Urinary oxygen sensor

Abstract

An elongate oxygen sensor (1, 201, 301, 401) for insertion into a urinary drainage lumen of an elongate catheter (101). The elongate oxygen sensor (1, 201, 301, 401) includes: a sensor tip (2, 202, 302, 402), located at a distal end of the elongate oxygen sensor (1, 201, 301, 401), having a first width; a spacer portion (10, 210, 310, 410), for spacing the sensor tip (2, 202, 302, 402) away from a wall of the urinary drainage lumen, the spacer portion (10, 210, 310, 410) having a second width (21, 221a, 221b, 321a, 321b, 421a, 421b), larger than the first width and located further from the distal end than the sensor tip; and a body portion (12, 212, 312, 412), located further from the distal end than the spacer portion (10, 210, 310, 410), the body portion having a third width, smaller than the second width.

Description

[0001] Urinary Oxygen Sensor

[0002] BACKGROUND OF THE INVENTION

[0003] This invention relates to an elongate oxygen sensor for insertion into a urinary drainage lumen of an elongate catheter, an apparatus for sensing urinary oxygen and a method of sensing urinary oxygen.

[0004] Indwelling urinary catheters (also called Foley catheters) are well known instruments for draining urine from a bladder continuously. Human or animal patients who are unwell or undergoing major surgery routinely have a bladder (Foley type) catheter inserted via the urethra, in order to allow urine to be continuously drained from the bladder. A Foley catheter is inserted through the urethra so that the distal end of the catheter sits in the patient's bladder. A small balloon is inflated near the tip of the catheter, inside the bladder, to hold the catheter in place. The catheter has a drainage lumen, along its length, for draining urine, and a second lumen for inflating and deflating the balloon as required.

[0005] It is known to sense urinary oxygen of urine within a catheter, or downstream (i.e. at a proximal, external end of the catheter). Urinary oxygen has been recognised as a useful medical indicator, particularly in relation to predicting or monitoring for acute kidney injury (AKI). In order to obtain clinically useful information, it is important that oxygen content of the urine is measured as accurately as possible.

[0006] SUMMARY OF THE INVENTION

[0007] From a first aspect, the invention provides an elongate oxygen sensor for insertion into a urinary drainage lumen of an elongate catheter, comprising: a sensor tip, located at a distal end of the elongate oxygen sensor, the sensor tip having a first width; a spacer portion, for spacing the sensor tip away from a wall of the urinary drainage lumen, the spacer portion located further from the distal end than the sensor tip, the spacer portion having a second width, larger than the first width; and a body portion, located further from the distal end than the spacer portion, the body portion having a third width, smaller than the second width. The spacer portion spaces (i.e. separates) the sensor tip away from the wall of the urinary drainage lumen. By this it will be understood that the spacer portion acts to keep the sensor tip from contacting the inner face of the (internal) wall of the urinary drainage lumen (e.g. to keep the sensor tip central within the urinary drainage lumen). Thus, it acts as a buffer which makes contact with the inner face of the lumen wall before the sensor tip contacts the wall, and thereby prevents (or helps to prevent) contact of the sensor tip with the wall, in particular as the oxygen sensor is inserted and moved along the drainage lumen (i.e. the spacer portion is for spacing the sensor tip away from the wall of the urinary drainage lumen (at least) during insertion of the sensor into the urinary drainage lumen).

[0008] Thus it will be seen that, in accordance with the invention, by providing a spacer portion further from the distal end than the sensor tip (i.e. behind the sensor tip), which has a larger width than both the sensor tip and the body portion, a buffering or centring effect is achieved by the spacer portion as the oxygen sensor is inserted into the urinary drainage lumen, preventing the sensor tip from touching an inner face of the wall of the lumen. Preventing contact of the sensor tip with the inner face of the lumen wall is important to achieve accurate oxygen measurement, since the lumen wall is commonly manufactured from a material (such as silicone) which absorbs oxygen, and therefore contact with an inner face of this wall may contaminate the sensor tip with oxygen and thereby affect the measurement, making it less accurate. Preventing contact of the sensor tip with the inner face of the lumen wall is also very important during insertion of the sensor. This is because there is a risk of damage to the sensor tip, which may be highly fragile, if contact occurs during insertion, e.g. due to friction occurring at the point of contact. This is particularly problematic if the sensor tip continues to be moved along the length of the lumen whilst in contact with the inner lumen wall such that the tip is dragged along the wall. The membrane and / or coating of the sensor tip may be particularly sensitive to damage. Thus the spacing function provided by the spacer portion helps to reduce the risk of sensor damage during insertion into the lumen by spacing the sensor tip away from the inner wall so as to prevent (or reduce the likelihood of) contact.

[0009] The body portion, located proximal of the spacer portion, has a smaller width than the spacer portion. This step down in width of the oxygen sensor provides the further advantage of allowing easier insertion of the oxygen sensor than if the larger width of the spacer portion were continued along the length of the body portion, as this would increase friction. It furthermore has the advantage that the spacer portion only minimally reduces the flowrate of urine as it passes past the sensor tip and through the urinary drainage lumen of the catheter to a drainage bag.

[0010] It will be understood that the width refers to the external width of each portion, i.e. from one outer edge to another outer edge, i.e. its extent from one side to another along a given direction. Thus, for a given width direction it is the maximum (exterior) extent, i.e. thickness, width that the portion has along that width direction.

[0011] The width will be understood as extending in a transverse plane, i.e. transverse to the length of the elongate oxygen sensor. It thus may be referred to as a transverse width. Thus the width may be understood as the extent along a width direction, where that a direction extends in a transverse plane, i.e. transverse to the length of the elongate oxygen sensor.

[0012] The width(s) referred to may be the transverse width through the centre (i.e. cross- sectional centre with respect to the transverse cross-section) of the referenced portion (including the sensor tip). Thus one some or all of the referenced widths may be a diameter (i.e. first width may be first diameter etc.), optionally a maximum or largest diameter. The sensor tip and / or the spacer portion and / or the body portion may have a circular (transverse) cross-section, thus the width may refer to the diameter of the circle. Again the shape of the cross-section will be understood as referring to its outer, external edge.

[0013] In some embodiments any or all of the widths referred to may refer specifically to the maximum (i.e. largest width) of that part in a particular transverse plane (i.e. of its widths along all width directions at a particular point along its length), of a respective portion.

