Device for monitoring blood leakage from wounds

A device for monitoring a skin surface for leakage of blood at, for example, a wound or a vascular access. The device comprises a patient unit, a connection unit and a monitor unit. The patient unit comprises a patch, including an adhesive layer to be attached to the skin surface of the patient. The adhesive layer is arranged to attach the patch to the skin so that a predetermined removal force, such as 30N, is required for removing the patch from the skin surface. A patient optical fiber is arranged at the patch and has a proximal end for connection to the connection unit. A patient connector is arranged at the distal end of a connection optical fiber. The connector has an opening passing through the connector, whereby the connection optical fiber is arranged in one end of the opening. The patient optical fiber may be inserted in the other end of the opening so that the proximal end of the patient optical fiber is arranged in register with the distal end of the connection optical fiber in order to transmit light between the optical fibers. A spring is arranged in the connector for exerting a force at the patient optical fiber at a side surface thereof for preventing unintentional withdrawal of the patient optical fiber. However, when the withdrawal force is larger than the removal force of the patch, the patient optical fiber is withdrawn from the connector. Thus, the patch is not removed from the skin even when a large force is exerted on the optical fibers.

FIELD OF INVENTION

The present invention relates to a device for monitoring of blood leakage from wounds. One particular field is monitoring of vascular access of a patient during extracorporeal treatment, such as dialysis.

BACKGROUND

WO2006/001759A1 issued to the assignee of the present invention, discloses a method and means for detection of blood leakage from wounds by means of an optical fiber. The optical fiber is arranged in a loop from a light source to a patch to be attached to the patient and back to a light detector. The light source and light detector are arranged in a monitoring device at a distance from the patch and may be attached to the arm of a patient. The loop comprises a sensor portion arranged at the patch and in which the optical fiber is bent with a small radius, so that the total internal reflection angle inside the optical fiber is approached or exceeded. A portion of the light transmitted through the optical fiber passes out through the sidewall of the optical fiber in the small radius sensor portion. When the sensor portion is exposed to a fluid, such as water or blood, the portion of the light passing out through the sidewall of the optical fiber in the small radius sensor portion increases, which may be sensed by the light detector as a decrease in light intensity, which may trigger an alarm.

The device according to WO2006/001759A1 operates well and is able to monitor for example a vascular access in an extracorporeal treatment, such as dialysis.

However, the manufacturing costs of said device may be further decreased. In addition, the amount of surplus material during manufacturing may be reduced. Furthermore, the security of the connection of the patient device to the monitor may be improved. However, a reduction of costs and operation requires a new technology to be used.

It is noted that the patient portion should be sterile and is disposable. However, the monitoring unit including the light source and detector and further electronic circuits is reusable. Thus, a reduction of costs per treatment may be obtained by reducing the costs of the disposable patient portion.

Another problem is relocation of the patch when the optical fiber is exposed to a force. When the patient is moving, the optical fiber may be influenced upon resulting in the fact that the patch is removed. This may remain unnoticed for a long time. When it is noticed, it is sometimes difficult to relocate the patch and it may be required to attach a new patch. If the relocation remains unnoticed, this is a safety risk.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to mitigate, alleviate or eliminate one or more of the above-identified deficiencies and disadvantages singly or in any combination.

In an aspect, there is provided a device for monitoring a skin surface for leakage of blood at a monitoring position, for example a wound or a vascular access. The device comprises a patient unit, a connection unit and a monitor unit. The patient unit comprises a patch, including an adhesive layer to be attached to the skin surface adjacent the monitoring position, whereby the adhesive is arranged to attach the patch to the skin so that an approximate predetermined removal force is required for removing the patch from the skin surface. The patient unit further comprises a patient optical fiber having an exposed distal end arranged in the patch and a proximal end for connection to the connection unit. The connection unit comprises a connection optical fiber, the distal end of which comprises a connector having an opening passing through the connector from one end to the other. The connection optical fiber is arranged in one end of the opening and the patient optical fiber may be inserted in the other end of the opening for being arranged with the proximal end of the patient optical fiber in contact with and in register with the distal end of the connection optical fiber. A spring is arranged in the connector for exerting a force at the patient optical fiber at a side surface thereof for preventing withdrawal of the patient optical fiber, until a predetermined withdrawal force is exerted on the patient optical fiber, whereby the withdrawal force is smaller than said removal force.

