Fluid responsiveness assessment in mechanically ventilated patients

Abstract

The disclosure relates to a method for assessing fluid responsiveness of a patient (3) connected to a breathing apparatus (2) providing mechanical ventilation to the patient (3). The method comprises the steps of initiating a fluid responsiveness assessment [FRA] period for assessing a degree of fluid responsiveness of the patient (3), determining a pulse pressure variation [PPV] and / or a stroke volume variation [SVV] of the patient (3) during the FRA period, and presenting information indicative of the fluid responsiveness of the patient (3) to an operator of the breathing apparatus (1) based on the determined PPV and / or SVV. The method further comprises the steps of determining a heartrate [HR] or pulse rate [PR] of the patient (3) during baseline ventilation of the patient (3) prior to the FRA period, calculating recommended FRA ventilation settings for the FRA period based on the determined HR and / or PR, wherein the recommended FRA ventilation settings comprises a recommended respiratory rate [RRFRA] and / or a recommended inspiratory-expiratory ratio [I:EFRA], and ventilating the patient (3) using the recommended FRA ventilation settings during the FRA period.

Description

[0001] Fluid Responsiveness Assessment in Mechanically Ventilated Patients

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a method, a computer program and a ventilation system for assessing fluid responsiveness of a patient connected to a breathing apparatus providing mechanical ventilation to the patient.

[0004] BACKGROUND ART

[0005] Hemodynamic monitoring, i.e. the continuous display and recording of hemodynamic parameters to inform about the status of the cardiovascular system, is an essential component in the initial and continued management of all critically ill patients treated in the emergency, operating room and in the intensive care unit (ICU).

[0006] One of the most important determinants of the status of the cardiovascular system is its effective volume of blood, or its volemia. There is a certain amount of blood within the cardiovascular system in a healthy state, called normo- or euvolemia, which is related to normal cardiovascular function and hence to an adequate delivery of oxygenated blood to all body tissues. In contrast, any decrease in intravascular volume or hypovolemia due to for example bleeding, dehydration, microcirculatory failure, third space fluid sequestration or excessive vasodilation may cause a deficit in oxygen delivery to tissues and if severe and / or prolonged enough may lead to organ failure.

[0007] A concept inherent to volemia is preload. Preload is defined as the volume of blood within the ventricles at the end of diastole that stretch the myocardial fibers to a certain sarcomere length necessary for a normal effective and efficient heart muscle contraction during systole. Any decrease in cardiac preload will result in a decrease in cardiac output and in systemic hypoperfusion of different degrees, which can frequently coexist with normal standard hemodynamic parameters such as mean arterial or central venous pressure.

[0008] Standard hemodynamic monitoring systems can easily detect severe hypovolemic states but often fail in diagnosing moderate to mild hypovolemia. This is an important limitation in the monitoring of critical care patients because when such occult hypovolemia remains for many hours it can be associated with several complications such as acute renal failure, heart ischemia, cerebral stroke or wound infection among others. This occult hypovolemia is manifested as a “preload dependency” which in medical terms means that the cardiovascular system operates at the steep portion of the Frank-Starling relationship. According to this relationship, the ventricle will respond with an increase in cardiac output (more often expressed as stroke volume, SV, or the volume ejected by the ventricle with each systole) in response to the administration of intravascular volume. In other words, the patient is “fluid responsive”.

[0009] Intravenous fluid administration is considered the first line intervention in hemodynamically unstable patients to restore euvolemia (or in other words, to optimize preload). However, only about 50% of hemodynamically unstable patients are fluid responsive and it has been clearly established that an excess of intravenous fluids (i.e. over-resuscitation) is associated with an increased morbi-mortality as it can precipitate lung edema, worsen cor pulmonale or induce left heart failure. Therefore, assessment of fluid responsiveness (i.e. the prospective identification of patients in whom intravenous administration of fluids increase cardiac output) is becoming an essential component in optimizing the intravascular volume status and avoiding the deleterious consequences of fluid overload.

[0010] Many tests and indices for assessing fluid responsiveness have been developed through the years. Examples of indices commonly used to evaluate fluid responsiveness is pulse pressure variation (PPV) and stroke volume variation (SVV). These parameters are commonly shown on commercially available monitors and used to evaluate the fluid responsiveness of a mechanically ventilated patient.

[0011] PPV is calculated as the difference between the maximum and minimum pulse pressures (systolic minus diastolic blood pressure) during at least one respiratory cycle, divided by the average of these pressures, expressed as a percentage:

[0012] A PPV greater than 12-13% typically indicates fluid responsiveness, meaning the patient is likely to respond to fluid administration with an increase in stroke volume or cardiac output. Values below this threshold suggest that the patient may not respond significantly to fluid administration.

[0013] SVV is calculated similarly to PPV but uses stroke volume measurements instead of pulse pressure. The stroke volume is measured at different points during the respiratory cycle, and the variation is expressed as a percentage:

[0014] An SW greater than 10-15% typically suggests that the patient is fluid responsive, indicating that stroke volume is likely to increase with fluid administration. Lower values indicate a lower likelihood of a significant response to fluids.

[0015] However, in clinical practice, PPV and SVV based fluid responsiveness assessment has been shown to have low applicability due to several limitations, including: low heart rate (HR) to respiratory rate (RR) ratio, irregular heart beats, mechanical ventilation with low tidal volume, increased intra-abdominal pressure, open thorax, and spontaneous breathing.

[0016] Thus, there is a need for improvement within the field of PPV or SVV based assessment of fluid responsiveness of mechanically ventilated patients.

[0017] SUMMARY

[0018] It is an object of the present disclosure to mitigate, alleviate or eliminate one or more of the above-identified deficiencies and disadvantages in the prior art.

[0019] In particular, it is an object of the present disclosure to address the above-described limitation related to use of PPV and SW in the assessment of fluid responsiveness in mechanically ventilation patients.

[0020] More specifically, it is an object of the present disclosure to solve or at least mitigate the limitation in PPV or SVV applicability in fluid responsiveness assessment, caused by low heart rate to respiratory rate (HR:RR) ratio.

[0021] These objects are achieved according to a first aspect of the present disclosure by a method for assessing fluid responsiveness of a patient connected to a breathing apparatus providing mechanical ventilation to the patient. The method comprises the steps of initiating a fluid responsiveness assessment (FRA) period for assessing a degree of fluid responsiveness of the patient, determining a PPV and / or an SW of the patient during the FRA period, and presenting information indicative of the fluid responsiveness of the patient to an operator based on the determined PPV and / or SVV. The method further comprises the steps of determining a heartrate (HR) or pulse rate (PR) of the patient during baseline ventilation of the patient prior to the FRA period, calculating recommended FRA ventilation settings for the FRA period based on the determined HR and / or PR, the recommended FRA ventilation settings comprising at least a recommended respiratory rate (RRFRA) and / or a recommended inspiratory-expiratory ratio (I :EFRA), and ventilating the patient using the recommended FRA ventilation settings during the FRA period.