[0014] In some embodiments, the first width, second width and third width may be defined in the same longitudinal plane i.e. such that treating the elongate direction of the elongate oxygen sensor as a linear axis, and defining a longitudinal plane containing this axis, the first width, second width and third width all extend along width directions with lie in this longitudinal plane and are mutually parallel. Thus, in some embodiments, the first width, second width and third width may be defined by the intersection between a (single) longitudinal plane, and respective transverse planes in each section (i.e. at length positions within the sensor tip, spacer portion, and body portion). Such widths may be understood as relating to effectively the same width direction defined in the different portions.

[0015] Features described herein above and further below in relation to a first width, a second width and a third width may, in some embodiments, be understood as referring to every (i.e. all) first widths, second widths and third widths (or diameters) of the respective portions (i.e. to be the case for each width of that portion), i.e. such that the width of the spacer portion in all transverse directions is larger than the respective width of the sensor tip and the body portion in all transverse directions.

[0016] The body portion and / or the spacer portion and / or the sensor tip may have a circular (outer) cross-section. The body portion and / or the spacer portion and / or the sensor tip may have a constant cross-sectional shape along their length, i.e. the same shape along their length.

[0017] Still further, the spacer portion advantageously provides a visual indicator which may be used to aid placement of the sensor tip in a position within the urinary drainage lumen that is beneficial for making oxygen measurements of urine. In particular, as detailed further below, the spacer portion assists a user to be able to place the sensor tip within the drain hole of the catheter (i.e. aligned along the length direction with the opening). This enables the oxygen sensor to detect the oxygen tension in free-flowing urine as soon as the urine enters the catheter. At this position minimal oxygen bearing artefacts will be present that could otherwise adversely affect the (true) oxygen value from the urine.

[0018] As set out above, the spacer portion may advantageously be used to position the sensor tip at a location within the urinary drainage lumen that is particularly suitable (possibly even optimum) for making urinary oxygen measurements (e.g. aligned with the drain hole, which may also be at a position close to, but not in contact with, the distal inner end surface of the urinary drainage lumen). Thus, according to a second aspect of the present invention, there is provided a method of sensing urinary oxygen using an elongate oxygen sensor, the elongate oxygen sensor comprising: a sensor tip, located at a distal end of the elongate oxygen sensor and having a first width; a spacer portion, for spacing the sensor tip away from a wall of the urinary drainage lumen, the spacer portion located further from the distal end than the sensor tip, the spacer portion having a second width, larger than the first width, and a body portion, located further from the distal end than the spacer portion, the body portion having a third width, smaller than the second width; the method comprising: inserting the elongate oxygen sensor into a urinary drainage lumen of an elongate catheter; aligning the sensor tip into a position within the urinary drainage lumen by observing the spacer portion through a drain hole in the elongate catheter; and collecting data using the elongate oxygen sensor.

[0019] It will be appreciated that the method may use the oxygen sensor in accordance with the first aspect set out above, having any of the further features described below, and also of the apparatus according to a third aspect as set out below. In some embodiments, the method further comprises inserting the elongate oxygen sensor and the elongate catheter into the bladder of a human or animal (e.g. separately or together).

[0020] In some embodiments, aligning the sensor tip comprises aligning a distal edge (or end) of the spacer portion with a proximal edge of the drain hole. In some embodiments, the method further comprises, after aligning the sensor tip, fastening or securing a fastener or securing means of a sensor port such that the fastener or securing means resist movement of the oxygen sensor relative to the urinary drainage lumen.

[0021] It will be appreciated that oxygen sensing (i.e. of oxygen within urine) is carried out at (i.e. using) the sensor tip. The spacer portion may be adjacent to the sensor tip (i.e. immediately next to it along the length of the oxygen sensor). The elongate oxygen sensor is suitable for insertion into the urinary drainage lumen. Thus, in at least some embodiments the sensor tip, the spacer portion, and (at least a part of) the body portion, are suitable for insertion into the urinary drainage lumen.

[0022] In some embodiments, the spacer portion may be formed separately from the body portion and / or the sensor tip. Such a separate spacer portion may be attached to the body portion and / or the sensor tip, as described further below. Alternatively, in other embodiments the spacer portion may be formed integrally with the body portion and / or the sensor tip (e.g. by a widening in an outer layer of the body portion). The body portion and the sensor tip may be formed integrally (e.g. provided by a single (optical) fibre or cable). The spacer portion may be formed from a plurality of pieces, which may optionally be separately attached to the body portion, to form the overall spacer portion. These pieces may thus be connected only via the body portion. For example, the spacer portion may be formed by a plurality of elongate (optionally linear) fins or protrusions extending (e.g. independently) from the body portion. In such embodiments the width of the spacer portion will be understood as the width of the overall shape which the pieces form, rather than the dimensions of a particular one of the pieces.

[0023] In some embodiments, the spacer portion comprises a ceramic material. This is advantageous since ceramic is highly impervious to oxygen, so there is little to no risk of the ceramic being contaminated by oxygen present in the lumen wall, and thereby being a source of artefacts in the measurements of the oxygen sensor. Ceramic material is also suitable for use within an MRI (magnetic resonance imaging) machine. The spacer portion may be formed from ceramic, i.e. consist of ceramic.

[0024] In some embodiments, the spacer portion comprises metal. This provides a hard- wearing material that is impervious to oxygen, however it is not MRI compatible. The spacer portion may be formed from metal, i.e. consist of metal.

[0025] In some embodiments, the spacer portion comprises a plastic material. This is MRI compatible, but it is an oxygen carrier so there is some risk of contamination by oxygen in the lumen wall. In some embodiments, the spacer portion is bonded to the body portion (e.g. to form a seal between the spacer portion and the body portion). For example, the spacer portion may be bonded to the body portion with epoxy. Using epoxy is particularly advantageous, since epoxy is a poor carrier of oxygen, so using epoxy for bonding reduces the risk of contamination of the spacer portion (and thus the sensor tip) by oxygen present in or on the body portion. Alternatively, the spacer portion may be bonded to the body portion using heat-shrink tubing.

[0026] In some embodiments, the spacer portion is bonded to the sensor tip (e.g. to form a seal between the spacer portion and the sensor tip). For example, the spacer portion may be bonded to the sensor tip with epoxy. Alternatively, the spacer portion may be bonded only at the body portion (i.e. not at the sensor tip). The absence of any bonding at the sensor tip may reduce the risk of contamination of the sensor tip due to the bonding.

