume is predetermined in that it is known and set before each delivery event, but in many embodiments the size of the volume will vary during use of the device depending on user input and other parameters that are sensed / monitored and processed by an algorithm within the control system.

[0015] A single delivery event can be a single ‘shot’ of substance delivered by the device, or could comprise a short sequence of shots as may be suitable or necessary to make up the predetermined volume for a single inhalation event.

[0016] The upper limit may be a single value to be used for all patients, for example calculated using average patient sample data. Alternatively, the upper limit may be adjustable to account for variation between patients, for example calculated using a targeted subset of data to provide a more bespoke limit for a particular patient or group of patients having a certain physical or physiological characteristic. The limit value could be selectable from a set or list of calculated values of this type.

[0017] Any increase in the total capacity of the medium tends to increase the overall size of the device or system, and can also create increased flow resistance, resulting in a poorer user experience and potentially less effective delivery of a substance. By providing a system where the medium is only ever required to receive a single dose, to be completely cleared during the next inhalation, any need for surplus capacity in the medium can be minimised, and the size of a pad, gauze or similar in the device can be minimised. The volatile substance may be a volatile anaesthetic agent, such as sevoflurane, or some other sedative, analgesic, anaesthetic, or other medicament for use in sedation and / or the treatment or management of pain. It remains possible, and potentially desirable, to provide some excess capacity in the pad to avoid saturation and pooling of medicament in rare instances where some small build-up of medicament does occur. However, instances of this in the proposed system are likely to be rare and minor, so any surplus capacity can be minimal.

[0018] Avoiding delivery of volumes of a substance that are too large to evaporate and be inhaled in a single breath helps to avoid any undesirable build-up of a substance, which significantly reduces the risk of uncontrolled or excessive doses being delivered during use. This allows a patient to have direct use / control of the device without the intervention of a skilled professional. The user may therefore be a patient undergoing a treatment or procedure. It is expected that the device will typically operate to deliver medicament at volumes significantly below the upper limit, so even in the event of a weaker than expected inhalation event there can be confidence that the complete volume delivered will be vaporised and inhaled in a single breath. It is envisaged that a user of the device will then be able to demand larger doses of medicament to manage their pain as required. With an ‘on demand’ system of this type, it can be expected that breathing will be strong when a user is alert and in sufficient pain to demand higher delivery volumes up to and including the upper limit.

[0019] The evaporation medium may comprise a pad of absorbent material, for example a cotton material, and may comprise multiple layers.

[0020] The evaporation medium may be positioned in a gas flow path within the patient delivery interface, such that inhaled air passes through the evaporation medium.

[0021] The evaporation medium may comprise perforations introduced to reduce flow resistance through the evaporation medium. Where a layered construction is used perforations may be introduced into only some of the layers, for example, the outermost layers may be unperforated. The delivery system may comprise a transmission tube for carrying the volatile substance from a substance reservoir to the evaporation medium. An end of the tube may open directly onto the evaporation medium to ensure that the delivered volumes of volatile substance reach the evaporation medium and do not impinge on and / or collect in other parts of the patient delivery interface.

[0022] The patient delivery interface may comprise a cover for the evaporation medium, for example in the form of a cup, for location upstream of the evaporation medium, with an inlet for inhaled air or gas. The cover may additionally comprise an aperture for receiving an end of the transmission tube, for example with a friction fit.

[0023] In the context of this description, references to upstream or downstream are made with reference to an inhalation.

[0024] The patient delivery interface may comprise a number of retaining features to prevent removal of the transmission tube from the aperture. The retaining features may take the form of small protrusions or pegs, for example on the cover / cup, and / or mounting bosses or similar for other components, around which the transmission tube can wind in a tortuous path. The inherent frictional resistance that this provides can be sufficient to prevent removal of the transmission tube from the aperture during use of the device, while still allowing the use of a frictional fit to simplify assembly and / or removal of the tube for cleaning or replacement when the patient delivery interface is dismantled.

[0025] The patient delivery interface may comprise a delivery chamber, in which the evaporation medium is housed. The cover or cup may be provided within and / or may form a part of the delivery chamber. The retaining features may comprise mounting bosses or similar for a removable outer cover or shell of the delivery chamber.

[0026] The patient delivery interface may comprise a one-way valve positioned downstream of the evaporation medium. The one-way valve may permit inhalation through or past the evaporation medium, but prevent exhalation passing through or past the evaporation medium, and may thus be considered an inhalation valve.

[0027] The patient delivery interface may comprise a respiration sensor for detecting inhalation and / or exhalation of a user. The respiration sensor may comprise a pressure sensor and / or a temperature sensor located within the patient delivery interface.

[0028] A pressure sensor can provide a relatively direct determination of the presence and / or rate of breathing based on fluctuations of pressure readings within a patient delivery interface such as a facemask, for example by taking a long term average of the pressure in the patient interface and comparing this to short term pressure measurements. Upper and lower bounds can be established around the long term average. An inhalation can then be detected when the short term measurement crosses from above the upper bound to below the lower bound. An exhalation can be detected when the short term measurement crosses from below the lower bound to above the upper bound. An indication of no breathing or removal of the mask can be provided if the short term measurement remains within the upper and lower bounds for an extended period of time. If no inhale or exhale is detected but the short term measurement is not within these bounds, then the long term average can be deemed incorrect and corrected.

[0029] Tidal volume can also be estimated by integrating the pressure within the interface over the duration of an inhalation. This provides a value which corresponds to the volume of the breath. The tidal volume can be calculated using an experimentally determined conversion factor. A rolling average, for example a four breath rolling average, of this tidal estimation can be taken to help smooth out fluctuations in the measurements.

[0030] Evaporation of a volatile substance causes a temperature drop, and the resulting cooling or air passing over or through an evaporation medium can be detected, and this can be used to determine when the volatile substance is being inhaled. Exhaled air will have been heated by the patient’s respiratory system, and will provide a notably higher temperature reading. The fluctuations between these higher and lower temperature readings provides a reliable indication of a user’s breathing. Detection of a higher temperature for a prolonged period of time would provide a strong indication that breathing has ceased or that the patient delivery interface has been removed.

[0031] Sensing or monitoring of respiration helps to coordinate or manage the timing of delivery of a substance to the evaporation medium. In particular, the device can monitor the respiration of a wearer and deliver the predetermined volume of substance during an exhalation so that it is available at the start of the next inhalation. Delivery at a proper time in the cycle helps to minimise loss of the substance, for example to evaporation when no inhalation is taking place, and also helps to ensure proper delivery to a patient. If the substance is delivered too late in the breathing cycle, then the inhalation may only carry it to the upper part of the respiratory tract.

[0032] As noted above, timing delivery to coincide with an exhalation is beneficial generally when the substance being delivered is a volatile substance that is required to evaporate for inhalation. As such, the invention further provides a device for delivering a volatile substance for inhalation (for example for relieving pain and / or delivering sedation), the device comprising a patient delivery interface with an evaporation medium for receiving a volatile substance, a delivery system for delivering the volatile substance to the evaporation medium, a respiration sensor for detecting inhalation and exhalation of a user, and a control system for controlling delivery of the volatile substance by the delivery system, wherein the control system is configured to deliver the volatile substance to the evaporation medium during an exhalation detected by the respiration sensor.

[0033] The single inhalation event used in control of the delivery can be a standardised inhalation based on historic data. However, in some embodiments, sensing respiration may extend to monitoring the inhalation strength and / or tidal volume, or instantaneous breathing rate, and feedback control could then be used to adjust the parameters of a single inhalation event based on sensed / monitored data. This could allow ongoing adjustment of the upper limit of the predetermined delivery volume during use.

[0034] For example, it is possible that the device could adjust individual delivery volumes based on a monitored breathing rate, to ensure that a desired volume over time (e.g. a per minute quantity) is maintained during use even if breathing rate fluctuates. If the system is provided with a desired per minute quantity for delivery, or similar, then the time since a previous detected breath can be used to set the volume for delivery with the next breath to maintain the per minute quantity over time. It will be understood that the adjusted individual doses can still be less than an upper threshold defined by the volume that can be cleared in a single inhalation event. In practice, a monitored reduction in breathing rate is likely to result in only a small increase of the delivered volume, well within the upper threshold.

[0035] However, failing to adjust delivery based on a slower breathing rate could, over time, result in significantly less than an optimum / intended volume of substance being provided to a patient.

[0036] Controlled delivery of a predetermined volume over time is advantageous in various circumstances. A further aspect of the present invention therefore provides a device for relieving pain and / or delivering sedation, the device comprising a patient delivery interface, a respiration sensor for detecting the breathing of a patient, a delivery system for delivering a delivery volume of pain- relieving and / or sedative substance to the patient delivery interface, and a control system for controlling the delivery system, wherein the control system is configured to monitor a breathing rate detected by the respiration sensor and to adjust the delivery volume based on changes in monitored breathing rate to maintain a desired delivery rate over time.

[0037] The desired delivery rate or per minute volume may be governed by a treatment algorithm and may vary during use, for example based on patient inputs or interaction with the device. The volume to be delivered can be calculated by sampling the treatment algorithm over a period between breaths (e.g. every 100ms) and summing those samples to get the total volume in ml. As already noted, it can be beneficial to coordinate delivery with an exhalation rather than an inhalation. When an exhale is detected, the output of the treatment algorithm can be summed for the period since the previous exhale. The summed volume can also be capped to ensure no unsafe levels are provided in a single breath / delivery and / or to ensure the volume can be cleared by a single inhalation event. This calculated delivery volume can then be provided, for example onto a gauze or other evaporation medium, during the exhale period to ensure it is available at the start of the following inhalation.

[0038] According to the design and control of the device, the evaporation medium should be free of volatile substance by the time a user is exhaling. A temperature sensor can, however, also potentially help to determine whether any volatile substance remains on the evaporation medium after an inhalation and adjust control of the device accordingly. For example, a temperature sensor located close to the evaporation medium could check for a general decrease in average temperature or a slower than expected temperature rise during / following inhalation, suggesting that excess substance has not evaporated as intended. This would be particularly effective if the temperature sensor is isolated from warmer exhaled air, for example by a one-way valve or similar.

[0039] The respiration sensor may additionally, or alternatively, allow the device to determine whether a patient’s breathing has been detected, and where breathing has not been detected to prevent or cease delivery of the pain-relieving and / or sedative substance to the patient. Where the pain-relieving and / or sedative substance is currently being delivered to the delivery interface, an output signal can be generated to cease delivery to the delivery interface. Where delivery of the pain-relieving and / or sedative substance to the delivery interface is yet to commence, an output signal can be generated to prevent commencing delivery to the delivery interface. The patient delivery interface may comprise a mask, for example a facemask that is positioned around the mouth and / or nose of a user, and may be secured in place with straps or similar fixings.

[0040] Delivery of the predetermined volume of volatile substance can be achieved through pulsed operation of a pump. Alterations of the predetermined volume can then be achieved by modifying the duration or number of pulses while a pump runs at a substantially constant rate, with a number of pulses making up the single delivery event. Alternatively, or additionally, the speed of the pump could be adjusted to alter the predetermined volume.

[0041] When delivering medicaments, particularly sedatives or similar, in gaseous or vapour form there is a risk that the environment around a patient / user could become contaminated due to leaks, either as the substance is vaporised for inhalation or where residual amounts remain in exhaled air. Effective sealing of a mask or other patient delivery interface to a user is therefore important, as is appropriate filtering of the exhaled air during use.