The proximal end of the patient optical fiber may be formed in that the optical fiber including its cover is cut at a substantially right angle or peeled and cut at a substantially right angle. The proximal end of the patient optical fiber may be polished, for example during the cutting operation.

The distal end of the patient optical fiber may be arranged for reflecting light passing along the optical fiber by total inner reflection when the distal end of the patient optical fiber is surrounded by air. Thus, the distal end of the patient optical fiber may be conical or frusto-conical or semi-spherical.

The connector comprises a cylindrical opening for receiving the proximal end of the patient optical fiber. The cylindrical opening has a diameter which is equal to or slightly larger than the outer diameter of the patient optical fiber, inclusive its cover.

The connector may comprise a radial spring member, which is arranged so that it normally covers an entrance to said cylindrical opening. The spring member may further comprise a hole, which may be moved into register with said cylindrical opening against a spring action by said spring member, whereby entrance of the patient optical fiber is enabled. When the spring is released, the hole exerts a force on the patient optical fiber. There may be arranged a second spring member inside the cylindrical opening, for example extending in the opposite direction compared to the first spring member.

For visual inspection of the connection point between the patient optical fiber and the connection optical fiber, there may be arranged a side hole between the connection point and the side surface of the connector.

DETAILED DESCRIPTION OF EMBODIMENTS

Below, several embodiments of the invention will be described. These embodiments are described in illustrating purpose in order to enable a skilled person to carry out the invention and to disclose the best mode. However, such embodiments do not limit the scope of the invention. Moreover, certain combinations of features are shown and discussed. However, other combinations of the different features are possible within the scope of the invention.

The general operation of a device according to the invention is the following. A patch is attached to the patient adjacent the site to be monitored, such as a vascular access of a dialysis patient. The patch comprises a compress for absorbing blood emitted from the vascular access, which is an indication of an alarm condition.

Embedded inside the patch is a distal end of an optical fiber, which may be shaped as a cone and is exposed to the surrounding atmosphere, which is air, inside the compress. The proximal end of the optical fiber is connected to a light transmitter and a photo detector. Light transmitted through the optical fiber towards the distal end is normally reflected back 180 degrees to the photo detector by total internal reflection at the distal end surface of the fiber. If blood reaches and is contacting the exposed conical surface of the optical fiber, the total internal reflection disappears at the contacting area and light passes out through the distal end of the fiber. Then, the signal level at the photo detector decreases, which may cause an alarm or an alert situation. The expression proximal and distal are as seen from the monitor side, which means that the distal end is closest to the needle, catheter or wound to be monitored for bleeding.

Bleeding may occur if a venous needle of a vascular access is removed during treatment. Normally, during an extracorporeal treatment, such as dialysis, blood is returned to the body via a venous needle. In such a treatment, the blood flow may be about 200 to 500 ml/min. If the venous needle accidentally is removed from the vein, the returning blood flow passes out of the needle instead of being returned to the patient. If such a situation remains unnoticed for only 2 minutes, a life threatening condition develops. However, when the venous needle is dislocated, blood is emitted and may be detected adjacent the blood access location. Often, the venous needle is rapidly removed far away from the access site, for example down the floor. However, the venous needle will emit a sufficient amount of blood to be detected at the access site even at a rapid removal. However, sometimes the blood left at the access site is very small, only a droplet, and the bulk of the blood is discharged for example at the floor. In addition, blood may leak from the vein and out through the hole in the skin left by the venous needle, at least for a short time duration. During the extracorporeal treatment, blood is also removed from a patient via an arterial needle. If such an arterial needle is removed or dislocated, this is not particularly dangerous, since such a dislocation only results in that blood is not removed out to the extracorporeal circuit, which only results in that the desired treatment is not achieved. However, the arterial needle access can also be monitored by the present embodiments of the invention. Also, other sites on the skin of a patient may be monitored for blood, such as a wound.

FIG. 1is a schematic overview of the components of a device10according to a first embodiment of the invention. The device10according to the first embodiment comprises a patient unit12, a connection unit14and a monitor unit16. The patient unit12is intended for attachment to a patient adjacent a wound or a vascular access to be monitored. The monitor unit16comprises electronic devices for monitoring the patient unit12. The connection unit14is for connection of the patient unit12to the monitor unit16.