[0027] In some embodiments, the body portion extends within the spacer portion (e.g. centrally within the spacer portion). Thus, the spacer portion may encircle (i.e. surround) or partially encircle the body portion. For example, the spacer portion may encircle the body portion by at least 180 degrees. The spacer portion may be a ring or a hollow cylinder or a partial ring or hollow cylinder (i.e. comprising an opening). The spacer portion may comprise an inner (open or closed) channel. Thus, in some embodiments, the spacer portion comprises an inner elongate channel i.e. a hollow extending from one end of the spacer portion to another along its length. The channel may be cylindrical (e.g. having a circular cross-section). The body portion may extend into (or throughout) the channel. The body portion may extend through the spacer portion, so as to also provide the sensor tip.

[0028] An inner diameter or inner width of the spacer portion (e.g. of the ring or hollow cylinder of the spacer portion) may be (approximately) equal to the third width (of the body portion) such that the spacer portion is friction-fit to the body portion. This may be provided as an alternative to the bonding described above, or in addition to improve adhesion and reduce the chances of the spacer portion falling off or moving relative to the body portion. It will be understood that the spacer portion may have any suitable cross-sectional shape in the transverse plane. Thus, in some embodiments, the spacer portion may have a cross-sectional shape (i.e. in a plane perpendicular to the elongate direction, in the transverse plane) that is circular, a partial circle, a concave polygon, e.g. comprising a plurality of protrusions, such as a cross-shape or star-shape, an oblong or a stadium. The concave polygon may optionally be a curved concave polygon, i.e. comprising at least one curved edge.

[0029] In some embodiments, the spacer portion comprises at least one elongate groove (i.e. extending along its length direction, e.g. along a direction substantially parallel to the elongate length of the sensor. The elongate groove may optionally also extend around the spacer portion, i.e. so as to spiral, or alternatively the at least one elongate groove may be linear. The spacer portion may comprise a plurality of (optionally linear) elongate grooves.

[0030] In some embodiments, a distal end of the spacer portion (i.e. the end closer to the sensor tip), may comprise a chamfered or bevelled edge. The distal end may be adjacent to the sensor tip. This chamfered or bevelled edge may give a smoother surface to the distal end of the spacer portion, making it less likely to catch on any surfaces it contacts on whilst being inserted into a catheter, thereby enabling smoother insertion into the catheter.

[0031] In some embodiments, the first width and the third width are (substantially) equal. This is particularly easily achieved when the same continuous cable or fibre provides the oxygen sensor, i.e. both the body portion and the sensor tip. Alternatively, the first width may be smaller than the third width. This may occur, for example, where an additional coating or cladding is provided around the body portion, but this is not present around the sensor tip. For example, the third width may be approximately twice the first width.

[0032] In some embodiments, the sensor is a luminescence oxygen sensor, optionally an optical fibre-based luminescence oxygen sensor. The sensor tip preferably comprises a material which is reactive to oxygen — preferably a luminescent sensor material. For example, the sensor tip may comprise a platinum-complex-based oxygen-sensitive indicator dye, such as platinum octaethylporphyrin. In some embodiments, the elongate oxygen sensor comprises a cable. The cable may contain one or more electrical conductors and / or one or more optical fibres. The cable may be an optical fibre. The cable may provide (at least) the body portion (i.e. a part of the cable may provide the body portion) and / or the sensor tip. The cable may extend through (i.e. within) the spacer portion. A tip (e.g. an exposed tip) of the cable may provide the sensor tip. Thus, the cable may extend all the way through the spacer portion. The body portion may be provided by an exposed portion of the cable (i.e. a portion of the cable which is not surrounded by any cladding or coating).

[0033] In some embodiments, the elongate oxygen sensor further comprises a coated portion, located further from the distal end than the body portion. The coated portion has a fourth width (e.g. diameter), larger than the third width (e.g. diameter). The coated portion may be provided by a portion of the optical fibre that is surrounded by (i.e. enclosed within) a coating or cladding (or a further coating or cladding, compared to the body portion). Thus, in some embodiments a portion of the cable (e.g. a portion that is not the sensor tip of the body portion) comprises an outer sleeve, e.g. of plastics material. The coating on this coated portion helps to protect a portion of the oxygen sensor, which remains outside of the catheter, from damage or wear. The coated portion may have a length of at least 40 cm, optionally at least 60 cm, further optionally at least 80 cm.

[0034] In some embodiments, the spacer portion may be longer (i.e. along the elongate direction of the sensor) than the sensor tip. It may be several times longer than the sensor tip, for example at least 3 times longer, optionally at least 5 times longer, further optionally at least (or approximately) 10 times longer.

[0035] In some embodiments, the body portion may be longer than the spacer portion. For example, at least 10 times longer, optionally at least 25 times longer.

[0036] The sensor tip may be at least 0.5 mm in length, optionally at least 1 mm in length.

[0037] The sensor tip may be approximately 1.5 mm in length. The sensor tip may be less than 5 mm in length, optionally less than 2 mm in length. Further details on the first width, second width and third width are provided below. It will be understood that as set out above, these properties may optionally refer to the maximum (i.e. largest) width of the particular portion, or every width of that portion (i.e. in a particular transverse plane). It may refer to first, second and third widths all defined in the same longitudinal plane, i.e. so as to compare widths along corresponding width directions. One, some or all of the widths may refer to diameters (i.e. transverse widths through the centre of the portion).

[0038] The first width may be less than 0.75 mm, optionally less than 0.5 mm. The first width may be approximately 0.25 mm or 0.5 mm.

[0039] The width of the oxygen sensor reduces proximally of the spacer portion, which has the advantage of improving flow and ease of insertion of the oxygen sensor. A shorter spacer portion may provide these advantages to a greater extent. The spacer portion may be less than 20 times the length of the sensor tip, optionally less than 15 times, further optionally less than (or approximately) 10 times. The spacer portion may be at least 5 mm in length, optionally at least 10 mm in length. The spacer portion may be approximately 14 mm in length. The spacer portion may be less than 50 mm in length, optionally less than 20 mm, further optionally less than 15 mm in length.