[0022] By calculating and using the recommended FRA ventilation settings during the FRA period, the RR and / or l:E used during the period of PPV and / or SSV determination can be adapted to the heartrate of the patient to prevent low HR:RR ratios (under-sampling of heartbeats with respect to the respiratory rate), thereby extending PPV and / or SSV applicability in the assessment of fluid responsiveness.

[0023] According to some embodiments, RRFRA is calculated based on the determined HR and / or PR of the ventilated patient and an acceptable range of heart-rate to respiratory-rate (HR:RR) ratios for the FRA period, in order to ensure that the ratio H R / RRFRA falls within the acceptable range of HR:RR ratios. Both under-sampling and over-sampling of heartbeats with respect to respiratory rate may change the range of PPV values and SVV values that correspond to fluid responsiveness of the ventilated patient . Therefore, the acceptable range of HR:RR ratios for the FRA period may comprise both a lower limit and an upper limit. Preferably, RRFRA is calculated such that the H R: RRFRA ratio is at least 2, more preferably at least 3, and most preferably at least 3,6. Likewise, RRFRA is preferably calculated such that the HR: RRFRA ratio is 10 or less, more preferably 9 or less, and most preferably 8 or less. Thus, according to a nonlimiting example, the acceptable range of HR:RR ratios may be an open range of > 3,6. According to another non-limiting example, the acceptable range of HR:RR ratios may be 3 to 9.

[0024] According to some embodiments, the method comprises the steps of presenting the recommended FRA ventilation settings to an operator of the breathing apparatus prior to initiation of the FRA period and initiating the FRA period in response to an acknowledgement of the recommended FRA ventilation settings by the operator. Although the method may be implemented such that the recommended FRA ventilation settings is used without approval from the operator, the recommended FRA ventilation settings is preferably presented to the operator in order for the operator to approve the settings before they are put into use. This improves patient safety and also facilitates interpretation by the operator of the fluid responsiveness status of the patient in view of the determined PPV and / or SSV.

[0025] Besides FRA ventilation settings relating to RRFRA and / or I:EFRA, the information that is presented to the operator prior to initiation of the FRA period may comprise a recommendation on a duration of the FRA period and / or information relating to a recommended change in a set pressure level or a tidal volume during the FRA period, which recommended change in pressure level or tidal volume aims at minimising a deviation between a clinical ventilation target (e.g. a minute ventilation) of the baseline ventilation and a predicted performance of the ventilation during the FRA period with respect to the clinical ventilation target, as will be further discussed below. Information about a potential deviation between the clinical ventilation target of the baseline ventilation and the predicted performance during the FRA period may also be presented to the operator in order for the operator to decide on whether or not it is worth to deviate from the clinical ventilation target in order to obtain a reliable assessment of fluid responsiveness during the FRA period.

[0026] The method may further comprise determining whether a current HR:RR ratio of the baseline ventilation is within the acceptable range of HR:RR ratios for the FRA period, and, if so, using the current ventilation settings as FRA ventilation settings during the FRA period. If, however, the current HR:RR ratio falls outside the acceptable range of HR:RR ratios for the FRA period, new recommended ventilation settings for the FRA period are calculated and used in order to improve the accuracy in the PPV and / or SW determination. Thus, according to some embodiments, the method may comprise the steps of determining a baseline HR:RR ratio based on the determined HR and / or PR of the patient and a set respiratory rate (RR) for the baseline ventilation, comparing the determined baseline HR:RR ratio with an acceptable range of HR:RR ratios for the FRA period, and calculating the recommended FRA ventilation settings and ventilating the patient using the recommended FRA ventilation settings only when the determined baseline HR:RR ratio falls outside the acceptable range of HR:RR ratios for the FRA period. This is advantageous in that no new ventilation settings for the FRA period needs to be calculated if the current ventilation settings are deemed to result in PPV and / or SSV measurements that constitute true indicators of fluid responsiveness given the PPV and / or SW threshold values used in the assessment. .

[0027] In order to ensure adequate ventilation of the patient also during the FRA period, the method may comprise a step of calculating the recommended FRA settings also based on a predicted ventilation performance during the FRA period with respect to at least one clinical ventilation target set for the baseline ventilation. For example, the method may comprise the step of calculating RRFRA and / or I: EFRA such that the HR: RRFRA ratio falls within an acceptable range of HR:RR ratios for the FRA period while RRFRA and / or I: EFRA minimises a deviation between a clinical ventilation target for the baseline ventilation and a predicted ventilation performance with respect to the at least one clinical ventilation target during the FRA period.

[0028] Furthermore, the recommended FRA settings may, besides RRFRA and / or I: EFRA, comprise a recommended pressure level (in pressure controlled ventilation) or a recommended tidal volume (in volume controlled ventilation) to be used during the FRA period. The recommended pressure level or tidal volume may be calculated as a pressure level or tidal volume that optimises a ventilation performance during the FRA period with respect to the at least one clinical ventilation target.

[0029] Thus, in some embodiments, the method comprises the steps of: calculating RRFRA and / or I :EFRA such that the H R: RRFRA ratio falls within an acceptable range of HR:RR ratios for the FRA period while RRFRA and / or I: EFRA minimises a deviation between a clinical ventilation target for the baseline ventilation and a predicted ventilation performance with respect to the at least one clinical ventilation target during the FRA period, and / or calculating recommended FRA ventilation settings further comprising a recommended pressure level or a recommended tidal volume, wherein the pressure level or tidal volume is calculated to eliminate or at least reduce the deviation between the clinical ventilation target for the baseline ventilation and the predicted ventilation performance during the FRA period with respect to the at least one clinical ventilation target, when used together with the recommended RRFRA and / or I: EFRA.

[0030] In some embodiment, the method comprises the steps of calculating recommended FRA ventilation settings including an RRFRA making H R: RRFRA fall within the acceptable range of HR:RR ratios for the FRA period, and a tidal volume (in VCV) or a driving pressure (in PCV) resulting in a tidal volume during the FRA period of at least 8 ml / kg predicted bodyweight of the patient. Thereby, both the limitation of low (or high) HR:RR ratios and the limitation of low tidal volumes are eliminated or at least substantially mitigated.

[0031] In some embodiments, the method comprises the steps of setting a recommended tidal volume for the FRA period to at least 8 ml / kg bodyweight of the patient and calculating RRFRA based on the set tidal volume and a minute ventilation of the baseline ventilation. In other embodiments, the method comprises the steps of first calculating a recommended respiratory rate, RRFRA , ensuring that H R: RRFRA falls within the acceptable range of HR:RR ratios for the FRA period, and then calculating a recommended tidal volume, preferably within the range of 8-12 ml / kg, that minimises a deviation between the minute ventilation of the baseline ventilation and the minute ventilation during the FRA period. This way, both the limitations of low (or high) HR:RR ratio and low tidal volume are avoided while also avoiding or at least minimising a deviation in minute ventilation between the baseline ventilation and the FRA period.