The patient unit12is shown in more detail inFIG. 2. The patient unit comprises a patch21of a flexible web material. The patch is covered by a plastics material22at the bottom side as seen inFIG. 2, over at least a portion thereof, as shown by broken lines23. The bottom side is facing away from the skin the patch is applied to the skin in a monitoring position. In addition, the upper side of the patch is partly covered by an adhesive layer24protected by a removable layer25. By removing the removable layer25, the adhesive layer24becomes exposed and may attach the patch to the skin of a patient, for example adjacent a vascular access. The adhesive is dimensioned so that a specific removal force is required for removing the patch from the skin surface. Such a removal force may be about 30 Newton.

A central portion of the pad is provided with a retainer26of a rigid material. The retainer26comprises a semicircular recess27in which a distal end of an optical fiber28is arranged. The distal end of the optical fiber28is arranged in a compress29of a soft material, which is able to absorb a fluid such as blood.

The patch is attached to the skin of a patient with the compress29arranged at the skin surface adjacent or over the vascular access. The vascular access may extend in the opposite direction in relation to the optical fiber28, so that the vascular access may be moved and even removed without influencing upon the patch and its attachment to the skin surface.

The exposed distal end of the optical fiber having it's covering peeled off is enclosed in the recess27of the retainer26. The distal end of the optical fiber extends out of the recess27for a short distance. The retainer26further comprises wings37and38, which are secured to the central portion of the patch, for example by means of an adhesive. In this manner, the optical fiber is firmly connected to the patch21.

The patch21is shown in a plan view inFIG. 3. The patch comprises two lugs39and40. When the retainer26is arranged in the position26′ shown inFIG. 3by broken lines with the optical fiber in the recess27, the lugs39and40are folded over the retainer wings37and38as shown by broken line arrows41and42inFIG. 3and glued in place by an adhesive. The optical fiber may also be kept in place in the retainer recess by means of an adhesive. By means of the retainer26, the distal end of the optical fiber will be firmly held in place in the middle of the patch as shown by broken lines28′ inFIG. 3.

The optical fiber is shown in an enlarged side view inFIG. 4. The distal end31of the optical fiber is exposed by removing a covering32of the fiber over a portion adjacent the end thereof, such as over a length of about 12 mm. The semicircular recess27of the retainer26may have a length of 8 mm and the portion of the optical fiber extending out of the retainer26may be about 4 mm. The distal end of the patient optical fiber is shaped as a cone33by machining the end of the fiber, for example by laser or by mechanical operation. The cone angle is approximately 90 degrees. The total length of the patient optical fiber may be for example about 100 mm.

The proximal end34of the fiber is cut at a right angle. The patient fiber proximal end surface is machined so that it is sufficiently transparent for light as explained in more detail below. The outer diameter of the optical fiber may be approximately 2.2 mm and the optical core of the optical fiber may have a diameter of about 0.75 mm.

The optical fiber is selected to be of standard quality. The core is made of a plastics material having an index of refraction, which as about 1.5 (PMMA plastics). The optic core is transparent for light at a red wavelength, such as 690 nm. Such a fiber can be obtained from many manufacturers at a very low price, for example Toray Japan.

Optical fibers of other qualities may be used, such as a fiber with a glass core. However, the properties of the optical fiber may be selected so that a standard fiber may be used, which makes the price low.

The optical fiber is normally straight, without any bends. However, the optical fiber may be exposed to smaller bends without influencing upon the operation of the device.

In alternative embodiments, the distal end of the fiber may have another shape than conical, as long as almost complete total internal reflection is obtained at the distal end, when it is surrounded by air. Such a shape may be semi-circular or drip-shaped35as shown inFIG. 5or frusto-conical36as shown inFIG. 6.

The compress29is attached over the exposed distal end of the patient optical fiber so that the distal end is embedded in the compress. When the compress comes into contact with a fluid, such as blood, the fluid will be sucked up by the compress and distributed inside the compress. When a predetermined amount of fluid, such as about 0.2 to 2 milliliters, have been absorbed by the compress, the fluid reaches the center of the compress and the distal end of the optical fiber enclosed therein. When the distal end of the optical fiber is exposed to or contacted by the fluid, the total internal reflection ceases.

The entire patient unit12is made in a manner so that it is as inexpensive as possible. The patient unit is disposable and is used only once per treatment. The patient unit should be sterilized.

The patient unit12is connected to the monitoring unit16by a connection unit14.