[0040] The second width may be less than 3 mm, optionally less than 2 mm. The second width may be approximately 1 mm or 1.5 mm. The second width may be at least twice the third width, optionally at least three times. The second width may be at least twice the first width, optionally at least three times, further optionally at least five times.

[0041] The body portion may be at least 20 cm in length, optionally at least 30 cm in length, further optionally at least 40 cm in length. The body portion may be approximately 42 cm in length. The body portion may be less than 75 cm in length, optionally less than 50 cm.

[0042] The third width may be less than 1.5 mm, optionally less than 1 mm. The third width may be approximately 0.5 mm or 0.75 mm.

[0043] In some embodiments, the second width (i.e. of the sensor portion) is approximately equal to the length of the sensor tip (i.e. along the elongate direction). The second width may be within 20% of the length of the sensor tip, optionally within 10%, further optionally within 5%. The second width may be less than 2 mm different to the length of the sensor tip, optionally less than 1 mm, further optionally less than 0.5 mm. This may further help to prevent artefacts in the measurements made using the sensor tip, since the sensor tip will not reach as far as the wall of the drainage lumen (i.e. an inner face of the wall), even if it is slightly bent relative to the spacer portion, since it is not longer enough to cover the space created by the spacer portion and to reach the lumen wall.

[0044] According to a third aspect of the present invention, there is provided an apparatus for sensing urinary oxygen, comprising: an elongate catheter comprising a urinary drainage lumen; and the elongate oxygen sensor as described above, suitable for insertion into the urinary drainage lumen.

[0045] It will be understood that the catheter has a distal end which sits, in use, in the bladder of a patient or subject, and a proximal end located away from the distal end, and remaining outside of the patient or subject. The oxygen sensor is insertable into the catheter (specifically into the urinary drainage lumen) such that the distal end of the oxygen sensor ultimately sits within the distal end of the catheter (i.e. the terms “distal” and “proximal” are used in a similar sense in reference to the oxygen sensor, the catheter and the urinary drainage lumen of the catheter.

[0046] The apparatus may advantageously be provided with the elongate oxygen sensor inserted within the elongate catheter, i.e. as a kit ready for insertion into a patient.

[0047] It will be understood that the urinary drainage lumen is a lumen suitable for draining of urine out of a human or animal bladder. The oxygen sensor thus does not travel within a separate lumen of the catheter, but rather within the same lumen through which urine is drained. The oxygen sensor therefore measures the oxygen content of the urine as it is drained from the bladder. In some embodiments, the elongate catheter comprises a drain hole, located towards the distal end of the catheter. The drain hole may, in some cases, be referred to as an eyelet. The urinary drainage lumen may be connected to the drain hole. In some embodiments, the elongate catheter comprises a drainage port, located towards the proximal end of the catheter (i.e. away from the distal end of the catheter). The urinary drainage lumen may be connected to the drainage port. Thus, in some embodiments the urinary drainage lumen connects the drain hole and the drainage port. The catheter may therefore be arranged so that urine is drained through the drain hole, along the urinary drainage lumen, and out of the drainage port.

[0048] The urinary drainage lumen may be defined by the wall (e.g. a single, continuous or substantially continuous wall). Thus, the wall may surround the urinary drainage lumen and may form a hollow cylindrical tube.

[0049] In some embodiments, the catheter comprises at least two drain holes, each located towards the distal end of the catheter. The drainage holes may be located opposite each other (e.g. facing each other across the width of the catheter, both located the same distance along its length).

[0050] In some embodiments, the elongate catheter comprises a sensor port, located towards (possibly at) the proximal end of the catheter. The urinary drainage lumen may be connected to the sensor port. The elongate oxygen sensor may be arranged to be inserted into the urinary drainage lumen through the sensor port. The drainage port may be separate from the sensor port, or alternatively the same port may provide both the drainage port and the sensor port (e.g. by providing one port which splits downstream into two branches). The sensor port preferably comprises a fastener or securing means for resisting or preventing movement of the oxygen sensor relative to the urinary drainage lumen. The fastener or securing means is preferably releasable. It may comprise a clamp or seal. It may additionally act to prevent fluid escaping around the outside of the oxygen sensor. The sensor port preferably comprises means for loosening the fastener or securing means, to allow the oxygen sensor to be moved freely within the catheter when required. The sensor port may, for instance, comprise a compressible annular bung — e.g., made of silicone — and a compression mechanism — e.g., a threaded plug. This may be used to compress the bung against the oxygen sensor, thereby increasing friction on the oxygen sensor, to resist movement, and effecting a seal around the oxygen sensor. In addition, or alternatively, the sensor port may comprise a Tuohy Borst. The urinary drainage lumen may comprise silicone or plastic material. The (entire) elongate catheter may be formed from silicone or plastic material. This is problematic in the context of placing an oxygen sensor within the urinary drainage lumen since plastic and silicone may have (e.g. atmospheric) oxygen dissolved into them, which can affect the measurements of the oxygen sensor and introduce artefacts if the oxygen sensor comes close to, or into contact with, the wall of the urinary drainage lumen. Thus, the oxygen sensor described above, in which the sensor tip is kept spaced apart from (the inner face of the) the wall by the spacer portion, is particularly advantageous in such catheters.

[0051] In some embodiments, no coating or lining is required on the inner face of the wall of the urinary drainage lumen. The relatively short length of the space portion, and relatively thin width of the sensor tip and body portion may allow easy insertion of the oxygen sensor into the lumen despite any friction which may occur with the material of the wall. Alternatively, the inner face of the wall of the urinary drainage lumen may be lined or coated with a layer that has a lower coefficient of friction than that of the material that defines the urinary drainage lumen (i.e. , than the material that is being lined or coated, which may be silicone in some embodiments). The layer may comprise fluorinated ethylene propylene (FEP) or polytetrafluoroethylene (PTFE) or a perfluoroalkoxy alkane (PFA). This has been found to facilitate insertion of the oxygen sensor, by allowing it to move easily within the catheter. The layer may be bonded to the wall of the urinary drainage lumen, or may simple sit within it — e.g., as a coextruded tube within the urinary drainage lumen.

[0052] The urinary drainage lumen has an inner diameter. The elongate oxygen sensor is suitable for insertion into the urinary drainage lumen. Thus, in at least some embodiments the first width, the second width and the third width are all smaller than the inner diameter. The urinary drainage lumen may have an inner diameter of at least 2 mm, optionally at least 3 mm, further optionally at least 5 mm.