[0042] In scenarios where a medicament is delivered over a relatively long period, to manage pain during a surgical procedure for example, the total medicament volume can be large, and thus a large filter capacity is needed to ensure a safe working environment for clinicians throughout the procedure. The safest way to achieve this is to provide a very large filter module, separate from the patient interface, and direct exhaled air from the patient delivery interface through tubing to the separate filter module. The size and capacity of the filter in such arrangements is typically several times larger than would be required for the total volume of medicament being delivered by the system, meaning that there is no risk whatsoever of any unfiltered gas or vapour leaving the system. However, this large size makes the filters, and the system overall, cumbersome, so that the system cannot be made portable, as would often be desirable. The additional tubing between a patient interface and a filter can also cause snag or trip hazards in an operating theatre or similar environment. In developing the device of the present invention, it was surprisingly found that a far more compact filter arrangement could be provided by carefully selecting the capacity of the filter element(s) to match the total volume of a substance deliverable to a user.

[0043] A further aspect of the present invention therefore provides a device for relieving pain and / or delivering sedation, the device comprising a patient delivery interface for delivering a vaporised or gaseous substance to a cavity for inhalation by a user, a reservoir for containing a predetermined volume of gaseous or volatile substance, and one or more exhalation filters in an outlet flow path from the cavity, wherein the total filter capacity of the one or more filters is equal to the predetermined volume of the substance in the reservoir.

[0044] Many inhalational agents, such as sevoflurane, are not metabolised by the body during use, or are metabolised only to a very small extent. Therefore, the proportion of a substance that is inhaled during use effectively has no bearing on the necessary filtering capacity.

[0045] Providing a predetermined volume of substance in the reservoir, for example by setting the maximum fill volume or otherwise controlling the filling of the reservoir, enables the necessary filtering capacity to be selected with confidence.

[0046] The exhalation filter may be an activated carbon filter.

[0047] The exhalation filter may comprise a filter cartridge with a housing for activated carbon having a flow path therethrough. The filter cartridge may comprise a hydrophobic barrier at one or both ends of the flow path.

[0048] Activated carbon filters, while generally efficient and lightweight, are typically unsuitable for use in moist or damp environments. The activated carbon has a tendency to absorb moisture in preference to other substances, resulting in dramatically reduced capacity or even saturation of the filter medium if there is a high degree of moisture in the gas being filtered. As a result, other filter media (such as PTFE, for example) are typically preferred for use in moist environments.

[0049] Any reduction in filter capacity should ideally be avoided, because this helps to minimise the overall size of any filter or filter cartridge. In addition, tuning or selecting filter capacity to match the total volume of substance deliverable by the device requires that the performance of the filter throughout its life can be predicted with a high degree of certainty. The amount of moisture present in exhaled air will differ between subjects and is extremely difficult to predict in advance, meaning that any reliable prediction of filter performance is also difficult to predict with any certainty.

[0050] Providing a filter cartridge with one or more hydrophobic barriers, for example hydrophobic polypropylene scrims, addresses this problem by keeping the moisture from exhaled air away from the activated carbon within the filter cartridge. The performance and total capacity of the filter cartridge therefore becomes far easier to predict.

[0051] The filter cartridge(s) may comprise a one-way valve to prevent inhaled air or other gas passing through the filter medium and potentially reducing the life of the filter.

[0052] The design principles ensure that the size and weight of the filter(s) or filter cartridge(s) can be minimised. The filter(s) may therefore be mounted on a face mask or similar patient delivery interface.

[0053] The filter cartridge(s) may be removably secured to the patient delivery interface, for example with a pop-fit.

[0054] With the filter capacity being determined by the maximum volume of substance deliverable to a patient, the life of a mask or other patient delivery interface can quite conceivably be greater than the life of the filter(s). It is therefore beneficial if the filter cartridge(s) can be replaced when exhausted. Even where the patient delivery interface is intended to be a single use product, it is important that the cartridge(s) can be easily separated / removed for recycling. The removable nature of the filter cartridge(s) also allows a smaller or larger size or capacity cartridge to be selected from a range in the event that the total amount of substance to be delivered by the device is smaller or larger than usual.

[0055] One or more filter cartridges may be provided, and where two or more removable filter cartridges are used there may be scope to substitute at least one of the removable filter cartridges with an alternative component. For example, for short term use a filter cartridge could be replaced by a substance reservoir and pumping / delivery system to provide an entirely self-contained system in a mask or similar.

[0056] The filter cartridge(s) may be removable from the patient delivery interface from one side only. For example, the filter cartridge(s) may be removable only from the inside of a mask body / shell.

[0057] Providing one or more removable filter cartridges is beneficial for at least the reasons mentioned above, but does risk a situation where the filtering of vapours or gasses could be compromised during use, either inadvertently or as a result of tampering or other misuse. This risk is mitigated by ensuring that a filter cartridge can only be removed from a mask body from the rear / inside, because a filter cartridge cannot then be removed from the mask while it is being worn. A pop-fit connection can thus be used to provide a simple releasable connection without compromising clinician safety. Alternative releasable connections, for example bayonet or screw fittings, could alternatively be used.

[0058] The invention as described herein concerns a device for relieving pain and / or delivering sedation. Pain may be relieved, and / or sedation provided, through the administration of medicaments of a variety of types, but in particular through the administration of sedatives, analgesics and / or anaesthetics. These medicaments may be administered alone or in combination to achieve the desired physical effect. In the context of the invention, ‘sedative’ is intended to refer to a medicament which induces a state of calm or sleep, ‘analgesic’ to a medicament which induces pain relief without the loss of consciousness and without total loss of feeling or movement, and ‘anaesthetic’ to a medicament which induces the loss of physical sensation with or without loss of consciousness.

[0059] The device of the invention may relieve pain and / or deliver sedation through the administration of one or more analgesics, anaesthetics and / or sedatives. Suitable pain-relieving or sedative substances are known in the art and may include sevoflurane, methoxyflurane, remifentanil, fentanyl, remimazolam, propofol and / or isoflurane. The pain-relieving and / or sedative substance used in the present invention may particularly be a volatile fluid, and may be selected from the list comprising, for example, sevoflurane, methoxyflurane, and isoflurane. The volatile pain-relieving and / or sedative substance may be inhaled by the patient.

[0060] Different analgesics, anaesthetics and sedatives take varying lengths of time to take effect in the body after administration begins (onset) and to cease acting on the body once administration finishes (offset). This depends at least in part on the way in which the medication is metabolised by the body and / or eliminated, the method of administration, and / or the way in the medication is redistributed within the body, eg whether it circulates in the bloodstream or migrates to fat and muscle tissues, reducing the clinical effect.

[0061] The medication for use in the present invention may particularly be a pain relieving and / or sedative substance having rapid onset and rapid offset, that is, that it begins acting in the body quickly after administration begins, and only remains clinically active for a short time after administration ceases. This enables rapid, responsive changes in the delivery of the pain-relieving and / or sedative substance, with changes in dosage being rapidly felt by the patient.

[0062] Typically, the pain-relieving and / or sedative substance used in the present invention has rapid offset, and exhibits complete reversal of clinical effect within 15 minutes, or within 10 minutes, or within 7 minutes, or within 5 minutes of the administration of a clinically effective dose. In particular, the medication may be an anaesthetic, for example sevoflurane. While commonly used as an anaesthetic, low doses of sevoflurane have been found to be an effective analgesic and sedative, with a typical offset time of five minutes or less, leading to quick patient recovery. Some memory loss of events occurring whilst under the influence of sevoflurane has also been reported by patients, which may be beneficial for patients in severe pain or undergoing a potentially traumatic procedure.

[0063] Even accounting for the realisation and approach taken above to filter design and implementation, a significant filter capacity is still required to ensure safe use of the device. This can present problems when attempting to mount one or more filters on a mask or similar patient delivery interface, as is desirable.

[0064] In order to maintain a reliable seal for different face sizes and / or shapes, it is desirable to maintain a degree of flexibility in the interface. This, however, becomes more difficult the more components need to be supported. In a delivery device as previously described there may be several components, for example for filtering exhaled gas, for providing display information and / or for providing and / or controlling delivery of a substance. These components can be relatively large and inflexible, and can significantly reduce the overall flexibility of a patient delivery interface.

[0065] A further aspect of the present invention therefore provides a patient delivery interface comprising a body with two or more distinct mounting sections for receiving components of the patient delivery interface, wherein the two or more mounting sections are separated on the body such that the components are mounted independently of each other.

[0066] The two or more mounting sections may comprise an aperture for receiving a filter cartridge.

[0067] Ensuring separate / independent mounting of components on the body helps to ensure they do not prevent the body from flexing as required to ensure a reliable seal. The components will be decoupled from each other, so that the inherent flexibility of the interface, resulting from the material making up the body, is not overly compromised.

[0068] A generally flexible body is preferable to ensure that the abovementioned flexibility is maintained. However, flexible materials may not provide adequate support for relatively large and / or heavy components that need to be mounted to the body. For example, the mask described herein comprises a central region housing components providing the delivery and vaporisation and various sensors and feedback elements, and a pair of filter cartridges. A degree of structural rigidity may be required to support these components on the mask body, but this risks compromising the seal provided by the mask during use.

[0069] The body may therefore provide a region of greater flexibility between the two or more mounting sections, provided for example by a thinning of material and / or by a softer / more flexible material in the relevant area(s). This may provide a living hinge between relatively rigid mounting sections. The living hinge may be substantially vertically oriented so that the flexibility is maintained in a lateral direction. Where the shape of the mask is relatively wide, there is a particular need to retain lateral flexibility in the mask to ensure that the integrity of a seal with the face of a wearer is maintained.

[0070] The body and / or mounting sections may be formed of polypropylene. The or each region of greater flexibility may be provided by a thinner section of polypropylene or may be formed from a material with a lower Shore hardness value, for example a Thermoplastic elastomer.

[0071] The mounting sections may be formed on or secured to a mask shell formed of a relatively more flexible material, for example in a two-step injection moulding process, so that the mask shell provides the region of greater flexibility. Alternatively, the mask shell may have regions formed of a more flexible material. A sealing member may be formed around the mask body, the sealing member arranged to engage the face of a wearer in use. The sealing member may be formed of a material of greater flexibility relative to the mask body. The mask body may be formed of a material of greater rigidity relative to the sealing member. The sealing member may be formed of an elastomeric material, e.g. a thermoplastic elastomer. The sealing member may be joined, fixed or connected to the mask body, for example by moulding / overmoulding during manufacture. The mask body and the sealing member may be formed in a multi-step, for example a two-step, injection moulding process. The sealing member may be fixed or connected to the mask body at a peripheral edge of the mask body.

[0072] The peripheral edge of the mask body may comprise at least one discontinuity. The at least one discontinuity may comprise a break, gap or interruption in what is otherwise a substantially smooth, continuous or consistent peripheral edge of the body portion.

[0073] The sealing member may comprise at least one projection or extension of material. The positioning of the at least one projection may correspond to the positioning of the at least one discontinuity, such that the at least one projection extends into the at least one discontinuity, i.e. upon fixing or connecting of the sealing member to the mask body. The at least one projection may therefore be fixed to (and within) the at least one discontinuity.