The connection unit14does not need to be sterilized, since it is relatively far away from the wound or vascular access. The connection unit can be used several times and for different patients. However, certain facilities may want to use the same connection unit for the same patient, when the patient returns for successive treatments. A hemodialysis patient normally obtains dialysis treatment each second day, or trice per week. The connection unit may be used for several hundreds of treatments or more.

Consequently, the connection unit can be made to be more expensive than the patient unit, which is disposable.

The connection unit14essentially comprises an optical fiber51provided with a patient connector52at the distal end and a monitor connector53at the proximal end, seeFIG. 1. The length of the connection optical fiber51may be for example 2 m, which is sufficient for attachment to a monitor unit16arranged at a dialysis machine. However, if the monitor unit is attached to the patient, for example at the arm of the patient, the connection unit may be much shorter, for example about 200 mm.

In another embodiment, the connection unit is integrated in the monitor unit16so that the connector52is arranged in the monitor unit and extends out from the monitor unit. In this embodiment, the patient optical fiber may be longer, for example about 250 mm as shown inFIG. 16.

The connection optical fiber may be winded into a bundle54as shown inFIG. 1. It is important that the optical fiber is not bent too sharply.

Since the connection unit should be used several times, it should be able to withstand normally occurring cleaning agents at a hospital, such as alcohol and acids. The optical fiber may be arranged inside a tube made of a plastics material, which is normally used in hospital environments, such as PVC or an elastomer material. The tube material may be transparent so that damages of the optical fibers are visible if visible light is used.

The optical fiber should be protected from being exposed to a small radius, as may occur if the fiber is kinked or bent sharply. Thus, the connecting fiber may be arranged inside a holder, such as a bobbin having a spindle or cylinder with flanges as described in connection withFIG. 12below.

The proximal end of the connection optical fiber comprises a standard connector53for connection to a light transmitter and receiver, as explained further below.

The distal end of the connection optical fiber comprises the patient connector52adapted for connection to the proximal end of the patient optical fiber28.

The patient connector52is shown in more detail inFIG. 7. The upper end of the connector52as shown inFIG. 7receives the connection optical fiber51as described above, in a cylindrical opening61, which may have a diameter of about 3.25 mm in order to receive the connection optical fiber62having a diameter of 0.8 mm and a transparent hose63having an external diameter of 3.2 mm and a material thickness of about 1.1 mm. The distal end of the connection optical fiber extends through a small hole65having a diameter of 0.8 mm, which is equally large as the core of the connection optical fiber66. The distal end67of the connection optical fiber51protrudes a few tenth of a millimeter out of the hole65as shown inFIG. 7. The optical fiber and the transparent hose are all secured inside the openings61and65, for example by an adhesive.

The core66of the connection optical fiber is not provided with any covering but the transparent flexible hose63. Thus, if the optical fiber is bent with a small radius, so that light leaks out of the fiber, such light will be visible through the hose63. If the light is red, as in one embodiment, such a bend will be visible since the fiber glows with a red light at such a position.

The patient connector52is generally cylindrical and comprises at the bottom end seen according toFIG. 7, a conical entrance opening71for insertion of the proximal end of the patient optical fiber. The entrance is generally conical, so that the patient optical fiber end can easily be inserted into the entrance opening.

A cylindrical recess72is connected to the entrance, so that the patient optical fiber may be inserted into the cylindrical opening via the entrance opening71. The cylindrical recess72has a diameter, which is slightly larger than the external diameter of the patient optical fiber, such as 2.3 mm. Thus, the patient optical fiber can be inserted through the entrance and into the cylindrical opening. Then, the proximal end of the patient optical fiber will be arranged in line with and in contact with the distal end of the connection optical fiber, which is protruding from the narrow hole65. In this way, light may be transmitted between the optical fibers.

It is important that the patient optical fiber is arranged in line with the connection optical fiber otherwise the transmission of light may be impaired. Thus, the cylindrical recess72has a length, which is adapted for ensuring that any mis-alignment between the optical fibers is as small as possible. A suitable length is about 10 mm.