[0053] In some embodiments, the drain hole (e.g. an edge of the drain hole or a centre of the drain hole) is arranged a first distance from the distal end of the urinary drainage lumen (i.e. from an inner end surface of the lumen). Where at least two drain holes are present, this may be the case for both of the drain holes (i.e. they may be the same distance from the distal end of the catheter). The length of the sensor tip (i.e. the length protruding from above the spacer portion, along the elongate direction) may be less than the first distance. As a result, when the spacer portion becomes visible through the drain hole, as the elongate oxygen sensor is moved up through the drainage lumen, the sensor tip will not yet be in contact with the end of the drainage lumen. This allows the spacer portion to be used as a visual indicator that the sensor tip has reached a reasonable sensing position, at, or close to, the drain hole. For example, the spacer portion and sensor tip may be configured (e.g. sized) such that aligning a distal edge of the spacer portion with a proximal edge of the drain hole places the sensor tip in a suitable (possibly optimum) position for sensing urinary oxygen. Positioning the sensor tip adjacent to the drain hole is advantageous for measuring urinary oxygen because the urine measured at this position has travelled a very short distance within the catheter, and therefore the risk of oxygen contamination of the urine from oxygen dissolved in the lumen wall (or of other kinds of contamination or artefacts in the measurement) is very low.

[0054] The urinary drainage lumen may extend along the whole length of the elongate catheter. The elongate catheter (and / or the urinary drainage lumen) may be at least 20 cm, further optionally at least 30cm, further optionally at least 40 cm. The elongate catheter may be less than 60 cm long, optionally less than 50 cm long. The oxygen sensor may be sized accordingly, to be accommodated (at least partially) within the elongate catheter (e.g. within a standard sized catheter). Thus, the total length of the sensor portion, the spacer portion and the body portion may be at least as long as the elongate catheter (e.g. longer than any of the lengths specified above).

[0055] The catheter preferably comprises an inflatable balloon located towards the distal end of the catheter (e.g., within 1 to 10 cm of the distal end). The inflatable balloon may be located further from the distal end than the spacer portion, when the oxygen sensor is positioned within the urinary drainage lumen. The catheter preferably also comprises an inflation lumen, connecting to the inflatable balloon. An inflation port may be located towards the proximal end of the catheter. The drainage port and inflation port may be located adjacent each other in a connecting portion of the catheter. The balloon may have any appropriate size or shape, for retaining the catheter in a bladder of a patient, as is known in the art. The catheter is preferably an indwelling urinary catheter, or Foley catheter. The catheter may be made primarily (e.g., at least half by mass) of silicone. The catheter may be a two-way catheter, or a three-way catheter (i.e. comprising three separate lumens).

[0056] Features of any aspect or embodiment described herein may, wherever appropriate, be applied to any other aspect or embodiment described herein. In particular, features described in relation to the elongate oxygen sensor and the elongate catheter may likewise be present in the described method and vice versa. Where reference is made to different embodiments or sets of embodiments, it should be understood that these are not necessarily distinct but may overlap.

[0057] BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Certain preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0059] Figure 1 is a side view showing an apparatus for sensing urinary oxygen according to an embodiment of the invention;

[0060] Figure 2 is a side view showing the elongate oxygen sensor of Figure 1;

[0061] Figure 3 is a magnified view showing the distal end of the apparatus of Figure 1 , viewed along the line 300;

[0062] Figure 4 is a magnified, partially cut-away side view showing the distal end of the apparatus of Figure 1 ;

[0063] Figure 5 is a partially cut-away perspective view showing the distal end of the apparatus of Figure 1;

[0064] Figure 6 is a flow chart showing a method according to an embodiment of the invention;

[0065] Figure 7 is a perspective view showing a distal end portion of the elongate oxygen sensor of Figure 2;

[0066] Figure 8 is a cross-sectional view of the spacer portion of the elongate oxygen sensor of Figure 7;

[0067] Figure 9 is a perspective view showing a distal end portion of an elongate oxygen sensor according to a second embodiment of the present invention;

[0068] Figure 10 is a cross-sectional view of the spacer portion of the elongate oxygen sensor of Figure 9; Figure 11 is a perspective view showing a distal end portion of an elongate oxygen sensor according to a third embodiment of the present invention;

[0069] Figure 12 is a cross-sectional view of the spacer portion of the elongate oxygen sensor of Figure 11 ;

[0070] Figure 13 is a perspective view showing a distal end portion of an elongate oxygen sensor according to a fourth embodiment of the present invention; and

[0071] Figure 14 is a cross-sectional view of the spacer portion of the elongate oxygen sensor of Figure 13.

[0072] DETAILED DESCRIPTION

[0073] Figure 1 shows an apparatus 100 for sensing urinary oxygen. The apparatus 100 includes a catheter 101 and an elongate oxygen sensor 1 , which is seen in greater detail in Figure 2. The catheter 101 includes a urinary drainage lumen 102 the external wall of which is visible in the view of Figure 1. The catheter 101 has a distal end 104, which is inserted in use into the bladder of a human or animal subject. The catheter 101 also has a proximal end 106.

[0074] An inflation port 108 and a combined drainage and sensor port 110 are each provided at the proximal end 106 of the catheter 101. Both ports 108, 110 are connected to the urinary drainage lumen 102. A balloon 112 is located close to the tip of the catheter 101 , i.e. close to the distal end 104. It is inflated via the inflation port 108, so as to secure the catheter 101 in position once the distal end 104 of the catheter 101 has been successfully inserted into a bladder.

[0075] A combined drainage and sensor port 110 is shown, through which pass both the oxygen sensor 1 , and also urine drained through the urinary drainage lumen 102. Although not shown in Figure 1 , a splitter may be attached to the combined drainage and sensor port 110, to create separate paths so that the oxygen sensor 1 exits through a first port (the sensor port) of the splitter, which is well sealed to prevent any leakage of urine out of this port, and urine is drained through a separate urinary drainage port.

[0076] Figure 2 shows the elongate oxygen sensor 1 which in Figure 1 is partially within the urinary drainage lumen 102 of the catheter 101. The elongate oxygen sensor 1 comprises an optical fibre 3, which extends throughout its length. This optical fibre 3 includes a sensor tip 2, located at a distal end 4 of the elongate oxygen sensor 1 (i.e. at the end which is close to or within the distal end 104 of the catheter 101 when positioned within the catheter 101 for use). The sensor tip 2 has a first diameter (i.e. its size along the width direction 8).