[0074] The at least one discontinuity may extend from the peripheral edge of the mask body into the material of the mask body, i.e. to create a recess or indent in the peripheral edge of the mask body. The at least one discontinuity may extend through the thickness of the mask body. The at least one discontinuity may extend substantially perpendicularly to the peripheral edge of the mask body.

[0075] The patient delivery interface may have a median plane that spans through the interface from front to back along a longitudinal axis of the interface which runs through the centre of the interface between upper and lower regions of the interface, the median plane corresponding to the median plane of a wearer when in use. The median plane of the interface may divide the interface into right-hand and left-hand sides. The at least one discontinuity may extend in a direction that is substantially aligned with the median plane. Preferably, the patient delivery interface is symmetrical about a median plane. Hence, preferably, the interface comprises an equal number of discontinuities in the body portion, and thus an equal number of corresponding projections, positioned either side of the median plane of the interface. Similarly, preferably, the discontinuities, and thus the corresponding projections, are positioned symmetrically about the median plane. Similarly, the interface may comprise an equal number of discontinuities positioned on upper and lower parts of the interface

[0076] The at least one discontinuity may be a cut-out portion, or a cut-away portion, in the mask body, which extends from the peripheral edge of the mask body. The at least one discontinuity may form at least two additional edges in the mask body, and those edges may be separated by the at least one projection, i.e. upon fixing or connecting of the sealing member to the mask body. The at least one discontinuity may comprise a generally ‘V’ shaped notch tapering away from the peripheral edge of the mask body.

[0077] The presence of at least one projection in a sealing member of a relatively more flexible material that projects into a discontinuity in the relatively more rigid mask body provides a fault line about which the interface has increased flexibility. This arrangement may therefore additionally or alternatively improve the lateral flexibility of the interface, by providing and / or enhancing one or more living hinges between the relatively rigid mounting sections. The at least one discontinuity may extend in a direction that is substantially aligned with the one or more living hinge. Given the advantages provided by these features in improving the flexibility in the interface, thereby maintaining a reliable seal for different face sizes and / or shapes, and in particular smaller face sizes, this arrangement may also be beneficial for patient delivery interfaces regardless of the need to support mounted components.

[0078] Hence, according to a further aspect of the invention, there is provided a patient delivery interface comprising a body portion and a sealing member, the sealing member being joined to the body portion about a peripheral edge of the body portion, the peripheral edge of the body portion having at least one discontinuity, and the sealing member having at least one projection that extends into the at least one discontinuity.

[0079] The at least one discontinuity may be a discontinuity relative to an otherwise smooth, continuous or consistent peripheral edge of the body portion.

[0080] A skilled reader will understand that the aspects of the invention described above may combine to provide further benefits. Optional features described in relation to one aspect of the invention can also be combined with other aspects, as appropriate.

[0081] Practicable embodiments of the invention are described in further detail below with reference to the accompanying drawings, of which:

[0082] Figure 1 shows a perspective view of a pain management system;

[0083] Figure 2 shows a perspective view of a facemask from the system of Figure 1 ;

[0084] Figure 3 shows a further perspective view of the facemask of Figure 2;

[0085] Figure 4 shows an exploded view of the facemask of Figures 2 and 3;

[0086] Figures 5a to 5c show part of an assembly sequence for the facemask of Figures 2 and 3;

[0087] Figure 6 is a part perspective view of the partly assembled facemask of Figures 2 and 3;

[0088] Figure 7 is a cross-sectional view thorough a delivery chamber of the facemask of Figures 2 and 3; Figure 8 is perspective view of an air / gas inlet component from the facemask of Figures 2 and 3;

[0089] Figure 9 is perspective view from the top of the partially assembled facemask of Figures 2 and 3;

[0090] Figure 10 is a cross-sectional view of the facemask of Figures 2 and 3;

[0091] Figure 11 shows an exploded view of a filter cartridge from the facemask of Figures 2 and 3;

[0092] Figure 12 shows a perspective view of a handset from the system of Figure 1 ;

[0093] Figures 13a and 13b show front and rear exploded views of the handset of Figure 12;

[0094] Figure 14 shows a horizontal cross-sectional view of the handset of Figure 8, viewed from above;

[0095] Figures 15a and 15b show front and rear perspective views of a spring used in the handset of Figure 8;

[0096] Figure 16 shows a rear perspective view of the handset of Figure 8, with the hinged lid in an open position;

[0097] Figures 17a and 17b show an expandable reservoir and medicament bottle for use in conjunction with the pain management system of the invention;

[0098] Figures 18a, 18b and 18c show the connection between the expandable reservoir and medicament bottle of Figures 17a and 17b, Figures 18b and 18c showing a cross-sectional view of the expandable reservoir and medicament bottle during (18c) and after (18b) connection;

[0099] Figure 19 shows the barrel and plunger which form the component parts of an expandable reservoir for use in conjunction with the pain management system of the invention;

[0100] Figure 20 shows an underside of the handset of Figure 12;

[0101] Figure 21 shows a perspective view of a transmission tube from the system of Figure 1 ;

[0102] Figure 22 shows an exemplary simulation of medicament delivery in use;

[0103] Figure 23 shows an exemplary simulation of medicament delivery in use;

[0104] Figures 24a-24d show a first notification sequence indicated by the mask of Figures 2 and 3 during operation of the pain management system of Figure 1 ;

[0105] Figures 25a-25d show a second notification sequence indicated by the mask of Figures 2 and 3 during operation of the pain management system of Figure 1 ;

[0106] Figures 26a-26d show a third notification sequence indicated by the mask of Figures 2 and 3 during operation of the pain management system of Figure 1 ;

[0107] Figure 1 generally shows a patient-controlled pain relief and / or sedation device 1 . Briefly, the device 1 comprises a facemask 10, to be placed around the nose and mouth of a user, and a handset 301 connected to the facemask 10 by a transmission tube 307. As will be described in detail later, the handset 301 comprises a reservoir of sevoflurane, or other medicament, for use as an analgesic and / or a sedative, and a user input to trigger delivery of the medicament to the facemask 10 via the transmission tube 307.

[0108] The device 1 provides user-controlled delivery of a medicament for inhalation to manage pain. Numerous design features are provided to address, mitigate, or overcome the concerns and risks associated both with patient-controlled sedation and with the use of inhalational delivery.

[0109] The mask 10 is shown in isolation in Figures 2 and 3, and comprises a shell or body 100 and a compliant / compressible seal 25, formed of elastomeric material, around the periphery of the body 100. The outer shape of the body 100 and design of the seal 25 are generally similar to those described in the applicant’s earlier patent application WO 2022 / 122974. As well as a chin cup 26 and nose engaging portion 27, the seal 25 comprises extended side portions 28 that, in use, extend laterally across the cheeks of the wearer. The seal 25 thus provides a large area to engage with the face, including over the softer skin of the cheeks, and thus improves the quality and reliability of the sealing provided. It has been found that extending the seal 25 laterally across the softer tissue of the cheeks allows an effective seal to be provided with a lower than usual degree of flexibility in the sealing member, at least in these regions. The minimal movement of the cheeks / cheekbones during talking or other jaw movement also helps to ensure that the seal is not compromised.

[0110] As can be seen in Figure 2, the mask body 100 additionally comprises ‘V’ shaped cut-out portions, into which projections 101 a, 101 b of the seal 25 extend, on an upper and lower part of the mask respectively. Corresponding cut-out portions and projections 101 a, 101 b of the seal 25 are provided on the other side of the chin cup 26 and the nose engaging portion 27 (the far side as shown). The projections 101 a,101 b of softer and / or more flexible seal material provide additional flexibility to the mask 10 in a lateral direction, allowing the mask 10 to expand or contract from a neutral state and accommodate larger or smaller face sizes. Although only shown in Figure 2, it should be understood that the cut-out portions and projections 101 a,101 b could be present in the mask as shown in all subsequent figures.

[0111] The seal 25 shown in Figures 2 and 3 is also more curved at the ends of the side portions 28 than that shown in WO 2022 / 122974. This curvature at both sides of the seal 25 has been found to further improve the sealing performance across a wider range of face sizes, making a single mask size more universal.

[0112] Elasticated straps 20 are provided to secure the facemask 10 to a wearer during use. The ends of the elasticated straps 20 are received in tabs 102 extending from the sides of the mask body 100. The tabs 102 provide a frictional engagement with the elasticated straps 20 so that the tension of the elasticated straps 20 can be adjusted in the conventional way.

[0113] The relatively large mask shell / body 100 supports and stabilises the compliant seal 25 where needed and also provides sufficient space for a centrally positioned delivery chamber 200 and for a pair of large capacity filter cartridges 50, one on either side of the delivery chamber 200. The depth and overall size of the chamber 200 and filter cartridges 50 can best be seen in the perspective view of Figure 3.

[0114] The delivery chamber 200 comprises a chamber housing 202 secured to the mask body 100. A generally tubular air / gas inlet 204 extends forwardly and downward from a lower side of the chamber 200. A pair of diametrically opposed cut-outs 206 are provided at the free end of the inlet 204, allowing connection to a standard T-piece if / when supplementary oxygen needs to be supplied to the mask 10 during use. Behind the inlet 204 can be seen a gas monitoring connector, e.g. an end tidal CO2 monitor connector 104, which is fluidly connected to the interior of the mask 10 through a monitoring port in the lower part of the mask body 100. It should be understood that the connector 104 could also monitor administered drug concentration, and allow peak concentration and end tidal concentration to be measured. An outwardly facing display 500 is provided on a front face of the chamber 200 to provide information about operation of the device 1 to an external observer such as a clinician.

[0115] Figure 4 shows an exploded view of the various components that make up the mask 10.

[0116] The exploded view shows that the mask body 100 can be considered to define separate regions. A central region 120 provides the rear part of the delivery chamber 200, and includes a locating boss 208 for the chamber housing 202. A filter cartridge aperture 150 is provided on either side of the central region 120.

[0117] Each filter cartridge 50 is independently insertable into and removable from one of the filter apertures 150 the mask body 100 from the rear or cavity side. This avoids potential tampering or inadvertent disconnection of the filter cartridges 50 from outside the mask 10 during use. A peripheral lip 52 and groove 54 are provided around a rear side of each of the filter cartridges 50. The filter cartridges 50 are received in the mask body 100 with a ‘pop’ fit, with the periphery of each filter aperture 150 engaging with the peripheral groove 54 of a respective cartridge 50. The peripheral lip 52 then abuts an inner surface of the mask body 100 to prevent removal of the cartridges 50 from the front / outside of the mask 10.

[0118] Each filter cartridge 50 comprises an aperture 60 through which a cavity within the cartridge 50 can be supplied with activated carbon granules.

[0119] A circular wall 210 extends outwardly from the central region 120 of the mask body 100, and surrounds an opening through the mask body 100. A vertical bar 212 spans the opening and provides support for a locator pin 214 which extends along the central axis defined by the circular wall 210. A flexible inhalation valve member 216 is received on the locator pin 214, followed by a gauze / pad 218 from which a delivered dose of sevoflurane evaporates and is inhaled in use. Figure 4 also shows that the generally tubular air / gas inlet 204 is a separate component from the mask body 100. A generally circular cup 220 is provided at an upper end of the tubular inlet, and is sized to fit over the end of the circular wall 210 to enclose the inhalation valve member 216 and pad 218. A medicament inlet port 222 is provided through the cup 220 so that sevoflurane can be delivered onto the pad 218 on demand.