[0032] The duration of the FRA period may be either predetermined or determined based on the ventilation performance during the FRA period with respect to the at least one clinical ventilation target of the baseline ventilation.

[0033] According to a second aspect of the present disclosure there is provided a computer program for a system for assessing fluid responsiveness of a patient connected to a breathing apparatus providing mechanical ventilation to the patient. The computer program comprises computer-readable instructions which, when executed by at least one processor of the system, cause the system to perform the above-described method.

[0034] According to a third aspect of the present disclosure there is provided a computer program product comprising a non-transitory data storage medium storing the above-mentioned computer program.

[0035] According to a fourth aspect of the present disclosure there is provided a system for assessing fluid responsiveness of a patient connected to a breathing apparatus providing mechanical ventilation to the patient. The system comprises at least one processor and at least one non- transitory data storage medium storing the above-mentioned computer program, and is configured to perform the above-mentioned method upon execution of the computer program by the at least one processor.

[0036] In some embodiments, the method is performed in full by the breathing apparatus itself, meaning that the breathing apparatus is devised and configured to determine the HR and / or PR of the patient, determine the PPV and / or SVV during the FRA period, and to present the information indicative of the fluid responsiveness of the patient, e.g. on a display of the breathing apparatus. In other embodiments, some of the method steps may be performed by the breathing apparatus whereas other methods steps are performed by a hemodynamic monitor to which the breathing apparatus is communicatively connected. For example, the hemodynamic monitor may be devised and configured to determine the HR and / or the PR of the patient and to calculate the recommended FRA ventilation settings. The FRA ventilation settings may then be transmitted to the breathing apparatus by the hemodynamic monitor for use during the FRA period. The hemodynamic monitor may then determine the PPV and / or SW of the patient during the FRA period and cause the information indicative of the fluid responsiveness of the patient to be presented on a display of the hemodynamic monitor and / or a display of the breathing apparatus. The breathing apparatus may also be communicatively connected to other types of devices, such as a remote monitoring device allowing the operation of the breathing apparatus and vital data of the patient to be monitored and / or controlled from a remote location. In such a scenario, it is contemplated that parts of the method may be performed by the remote display device.

[0037] Thus, according to this fourth aspect of the present disclosure there is provided a system for assessing fluid responsiveness of a patient connected to a breathing apparatus providing mechanical ventilation to the patient. The system comprises at least one processor configured to initiate an FRA period for assessing a degree of fluid responsiveness of the patient, determine a PPV and / or an SSV of the patient during the FRA period, and present information indicative of the fluid responsiveness of the patient to an operator of the breathing apparatus based on the determined PPV and / or SVV. The at least one processor is further configured to determine a heartrate (HR) or a pulse rate (PR) of the patient during baseline ventilation of the patient prior to the FRA period, calculate recommended FRA ventilation settings for the FRA period based on the determined HR and / or PR, wherein the recommended FRA ventilation settings comprise at least a recommended respiratory rate (RRFRA) and / or a recommended inspiratory-expiratory ratio (I:EFRA), and to control the breathing apparatus to ventilate the patient using the recommended FRA ventilation settings during the FRA period.

[0038] According to some embodiments, the at least one processor is configured to calculate RRFRA based on the determined HR and / or PR of the patient and an acceptable range of HR:RR ratios for the FRA period.

[0039] According to some embodiments, the at least one processor is further configured to present the recommended FRA ventilation settings to an operator of the breathing apparatus prior to initiation of the FRA period, and to initiate the FRA period in response to an acknowledgement of the recommended FRA ventilation settings by the operator.

[0040] According to some embodiments, the at least one processor is configured to determine a baseline HR:RR ratio based on the determined HR and / or PR of the patient and a set RR for the baseline ventilation, compare the determined baseline HR:RR ratio with an acceptable range of HR:RR ratios for the FRA period, and calculate the recommended FRA settings and ventilate the patient using the recommended FRA settings only when the determined HR:RR ratio falls outside the acceptable range of HR:RR ratios for the FRA period.

[0041] According to some embodiments, the at least one processor is configured to control the breathing apparatus to return to baseline ventilation after the FRA period by automatically switching from the recommended FRA ventilation settings to ventilation settings used during the baseline ventilation.

[0042] According to some embodiments, the at least one processor is configured calculate the recommended FRA ventilation settings based on a predicted ventilation performance (using the recommended FRA ventilation settings) with respect to at least one clinical ventilation target set for the baseline ventilation.

[0043] According to some embodiments, the at least one processor is configured to: calculate RRFRA and / or I :EFRA such that the H R: RRFRA ratio falls within the acceptable range of HR:RR ratios for the FRA period while RRFRA and / or I: EFRA minimises a deviation between a clinical ventilation target for the baseline ventilation and a predicted ventilation performance with respect to the at least one clinical ventilation target during the FRA period, and / or calculate recommended FRA ventilation settings further comprising a pressure level or a tidal volume, wherein the pressure level or tidal volume is calculated to eliminate or at least reduce the deviation between the clinical ventilation target for the baseline ventilation and the predicted ventilation performance with respect to the at least one clinical ventilation target during the FRA period, when used together with the recommended RRFRA and / or I: EFRA

[0044] According to some embodiments, the at least one processor is configured to set a recommended tidal volume for the FRA period to at least 8 ml / kg predicted bodyweight of the patient, and to calculate RRFRA based on the set tidal volume and a minute ventilation of the baseline ventilation.

[0045] Effects and features of the second through fourth aspects of the disclosure are to a large extent analogous to those described above in connection with the first aspect.

[0046] Other effects and advantages of the method, computer program and breathing apparatus of the present disclosure will become apparent from the detailed description following hereinafter. BRIEF DESCRIPTIONS OF THE DRAWINGS

[0047] The above objects, as well as additional objects, features and advantages of the present disclosure, will be more fully appreciated by reference to the following illustrative and nonlimiting detailed description of example embodiments of the present disclosure, when taken in conjunction with the accompanying drawings, of which:

[0048] Figure 1 illustrates an exemplary embodiment of a ventilation system for assessing fluid responsiveness of a patient connected to a breathing apparatus providing mechanical ventilation to the patient.

[0049] Figure 2 is a flowchart illustrating a method or manoeuvre for assessing fluid responsiveness of a mechanically ventilated patient, according to an exemplary embodiment of the present disclosure.

[0050] DETAILED DESCRIPTION

[0051] The proposed method, computer program and ventilation system for assessing fluid responsiveness of a mechanically ventilated patient will now be described with reference to the accompanying drawings, in which preferred exemplary embodiments of the disclosure are shown. It should be understood, however, that the method, computer program and breathing apparatus may be embodied also in other forms and the disclosure should not be construed as limited to the exemplary embodiments disclosed herein.

[0052] It is also to be understood that the terminology used herein is for purpose of describing particular embodiments only, and is not intended to be limiting. It should be noted that, as used in the specification and the appended claim, the articles "a", "an", "the", and "said" are intended to mean that there are one or more of the elements unless the context explicitly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may include several devices, and the like. Furthermore, the words "comprising", "including", "containing" and similar wordings does not exclude other elements or steps.