Adjacent the transition between the entrance opening71and the cylindrical recess72, there is arranged a spring member73, which is further shown in perspective inFIG. 8. The spring member comprises a radial portion74, which extends over the cylindrical recess72and at least partly occludes this recess72. The radial portion74comprises a hole75having a diameter, which is slightly larger than the outer diameter of the patient optical fiber. The spring member73further comprises an operation portion77extending along the outer side of the connector as shown inFIG. 7. At the connection between the radial portion74and the operation portion77, there is a bend over slightly more than 90 degrees so that there is formed a distance76between the spring and the connector. Upon pressure at said bend, the radial portion74is moved in the radial direction against the spring action of the spring member. During such a movement, the hole75in the radial portion74comes into register with the cylindrical recess72in the connector, whereby a patient optical fiber may be inserted in the cylindrical recess72as described above. When the pressure on the bend of the spring is relieved, the sides of the hole75will exert a pressure at the side surface of the patient optical fiber, thereby retaining the optical fiber in the connector.

The spring73and the hole75are dimensioned so that there is required a specific force for removing the patient optical fiber. This force is dimensioned so that the withdrawal force is smaller than the force required to remove the patch from the skin of the patient by pulling the fiber patient optical fiber. The adhesive of the patch may be dimensioned so that a force of about 30 Newton is required for removing the patch. In this case, the force required for withdrawing the patient optical fiber from the connector is smaller than 30 N, for example about 20 N. On the other hand, the force required for withdrawing the fiber from the connector should be sufficiently large for preventing unintended withdrawal of the fiber. Such a safe force would be about 10 N or larger. In other applications, a minimum safe force for withdrawing the fiber would be for example 15 N.

By this measure, it is ensured that the connector releases the patient optical fiber before the patch is removed from the patient, in case a large force acts upon the connection optical fiber. If this happens, it is easier to re-attach the optical fiber to the connector than to replace the patch on the skin of the patient.

If the patient optical fiber is withdrawn from the connector, this action results in the fact that the reflected light from the patient distal fiber end ceases. Thus, an alarm is initiated and the optical fiber may be re-attached or relocated into the connector. However, if the patch is removed from its position, without withdrawal of the optical fiber from the connector52, this fact is not easily detected. Thus, it is an important safety feature that the optical fiber is withdrawn from the connector before the patch is dislocated.

The force from the spring member73acts upon the patient optical fiber in the radial direction. By this action, the optical fiber is forced against the side surface of the cylindrical recess72. By this action, the patient optical fiber is arranged more closely in line with the connection optical fiber.

FIG. 9is a cross-sectional view of an alternative patient connector unit80. The connector unit80is substantially similar to the connection unit shown inFIG. 7. However, the connection unit80is provided with a second spring member83arranged opposite to the first spring member73. Thus, the two spring members may be operated at the same time by a single hand of the user. By arranging two spring members, the safety is increased. In addition, it is ensured that the patient optical fiber is properly inserted into the cylindrical opening, because, if the patient optical fiber is not pushed entirely into the opening, the second spring member83will spring back to its original position. Such a spring back position may be indicated by a colored portion at the spring member at position84. Thus, the portion of the spring83extending inside the connector unit80may have a red color. When the spring83is relieved, a part of the red color portion84becomes visible from the outside.

In addition, there may be arranged an inspection hole85extending from the point of contact between the patient optical fiber and the connection optical fiber. If there is improper contact, there will be a leakage of light, which is visible through the hole85as a red light, if red light is used in the optical fiber. Instead or in addition to the hole85, there may be arranged light guides which guides the light out to the periphery of the connector, for example at several positions.

In addition, the monitor device is arranged to test the connection and indicate malfunction if the amount of light returned to the photo detector is smaller than expected. If the operation is normal, for example about 90% of the emitted light is sensed by the detector, whereby light is lost during the transmission through the optical fibers, in the connectors and at the distal end. When the distal end is contacted by or exposed to blood or a fluid, the detector signal decreases to about 25% to 40% of the emitted light during a relatively short time of about less than 1-2 seconds. If the detector is slowly exposed to fluid such as sweat, the signal level at the detector continuously decreases over a relatively long time, such as a decrease of about 10% or less over 10 seconds. If the patient optical fiber is withdrawn, the signal at the detector decreases to about 10% of the emitted light or even lower. Thus, the detector is able to differentiate between such conditions.

When the distal end of the patient optical fiber is exposed to blood, the light returned to the detector is mainly light, which has passed out into the blood and illuminates the blood. A part of the red light returned or scattered by the blood enters the patient optical fiber and is sent back to the detector.

If the patient optical fiber is withdrawn from the connector, there is substantially no light returned to the detector.