[0120] Finally, Figure 4 shows a PCB 224 to be mounted in front of the other components within the chamber housing 202. The PCB in the illustrated example comprises a ring 502 of front facing LEDs which form a part of the display 500 visible from the front of the housing 202. Several housing mounting bosses 226 extend forward of the circular wall 210 to support and secure the PCB 224 and chamber housing 202 to the mask body via screw holes 228 provided in the chamber housing 202.

[0121] For various reasons, it is important that the mask can provide a reliable seal with a patients’ face. As already described, the overall shape and size of the mask body 100 and seal 25 has been found to provide a good level of sealing, but a further consideration is that a single mask should ideally be suitable for a range of different face sizes and / or shapes. It is typically easier to accommodate a range of face sizes and shapes when a mask has a high degree of inherent flexibility, and is thus able to deform and conform to a particular face size and shape. In the present invention, the mask body 100 is required to support several relatively large components / modules, and the required strength and stability of construction is generally incompatible with a desire for a flexible mask body.

[0122] The design of the described mask body 100 in three different sections helps to maintain a reasonable degree of flex in the mask body 100 while still providing suitable support for the delivery chamber 200 and the filter cartridges 50. Separately mounting the filter cartridges 50 and the components making up the delivery chamber 200 ensures that these components do not prevent the mask body 100 from flexing as they would if all mounted together. For example, the mask body 100 can still flex between the component mountings, and this particularly helps to maintain a good degree of lateral flexibility, so that the extended side portions 28 of the seal 25 can maintain contact with the cheeks of a wearer. The projections 101 a, 101 b of the seal 25 of Figure 2 generally align with the gaps between the delivery chamber 200 and the filter cartridges 50 to help provide lines of flexibility, or living hinges, within the mask. The living hinges could be further enhanced by thinning the material of the mask body 100 or introducing regions of softer or more flexible material in these regions.

[0123] Figures 5a, 5b and 5c show the assembly of the central components within the delivery chamber 200.

[0124] Figure 5a shows the inhalation valve member 216 installed on the locator pin 214 within the circular wall 210. The vertical bar 212 is shown faintly in Figure 5a, but is positioned behind the inhalation valve member 216 as shown. A retaining ring 230 extends inwardly from the circular wall 210 to hold the inhalation valve member 216 in place against the vertical bar. Evenly spaced radial fingers 232 extend inwardly from the retaining ring 230 across the outer face of the inhalation valve member 216. It will be understood that the retaining ring 230 and radial fingers 232 prevent deformation of the inhalation valve member 216 towards the outside of the mask 10, while the single vertical bar 212 still allows deformation and / or deflection of the inhalation valve member 216 to the interior of the mask on inhalation. A one-way valve is therefore provided to allow flow on inhalation but to prevent flow on exhalation.

[0125] A hollow tubular boss 234 is centrally provided above the one-way valve, and provides a passageway into the interior of the mask body.

[0126] Figure 5b shows the pad 218 also assembled on the locator pin 214. The pad 218 is arranged outside and overlying the inhalation valve member 216 retaining ring 230 and radial fingers 232. The pad 218 thus further helps to prevent outward deflection or deformation of the inhalation valve member 216. The retaining ring 230 and radial fingers 232 maintain a small space behind the pad 218 so that the inhalation valve member 216 does not directly abut a surface of the pad and potentially inhibit the evaporation of a medicament. The spacing also helps to avoid the risk of the inhalation valve member 216 sticking to the wet pad 218 once medicament is delivered.

[0127] The installation of the air / gas inlet 204 is shown in Figure 5c. The cup 220 closes the opening provided by the circular wall 210, leaving the medicament inlet port 222 open to receive an end of the transmission tube 307 for delivering sevoflurane or another medicament to the pad 218. A pair of pegs 225 is also provided on the front / outer surface of the cup 220 to help guide and retain the transmission tube 307, as will be described further below.

[0128] It will be understood from Figures 5a-5c that air and / or any supplemental oxygen or other gas can enter only through the air / gas inlet 204 as indicated by arrow 236. Any gas flow must, therefore, pass through the pad 218 and then through the oneway valve to enter the cavity of the mask 10. Directing inhaled air / gas flow through the pad 218 helps to drive evaporation of the medicament, and is more efficient than simply passing a flow over a wicking surface or reservoir.

[0129] The gauze / pad 218 in the illustrated example is provided as a disc of material 28mm in diameter and 1 .3mm thick. The pad 218 has a multi-layer construction, specifically comprising five layers of perforated cotton, forming a 'core’ of the pad 218, faced with unperforated cotton on both sides. The perforations in adjacent perforated layers are offset so that the holes in the core do not line up. Testing has shown that it is possible to deliver a 3-4% concentration of sevoflurane from such a pad 218 by delivering 2ml per minute onto a pad in a breathing simulator at 20 breaths per minute and 500ml tidal flow. The evaporation rate has found to be such that a single dose delivered to the pad 218 at the end of an exhalation can fully evaporate during the following inhalation.

[0130] The system and its control architecture are designed to avoid a buildup of sevoflurane within the mask, and specifically to try and ensure that each delivered dose from the handset 301 evaporates from the pad 218 and is inhaled in a single inhalation event. Nonetheless, the capacity of the pad 218 can be selected so that a small amount of additional medicament delivered to the pad 218 can be retained if desired, for example if the demanded flow is greater than the evaporation rate for a short time. Retaining a small amount of additional medicament on / in the pad helps to avoid immediate leaking or pooling of liquid, which could result in inhalation or ingestion in excessive or unsafe concentrations.

[0131] Cotton provides a good level of fluid retention, strong wicking properties for distributing the medicament across the pad 218, and a relatively low resistance to breathing. However, other similar materials could be used with minimal changes to the design. A foam pad or foam core faced with cotton or similar could, for example, be used.

[0132] Figure 6 shows a perspective view of part of the mask 10, from below. The transmission tube 307 is shown entering the mask 10 from below to help minimise the risk of the tube 307 tangling or snagging on other equipment or interfering with movements of a patient or a clinician during use. The tube 307 enters the delivery chamber 200 behind the air / gas inlet 204 and then coils between the pegs 225 and then between the two upper housing mounting bosses 226 and the hollow tubular boss 234 before being received in the medicament inlet port 222. For simplicity, the end of the transmission tube 307 is, in use, received in the medicament inlet port 222 with a friction fit. The tortuous path taken by the transmission tube 307, as shown in Figure 6, provides some additional support and frictional resistance to help avoid inadvertent removal or disconnection from the medicament inlet port 222 during use, for example if a user pulls on the tube 307 or handset 301 .

[0133] The interior of the delivery chamber 200 of the fully assembled mask can be seen in the cross-sectional view of Figure 7. The cross-section shows the arrangement of the inhalation valve member 216 and pad 218, with a space in between, and additionally shows several sections of the transmission tube 307 as it winds through the delivery chamber 200 and is received in the medicament inlet port 222 for delivering a dose of sevoflurane onto the pad 218 on demand. A grate 238 within the air / gas inlet 204 is also shown. A pressure monitoring port 134, at the interior end of the hollow tubular boss 234, can also be seen in cross section. The hollow tubular boss 234 provides a fluid passageway from the pressure monitoring port 134 to a pressure sensor 240 mounted on the rear side of the PCB 224, allowing real-time pressure measurements to be taken from within the mask 10, which in turn enables monitoring of the patient’s breathing in use. It would also be possible to use a temperature sensor within the delivery chamber 200, adjacent the pad 218, to monitor breathing, based on the temperature changes resulting from evaporation of the medicament from the pad 218 during use, and this may also assist in determining whether medicament is building up on the pad so that delivery rates can be adjusted.

[0134] Above the pressure sensor 240, also on the rear of the PCB 224, is a rear facing LED 242b for providing stimuli and / or feedback to a wearer of the mask. The visible LED 242b is a central LED of a group of three laterally spaced LEDs, collectively referred to as 242, provided on the rear of the PCB 224. A light guide may also be provided by the material making up an upper part of the mask body 100, for example the mounting boss 208, to direct the light from one or more of the LEDs 242 towards the eyes of the wearer.

[0135] Figure 8 shows a rear view of the air / gas inlet 204 and cup 220. Various features can be seen on the rear of the cup 220, most notably the outlet of the medicament inlet port 222 and a central hole 244 for receiving the end of the locator pin 214. As can be seen from Figure 7, these features contact the outermost face of the pad 218 so that the medicament inlet port 222 opens directly onto the pad 218. This helps to avoid medicament dripping from the port 222 and pooling within the delivery chamber 200 rather than being absorbed by the pad 218. However, it can also be seen from Figure 8 (and from Figure 10 below) that a space / void is provided within the cup 220 to help ensure airflow across the whole diameter of the pad 218. A cutout 207, for receiving the transmission tube 307 as it enters the chamber 200, is also shown in Figure 8. Figure 9 shows a perspective view from the top of the assembled mask 10 with the housing cover 202 removed. The view shows part of the internal cavity 110 defined by the mask body. It can also be seen that the gas monitoring connector 104 extends into this cavity 110 to monitor readings from within the mask body 100. The inhalation valve member 216 can also be seen, positioned centrally between the two filter cartridges 50. The three spaced LEDs 242a, 242b and 242c (collectively 242) can also be seen on the rear surface of the PCB 224. It will be understood that the left and right LEDs 242a, 242c are best placed to be seen by a wearer during use. However, all three LEDs 242 may be used to send alerts and / or stimuli to a wearer, with the use of light guides allowing even quite directional light from the central LED 242b to be directed towards the eyes of the user. Alternative embodiments may, therefore, use only two laterally spaced LEDs, or even just a single LED. Using more than one LED allows alternate flashing of separate LEDs or some other ‘pattern flashing’ of a group of LEDs. These more unusual light patterns can be more effective in attracting the attention of a wearer.

[0136] A complete cross section through the mask 10 is shown in Figure 10. Unlike in Figure 7, the cross-section of Figure 10 is taken off-centre, and shows that an open cavity / void 246 in front of the pad 218 is provided by the cup 220, as discussed above in relation to Figure 8. The majority of a front surface of the pad 218 is open to this cavity 246 to maximise the area that inhaled air / gas can reach to reduce flow resistance and aid with vaporisation of a medicament, particularly at high flow rates. There is a challenging balance for the pad 218 to strike between providing suitable fluid retention / evaporation characteristics and minimising flow resistance, so it is important to ensure as much of the pad as possible remains open to flow.

[0137] The cross-section of Figure 10 also passes through one of the radial fingers 232 that maintains a spacing between the pad 218 and inhalation valve member 216 as previously described, and through the rightmost rear facing LED 242c. The rear surface of one of the filter cartridges 50 can also be seen in Figure 10, with the peripheral lip 52 abutting an internal wall 106 of the mask body 100. An opening 56 in the rear of the filter cartridge 50 provides a one-way exhalation valve. The mask 10 therefore provides a flow path whereby all inhaled air / gas passes through the pad 218 and the one-way inhalation valve, and all exhaled air and other substances from within the cavity 1 10 exit the mask 10 through the filter cartridges 50.

