Abstract:
The present invention is directed to a system and method for monitoring the physiological parameters of an organ or tissue during and after surgery. The system has a probe and a monitoring unit. In one embodiment the probe includes features for convenient, fixed and releasable attachment to surgical drains without interfering with their normal fluid-draining function while utilizing their suction to enhance the probe-to-tissue interface for improved sensing. An applicator is provided to facilitate such attachment. The monitoring unit which controls the sensors of the probe includes a processor to process, record and display the sensor data. This system may be valuable for monitoring transplanted organs and tissue grafts during the critical postoperative period when most of the clinical complications, such as vascular thrombosis, may occur.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This Application claims the benefit of U.S. Provisional Application No. 60/738,011, filed Nov. 17, 2005, entitled Methods and Probes for Tissue Monitoring, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a system and method for monitoring tissue during and after surgery, in particular, a system and method utilizing an attachable probe that adheres to surgical drains for enhanced interfacing with the tissue. 
     BACKGROUND OF THE INVENTION 
     Vascular complications may occur after organ transplantation which can compromise the survival of the organ and, in some cases, the patient. Surgical resection of some organs such as the liver may introduce vascular complications to the remaining portion of the organ depending on the type and extent of the resection. This makes it important to monitor the surgically affected organs during the postsurgical period for the early detection of complications which may enable organ-saving intervention before the occurrence of irreversible tissue damage or total organ loss. 
     For example, monitoring of hepatic oxygenation is essential after liver transplantation and resection. Currently, the measurement of the liver enzymes and clotting factors via blood analysis is the only reliable way to monitor liver dysfunction. Changes in these laboratory values can be detected only after significant liver damage has already occurred and hence intervention usually takes place retrospectively. Also, these tests have no dynamic value since they indicate the liver condition only at the time when the blood sample is withdrawn. 
     Current organ monitoring technology offers probes that may require stitching or gluing to the tissue and therefore may not be easy to apply or remove especially if used inside the body, which has been a key limitation to wide acceptance in the medical field. Probe stitching to the surface of an organ may also disturb the local microvasculature, cause subcapsular hematoma, and interfere with the measurement of the probe. Following are some examples of commercially available organ and tissue monitoring technologies. 
     Thermodilution organ monitoring technology such as that produced by Hemedex Inc., MA, uses a catheter-like probe that is inserted into the organ to measure its perfusion using thermodilution. The tip of the catheter-like probe includes a thermistor that is heated to remain slightly above the tissue temperature. The local perfusion is estimated from the power used in heating the thermistor, which generally depends on the ability of the tissue to dissipate heat by both thermal conduction within the tissue and by thermal convection due to tissue blood flow. This organ-invasive probe may cause bleeding, subcapsular hematoma, and may require extra care during insertion to avoid the puncture of underlying vessels. 
     Doppler ultrasound graft monitoring technology such as that produced by Cook Vascular Inc., PA, uses a suturable cuff probe that is fitted around the vessels supplying the tissue to assess its blood flow using Doppler ultrasound. Post-monitoring, the cuff probe may be difficult to remove and may left permanently around the vessel. 
     Optical tissue monitoring technology such as that produced by Spectros Corporation, CA, uses button-like probes are stitched to the tissue to measure its oxygen saturation using reflectance spectroscopy (e.g. Stitching can complicate probe application and removal. Also, stitching may disturb the local microcirculation and introduces measurement errors. 
     Laser Doppler Flowmetry tissue monitoring technology such as that produced by Perimed A B, Sweden, uses button-like probes are stitched to the tissue to measure its blood perfusion using laser Doppler flowmetry. Again, stitching can complicate probe application and removal and disturb the local microcirculation thereby introducing measurement errors. 
     US Publication No. US 2004/0230118A1 with publication date Nov. 18, 2004 discloses a Jackson-Pratt (JP) surgical drain with embedded sensors for monitoring organs and tissues. One disadvantage of this configuration is the inability of the user to select the location of the sensors along the length of the drain. In addition, this configuration is constrained to a specific category of surgical drains having a shape and cross-section that can accommodate embedded sensors. 
     Surgical drains (or surgical wound drains, used interchangeably herein) are routinely used in and after many surgical procedures to drain the wound exudate out of the body. Some well-known examples of the surgical drains are the Jackson-Pratt (JP) drains (e.g. Jackson F E and Fleming P M, “Jackson-Pratt brain drain: use in general surgical conditions requiring drainage,” International Surgery, Vol. 57, No 8, page 658-659, 1972), and the flat drains (e.g. U.S. Pat. No. 4,317,452 and U.S. Pat. No. 4,257,422), and the Blake drains (e.g. U.S. Pat. Des. 288,962, U.S. Pat. No. 4,398,910, and U.S. Pat. No. 4,465,481). Surgical drains are generally used with a vacuum source to remove wound exudate postoperatively. 