[0077] The elongate oxygen sensor 1 further includes a spacer portion 10, for spacing the sensor tip 2 away from the wall of the urinary drainage lumen 102. As can be seen in Figure 2, the spacer portion 10 is located further from the distal end 4 of the oxygen sensor 1 than the sensor tip 2, and therefore closer towards the proximal end 6. The dashed lines passing through the spacer portion 10 illustrate the optical fibre 3 passing through the spacer portion 10, which is hollow and cylindrical. In this example the spacer portion 10 is made of a ceramic material. The spacer portion has a second diameter, along the width direction 8, which is larger than the diameter of the sensor tip (i.e. larger than the first diameter).

[0078] The optical fibre 3 also defines a body portion 12. The body portion 12 is located further from the distal end 4 than the spacer portion 10. The body portion 12 has a third diameter, smaller than the second diameter. In the illustrated example the first diameter and the second diameter are substantially the same. However, the body portion 12 may include one or more outer coating layers, which may not be present at the sensor tip 2, such that the third diameter may be larger than the first diameter.

[0079] The optical fibre 3 further defines a coated portion 14, which has a fourth diameter which is larger than the third diameter. The fourth diameter may also be larger than the spacer portion (i.e. the thickest part of the oxygen sensor 1 may be the coated portion). This larger diameter is not a problem since the coated portion 14 may not be intended for insertion into a catheter, since it is located so far from the distal end. In this example the coated portion 14 is provided by the same optical fibre as provides the body portion 12 and the sensor tip 2, but this section of the optical fibre is covered by one or more (further) coatings, giving it a larger diameter. The dashed lines within coated portion 14 illustrate the optical fibre 3 passing through this coated portion 14. The dashed lines within the body portion 12 illustrated that this body portion 12 may extend proportionally further along the elongate direction than is illustrated in Figure 2. Figures 3 and 4 show magnified views of the distal end 104 of the catheter 101, with the distal end 4 of the elongate oxygen sensor 1 positioned inside the drainage lumen 102. Figure 3 shows a view from above, along the line 300 shown in Figure 1. Figure 4 shows a view of the same side as is shown in Figure 1 , but in which a part 400 of the catheter wall has been cut away to show the inside of the drainage lumen 102 and the elongate oxygen sensor 1 more clearly.

[0080] The wall 34 of the urinary drainage lumen 102 is seen in cross-section in Figure 4. The wall 34 forms a hollow cylindrical tube, defining the urinary drainage lumen 102. The urinary drainage lumen 102 has an inner diameter 48, i.e. the distance between opposing faces of the wall 34 is the inner diameter 48. It can be seen that the spacer portion 10 (which is the widest part of the oxygen sensor 1 that is inserted into the urinary drainage lumen 102) has a diameter which is smaller than the inner diameter 48 of the lumen 102. Thus, the oxygen sensor 1 is able to be easily inserted and to slide within the lumen 102.

[0081] Although not visible in the view of Figures 3 and 4, it is shown in Figure 2 that at the proximal end of the spacer portion 10 the diameter of the oxygen sensor 1 reduces (i.e. steps down) to the third diameter of the body portion, which is lower than the second diameter of the spacer portion 10. This reduction in diameter, on the portion of the oxygen sensor 1 which is located, in use, within the lumen 102 reduces any negative impact of the oxygen sensor 1 on urine flow through the catheter. If the thicker, second diameter were maintained along the body portion, throughout the rest of the lumen 102, this could have a significant impact on urine flow, restricting flow to below a desirable level. The illustrated arrangement reduces this effect.

[0082] It can be seen in these Figures that the distal end 104 of the catheter 101 includes a first drain hole 30 and a second drain hole 32, each connected to the urinary drainage lumen 102. The drain holes 30, 32 are at the same position length-wise along the catheter 101 , but are on opposite sides of the catheter 101. When the catheter 101 is in place within a bladder, urine is drained through these holes 30, 32 into the urinary drainage lumen 102, along that lumen and then out through the drainage port, which may be attached (e.g. split out from) the combined drainage and sensor port 110. In the view of Figure 3, the sensor tip 2 and an upper edge of the spacer portion 10 are visible through the drain hole 30. This is approximately the position in which it is desirable to take oxygen measurements of urine using the oxygen sensor 1, since the measurements are taken as the urine first enters the drainage lumen 102 and therefore there is very little chance that any contamination has occurred which could make the measurement less accurate. It will be appreciated that the spacer portion 10 provides a helpful visual indicator which can aid in aligning the sensor tip 2 in this advantageous position. When inserting the oxygen sensor 1 into the catheter 101 a user may observe when the spacer portion 10 first becomes visible through the drain hole 30, and then stop inserting the oxygen sensor 1 any further into the lumen. This allows the sensor tip 2 to be conveniently and accurately positioned in a particularly advantageous position for measurement.

[0083] It will be appreciated that this alignment of the sensor tip using the drain hole is carried out by a user before insertion of the catheter and oxygen sensor together (i.e. the apparatus) into the patient. The user may insert the oxygen sensor 1 to the desired position, fix it in place within the catheter 101 (e.g. using a fastener or securing means provided at the sensor port 110 as described above), before inserting the catheter 101 (with the sensor still inside) into the bladder of a patient. Alternatively, the user may insert the oxygen sensor 1 to the desired position, aligning it using the spacer portion 10 as a visual guide as explained above, and they may then mark a portion lower down the oxygen sensor 1 (e.g. on the body portion or the coated portion) that is aligned with a feature of the catheter 101 , and then use this secondary alignment feature to insert the oxygen sensor 1 to a desired position within a catheter which has already been inserted into the bladder of a patient.

[0084] It will be appreciated that the dimensions of the drain hole 30 and the sensor tip 2 may be selected to affect the alignment that is achieved using the spacer portion 10 as a visual indicator. In the partially cut-away view of Figure 4, the inner end surface 40 of the urinary drainage lumen 102 is visible. Adjacent to this, the catheter 101 includes a solid tip portion 42, which is an area of catheter wall within which the drainage lumen does not extend, i.e. it is a solid wall rather than hollow cylinder. This denser tip portion 42 aids insertion of the catheter into a subject. There is a first distance 44 between the inner end surface 40 and the drain holes 30, 32. It can be seen that this first distance 44 is considerably longer than the length 46 of the sensor tip 2. Thus, provided that insertion of the oxygen sensor 1 is stopped reasonably promptly once the spacer portion 10 is visible through the drain hole 30, 32, the sensor tip 2 will not come close to contacting the inner end surface 40, thereby reducing a risk of the oxygen measurement being inaccurate due to contact with the inner end surface 40.