[0138] One factor potentially preventing or limiting the wider adoption of inhalational analgesics and / or sedatives is the risk of contamination of the atmosphere in an operating theatre. Gases or vapours from volatile liquids that are either not inhaled or remain in a patients exhaled air can, if not controlled, quickly build up in a confined space and be detrimental to clinicians or others in the space. Any breathing mask used in the administration of such substances should, therefore, mitigate these risks by providing a robust / reliable seal (as described above) and through effective / efficient filtration of excess and / or exhaled substances.

[0139] The large filter cartridges 50 provided on the mask body help to ensure that the filtering of exhaled gases and / or vapours is sufficient to avoid a build-up. The construction of each filter cartridge 50 is shown in the exploded view of Figure 1 1 .

[0140] The filter cartridges 50 comprise a front casing 58, which defines a cavity to receive the activated carbon, and a rear casing 64 to close the cavity. The rear casing 64 comprises the opening 56 which, together with an exhalation valve member 66, forms the one-way exhalation valve. A first hydrophobic scrim 68 is provided on a scrim support 70 located between the front casing 58 and the exhalation valve member 66. A second hydrophobic scrim 74 is provided inside the front casing across the exhaust openings 76 in the front of the front casing 58. The first and second hydrophobic scrims 74,76 in the illustrated example are formed from polypropylene.

[0141] Activated carbon is a preferred filter medium in many applications due to its low weight and efficient performance. However, it is typically avoided in moist environments because the adsorbent properties of the material tend to absorb moisture first, leading to reduced capacity or even saturation of the filter. The first and second hydrophobic scrims 74,76 prevent moisture ingress into the cavity of the filter cartridge, ensuring that the filtering remains effective and thus allowing the use of activated carbon to filter moist exhaled air. The scrim support 70 additionally helps to secure the exhalation valve member 66 in place within the filter cartridge 50.

[0142] When assembled, the components provide a filter cartridge 50 with a contained internal volume to receive the activated carbon. A cover 62 is provided to close the aperture 60, which is in a wall of the front casing 58 that is obscured from view in Figure 11 . this means that the cartridge 50 is potentially refillable / rechargeable. As an alternative, the filter cartridge may be made completely disposable. Various sizes of cartridge, either re-fillable or disposable, may be provided to account for different volumes of sevoflurane stored in the handset.

[0143] The rear casing 64 comprises the peripheral lip 52, around the rear of the filter cartridge 50, that engages with an internal wall 106 of the mask body 100 as the filter cartridges 50 are inserted from the cavity 110 side. The rear casing 64 also defines the base of the groove 54 that provides the ‘pop’ fit with the filter aperture 150.

[0144] The capacity or fill level of the filter cartridges 50 may be defined by or selected based on the volume of medicament contained in the handset 301 prior to use. That is, the capacity of the filter cartridges 50 may be specifically selected so that they provide sufficient filtering for the entire volume of sevoflurane available for use during a particular procedure. As will be explained below, the volume of medicament held in handset is set prior to use of the device, and cannot then be adjusted, i.e. the reservoir cannot be refilled once the device is in use. A particular filter volume can thus be selected based on the intended use of the device with confidence that the filter capacity will be sufficient. The handset 301 of the device 1 is shown in Figure 12. The handset 301 comprises a housing having a wrist portion 302 and an end portion 303. The end portion 303 is rounded, with a bulbous shape which fits comfortably within the user’s hand. The wrist portion 302 extends outwardly from the end portion 303, the wrist and end portions 302,303 being joined together by a concave curved surface on an upper side of the housing, and by a substantially planar surface on the underside of the housing.

[0145] The construction and overall structure of the handset can be seen in Figures 13a and 13b. The underside of the housing comprises a cradle 409 which forms the underside of both the wrist and end portions 302, 303, and the lower part of the front face of the end portion 303. The cradle 409 comprises mounting bosses 413 which extend upwardly from the cradle, and the lower part of the front face comprises a substantially semi-ovular cut-out 415 with a recessed wall 416 positioned behind. The cradle 409 further comprises loops 314, 315 and slots for the receipt of the straps 305, 306, as described in further detail in relation to Figure 20.

[0146] The cradle 409 receives and engages with a central section 410, the central section 410 comprising the side walls 412 of the handset between which are retained the battery and reservoir compartments 309, 310, guide member 407, horizontal bar 417, activation switch 406 and peristaltic pump 334. The transmission tube 307 is fluidly connected to the peristaltic pump 334 and extends from the rear of the handset 301 , and, as described above, is connected to the delivery chamber 200 of the facemask 10. These features are discussed in further detail below.

[0147] The upper side of the housing is formed of two components: a domed lid 411 and a hinged lid 308. The domed lid 411 forms the upper side, and the upper part of the front face, of the end portion 303. Similarly to the cradle, the upper part of the front face of the domed lid 411 comprises a substantially semi-ovular cut-out 418 with a recessed wall 419 positioned behind. The domed lid 411 engages with the mounting bosses 413 which support and secure the domed lid 411 to the cradle 409, covering the peristaltic pump 334, guide member 407, horizontal bar 417 and activation switch 406 within the central section 410, but leaving the battery and reservoir compartments 409, 410 exposed.

[0148] The hinged lid 308, which forms the upper surface of the wrist portion 302, is hingedly attached to the domed lid 411 and, when closed, covers the battery and reservoir compartments 309, 310 as described in further detail in relation to Figure 16 below.

[0149] The handset 301 further comprises a button 304 and a spring 403, which together form the user input.

[0150] The button 304 is located on a front face of the end portion 303 of the handset 301 . It is retained between the semi-ovular cut-outs 415, 418 of the cradle 409 and domed lid 411 . The button 304 is substantially oval in shape, and extends over a significant portion of the front face of the rounded end portion 303, providing a large surface area for the user to press. The button 304 has a convex form, and its shape follows the contours of the bulbous end portion 303 of the handset 301 . In use, the user’s palm lies across and over the domed lid 411 such that their fingers rest on the button 304 on the front face of the end portion 303, while their wrist rests on the hinged lid 308, which forms the upper surface of the wrist portion 302.

[0151] The button 304 is a floating button which can be pressed from almost any angle, increasing usability for patients with restricted movement. The button 304 comprises a domed surface 401 with an integrally formed central column 402, the central column 402 extending rearwardly from the concave face of the domed surface 401 . A rearwardly extending wall 423 extends outwardly from the periphery of the concave face of the domed surface 401 , the rearwardly extending wall 423 further comprising four tabs 424 spaced at regular intervals about its outer circumference. In use, the convex face of the domed surface 401 is pressed by the user to activate the device. A spring 403, comprising an arcuate resilient strip 404, is mounted within the handset and positioned behind the concave face of the domed surface 401 , such that the end of the central column 402 distal to the domed surface 401 contacts the resilient strip 404, and the spring 403 is orientated such that the resilient strip 404 is biased towards the central column 402.

[0152] The spring 403 is shown in isolation in Figures 15a and 15b, and comprises an arcuate resilient strip 404 retained within a rectangular mount 408. Within the central section 410 of the handset a horizontal bar 417 extends between the sidewalls 412, with a guide member 407 depending from a central point on the horizontal bar 417 and extending outwardly towards the front of the handset 301 . When installed in the handset, the rectangular mount 408 of the spring rests against the front of the recessed walls 416,419, and is supported by features on a front face of the lower recessed wall 416 and by notches provided in side walls at either end of the lower recessed wall 416 to locate the spring 403 in the correct position. A hollow post 405 extends rearwardly from the centre of the resilient strip 403 and receives the guide member 407, the hollow post being movable longitudinally along the guide member 407. The end of the hollow post 405 distal to the resilient strip 404 is positioned adjacent to or in contact with an activation switch 406, such that longitudinal movement of the hollow post 405 along the guide member 407 causes the activation switch 406 to be pressed.

[0153] The spring 403 is mounted within the handset behind the button 304, such that the end of the central column 402 distal to the domed surface 401 contacts the spring. When pressure is applied to the domed surface 401 of the button 304 by the user, pushing it towards the spring 403 and pushing the rearwardly extending wall 423 into abutment with the recessed walls 416, 419 on the cradle 409 and domed lid 411 , the central column 402 exerts a force on the spring, pushing against the bias of the resilient strip 404. This force causes the resilient strip 404 to deform and consequently move the post 405 longitudinally along the guide member 407, pressing the activation switch 406 and thereby registering a user input. When the pressure on the button 304 is released the resilient strip 404 returns to its original arcuate shape, pushing the central column 402 and domed surface 401 back into their original positions such that the tabs 424 engage with the internal periphery of the semi ovular cut-outs on the dome and cradle 415, 418, retaining the button 304 within the handset. This moves the post 405 out of engagement with and hence releases the activation switch 406. Engagement of the tabs 424 with the internal periphery of the semi ovular cut-outs 415, 418 also creates pivot points about the edge of the button 304 such that, if pressure is only applied to one edge of the button 304 by the user, the button 304 will pivot about the tab or tabs 424 adjacent to an opposing edge of the button. This causes the centre of the button and hence the central column 402 to move towards the spring, ensuring that pressure is still applied to the resilient strip 404 by the central column 402 regardless of the angle or position from which the button is pressed.

[0154] Referring back to Figure 12, the handset 301 further comprises straps 305, 306 for attaching the handset 301 to the user’s arm and / or wrist. The straps 305, 306 extend from a first side of the handset to a second side of the handset, forming a loop for retaining the patient’s arm and / or wrist. The straps 305, 306 are adjustable, and can be adjusted to fit the patient’s arm and prevent undue movement of the handset relative to the patient’s arm, even if the patient’s arm moves or falls. The attachment of the straps 305, 306 to the handset 301 is described in further detail in relation to Figure 20.

[0155] The wrist portion 302 of the handset comprises an openable housing, as shown in Figure 16. The openable housing comprises a hinged lid 308 which opens to reveal a battery compartment 309 and reservoir compartment 310 (batteries and reservoir not shown). The reservoir compartment 310 comprises a channel 328 for receiving an expandable reservoir filled with a pain-relieving and / or sedative substance, and an aperture 329 shaped to receive a connecting portion of the reservoir. The aperture 329 is broadly circular, and further comprises a laterally extending cut-out 311 shaped to receive a flange 330 which extends outwardly from the reservoir, as will be described in more detail later. Once inserted through the aperture 329, the reservoir 322 is engaged by a reservoir receiver (not shown), the reservoir receiver being connected to the inlet of the tube 335 of a peristaltic pump 334 housed within the end portion 303 as shown in Figure 13a. A peristaltic pump 334 has a fixed displacement and so, when in operation, the pump draws fixed aliquots of medication from the reservoir 322, transferring it to the transmission tube 307.

[0156] Two buttons 312, 313 are also located within the housing, proximate to the hinge of the hinged lid 308. The two buttons 312, 313 may be used to adjust parameters for correct operation of the device, for example to adjust the dosage and / or to set the dose profile of the medicament. Also visible are loops 314, 315, integrally formed with the body of the handset 301 , which provide retention means for the straps 305,306 (not shown in Figure 16). The transmission tube 307 is clearly shown extending from the rear of the handset 301 .

[0157] Figure 17a shows an expandable reservoir 322 for use with the handset 301 of the invention.

[0158] The expandable reservoir 322 comprises a barrel 325 having a proximal end and a distal end, and a plunger 326, the plunger 326 being inserted into the barrel 325 at the distal end and being slidable longitudinally within the barrel 325. The proximal end of the barrel 325 comprises a connection formation 323 to enable the syringe to be connected to a proprietary adaptor 324 on a medicament bottle 340, as shown in Figure 17b. The connection formation 323 additionally forms the connecting portion which forms a fluid connection between the reservoir and the handset 301 , as described above.