[0053] The present disclosure relates in general to an automated or semi-automated method or manoeuvre for assessing fluid responsiveness of a mechanically ventilated patient based on a monitored pulse pressure variation (PPV) or stroke volume variation (SW) of the patient. The method may be performed by a ventilation system including a breathing apparatus providing mechanical ventilation to the patient. Figure 1 shows an exemplary embodiment of such a ventilation system 1. The system 1 comprises a breathing apparatus 2 for providing mechanical ventilation to a patient 3.

[0054] The breathing apparatus 2 may be any type of apparatus capable of providing mechanical ventilation to the patient 3 through the supply of pressurised breathing gas to the airways of the patient 3. Ventilators and anaesthesia machines are non-limiting examples of such breathing apparatuses.

[0055] The breathing apparatus 2 is connected to the patient 3 via a patient circuit comprising an inspiratory line 5 for supplying breathing gas to the patient 3, and an expiratory line 7 for conveying expiration gas away from the patient 3. The inspiratory line 5 and the expiratory line 7 are connected to the patient 3 via a patient connector 13, such as an endotracheal tube. The inspiratory line 5 and the expiratory line 7 may be connected to the patient connector either directly (if using double lumen tubing) or via a Y-piece. In the illustrated example, the inspiratory line 5 and the expiratory line 7 are connected to a common line 9 via a Y-piece 11, which common line is connected to the patient 3 via the patient connector 13.

[0056] The breathing apparatus 2 comprises a control unit or control computer 15 for controlling the ventilation of the patient 3 based on ventilation settings set by an operator of the breathing apparatus 2 and / or automatically set by the breathing apparatus 2 based on measurements obtained by various sensors of the ventilation system 1. The control computer 15 controls the ventilation of the patient 3 by controlling a pneumatic unit 17 of the breathing apparatus 2, which pneumatic unit 17 may comprise various gas regulating means for regulating a flow of respiratory gas to and / or from the patient 3 based on control signals from the control computer 15. The pneumatic unit 17 is typically connected to one or more gas sources 19, 21 for receiving one or more breathing gases, and to the inspiratory line 5 for regulating a flow of inspiration gas to be delivered to the patient 3. The pneumatic unit 17 is typically also connected to the expiratory line 7 for regulating a flow of expiration gas from the patient 3. The pneumatic unit 17 may comprise any type of gas mixing and flow regulating means known in the art of ventilation, including but not limited to gas mixing chambers, controllable gas mixing valves, turbines, controllable inspiration and / or expiration valves, etc.

[0057] The breathing apparatus 2 may further comprise one or more flow sensors 23, 23’, 23” for measuring respiratory flow, and one or more pressure sensors 25, 25’, 25” for measuring respiratory pressure. The flow sensor may be a proximal flow 23 sensor located close to the patient 3 (e.g. in or close to the Y-piece 11) and configured to measure both an inspiratory flow of breathing gas delivered to the airways of the patient 3 during inspiration, and an expiratory flow of gas exhaled by the patient 3 during expiration. Likewise, the pressure sensor 25 may be a proximal pressure sensor located close to the patient 3 (e.g. in or close to the Y-piece 11) and configured to measure, during both inspiration and expiration, a proximate patient pressure substantially corresponding to an airway pressure of the patient 3. Alternatively or in addition to the flow sensor 23 and the pressure sensor 25 disposed in the Y-piece 11 of the patient circuit, the breathing apparatus 2 may comprise one or more internal flow sensors 23’, 23” for measuring respiratory gas flow, and / or one or more internal pressure sensors 25’, 25” for measuring respiratory gas pressure.

[0058] The breathing apparatus 2 may further comprise a display 32 for presenting information related to the ongoing ventilatory treatment of the patient 3. Such information may comprise current ventilation settings, alarm settings, various pressure and / or flow curves, information on clinical ventilation targets, etc. The display 32 may be a touchscreen allowing an operator to change settings and input information to the breathing apparatus 2, e.g. via a graphical user interface (GUI) presented on the display 32.

[0059] The control computer 15 comprises a processor 30 and a memory 31. The processor 30 may be constituted by e.g. a microprocessor, and the memory 31 may be constituted by e.g. a non- transitory memory hardware device. The memory 31 stores one or more computer programs for controlling the operation of the breathing apparatus 2, including a computer program comprising instructions for causing the breathing apparatus 2 to perform or participate in the performance of a fluid responsiveness assessment in accordance with the principles of the present disclosure. In the illustrated exemplary embodiment, the computer program for fluid responsiveness stored in the breathing apparatus 2 is a first computer program component configured to exchange data with a second computer program component residing in a hemodynamic monitor 4 of the ventilation system 1 , and to control the breathing apparatus 2 based on data received from the hemodynamic monitor 4.

[0060] The hemodynamic monitor 4 is configured to monitor various parameters relating to the function and performance of the cardiovascular system of the patient 3. Non-limiting examples of parameters that may be monitored by the hemodynamic monitor 4 include arterial blood pressure (e.g., systolic, diastolic and / or mean arterial pressure), cardiac output, PPV, SW, heart rate and rhythm, parameters relating to oxygen delivery and consumption, such as mixed venous oxygen saturation (SvO2) and arterial oxygen saturation (SaO2), etc. In the illustrated embodiment, the hemodynamic monitor 4 is seen to be connected to at least a heart rate sensor 6 for measuring a heart rate and / or a pulse rate of the patient 3, such as an electrocardiogram (ECG) sensor, and to a blood pressure sensor 8 for measuring a blood pressure of the patient 3. In this exemplary embodiment, the blood pressure sensor 8 is an arterial line which may be inserted e.g. into the radial artery, the femoral artery, the brachial artery or the dorsalis pedis artery of the patient 3 in order to continuously monitor blood pressure. The arterial line 8 comprises a pressure transducer and pressure tubing (not shown) for continuous blood pressure monitoring. In other embodiments, the blood pressure sensor 8 may be a non-invasive blood pressure sensor, such as an oscillometric blood pressure sensor comprising an inflatable cuff placed around the upper arm, wrist or ankle, a finger cuff sensor using the volume clamp method to measure blood pressure, an arterial tonometry sensor for measuring blood pressure through the skin of the patient, or a pulse transit time (PTT) sensor for determining the blood pressure from the time it takes for a blood pressure pulse to travel between two arterial sites. As will be discussed below, for the purpose of assessing fluid responsiveness of the ventilated patient 3 in accordance with the principles of the present disclosure, the system 1 should be able to determine at least one of the heart rate and the pulse rate of the patient. To this end, the hemodynamic monitor 4 may also be configured to determine the pulse rate of the patient 3 by means of the blood pressure sensor 8, e.g. from a blood pressure curve derived from blood pressure measurements obtained by the blood pressure sensor. It should hence be appreciated that the heart rate sensor 6 is not an essential component of the system 1.