FIG. 10shows a further embodiment of the connector shown inFIG. 7. The connection optical fiber51is shorter and extends only partially through the hole65so that the distal end of the optical fiber ends at87as shown inFIG. 10. The end of the small hole65facing towards the patient optical fiber is chamfered as shown at88, so that a conical entrance into the small hole65is obtained. The patient optical fiber is provided with a proximal end in which the covering42is partly peeled off and a portion of the core of the optical fiber is exposed. The core of the patient optical fiber extends into the hole65into abutment with the distal end of the connection optical fiber. Otherwise, the operation is substantially the same as the embodiment described with reference toFIG. 7.

FIG. 11is a cross-sectional view of another embodiment in which a withdrawal force is exerted by one or several rotational members78. Each rotational member78is arranged so that rotation in one direction may take place without any restriction, but rotation in the opposite direction is prevented. Four rotational members78or rollers are shown inFIG. 11. The rotational members78are arranged so that insertion of a patient optical fiber into the cylindrical recess82may take place without any hindrance, since the rollers easily rotate in a corresponding direction. However, once entered, the optical fiber cannot easily be withdrawn, because the rollers are prevented from rotation in the direction in which the optical fiber is withdrawn. The rollers retain the optical fiber in the cylindrical recess82by friction. The frictional force exerted by the roller against the side-wall of the optical fiber is controlled by a spring79, which acts upon the roller82as shown inFIG. 11for one of the rollers. The force of the spring is adjusted by a screw81. The other rollers may or may not be provided with similar spring and screw members. The rollers may be made of a slightly elastic material, such as rubber.

FIG. 12is a perspective view of a connection optical fiber51, provided with a patient connector52and a monitor connector53. Only one revolution is shown inFIG. 12but there may be several revolutions as shown inFIG. 1, depending on the length of the optical fiber51.

FIG. 13is a perspective view of a bobbin90for enclosing the optical fiber51during transport and storage, between uses thereof.FIG. 14is a cross-sectional view of the bobbin90. As shown, the bobbin comprises a central portion91, which is circular or oval. The inner wall of the central portion91may be slightly curved as shown inFIG. 14.

Two flanges92and93are attached at each end of the central portion91. The flanges are inclined towards each other and form together with the central portion a triangular space, inside which the connection optical fiber may be arranged. The flanges are elastic so that they may be removed from each other and open the triangular space for insertion or removal of the optical fiber. The walls of the flanges92and93may be reinforced by springs made from wire and having the same shape as the cross-section and being arranged at suitable distances along the periphery of the bobbin.

The central portion is arranged complementary to a monitoring device16shown inFIG. 15. The monitoring device is shown in an exploded view to shown the internal units of the monitoring device.

The outer shape of the monitoring device fits snuggly in the central portion91. Because of the slightly curved inner surface of the central portion91as shown inFIG. 14, the central portion91is retained on the monitoring device.

The monitoring device comprises electronic circuits94arranged for performing the monitoring operation as described above. The exact arrangement of the electronic units is not critical, but has to fulfill all requirements of safe operation as required for medical device use in hospital or home care. The monitoring device comprises an optical module, comprising a female connector95, a light source and a photo detector. The optical module98may for example by an optical unit of the type LD655 made by OECA, Germany, and comprises a 655 nm laserdiode and a Silicon PIN photodiode. Both units are coupled to a ST-Port for POF using a dielectrical beamsplitter.

The monitoring device further comprises a battery96, a microprocessor (not shown) and several light emitting diodes LEDs and several switches. A piezo-electric buzzer (not shown) provides an audible alarm. In addition, a piezo-electric horn and driver (not shown) may be arranged for emitting a loud noise in a critical situation, sounding like a fire alarm signal.

At the middle of the monitoring device, there is arranged a start button97and at the bottom side of the monitoring module there are arranged several electrical connectors for connection to the hospital monitoring system or other external alarm system or other medical device. In addition, communication with the hospital monitoring system may take place by wireless devices.

The monitoring device is arranged to emit a light beam via the laserdiode into the connection optical fiber51, which is connected to the female connector95. The light is further transmitted from the connection optical fiber51to the patient optical fiber31via the patient connector52. The light reaches the distal end of the patient optical fiber and is normally exposed to total internal reflection at the surfaces of the distal end. The light passes back along the patient optical fiber and to the connection optical fiber and finally reaches the photo detector.