[0159] The connection formation 323 enables a secure connection between the proximal end of the barrel 325 and a proprietary adaptor 324 on the medicament bottle 340, while permitting the transfer of a pain-relieving and / or sedative substance between the bottle 340 and reservoir 322. The connection formation 323 comprises two concentric rings 331 , 332 which extend outwardly from the proximal end of the barrel 325. The outer ring 331 extends outwardly from the periphery of the proximal end of the barrel 325 and forms a friction fit with the proprietary adaptor 324, creating a fluid-tight seal. The wall of the outer ring 331 comprises two cutout sections 420 to engage with corresponding formations 421 on the proprietary adaptor 324. The inner ring 332 is shorter than the outer ring 331 and comprises cut-out sections 333, such that at least an upper section of the inner ring 332 is broken into three segments. In use, the inner ring 332 presses on the spigot 422 of the adaptor 324, breaking the seal and allowing medicament to flow out of the bottle 340. The cut-out sections 333 provide spaces through which the medicament can flow to the centre of the connection formation and through a channel 425 which extends through the inner ring 332 and into the barrel 325.

[0160] The reservoir 322 is filled with a predetermined amount of a pain-relieving and / or sedative substance prior to insertion in the handset 301 . Prior to filling the reservoir 322, the plunger 326 is depressed. Once the reservoir 322 is attached to the proprietary adaptor 324 on the medicament bottle 340, the reservoir 322 and bottle340 are inverted and the plunger 326 drawn out (as shown in Figure 18a, and in cross-section in Figures 18b and 18c), thus creating a vacuum which sucks the medicament into the reservoir 322. The outer ring prevents loss of medicament to the atmosphere during this process.

[0161] The connection formation 323 prevents the reservoir from being connected to any vessel which does not carry the proprietary connector 324, thus ensuring that the syringe can only be filled with the medicament for which the device and its safety mechanisms have been designed.

[0162] The plunger 326 comprises a narrowed section forming a defined point of weakness 327, which can be seen in Figure 19. The point of weakness 327 is positioned such that, when the plunger 326 has been drawn out to fill the barrel 325 with the correct dosage of medicament, the point of weakness 327 is located at or just above the distal end of the barrel 325. Once the expandable reservoir 322 has been filled with medicament, the plunger 326 is snapped off at the point of weakness 327. Snapping off a portion of the plunger 326 in this manner prevents the reservoir from being refilled and reused. The requirement to snap off the plunger 326 is enforced as the reservoir compartment 310 in the handset 301 is sized such that a full reservoir 322 will only fit into the syringe compartment 310 when the plunger 326 has been snapped off. The barrel 325 further comprises a flange 330 protruding from a side close to or at its proximal end. The flange 330 extends outwardly from, and extends a short distance longitudinally along, the outer ring 331 of the connection formation 323, as shown in Figure 19. When the full reservoir 322 is inserted into the reservoir compartment 310 on the handset 301 , the connection formation 323 and flange 330 on the barrel 325 pass through the aperture 329 and associated laterally extending cut-out 311 . When correctly inserted, the flange 330 engages with a micro-switch (not shown) within the aperture 329. Actuation of the micro-switch confirms that the reservoir 322 has been correctly loaded into the handset 301 , and activates the device 1 .

[0163] The underside of the handset 301 is shown in Figure 20. The underside of the handset 301 comprises a window 316 in a position corresponding to the position of the reservoir compartment 310 in the interior of the handset 301 , such that the reservoir 322 is visible through the window 316. This enables the level of medicament remaining within the reservoir 322 to be monitored while the device is in use.

[0164] Also visible are two loops 314, 315 and two slots 317, 318 for attachment of the straps 305, 306, the straps being used to secure the handset 301 to the user’s wrist and hand and prevent dislodgement or dropping during use. Strap 305 passes from the interior of the handset 301 , where it is secured, and through the slot 318 to the exterior of the handset. The strap 305 then passes over the upper side of the handset and through the corresponding loop 315. The tension of the strap is adjusted by altering the amount of the strap 305 which is pulled through the loop 315. The free end of the strap 305 (that which has passed through the loop 315) may comprise a buckle, toggle, cleat or other adjustable locking means (not shown) to prevent the strap from sliding back through the loop 315 and permit future adjustment. The second strap 306 is attached to the second slot 317 and loop 314 in the same manner.

[0165] The transmission tube 307 (shown in further detail in Figure 21 ) extends from the rear of the handset 301 and, as described above, is connected to the delivery chamber 200 of the facemask 10, operationally connecting the handset 301 and facemask 10.

[0166] The transmission tube 307 comprises a tube having a silicone body, and having first and second lumens 319, 320 extending longitudinally through the tube. The first lumen 319 has a diameter of approximately 2.5mm and carries electrical wires 321 , electronically connecting the mask 10 and the handset 301 . The second lumen 320 has a narrower diameter than the first lumen 319, of approximately 1 mm, and carries the medicament from the handset 301 to the mask 10, where it is evaporated for inhalation by the user as previously described.

[0167] The transmission tube 307 enters the rear of the handset 301 . Inside the handset 301 , the second lumen 320 of the tube is connected to the tube of the peristaltic pump 334 at its outlet. As previously described, the reservoir 322 is fluidly connected to the tube of the peristaltic pump at its inlet 335. Thus, when the pump 334 is in operation, predetermined aliquots of medication are drawn from the expandable reservoir 322, through the peristaltic pump 334, and pass into the second lumen 320 of the transmission tube 307 to be carried to the facemask 10.

[0168] In use, delivery of the medicament from the handset 310 to the facemask 10 is controlled by a control algorithm that is carried out by a controller. The control algorithm consists of a number of components that in combination determine an output signal that controls the delivery rate of the medicament. Although described individually below, each of the algorithm components runs simultaneously, each influencing the output signal that controls the delivery rate of the medicament.

[0169] Breath detection

[0170] A breath detection component of the algorithm is initiated upon turning on of the device 1 . At regular intervals of approximately 10 milliseconds, the controller requests an input signal from the pressure sensor 240 that is indicative of a realtime pressure within the mask 10. A long term average of the pressure within the mask 10 is also recorded, and on top of this there is some level of hysteresis whereby an upper and lower bound are added to the long term average. The realtime measurement from the pressure sensor 240 is compared with the long term average and the upper and lower bounds to detect breathing. Since fluctuations in the pressure within the mask 10, e.g. when the real-time pressure reading falls outside the upper and lower bounds, are indicative of a patient’s breathing, the controller is able to sense, from the input signal, whether the mask is being worn by a patient.

[0171] If the real-time measurement remains within the upper and lower bounds for an extended period of time, then there is an indication that breathing is absent or that the mask has been removed or is not being worn correctly. If no inhale / exhale is detected but the short term or real-time measurement is not within these bounds, then the long term average is deemed incorrect and is corrected.

[0172] Before commencing delivery of the medicament from the handset 301 to the facemask 10, if patient breathing is detected, then delivery of the medicament to the pad 218 is enabled. If patient breathing is not detected, then delivery of the medicament to the pad 218 is disabled. This ensures that medicament is not delivered to the pad 218 when the facemask 10 is not being worn, reducing waste and preventing buildup of medicament on the pad 218, which could otherwise lead to overdose should the mask be temporarily removed and repositioned on the patient after such buildup.

[0173] During delivery of the medicament from the handset 301 to the facemask 10, if patient breathing is detected, then delivery of the medicament is allowed to continue. If patient breathing is no longer detected, then delivery of medicament is ceased immediately. This enables detection of the mask having been removed, ensuring that medicament is not delivered to the facemask 10 when not being worn, reducing waste and preventing exposure of the medicament to the ambient environment, as well as preventing buildup of medicament on the pad 218, which could otherwise lead to overdose should the mask be temporarily removed and repositioned on the patient after such buildup. Fluctuations in the pressure within the mask 10 are also indicative of the patient’s breathing cycle, i.e. when they are in an inhalation phase and when they are in an exhalation phase. In particular, a drop in pressure within the facemask 10 is indicative of the patient breathing in, and an increase in pressure within the facemask 10 is indicative of the patient breathing out. More specifically, an inhale is detected when the short term or real-time pressure measurement crosses from above the upper bound of the long term average to below the lower bound, and vice versa for exhale.

[0174] By receiving regular input signals from the pressure sensor 240, the controller is therefore able to determine when the patient is inhaling, and when the patient is exhaling. In some embodiments, this may enable the controller to control the timing of the pump to deliver medicament to the pad 218 of the facemask 10, for example to coordinate delivery with an exhalation such that the medicament is available for inhalation from the pad 218 when the patient next inhales.

[0175] The medicament delivery can also be controlled to provide a single dose size suitable for a single inhalation event. This individual dose size can be pre-set based on established clinical data, or can be tuned for a specific case (for example based on the age, size, weight, and / or lung capacity of a patient).

[0176] Determination of delivery rate

[0177] A continuous delivery component of the algorithm calculates a continuous medicament delivery rate based at least in part on a patient input received via button 304. The continuous delivery component and the continuous medicament delivery rate may otherwise be referred to as a low response component and a low response medicament delivery rate. A rapid delivery component of the algorithm calculates a rapid medicament delivery rate based at least in part on a patient input received via button 304. The rapid delivery component and the rapid medicament delivery rate may otherwise be referred to as a high response component and a high response medicament delivery rate. These components of the algorithm run simultaneously to provide a combined output delivery rate that is based at least in part on the same patient input received via button 304.

[0178] Figure 22 illustrates the response of these components of the algorithm to various patient inputs received during medicament delivery.

[0179] In this example, the controller compares the continuous delivery component and the rapid delivery component, and the output delivery rate is equivalent to the higher of the two components. Hence, the output delivery rate is not plotted in Figure 22. Where the continuous delivery component is higher than the rapid delivery component, the device is described herein as delivering medicament in a continuous mode. Where the rapid delivery component is higher than the continuous delivery component, the device is described herein as delivering medicament in a rapid mode.

[0180] The graph of Figure 22 is split into four phases 900, 910, 920, 930 for illustrative purposes and ease of description. In reality, the graph represents an ongoing simulation of these components of the algorithm for a given scenario.

[0181] At the start of phase 900, medicament delivery is yet to commence, as the button 304 has not been pressed by the patient. Around halfway through phase 900, the patient first presses button 304, initiating medicament delivery. In response to the patient pressing button 304, the controller sends a signal to the rear facing LED(s) 242 to flash, thereby confirming to the patient that the button press has been successful and registered by the device 1 .

[0182] At this early stage of medicament delivery, both the continuous delivery component and the rapid delivery component experience a small increase, by the same amount, i.e. with a step-like rise, and the output delivery rate is therefore equal to both components, and deemed to be in the continuous mode.

[0183] In the second half of phase 900, the patient presses button 304 a further four times, as can be seen by the four incremental step increases in both the continuous delivery component and the rapid delivery component. The increases in the rapid delivery component are much larger than those in the continuous delivery component at this early stage of requesting pain relief and / or sedation, to rapidly respond to the patient’s needs.