[0085] Figure 5 is a perspective view of the distal end 104 of the catheter 101 of Figure 1. In this perspective view the same part 400 of the catheter outer wall has been cut-away to show the internal parts - in particular the drainage lumen 102 and the oxygen sensor 1.

[0086] Figure 6 is a flow chart showing a method according to an embodiment of the invention. The method uses the elongate catheter 100 and the oxygen sensor 1 of Figures 1-5.

[0087] In a first stage 600, the elongate oxygen sensor 1 is inserted into the urinary drainage lumen 102. Next, at stage 602, the sensor tip 2 is aligned into a good position for measurement of urinary oxygen using the spacer portion 10 as a visual indicator, by observing the spacer portion 10 through the drain hole 30, as described above.

[0088] Next, at an optional stage 604, the elongate oxygen sensor 1 is inserted into the bladder of a human or animal. In order to do this, the oxygen sensor 1 may be removed from the urinary drainage lumen 102, and then re-inserted after the catheter 100 has been inserted into the bladder. Alternatively, the oxygen sensor 1 may remain within the urinary drainage lumen 102 as the catheter 100 is inserted into the bladder. Thus, the oxygen sensor 1 and the catheter 100 may be inserted into the bladder together or separately.

[0089] Finally, at stage 606, data is collected using the elongate oxygen sensor 1 , in order to sense oxygen content.

[0090] Figure 7 is a perspective view showing a distal end portion of the elongate oxygen sensor 1 of Figure 2, and Figure 8 is a transverse cross-sectional view of the spacer portion 10 of this elongate oxygen sensor 1 , i.e. showing a transverse plane through the spacer portion 10, perpendicular to the elongate axis.

[0091] It can be seen that in this embodiment, as described above, the spacer portion 10 has the form of a hollow cylinder, i.e. an elongate ring. This spacer portion 10 thus has a cross-sectional shape which is a circular ring, as seen in Figure 8. In this, and the further examples described below, the spacer portion 10 thus contains an internal elongate channel 25, sized and shaped to accommodate the body portion 12 extending through it as illustrated by the dashed lines in Figure 2. Thus, the channel has an inner diameter 23 approximately equal to the outer diameter of the body portion 12.

[0092] Although the illustrated examples show the spacer portion 10 including a hollow arranged to accommodate the whole transverse (i.e. cross-sectional) size of the body portion within it, it will be understood that in other examples the spacer portion 10 may have only certain components of the sensor, i.e. not all of the parts making up the body portion, passing through it, and / or it may be formed integrally with other parts of the elongate oxygen sensor 1 , i.e. such that it is not ordinarily understood as including a channel, and may be understood as a solid object, not comprising a hollow.

[0093] A distal end of the spacer portion 10, adjacent to the sensor tip 2, has a chamfered edge 27, i.e. an angled edge where the angle is cut away to form a sloping edge.

[0094] Widths of the spacer portion 10 will be understood as its extent along different width directions, all extending along the transverse plane (i.e. across the page in the view seen in Figure 8). An example width is labelled as 21. In this particular example, the widths are all diameters, i.e. transverse widths extending through the centre 29 of the cross-section. Since this spacer portion 10 is circular in cross-section its width, referred to above as diameter, is the same along all width directions.

[0095] Figure 9 is a perspective view showing an end portion of an elongate oxygen sensor 201 according to a second embodiment of the present invention. Figure 10 is a cross- sectional view of the spacer portion 210 of this elongate oxygen sensor 201, showing a transverse plane through the spacer portion 210. Many features of this elongate oxygen sensor 201 are alike with those described in relation to the first embodiment, and therefore will not be described again. Only the differences, which relate specifically to the shape of the spacer portion 10, will be described herein. Corresponding reference numerals to the first embodiment are used herein for ease of reference where applicable, with each reference number value increased by 200 for the second embodiment relative to the reference numerals used in relation to the first embodiment.

[0096] In this example, the spacer portion 10 has a cross-sectional shape (i.e. in the transverse plane) that is approximately cross-shaped, with curved edges. This shape may also be understood as a star shape with effectively four vertices or protrusions 31a, 31b, 31c, 31 d. This will be understood as an example of a concave polygon. It will be understood that the cross-sectional shape may alternatively have fewer or more protrusions (e.g. vertices), i.e. three protrusions, five protrusions etc.

[0097] The shape defines four elongate grooves 33a, 33b, 33c, 33d extending along the elongate length of the spacer portion 10, positioned between adjacent protrusions of the cross-sectional shape. It will be understood that in use these grooves help to allow greater flow of urine past the spacer portion 10 and through the catheter.

[0098] A first width 221a extending along a first width direction 223a and a second width 221b extending along a second width direction are illustrated. It will be understood that other widths may be defined along other directions in the transverse plane shown in Figure 8. In this example the widths pass through the centre of the cross-section and will therefore be understood as diameters. It can be seen that in this example all widths of the spacer portion 210 (i.e. along all the width directions) are larger than the diameter of the body portion, since this is equal to the inner diameter of the hollow within the spacer portion 10.

[0099] Figure 11 is a perspective view showing a distal end portion of an elongate oxygen sensor 301 according to a third embodiment of the present invention. Figure 12 is a cross-sectional view of the spacer portion 310 of this elongate oxygen sensor 301. Again, only the differences, which relate specifically to the shape of the spacer portion, will be described herein. Corresponding reference numerals to the first embodiment are used herein for ease of reference where applicable, with each reference number value increased by 300 for the third embodiment relative to the reference numerals used in relation to the first embodiment.

[0100] In this example the spacer portion 310 has a stadium cross-sectional shape, i.e. of a rectangle with semicircles at its opposing short ends, as seen in Figure 12. For reference its maximum width 321a (extending along the horizontal direction in Figure 12) and its minimum width 321b (extending along the vertical direction in Figure 12) are labelled. Again it will be appreciated that all widths of the spacer portion 310, extending along all the width directions in the transverse plane, are larger than the width of the body portion, since the minimum width 321b is larger than the body portion width, as illustrated.