[0061] The hemodynamic monitor 4 comprises a display 32’ for presenting information relating to the monitored parameters. The display 32’ may be a touchscreen allowing an operator to change settings and input information to the hemodynamic monitor 4, e.g. via a GUI presented on the display 32’.

[0062] The hemodynamic monitor 4 further comprises a control computer 15’ including a processor 30’ and a memory 3T. The processor 30’ may be constituted by e.g. a microprocessor, and the memory 3T may be constituted by e.g. a non-transitory memory hardware device. The memory 3T stores the above-mentioned second computer program component, which computer program component is configured to exchange data with the first computer program component residing in the breathing apparatus 2.

[0063] The breathing apparatus 2 and the hemodynamic monitor 4 are communicatively connected to each other via a communication interface 10, which may be a wired or wireless communication interface. In some embodiments, the communication interface 10 may be a wired interface, such as an RS 232C serial interface or an Ethernet interface. In other embodiments, the communication interface 10 may be a wireless interface, such as a Bluetooth or WiFi interface.

[0064] The function for assessing fluid responsiveness of the ventilated patient 3 will now be described with reference to Fig. 2, with simultaneous reference still made to the ventilation system in Fig. 1.

[0065] Fig. 2 is a flowchart illustrating a method or manoeuvre for assessing fluid responsiveness of a mechanically ventilated patient 3, according to an exemplary embodiment of the present disclosure. The method is a computer-implemented method that is performed in response to execution of the above-mentioned computer program for fluid responsiveness assessment by at least one processor of the ventilation system 1.

[0066] In a first step, S1, baseline ventilation is provided to the patient by the breathing apparatus 2.

[0067] The baseline ventilation is provided in any of a pressure controlled ventilation (PCV) mode or a volume controlled ventilation (VCV) mode. In both PCV and VCV, the respiratory rate (RR) and the l:E ratio can be set by an operator, or automatically set to default values, whereby the control computer 15 of the breathing apparatus 2 controls the pneumatic unit 17 to deliver breaths in accordance with the RR and l:E ratio settings. The RR and l:E ratio, as well as e.g. pressure levels (in PCV) or tidal volume (in VCV), are typically set to achieve one or more clinical ventilation targets. The clinical ventilation targets may, for example, include a target for a minute ventilation (MV) of the patient 3.

[0068] In a second step, S2, a heartrate (HR) and / or a pulse rate (PR) of the patient 3 is determined. In the exemplary system setup illustrated in Fig. 1 , this is performed by the hemodynamic monitor 4 based on the signals obtained by the heartrate sensor 6. In other embodiments, however, the step of determining RR and / or PR may be performed by the breathing apparatus 2 itself, or by another dedicated device to which the breathing apparatus is communicatively connected.

[0069] The HR and / or PR of the patient 3 may be monitored continuously during baseline ventilation, or it may be determined in response to a request from an operator to perform a fluid responsiveness assessment, e.g. as requested by the operator by giving a command for fluid responsiveness assessment via the GUI presented on any of the displays 32 or 32’. In a third step, S3, recommended FRA ventilation settings including at least a recommended respiratory rate, RRFRA, and / or a recommended inspiratory-to-expiratory ratio, I:EFRA, for the FRA period are calculated based on the determined HR and / or PR of the patient.

[0070] The recommended respiratory rate, RRFRA, for the FRA period is preferably calculated based on both the HR and / or PR of the patient determined in step S2 and an acceptable range of HR:RR ratios. Thereby, RRFRA can be calculated such that the HR: RRFRA ratio falls within a range of HR:RR ratios that prevent false negatives and / or false positives in the fluid responsiveness assessment. Some previous studies suggest that the HR:RR ratio should be at least 3,6 in order for PPV and SVV to avoid false negatives. However, during certain circumstances, an HR:RR ratio of 2 or more may be sufficient to reach a sufficient degree of certainty in the fluid assessment. Therefore, a lower limit of the acceptable range of HR:RR ratios may e.g. be 2, more preferably 3, and most preferably 3,6. Likewise, to avoid false positives in the fluid responsiveness assessment, the acceptable range of HR:RR ratios may also have an upper limit. The upper limit of the acceptable range of HR:RR ratios may e.g. be 10, more preferably 9, and even more preferably 8.

[0071] Just like the HR:RR ratio, the l:E ratio also has an impact on the PPV and SVV of the ventilated patient 3, with a more balanced inspiration and expiration time (e.g., an l:E ratio of 1 :1) leading to higher PPV values. This is due to the fact that a more balanced inspiration and expiration time leads to a larger difference in PPmax and PPmin (see Eq. 1), thus resulting in a higher PPV value. This means that even for acceptable HR:RR ratios, too low or too high l:E ratios may still create false negatives or false positives in the fluid responsiveness assessment due to the effect of the l:E ratio on the PPV of the patient. In particular, there is a risk for false negatives in the fluid responsiveness assessment for a combination of high respiratory rates (low HR:RR ratio) and long expiration times (low l:E ratio). Therefore, instead or in addition to determining a recommended respiratory rate, RRFRA, for the FRA period, a recommended l:E ratio, I:EFRA, that will prevent false positives and false negatives in the fluid responsiveness assessment may be determined and suggested for the FRA period. In some embodiments, the recommended FRA ventilation settings may hence comprise a recommended l:E ratio, I:EFRA, suggested for use during the FRA period with a current respiratory rate of the baseline ventilation, or a new recommended respiratory rate for the FRA period. In particular, the recommended FRA ventilation settings may comprise a recommended l:E ratio that is increased compared to a current l:E ratio of the baseline ventilation in scenarios where a current respiratory rate of the baseline ventilation makes the current HR:RR ratio of the baseline ventilation fall within the acceptable range of HR:RR ratios for the FRA period but still close to a lower limit of the acceptable range of HR:RR ratios (e.g. closer to the lower limit than a certain threshold value). In this scenario, a change of the inspiratory and / or expiratory time to obtain a more balanced l:E ratio may be sufficient to avoid false negatives in the fluid responsiveness assessment.

[0072] From the above it should be appreciated that the recommended ventilation settings may comprise any or both of a recommended respiratory rate, RRFRA, and a recommended l:E ratio, I:EFRA. It should also be appreciated that I:EFRA may be determined based on a current respiratory rate of the baseline ventilation, or the recommended respiratory rate, RRFRA, suggested for the FRA period. Similarly, it should be appreciated that the recommended respiratory rate, RRFRA, may be determined based on a current l:E ratio of the baseline ventilation, or the recommended l:E ratio, I:EFRA, suggested for the FRA period. In some embodiments, RRFRA and / or I:EFRA may be determined based on an acceptable range of combined HR:RR ratios and l:E ratios for the FRA period, such that a combination of a recommended respiratory rate, RRFRA, and a recommended l:E ratio, I:EFRA, falls within the acceptable range of combined HR:RR ratios and l:E ratios for the FRA period.