[0184] The step increase in the rapid delivery component is dependent on the value of the rapid delivery component at the time of the button press. In particular, each press of the button 304 increases the rapid delivery component by a fraction or percentage of the difference between the instantaneous value of the rapid delivery component and a maximum delivery rate. The maximum delivery rate may be a maximum delivery rate permitted of the pump, or a preset maximum delivery rate that is dependent on the patient, for example based on their weight. Hence, where the rapid delivery component is higher, the step increase is lower, and where the rapid delivery component is lower, the step increase is higher.

[0185] In contrast, the step increases in the continuous delivery component are equal for each press of the button 304, irrespective of the value of the continuous delivery component at the time of the press. For example, each press of the button 304 may increase the continuous delivery component by 0.2ml / min, up to a predetermined maximum threshold.

[0186] These four presses of the button 304 in a short time period cause the rapid delivery component to increase at a much quicker rate than the continuous delivery component, and thus the output delivery rate is governed by the rapid delivery component throughout the remainder of phase 900, and the pump is operating in the rapid mode.

[0187] In phase 910 of Figure 22, the patient does not press the button 304, and the rapid delivery component decreases towards the continuous delivery component. In turn, the output delivery rate also decreases in the same way, still being governed by the rapid delivery component, because the rapid delivery component remains higher than the continuous delivery component. The continuous delivery component also decreases, but at a much slower rate such that the decrease is imperceptible in phase 910 of Figure 22. In this embodiment, the rate of decrease of the continuous delivery component is a predetermined constant rate of decrease throughout delivery of the medicament.

[0188] However, in alternative embodiments, it is envisaged that the rate of decrease could be variable, for example dependent on the instantaneous rate of delivery, or the rate of delivery at the last press of the button 304.

[0189] In this example, because the rapid delivery component is still higher than the continuous delivery component, and thus the pump is operating in the rapid mode, the continuous delivery component continuously decreases throughout the absence of a button press by the patient. However, if the rapid delivery component were to decrease enough to become lower than the continuous delivery component, and the pump began to operate in the continuous mode, then the continuous delivery component would vary as described in relation to the breath detection component of the algorithm and Figure 23 below.

[0190] In phase 920 of Figure 22, the process described in relation to phases 900 and 910 is repeated a plurality of times. Each time the patient presses button 304, the continuous delivery component experiences a step increase by the fixed amount, and the rapid delivery component experiences a step increase that is typically larger than the step increase in the continuous delivery component, but varies dependent on the value of the rapid delivery component at the time of the button press.

[0191] In the absence of the patient pressing the button 304, the rapid delivery component decreases in the same way as in phase 910, and the continuous delivery component decreases at a constant rate, as described above.

[0192] It can be seen from phase 920 of Figure 22 that the rate of the decrease in the rapid delivery component is different for each of the button presses. This rate of decrease in the rapid delivery component is dependent on the time that has passed since the button was last pressed. Specifically, the longer it has been since the button 304 was last pressed, the quicker the rate of decrease in the rapid delivery component. This protects the patient from prolonged exposure to higher doses of medicament when unnecessary for pain relief and / or sedation.

[0193] Throughout phase 920, because the rapid delivery component remains higher than the continuous delivery component throughout, the pump continues to operate in the rapid mode. Although the pump is operating in the rapid mode, the algorithm continues to calculate and monitor the continuous delivery component, as can be seen by the continued increases in the continuous delivery component throughout phase 920, in response to the patient pressing button 304.

[0194] At the start of phase 930 of Figure 22, a dosage monitoring component of the algorithm determines that the continuous delivery component has reached a predetermined threshold. The dosage monitoring component of the algorithm operates by continuously monitoring the continuous delivery component against said predetermined threshold, and intervening when the continuous delivery component reaches said predetermined threshold, by decreasing the rapid delivery component. In alternative embodiments, the dosage monitoring component may additionally or alternatively continuously monitor the time the device has spent in the rapid mode against a predetermined threshold, and intervening when the cumulative time the device has spent in the rapid mode reaches said predetermined threshold, by decreasing the rapid delivery component.

[0195] Once the dosage monitoring component of the algorithm determines that the continuous delivery component has reached a predetermined threshold, the rapid delivery component is disabled such that further presses of the button 304 do not cause an increase in the rapid delivery component.

[0196] Hence, although the patient continues to press the button 304 in phase 930, the rapid delivery component decreases towards the continuous delivery component. In this embodiment, in response to the dosage monitoring component reducing the rapid delivery component, the rapid delivery component decreases at a rate that is slower than the rate of decrease in the rapid delivery component during normal operation of the device 1 in the rapid mode. However, it is envisaged that in alternative embodiments, the rate of decrease may be similar to, or faster than, the rate of decrease in the rapid delivery component during normal operation of the device 1 in the rapid mode.

[0197] At the end of phase 930, the rapid delivery component decreases to a level that is below the continuous delivery component, and at this point the pump begins to operate in the continuous mode, i.e. the output delivery rate becomes governed by the continuous delivery component.

[0198] This transition from the rapid mode into the continuous mode is illustrated in Figure 23, which illustrates the transition from phase 930 of Figure 22 into phase 935. Phase 935 represents medicament delivery in the continuous mode, where the continuous delivery component is greater than the rapid delivery component, and the output delivery rate is therefore equivalent to the continuous delivery component. Hence, the continuous delivery rate is not plotted in phase 935 of Figure 23. Phase 935 is described in greater detail in relation to consciousness checks below.

[0199] Once the device 1 has been forced out of operating in the rapid mode, the device 1 remains locked out of operating in the rapid mode until the continuous delivery component decreases below the predetermined threshold again, or in the alternative embodiment described above, until the cumulative time spent in the rapid mode by the device 1 decreases below the predetermined threshold.

[0200] In the meantime, whilst operating in the continuous mode, continued presses of the button 304 would cause the continuous delivery component to increase by the fixed step increase, until the continuous delivery component reaches a predetermined maximum, or maintain the continuous delivery component at the predetermined maximum if presses of the button 304 are frequent. Consciousness checks

[0201] A consciousness component of the algorithm monitors the consciousness of the patient when the pump is operating in the continuous mode. No consciousness checks are carried out when the pump is operating in the rapid mode, because the reduction in the rapid delivery component is quick enough that the device 1 will only remain in the rapid mode if the button 304 is pressed regularly, thereby indicating that the patient is conscious. Indeed, in order to remain in the rapid mode, the patient will typically need to press the button 304 more often than a consciousness check would occur, thus negating the need for consciousness checks in the rapid mode.

[0202] However, when the pump is operating in the continuous mode, the controller regularly performs a consciousness check by sending output signals to illuminate the rear facing LED(s) 242, e.g. with a single flash or multiple flashes, or flashing patterns using the three spaced LEDs 242a, 242b and 242c, which indicates to the patient to confirm that they remain conscious, by pressing the button 304. In response to the patient pressing button 304, the controller sends a signal to the rear facing LED(s) 242 to flash, thereby confirming to the patient that the button press has been successful and registered by the device 1 .

[0203] Once the LED(s) 242 has / have been illuminated, the controller monitors the time taken for the patient to respond by pressing the button 304. The controller then compares the patient response time with a predetermined threshold response time to determine whether the patient is conscious enough. Typically, it is deemed that if the patient presses the button 304 within 0.6 seconds, then they are deemed to be conscious enough.

[0204] If the patient response time is less than the threshold response time, then delivery of the medicament continues, and a further consciousness check is conducted in due course. If the patient response time is longer than the threshold response time, then the controller determines that the consciousness check has been failed, and that the patient has become too sedated. In response to the patient failing a consciousness check, a secondary consciousness check is performed in the same way as the primary consciousness check, for example 15 seconds after the failed primary consciousness check. In response to failing a secondary consciousness check, it is confirmed that the patient has become too sedated and medicament delivery to the facemask 10 ceases. In response to passing a secondary consciousness check, the controller returns to performing primary consciousness checks. This ensures that delivery does not cease where the patient has simply missed the response to a primary consciousness check by accident. In alternative embodiments, the secondary consciousness check may be performed quickly, or immediately, after the failed primary consciousness check, i.e. in a small fraction of the time that would otherwise elapse between primary consciousness checks.

[0205] The first consciousness check is performed shortly after the pump starts to operate in the continuous mode, i.e. shortly after the end of phase 930 and shortly after the start of phase 935 in the example of Figure 23. The first consciousness check is typically conducted after a predetermined time interval following the last press of the button 304 in the rapid mode, or following commencement of delivery in the continuous mode. In alternative embodiments, the timing of the first consciousness check may additionally or alternatively depend on the time that has elapsed since the button 304 was last pressed by the patient to request pain relief and / or sedation, and the output delivery rate at that moment. Specifically, in this alternative, the longer it has been since the button 304 was last pressed, and the higher the output delivery rate was at the moment, the quicker the first consciousness check occurs once the pump begins to operate in the continuous mode. This is because as more time elapses, particularly after delivery of a high volume of medicament to the patient, the need to check on the status of the patient becomes more urgent, i.e. because they are more likely to have become too sedated.

[0206] When operating in the continuous mode, the consciousness checks are performed at regular time intervals, for example every 15 seconds. In alternative embodiments, the length of the time intervals between consciousness checks may be dependent on the output delivery rate at that moment in time, and may therefore be irregular. In particular, where the output delivery rate is higher, the consciousness checks are performed more regularly, because the risk of losing consciousness is higher. In contrast, where the output delivery rate is lower, the consciousness checks are performed less regularly, because the risk of losing consciousness is lower. Indeed, where the output delivery is particularly low, for example below a predetermined threshold, the consciousness checks may cease altogether, i.e. because the chance of the patient being unconscious is significantly low.

[0207] Phase 935 of Figure 23 illustrates the carrying out of consciousness checks, where the output delivery rate is plotted over time. At point in time 940, the device 1 begins to operate in the continuous mode, and thus at point in time 950, it is determined that a first consciousness check should be performed, because 15 seconds has elapsed since commencing operation in the continuous mode. An output signal is sent to illuminate the rear facing LED(s) 242, and because the patient presses the button 304 to confirm their consciousness within 0.6 seconds, the check is deemed to have been passed. In response, at point in time 955, the continuous delivery component, and hence the output delivery rate, are increased, because it is deemed safe to deliver more medicament to the patient to maintain their current level of pain relief and / or sedation.

[0208] After the initial step increase in the continuous delivery component and the output delivery rate, the continuous delivery component, and hence the output delivery rate, begin to decrease again. At point in time 960, following a further 15 seconds, a further consciousness check is performed, and an output signal is again sent to illuminate the rear facing LED(s) 242.

[0209] Again, the patient presses the button 304 to confirm their consciousness, and because the patient’s response is within 0.6 seconds, the check is deemed to have been passed. In response, at point in time 965, the continuous delivery component, and hence the output delivery rate, are increased, because it is deemed safe to deliver more medicament to the patient to maintain their current level of pain relief and / or sedation. After the initial step increase in the continuous delivery component and the output delivery rate, the continuous delivery component, and hence the output delivery rate, begin to decrease again.

[0210] Whilst the patient continues to pass the consciousness checks, this process continues until a) the patient presses the button 304 without being requested, indicating that they are in pain and wish to receive more pain relief and / or sedation, triggering the continuous delivery component and the rapid delivery component of the algorithm to function as described above, or b) the patient fails a primary consciousness check and a subsequent secondary consciousness check, thereby triggering cessation of medicament delivery.