[0101] Figure 13 is a perspective view showing an end portion of an elongate oxygen sensor 401 according to a fourth embodiment of the present invention. Figure 14 is a cross- sectional view of the spacer portion 410 of this elongate oxygen sensor 401. Again, only the differences, which relate specifically to the shape of the spacer portion, will be described herein. Corresponding reference numerals to the first embodiment are used herein for ease of reference where applicable, with each reference number value increased by 400 for the fourth embodiment relative to the reference numerals used in relation to the first embodiment.

[0102] In this embodiment, the spacer portion 410 has a cross-sectional shape which is a partial circle, or partial ring. It thus only partially encircles the body portion 412, as seen in Figure 13.

[0103] A first width 421a, along a vertical width direction, and a second width 421b, along a horizontal width direction, are labelled in Figure 14 for reference. It can be seen that the second width 421b, along the horizontal direction with reference to the view of Figure 14, does not extend through the cross-sectional centre of the shape. Again in this example, all widths of the spacer portion 410 are larger than the width of the body portion 412. The second width 421b corresponds to the diameter of the circle which defines the partial-circle shape of the spacer portion 410.

[0104] It will be appreciated by those skilled in the art that the invention has been illustrated by describing one or more specific embodiments thereof, but is not limited to these embodiments; many variations and modifications are possible, within the scope of the accompanying claims.

Claims

Claims1. An elongate oxygen sensor for insertion into a urinary drainage lumen of an elongate catheter, comprising: a sensor tip, located at a distal end of the elongate oxygen sensor, the sensor tip having a first width; a spacer portion, for spacing the sensor tip away from a wall of the urinary drainage lumen, the spacer portion located further from the distal end than the sensor tip, the spacer portion having a second width, larger than the first width; and a body portion, located further from the distal end than the spacer portion, the body portion having a third width, smaller than the second width.

2. The elongate oxygen sensor of claim 1, wherein the spacer portion comprises a ceramic material.

3. The elongate oxygen sensor of claim 1 or 2, wherein the spacer portion is bonded to the body portion.

4. The elongate oxygen sensor of claim 3, wherein the spacer portion is bonded to the body portion with epoxy.

5. The elongate oxygen sensor of any preceding claim, wherein the elongate oxygen sensor comprises a cable providing the body portion and the sensor tip, wherein the cable extends through the spacer portion.

6. The elongate oxygen sensor of any preceding claim, wherein the spacer portion is a ring or a partial ring or a hollow cylinder or partial hollow cylinder.

7. The elongate oxygen sensor of any preceding claim, wherein the spacer portion is longer than the sensor tip.

8. The elongate oxygen sensor of any preceding claim, wherein the body portion is longer than the spacer portion.

9. The elongate oxygen sensor of any preceding claim, wherein the second width is at least twice the first width.

10. The elongate oxygen sensor of any preceding claim, wherein the second width is approximately equal to the length of the sensor tip.

11. The elongate oxygen sensor of any preceding claim, wherein the spacer portion is adjacent to the sensor tip.

12. The elongate oxygen sensor of any preceding claim, wherein the sensor tip, the spacer portion, and at least a part of the body portion, are suitable for insertion into the urinary drainage lumen.

13. The elongate oxygen sensor of any preceding claim, wherein the spacer portion has a cross-sectional shape that is circular, a partial circle, a concave polygon, an oblong or a stadium.

14. The elongate oxygen sensor of any preceding claim, wherein a distal end of the spacer portion comprises a chamfered or bevelled edge.

15. The elongate oxygen sensor of any preceding claim, wherein the spacer portion comprises at least one elongate groove.

16. The elongate oxygen sensor of any preceding claim, wherein the first width is a first diameter, wherein the second width is a second diameter and wherein the third width is a third diameter.

17. An apparatus for sensing urinary oxygen, comprising: an elongate catheter comprising a urinary drainage lumen; and the elongate oxygen sensor of any preceding claim, suitable for insertion into the urinary drainage lumen.

18. The apparatus of claim 17, wherein the urinary drainage lumen has an inner diameter, and wherein the first width, the second width and the third width are all smaller than the inner diameter.

19. The apparatus of claim 17 or 18, wherein the elongate catheter comprises a drain hole, located towards the distal end of the catheter, wherein the urinary drainage lumen is connected to the drain hole.

20. The apparatus of claim 19, wherein the elongate catheter comprises at least two drain holes, each located towards the distal end of the catheter, wherein the drainage holes are located opposite each other.

21. The apparatus of claim 19 or 20, wherein the drain hole is arranged a first distance from a distal end of the urinary drainage lumen, wherein the length of the sensor tip is less than the first distance.

22. The apparatus of any of claims 19 to 21 , wherein the elongate catheter comprises a sensor port, located towards the proximal end of the catheter and connected to the urinary drainage lumen, wherein the elongate sensor is arranged to be inserted into the urinary drainage lumen through the sensor port, and wherein the sensor port further comprises a fastener or securing means for resisting or preventing movement of the oxygen sensor relative to the urinary drainage lumen.

23. A method of sensing urinary oxygen using an elongate oxygen sensor, the elongate oxygen sensor comprising: a sensor tip, located at a distal end of the elongate oxygen sensor and having a first width; a spacer portion, for spacing the sensor tip away from a wall of the urinary drainage lumen, the spacer portion located further from the distal end than the sensor tip, the spacer portion having a second width, larger than the first width, and a body portion, located further from the distal end than the spacer portion, the body portion having a third width, smaller than the second width; the method comprising: inserting the elongate oxygen sensor into a urinary drainage lumen of an elongate catheter; aligning the sensor tip into a position within the urinary drainage lumen by observing the spacer portion through a drain hole in the elongate catheter; and collecting data using the elongate oxygen sensor.

24. The method of claim 23, wherein aligning the sensor tip comprises aligning a distal edge of the spacer portion with a proximal edge of the drain hole.

25. The method of claim 23 or 24, further comprising, after aligning the sensor tip, fastening or securing a fastener or securing means of a sensor port such that the fastener or securing means resist movement of the oxygen sensor relative to the urinary drainage lumen.

26. The method of any of claims 23 to 25, further comprising inserting the elongate oxygen sensor and the elongate catheter into the bladder of a human or animal.

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