[0073] In order to ensure adequate ventilation of the patient also during the FRA period, the recommended FRA settings may also be calculated based on a predicted ventilation performance during the FRA period (i.e., using the recommended FRA ventilation settings) with respect to at least one clinical ventilation target set for the baseline ventilation. Changing the respiratory rate and / or the l:E ratio during the FRA period may affect the ventilation performance during the FRA period with respect to clinical ventilation targets set for the baseline ventilation. For example, the change in RR and / or l:E ratio between the period of baseline ventilation and the FRA period may introduce a change in the minute ventilation (MV) of the patient. Therefore, the recommended FRA settings may be determined as a trade-off between optimal HR:RR ratio for fluid responsiveness assessment and optimal ventilation performance during the FRA period with respect to the at least one clinical ventilation target.

[0074] In some embodiments, the method may comprise a step of determining the recommended FRA settings by minimising a deviation between a clinical ventilation target for the baseline ventilation (e.g. a set minute ventilation) and a predicted ventilation performance during the FRA period with respect to the at least one clinical ventilation target. For example, the method may comprise a step of calculating RRFRA and / or I:EFRA such that the HR: RRFRA ratio falls within the acceptable range of HR:RR ratios while minimising a deviation with respect to the at least one clinical ventilation target between baseline ventilation and ventilation using the recommended FRA settings. Furthermore, the recommended FRA settings may, besides RRFRA and / or I: EFRA, comprise a recommended pressure level (in PCV) or tidal volume (in VCV) to be used during the FRA period. The recommended pressure level in PCV may include any of, or any combination of, a peak inspiratory pressure (PIP), a PEEP, or a driving pressure (typically defined as the difference between PIP and PEEP). The recommended pressure level or tidal volume may be calculated as a pressure level or tidal volume that optimises a ventilation performance during the FRA period with respect to the at least one clinical ventilation target. For example, the recommended pressure level or tidal volume may be calculated such that the above- mentioned deviation with respect to the at least one clinical ventilation target between baseline ventilation and ventilation during the FRA period is minimised by the recommended FRA ventilation settings. Thus, in some embodiments, RRFRA and / or I : EFRA is calculated such that the H R: RRFRA ratio falls within the acceptable range of HR:RR ratios while minimising a deviation with respect to the at least one clinical ventilation target between baseline ventilation and ventilation during the FRA period. Thus, if RRFRA and / or I : EFRA cannot be calculated such that the deviation is fully eliminated, the method may comprise a step of calculating a recommended pressure level (in PCV) or tidal volume (in VCV) that eliminates or at least further reduces the deviation from the clinical ventilation target when used together with RRFRA and / or I : EFRA during the FRA period.

[0075] In some embodiments, the method may comprise the steps of first setting a recommended tidal volume to be delivered to the patient during the FRA period, and then calculating a recommended respiratory rate, RRFRA, which, given the determined tidal volume, results in an MV substantially corresponding to the MV of the baseline ventilation. Preferably, the tidal volume of the FRA period should be at least 8 ml / kg bodyweight of the patient in order to address also the known limitation of low tidal volume during PPV or SW based assessment of fluid responsiveness (see background). In recent clinical practice, the tidal volume during baseline ventilation is commonly set lower than 8 ml / kg. Thus, the method may comprise the steps of first setting a recommended increased tidal volume of 8 ml / kg for the FRA period, and then calculating a recommended decreased respiratory rate which, given the tidal volume of 8 ml / kg, results in an MV during the FRA period substantially corresponding to the MV of the baseline ventilation. In volume-controlled modes of ventilation, this means that the recommended FRA ventilation settings may comprise a tidal volume of approximately 8 ml / kg, and a respiratory rate calculated based on the tidal volume and the MV of the baseline ventilation. In pressure-controlled modes of ventilation, this means that the recommended FRA ventilation settings may comprise a driving pressure resulting in a tidal volume of approximately 8 ml / kg, and a respiratory rate calculated based on the tidal volume and the MV of the baseline ventilation. The goal of this particular approach for calculation of recommended FRA ventilation settings is to fulfil both the HR:RR ratio and the tidal volume criteria for PPV or SW based assessment of fluid responsiveness. If it turns out that there is no respiratory rate that falls within the acceptable range of HR:RR ratios for the FRA period while resulting in an MV corresponding to that of the baseline ventilation with a tidal volume of 8 ml / kg, then the tidal volume for the FRA period may be increased until there is a combination of a RR and tidal volume that fulfils both the criteria of the HR:RR ratio falling within the acceptable range of HR:RR ratios for the FRA period and the tidal volume being at least 8 ml / kg predicted bodyweight during the FRA period. The tidal volume for the FRA period should preferably not exceed a maximum tidal volume limit, e.g. corresponding to 12 ml / kg. In some embodiments, obtaining an acceptable HR:RR ratio during the FRA period may take precedence over maintaining a desired MV during the FRA period and, therefore, if the tidal volume required to maintain the MV with a HR:RR ratio that falls within the acceptable range of HR:RR ratios exceeds the maximum tidal volume limit, then the recommended RR is determined to keep the HR:RR ratio for the FRA period within the acceptable range of HR:RR ratios and the tidal volume is set to the maximum tidal volume limit. This way, both the HR:RR ratio and the tidal volume criteria are met while allowing a slight decrease in minute ventilation during the FRA period.

[0076] The calculation of recommended FRA ventilation settings may be performed by the breathing apparatus 2, the hemodynamic monitor 4, or even a server (not shown) or other device to which the breathing apparatus 2 and / or the hemodynamic monitor 4 is communicatively connected. The device that performs the calculation must have access to the HR and / or PR of the patient determined in step S2. Preferably, in order to determine whether a change in RR and / or l:E ratio is required, the device that performs the calculation should also have access to the RR and l:E ratio used during the baseline ventilation. Furthermore, in order to calculate recommended FRA ventilation settings that minimises any deviation from a clinical ventilation target of the baseline ventilation, the device performing the calculation should also have access to information on clinical ventilation targets of the baseline ventilation, such as a minute ventilation of the baseline ventilation. In the exemplary system setup illustrated in Fig. 1, the breathing apparatus 2 is configured to communicate data relating to RR and l:E ratio settings and clinical ventilation targets to the hemodynamic monitor 4 via the communication interface 6, whereby the hemodynamic monitor 4 calculates the recommended FRA ventilation settings and sends them back to the breathing apparatus 2 for subsequent use during the FRA period.

[0077] Step S3 may be preceded by a step (not shown) of determining a baseline heart-rate to respiratory-rate (HR:RR) ratio based on the HR and / or the PR of the patient 3 determined in step S2, together with the respiratory rate set for the baseline ventilation. If the baseline HR:RR ratio falls within an acceptable range of HR:RR ratios for the FRA period, or if the combination of the baseline HR:RR ratio and the baseline l:E ratio falls within the acceptable range of combined HR:RR ratios and l:E ratios for the FRA period, no adjustment to the baseline RR setting (or l:E ratio setting) is needed. However, if the baseline HR:RR ratio or the combination of the baseline HR:RR ratio and the baseline l:E ratio fall outside the respective acceptance range, e.g. due to under-sampling or over-sampling of heartbeats with respect to the respiratory rate, the method proceeds to step S3 in which a new recommended respiratory rate and / or l:E ratio for the FRA period is calculated.