If the distal end of the patient optical fiber is not covered with a fluid, almost all of the emitted light is reflected back to the photodiode. Only a small portion is lost because of transmission losses and in the two connectors. Normally, more than 90% of the emitted light is reflected back to the photo detector.

On the other hand, when the distal end is at least partly covered by blood, the light is not reflected by the conical surfaces and only a small portion, such as less than 50%, of the emitted light is returned to the photo detector. It is mainly light which is scattered and redirected by the blood back into the optical fiber which is returned. There is also a leakage in the connectors.

By monitoring the amount of light received by the photodiode, the presence of blood at the patch may be monitored. The device is very sensitive, since a large decrease in light received by the photodiode is obtained when the distal end is contacted by blood.

For example, the returned light is decreased to less than 50% when blood is sensed.

The compress may also absorb water, such as sweat. Water has substantially the same influence upon the optical properties of the distal end. Thus, if the compress is soaked with sweat or if water is spilled at the compress, a false alarm may be emitted. However, this problem may be solved by the electronic circuits and software in the monitoring device. Normally, the presence of sweat increases very slowly. Thus, a slow decrease in the returned light is an indication of the fact that sweat may disturb the monitoring operation. In such a situation, the monitoring device may emit an indication that the compress should be replaced.

If the signal decreases slowly, it is an indication of a situation that should not cause a blood alarm. Thus, a blood alarm signal is only generated if the decrease in returned light is sudden. For example, a decrease of returned light by more than 40% during less than 3 seconds may result in an alarm.

The bobbin is not required in certain applications, but the optical fiber may be sufficiently short as shown inFIG. 12in order not to need to be winded, or may be winded outside the monitor unit.

In another embodiments, the connection unit and the monitor unit may form a single unit by having the connection optical fiber directly connected to the monitor unit without a monitor connector53or without a connection unit14. Such an embodiment is shown inFIG. 16. The patient connector104is integrated in the monitor unit106, and the patient optical fiber102is inserted directly into the patient connector104and withheld therein with a predetermined force, which is sufficiently low, such as 15N. The monitor unit106is attached to the arm of the patient, for example by a strap. The patient connector104may be connected to the monitor unit106with an elastic device so that the patient connector104is easily moveable over one or several centimeters in the longitudinal direction of the patient connector, in order to accommodate normal movements of the patient and the device.

In still another embodiment shown inFIG. 17, the patient connector52may comprise the optical unit98, seeFIG. 15, which is now integrated in the patient connector. The optical unit108is shown only schematically as a circular unit. Several electrical wires107and109connect the optical unit108with the monitor unit106or16. The patient connector105provided with the optical unit108is attached to the arm of the patient with a strap or tape.

The disposable patient unit can be made very inexpensively, since the patient optical fiber does not need any expensive machining or treatment. It is only required to form the distal end into a conical surface and to cut the proximal end at substantially 90 degrees. The surface of the exposed fiber core may need some machining so that any irregularities caused by the machining is removed, such as polishing. Often, the cutting and polishing can be made in one and the same step by a cutting disk. If the cutting action is performed by a laser, the surfaces normally do not need any post-treatment.

The length of the patient optical fiber is as small as possible, but so that the proximal end is sufficiently long away from the area to be kept sterile. Such a length may be about 100 mm.

Another type of patient unit12may be used, for example of the type shown in the patent documents WO 2006/001759 and WO 2008/123814. The patient optical fiber in these constructions is a double optical fiber extending in a loop. The proximal end of the double optical fiber may be inserted in a patient connector52, which is modified so that the cylindrical recess72is oval. The connector optical fiber may comprise double fibers. Alternatively, the modified patient connector may comprise a beam splitter. In the embodiment ofFIG. 17, the optical unit108may comprise a laser diode, which is arranged in line with one of the double optical fibers and a photo detector, which is arranged in line with the other optical fiber of the double optical fibers. Other modifications may arise to a skilled person.

The light used in the embodiment described above may comprise red light of a wavelength of about 630 to 690 nm. Many different commercial laser diodes are made by many different manufacturers and such laser diodes may be obtained at a low price. Also photo detectors are inexpensive for light in this wavelength area. Infrared light may be used as an alternative.

Although the present invention has been described above with reference to specific embodiment and experiments, it is not intended to be limited to the specific form set forth herein. Rather, the invention is limited only by the accompanying claims and, other embodiments than those specified above are equally possible within the scope of these appended claims.