[0211] In response to each passed consciousness check, the delivery rate is increased by a fraction or percentage of the decrease in the delivery rate enforced between checks. For example, between points in time 940 and 950, the delivery rate is decreased by a predetermined amount, and in response to passing the consciousness check at point in time 950, the delivery rate is increased by 80% of that predetermined amount. This creates a cumulative decrease in the delivery rate during operation in the continuous mode, enabling fine adjustment of the delivery rate to the minimum rate required to maintain sufficient pain relief and / or sedation for the patient, whilst allowing the patient to reduce the delivery rate as they begin to feel more comfortable.

[0212] In this embodiment, the output delivery rate decreases at a constant rate between consciousness checks. However, in alternative embodiments it is envisaged that the decrease in the delivery rate may decrease at an alternative rate. For example, the decrease in the delivery rate may be dependent on the instantaneous delivery rate, e.g. at the time of pressing the button 304 in response to the most recent consciousness check. In particular, the rate of decrease may be higher where the delivery rate is higher, and lower where the delivery rate is lower. In an alternative embodiment, it is envisaged that if the patient fails to respond to a consciousness check, the decrease in delivery rate continues at the same rate, but if the patient successfully responds to the consciousness check, the delivery rate decreases, but at a slower rate. In another alternative embodiment, it is envisaged that if the patient fails to respond to a consciousness check, the delivery rate decreases at a faster rate, but if the patient successfully responds to the consciousness check, the delivery rate continues to decrease at the same rate. In another alternative embodiment, it is envisaged that if the patient fails to respond to a consciousness check, the delivery rate continues to decrease at the same rate, or a faster rate, but if the patient successfully responds to the consciousness check, the delivery rate is maintained at the current or instantaneous rate, e.g. for a predetermined amount of time.

[0213] Where the above description of the specific embodiments discusses a “delivery rate” of medicament, in reality, it is envisaged that for some pumps in this field this may be better defined by reference to a volume of medicament delivered in a certain time period. For example, a delivery rate of 2ml / min may be delivered by delivering 4ml / min for 30 seconds, and stopping delivery for 30 seconds. The output rate of the pump is therefore 4ml / min, but the delivery rate of medicament to the facemask 10 is 2ml / min. Increasing the delivery rate to 3ml / min may therefore be implemented by delivering 4ml / min for 45 seconds, and stopping delivery for 15 seconds. Similarly, a delivery rate of 2ml / min may be delivered by alternating between delivering 4ml / min for 3 seconds, and stopping delivery for 3 seconds, for 10 intervals of each, giving an overall delivery rate of medicament to the facemask 10 of 2ml / min. Increasing the delivery rate to 3ml / min may therefore be implemented by alternating between delivering 4ml / min for 4.5 seconds for and stopping delivery for 1 .5 seconds, for 10 intervals of each.

[0214] Hence, the output of the pump may be the same, but may be pulsed to the facemask 10 over a different time period, to achieve a different delivery rate to the facemask 10. This may be particularly relevant when using a stepper motor to drive delivery of the medicament, which may be beneficial in ensuring accurate and precise dosing / delivery. LED rinq

[0215] The LEDs of display 500 shown in Figures 2-4 are used during operation to provide various status updates to a user or operator. The following notification sequences are described in relation to the specific LED ring 502 of Figures 2-4, which has eight LEDs in a circular shape. However, it will be understood that the same notification sequences could be provided by a plurality of LEDs provided in a different shape, and / or being different in number, and that different colours could be used to indicate different statuses from those specifically described below.

[0216] Figures 24a-24d illustrate a first notification sequence, in which one or more of the LEDs is illuminated in purple to indicate that the device is priming. Once the reservoir 322 has been correctly inserted into the handset 301 and the microswitch activated by the flange 330 as previously described, provided the battery is connected, the device 1 begins the priming process. During priming of the device 1 , the peristaltic pump 334 draws and transmits sufficient medication from the reservoir 322 to the transmission tube 307 to fill the transmission tube 307 between the handset 301 and the mask 10, but does not begin delivery of the medication onto the gauze / pad 218. During priming, actuation of the button 304 will not cause delivery of medication to the mask 10. During priming, medicament will be delivered to the facemask 10 regardless of the breath detection component of the algorithm, but not to the pad 218.

[0217] Here, the number of illuminated LEDs of LED ring 502 corresponds to a proportion or percentage of the priming completed. The number of illuminated LEDs therefore increases in a clockwise direction as priming progresses, starting from the LED positioned towards the top of the outwardly facing display 500.

[0218] For example, each LED that is illuminated in purple may be indicative of the device being approximately 12.5% primed. Hence, the first LED showing being illuminated in purple may indicate that the device is approximately 12.5% primed, two LEDs being illuminated in purple may indicate that the device is 25% primed (as illustrated in Figure 24a), four LEDs being illuminated in purple may indicate that the device is 50% primed (as illustrated in Figure 24b), 6 LEDs being illuminated in purple may indicate that the device is 75% primed (as illustrated in Figure 24c), and so on. These percentages are an example only, and in general, each LED being illuminated is indicative of the device being further towards being fully primed.

[0219] Once the device is fully primed, all eight of the LEDs are illuminated in purple, to indicate that priming is complete (as illustrated in Figure 20d). Upon completion of priming, the device 1 checks whether the device battery is full., The device 1 may also check whether the reservoir 322 is full, for example by issuing a request to the operator to confirm that the reservoir 322 is new, thereby confirming that it is full. Upon confirmation of the full battery (and the full reservoir, where applicable), all eight of the LEDs are illuminated in green, indicating to the user or operator that the device is fully primed and ready for normal operation, i.e. the handset 301 is ready to deliver medicament to the facemask 10.

[0220] Figures 25a-25d illustrate a second notification sequence, which runs during delivery of the medicament from the handset 301 to the facemask 10. In this second notification sequence, 7 of the 8 LEDs in the LED ring 242 remain illuminated in green, whilst a single LED is illuminated in blue. The LED illuminated in blue changes over time, so that the blue LED appears to move in a clockwise manner around the LED ring over time, as illustrated in Figures 20a-20b, indicating that breathing is continually being detected and delivery of the medicament is ongoing.

[0221] Figures 26a-26d illustrate a third notification sequence, which runs in combination with the second notification sequence during delivery of the medicament from the handset 301 to the facemask 10. In this third notification sequence, the number of LEDs illuminated in green is indicative of the amount of medicament remaining in the reservoir 322. The number of LEDs illuminated in green therefore reduces in an anticlockwise direction during delivery of the medicament to the facemask 10, finishing with the LED positioned towards the top of the outwardly facing display 500.

[0222] As with the first notification sequence, each LED that is illuminated in green is indicative of how full the reservoir 322 is. For example, each LED that is illuminated in green may represent the reservoir 322 being approximately 12.5% full. Hence, when the eighth LED is the last LED illuminated in green, as in Figure 26a, the reservoir 322 is approximately 100% full. When the sixth LED is the last LED illuminated in green, as in Figure 26b, the reservoir 322 is approximately 75% full. When the fourth LED is the last LED illuminated in green, as in Figure 26c, the reservoir 322 is approximately 50% full. When the second LED is the last LED illuminated in green, as in Figure 26d, the reservoir 322 is approximately 25% full.

[0223] Once the reservoir 322 drops to being approximately 10% full, the last two LEDs are illuminated in yellow, and pulse or flash to indicate to the operator that the reservoir 322 is almost empty.

[0224] Once the reservoir 322 is completely empty, the last LED is illuminated in yellow, and pulses or flashes to indicate to the operator that the reservoir 322 is empty.

[0225] A single, yellow, flashing or pulsing LED may be used during the setup of a device 1 to notify the operator that the device 1 has been used before. All 8 LEDs flashing or pulsing in yellow during the setup of a device 1 may be used to notify the operator that the device 1 has a software or hardware fault. That fault may be, for example, that the battery is low, or that a component of the device 1 is missing or misconnected.

[0226] Various other modifications of the embodiments described above would also be apparent to a skilled reader. As such, it is emphasised that the forgoing description is provided by way of example only, and is not intended to limit the scope of protection as defined with reference to the appended claims.

Claims

Claims:1 . A device for relieving pain and / or delivering sedation, the device comprising a patient delivery interface with an evaporation medium for receiving a volatile substance for inhalation, a delivery system for delivering the volatile substance to the evaporation medium and a control system for controlling delivery of the volatile substance by the delivery system, wherein the control system is configured to deliver a predetermined volume of volatile substance in a single delivery event, the predetermined volume having an upper limit calculated as that which can be completely vaporised from the evaporation medium and inhaled by a user in a single inhalation event.

2. A device according to claim 1 , wherein the evaporation medium comprises a pad of absorbent material.

3. A device according to claim 2, wherein the evaporation medium comprises multiple layers of a cotton material.

4. A device according to any preceding claim, wherein the evaporation medium is positioned in a gas flow path within the patient delivery interface, such that inhaled air passes through the evaporation medium5. A device according to any preceding claim, wherein perforations are introduced into the evaporation medium.

6. A device according to any preceding claim, further comprising a transmission tube for carrying the volatile substance from a substance reservoir to the evaporation medium, wherein an end of the transmission tube opens directly onto the evaporation medium.

7. A device according to claim 6, further comprising a cover for the evaporation medium, the cover comprising an aperture for receiving an end of the transmission tube.

8. A device according to claim 7, wherein the transmission tube is received in the aperture with a friction fit.

9. A device according to claim 7 or 8, wherein the patient delivery interface comprises retaining features to prevent removal of the transmission tube from the aperture.

10. A device according to any preceding claim, wherein the patient delivery interface comprises a delivery chamber, in which the evaporation medium is housed.

11. A device according to any preceding claim, wherein the patient delivery interface comprises an inhalation valve positioned downstream of the evaporation medium.

12. A device according to any preceding claim, wherein the patient delivery interface comprises a respiration sensor for detecting inhalation and / or exhalation of a user.

13. A device according to claim 12, wherein the respiration sensor comprises a pressure sensor and / or a temperature sensor.

14. A device according to claim 12 or 13, wherein the control system is configured to deliver the predetermined volume of volatile substance to the evaporation medium during a detected exhalation.

15. A device according to any preceding claim, wherein the patient delivery interface comprises a mask for securing around the nose and / or mouth of a user.

16. A device for relieving pain and / or delivering sedation, the device comprising a patient delivery interface for delivering a vaporised or gaseoussubstance to a cavity for inhalation by a user, a reservoir for containing a predetermined volume of gaseous or volatile substance, and one or more exhalation filters in an outlet flow path from the cavity, wherein the total filter capacity of the one or more filters is equal to the predetermined volume of the substance in the reservoir.

17. A device according to claim 16, wherein the or each exhalation filter is an activated carbon filter.

18. A device according to claim 16 or 17, wherein the or each exhalation filter comprises a filter cartridge having a flow path therethrough, and wherein the filter cartridge comprises a hydrophobic barrier at one or both ends of the flow path.

19. A device according to claim 18, wherein the hydrophobic barrier comprises a polypropylene scrim.

20. A device according to claim 18 or 19, wherein the filter cartridge comprises a one-way exhalation valve.21 . A device according to any of claims 16 to 20, wherein the or each exhalation filter is mounted on the patient delivery interface.

22. A device according to claim 21 , wherein the or each exhalation filter is removably secured to the patient delivery interface.

23. A device according to claim 22, wherein the or each exhalation filter is removable from the patient delivery interface from one side only.

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