[0078] The method may be a fully automatic method where the FRA period is automatically initiated and the recommended FRA ventilation settings are automatically put into use during the FRA period, or it may be a semi-automatic method where the operator is presented with information relating to the recommended FRA ventilation settings and, optionally, the effect of the recommended FRA ventilation settings on one or more clinical ventilation targets set for the ongoing baseline ventilation, and asked to confirm use of the recommended FRA ventilation settings before the FRA period is initiated and the recommended FRA ventilation settings are put into use. The information that is presented to the operator may also comprise additional information relating to the FRA period or the process for fluid responsiveness assessment, such as a duration of the FRA period, an indication of reliability of the fluid responsiveness assessment should the FRA period be initiated using the recommended ventilation settings, etc.

[0079] In some embodiments, the information relating to the recommended ventilation settings that are presented to the operator may comprise a range of recommended values for one or more of the ventilation settings. For example, the presented information may comprise a recommended range of respiratory rates, RRFRA, a recommended range of l:E ratios, I:EFRA, a recommended range of pressure levels (in PCV), and / or a recommended range of tidal volumes (in VCV). The operator may then select the one or more ventilation settings to be used during the FRA period from the recommended range or ranges of ventilation settings.

[0080] In some embodiments, the information relating to the recommended ventilation settings may comprise an indicator (e.g. a green or a red symbol) indicative of whether a currently selected ventilation setting, or combination of ventilation settings, correspond to the recommended ventilation settings for the FRA period. In this case, the operator may be allowed to select ventilation settings without limitation to the recommended ventilation settings, whereas the indicator dynamically indicates whether the current selection of ventilation settings corresponds to the recommended ventilation settings. Thus, the method may comprise an optional step S4 of presenting information relating to the recommended FRA ventilation settings to a system operator, and an optional step S5 of requesting the operator to confirm use of the recommended FRA ventilation settings before switching to the recommended ventilation settings and initiating the FRA period. If the operator confirms use of the recommended FRA ventilation settings, the method proceeds to step S6.

[0081] In step S6, the baseline ventilation is aborted and the FRA period is initiated by starting to ventilate the patient 3 with the recommended FRA ventilation settings (step S7).

[0082] In a next step S8 occurring during ventilation of the patient 3 with the recommended FRA ventilation settings, the PPV and / or SVV of the patient is determined. As discussed above, the determination of PPV and / or SVV may be performed by any of the breathing apparatus 2 or the hemodynamic monitor 4 by use of various sensors and techniques. In the exemplary system setup illustrated in Fig. 1 , the hemodynamic monitor 4 is configured to determine the PPV and / or SVV of the patient 3 based on sensor signals obtained by a blood pressure sensor of the arterial line 8.

[0083] In a final step S9, the fluid responsiveness of the patient 3 is assessed based on the determined PPV and / or SVV, and information indicative of a degree of fluid responsiveness of the patient 3 is presented to the operator on a display of the ventilation system 1 , e.g. the display 32 of the breathing apparatus 2 and / or the display 32’ of the hemodynamic monitor 4.

[0084] The actual assessment of fluid responsiveness typically involves a step of determining a degree of fluid responsiveness of patient based on the PPV and / or SVV determined during the FRA period. In some embodiments, the assessment may be binary in the meaning that the patient is judged to be either “fluid responsive” or “not fluid responsive”. For example, the patient 3 may be judged to be fluid responsive if the PPV is greater than 12-13% and / or if the SW is greater than 10-15%. That the patient is fluid responsive may, in this context, mean that the patient is likely to respond with an increase in cardiac output to a 500 mL saline infusion.

[0085] The information that is presented to the operator as a result of the fluid responsiveness assessment may comprise any type of symbols or text indicative of the fluid responsiveness of the patient 3. For example, the information may comprise only the determined PPV and / or SW value, in order for the operator herself to draw any conclusions about the likelihood of the patient responding to fluid administration. In other embodiments, the information may comprise a recommendation as to whether fluid should be administered or not, based on the determined PPV and / or SVV value.

[0086] The assessment of fluid responsiveness may be performed by any of the breathing apparatus 2, the hemodynamic monitor 4, or a server or remote device to which the breathing apparatus and / or the hemodynamic monitor 4 is communicatively connected. In the exemplary system setup illustrated in Fig. 1 , the hemodynamic monitor 4 is configured to assess the fluid responsiveness of the patient based on the determined PPV and / or SVV, and to cause the information indicative of the degree of fluid responsiveness of the patient to be presented on any or both of display 32 of the breathing apparatus 2 and the display 32’ of the hemodynamic monitor 4.

[0087] The duration of the FRA period should be long enough in order for the recommended FRA ventilation settings to have effect on the hemodynamic system of the ventilated patient. The time until a change in ventilation settings has a noticeable hemodynamic effect is at least partly governed by the pulmonary transit time (approximately 4-8 seconds). Therefore, the FRA period should preferably be at least 5 seconds, preferably at least 10 seconds, and more preferably at least 30 seconds. Typically, in order to ensure that the use of the recommended FRA ventilation settings has had a desired effect, the duration of the FRA period is around 1-2 minutes.

[0088] At the same time, if the use of the recommended FRA settings results in a deviation from the clinical ventilation target, e.g. a set minute ventilation of the baseline ventilation, the duration of the FRA period should be short enough to maintain an acceptable mean ventilation performance with respect to the clinical ventilation target over time. Therefore, the duration of the FRA period may be either predetermined or determined based on the ventilation performance during the FRA period with respect to the at least one clinical ventilation target of the baseline ventilation.

[0089] In some embodiments, the FRA period may hence be a relatively short period during which baseline ventilation settings are temporarily changed to the recommended FRA ventilation settings in order to reliably determine PPV and / or SW. After PPV and / or SW determination, the FRA period may be aborted and baseline ventilation resumed by automatically switching from the recommended FRA ventilation settings back to the ventilation settings used during the baseline ventilation. In other embodiments, the FRA period may be a relatively long period or even a permanent ventilation state during which PPV and / or SVV is repeatedly or continuously determined, which ventilation state effectively becomes a new baseline ventilation. For example, if the deviation between the clinical ventilation target for the baseline ventilation and the predicted ventilation performance during the FRA period with respect to the clinical ventilation target falls within an acceptable range, the patient 3 may be permanently ventilated using the recommended FRA ventilation settings, whereby reliable PPV and / or SVV values may be obtained continuously to provide for continuous and reliable fluid responsive assessment of the ventilated patient.

Claims

CLAIMS1 . A method for assessing fluid responsiveness of a patient (3) connected to a breathing apparatus (2) providing mechanical ventilation to the patient (3), the method comprising the steps of: initiating (S6) a fluid responsiveness assessment [FRA] period for assessing a degree of fluid responsiveness of the patient (3); determining (S8) a pulse pressure variation [PPV] and / or a stroke volume variation [SW] of the patient (3) during the FRA period, and presenting (S9) information indicative of the fluid responsiveness of the patient (3) to an operator of the breathing apparatus (2) based on the determined PPV and / or SVV, characterised by the steps of: determining (S2) a heartrate [HR] or pulse rate [PR] of the patient (3) during baseline ventilation of the patient (3) prior to the FRA period; calculating (S3) recommended FRA ventilation settings for the FRA period based on the determined HR and / or PR, the recommended FRA ventilation settings comprising a recommended respiratory rate [RRFRA] and / or a recommended inspiratory-expiratory ratio [I:EFRA], and ventilating (S7) the patient (3) using the recommended FRA ventilation settings during the FRA period.

2. The method of claim 1 , wherein RRFRA is calculated based on the determined HR and / or PR of the patient (3) and an acceptable range of heart-rate to respiratory- rate [HR:RR] ratios for the FRA period.

3. The method of claim 1 or 2, further comprising the steps of: presenting (S5) the recommended FRA ventilation settings to an operator of the breathing apparatus (2) prior to initiation of the FRA period, and initiating (S6) the FRA period in response to an acknowledgement of the recommended FRA ventilation settings by the operator.

4. The method of any of the preceding claims, further comprising the steps of: determining a baseline heart-rate to respiratory-rate [HR:RR] ratio based on the determined HR and / or PR of the patient (3) and a set respiratory rate [RR] for the baseline ventilation; comparing the determined baseline HR:RR ratio with an acceptable range of HR:RR ratios for the FRA period, andcalculating the recommended FRA ventilation settings and ventilating the patient (3) using the recommended FRA ventilation settings only when the determined baseline HR:RR ratio falls outside the acceptable range of HR:RR ratios for the FRA period.

5. The method of any of the previous claims, further comprising the step of: automatically returning to baseline ventilation after the FRA period by automatically switching from the recommended FRA ventilation settings to ventilation settings used during the baseline ventilation.

6. The method of any of the previous claims, wherein the recommended FRA ventilation settings are calculated based on a predicted ventilation performance during the FRA period with respect to at least one clinical ventilation target set for the baseline ventilation.

7. The method of claim 6, comprising a step of: calculating RRFRA and / or I :EFRA such that the H R: RRFRA ratio falls within an acceptable range of HR:RR ratios for the FRA period while RRFRA and / or I: EFRA minimises a deviation between a clinical ventilation target for the baseline ventilation and a predicted ventilation performance with respect to the at least one clinical ventilation target during the FRA period, and / or calculating recommended FRA ventilation settings further comprising a pressure level or a tidal volume, wherein the pressure level or tidal volume is calculated to eliminate or at least reduce the deviation between the clinical ventilation target for the baseline ventilation and the predicted ventilation performance with respect to the at least one clinical ventilation target during the FRA period, when used together with the recommended RRFRA and / or I: EFRA.

8. A computer program for a system (100) for assessing fluid responsiveness of a patient (3) connected to a breathing apparatus (2) providing mechanical ventilation to the patient (3), characterised in that the computer program comprises computer-readable instructions which, when executed by at least one processor (30, 30’) of the system (100), cause the system to perform the method of any of the preceding claims.

9. A system (100) for assessing fluid responsiveness of a patient (3) connected to a breathing apparatus (2) providing mechanical ventilation to the patient (3), the system (100) comprising at least one processor (30, 30’) configured to: initiate a fluid responsiveness assessment [FRA] period for assessing a degree of fluid responsiveness of the patient (3);determine a pulse pressure variation [PPV] and / or a stroke volume variation [SW] of the patient (3) during the FRA period, and present information indicative of the fluid responsiveness of the patient (3) to an operator of the breathing apparatus (2) based on the determined PPV and / or SVV, characterised in that the at least one processor is further configured to: determine a heartrate [HR] or pulse rate [PR] of the patient (3) during baseline ventilation of the patient (3) prior to the FRA period; calculate recommended FRA ventilation settings for the FRA period based on the determined HR and / or PR, the recommended FRA ventilation settings comprising a recommended respiratory rate [RRFRA] and / or a recommended inspiratory-expiratory ratio [I:EFRA], and control the breathing apparatus (2) to ventilate the patient (3) using the recommended FRA ventilation settings during the FRA period.

10. The system (100) of claim 9, wherein the at least one processor (30, 30’) is configured to calculate RRFRA based on the determined HR and / or PR of the patient (3) and an acceptable range of heart-rate to respiratory-rate [HR:RR] ratios for the FRA period.

11. The system (100) of claim 9 or 10, wherein the at least one processor (30, 30’) is further configured to: present the recommended FRA ventilation settings to an operator of the breathing apparatus (2) prior to initiation of the FRA period, and initiate the FRA period in response to an acknowledgement of the recommended FRA ventilation settings by the operator.

12. The system of any of the claims 9-11 , wherein the at least one processor (30, 30’) is configured to: determine a baseline heart-rate to respiratory-rate [HR:RR] ratio based on the determined HR and / or PR of the patient (3) and a set respiratory rate [RR] for the baseline ventilation, compare the determined baseline HR:RR ratio with an acceptable range of HR:RR ratios for the FRA period, and calculate the recommended FRA settings and ventilate the patient (3) using the recommended FRA settings only when the determined HR:RR ratio falls outside the acceptable range of HR:RR ratios for the FRA period.

13. The system of any of the claims 9-12, wherein the at least one processor (30, 30’) is configured to control the breathing apparatus (2) to return to baseline ventilation after the FRA period by automatically switching from the recommended FRA ventilation settings to ventilation settings used during the baseline ventilation.

14. The system of any of the claims 9-13, wherein the at least one processor (30, 30’) is configured to calculate the recommended FRA ventilation settings based on a predicted ventilation performance during the FRA period with respect to at least one clinical ventilation target set for the baseline ventilation.

15. The system of any of the claims 9-14, wherein the at least one processor (30, 30’) is configured to: calculate RRFRA and / or I :EFRA such that the H R: RRFRA ratio falls within an acceptable range of HR:RR ratios for the FRA period while RRFRA and / or I: EFRA minimises a deviation between a clinical ventilation target for the baseline ventilation and a predicted ventilation performance with respect to the at least one clinical ventilation target during the FRA period, and / or calculate recommended FRA ventilation settings further comprising a pressure level or a tidal volume, wherein the pressure level or tidal volume is calculated to eliminate or at least reduce the deviation between the clinical ventilation target for the baseline ventilation and the predicted ventilation performance with respect to the at least one clinical ventilation target during the FRA period, when used together with the recommended RRFRA and / or I: EFRA.

Images