     SUMMARY OF THE INVENTION 
     The present invention discloses a method and system for monitoring tissue (or organs, used interchangeably herein) utilizing a versatile probe that may be mounted on various types of surgical drains for the seamless integration into surgical procedures. The system is comprised of a probe and a monitoring unit. The probe may include sensors to measure the physiological parameters of the tissue, a means to adhere to a surgical drain, and through openings that couples to the openings of the surgical drain to allow the passage and drainage of the local wound fluids. 
     The application and removal of the disclosed probe may not require any additional effort, training or skills beyond that required for the routine application and removal of surgical drains. The probe does not need to be stitched or glued to the tissue as the normal suction of the drain creates local vacuum that brings the probe and the adjacent tissue together thereby holding the probe in position and maintaining good contact between its sensors and the tissue. Furthermore, the sensors of the probe maintain good contact with the tissue because the normal suction of the drain clears the wound fluids that may otherwise isolate the sensors from the tissue and impede their measurement. Moreover, the probe is of a design such that it can be manufactured with greater ease. 
     Depending on the intended application, the probe may include sensors to measure tissue oxygenation (e.g. percent oxygen saturation, oxygen partial pressure, etc.), perfusion, temperature, pressure, pH, water content, and/or the concentration of biological material (e.g. bile, hemoglobin, etc.) or exogenous materials (e.g. drugs, cytotoxins, etc.). For example, percent oxygen saturation (SaO2) may be the preferred physiological parameter for monitoring transplanted organs and tissue grafts which are susceptible to thrombosis in their newly connected vessels. The monitoring unit which controls the sensors of the probe may include a processor to process, record and display the sensor data. 
     In one embodiment, the openings of the probe may be holes that are arranged to hydraulically couple to the holes of one surgical drain type. In another embodiment, the openings of the probe may be elongated slots that are arranged to hydraulically couple to the grooves of another surgical drain type. 
     The monitoring unit which controls the sensors of the probe may include a processor to process, record and display the sensor data. 
     In one method, the probe may be attached to a surgical drain, both implanted in the body next to the tissue to be monitored, and the probe anchored at the desired position by the vacuum-induced compression of the surrounding tissues created by the normal suction action of the surgical drain. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an embodiment of a probe and a monitoring unit in accordance with the present invention. 
         FIG. 2A  shows a top view of the probe of  FIG. 1 . 
         FIG. 2B  shows a side view of the probe of  FIG. 1 . 
         FIG. 2C  shows a front view of the probe of  FIG. 1 . 
         FIG. 3A  shows an embodiment of a probe mounted on a surgical drain with draining holes. 
         FIG. 3B  shows an embodiment of the probe mounted on a surgical drain with draining grooves. 
         FIG. 3C  shows another embodiment of the probe mounted on an alternative surgical drain with draining grooves. 
         FIG. 3D  shows another embodiment of the probe mounted on a surgical drain with draining holes. 
         FIG. 4A  shows an embodiment of the probe on its applicator. 
         FIG. 4B  shows an embodiment of the probe on an applicator having guide pins. 
         FIG. 5  shows an embodiment of the probe with a line sensor. 
         FIG. 6A  is a bottom view of the line sensor of  FIG. 5 . 
         FIG. 6B  is a side view of the line sensor of  FIG. 5 . 
         FIG. 6C  is a front view of the line sensor of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A preferred embodiment of a probe  100  of the present invention is shown in  FIG. 1  and  FIG. 2 . The illustrated embodiment of the probe  100  is generally elongated, flat and rectangular in shape. A typical probe length  101  may range between 1 to 6 cm and a typical width  103  may range between 5 to 15 mm. The probe may be made of flexible material such as medical grade silicone and may be reinforced by an embedded fiber mesh (not shown) to enhance its structural integrity. For in-vivo applications, the probe may be preferably made of a radiopaque material such as barium-loaded silicone. 
     The probe  100  may have a probe body with a first surface  102  and a second surface  104 . The first surface  102  may include one or more sensors  106  for measuring one or more physiological parameters of an adjacent tissue or organ. Depending on the intended application, the probe may include sensors to measure tissue oxygenation (e.g. percent oxygen saturation, oxygen partial pressure, etc.), perfusion, temperature, pressure, pH, water content, and/or the concentration of biological material (e.g. bile, hemoglobin, etc.) or exogenous materials (e.g. drugs, cytotoxins, etc.). 
     The second surface  104  of the probe may have an adhesive  108  to facilitate the attachment of the probe  100  to surfaces, instruments or devices such as a surgical drain  120  shown in  FIG. 3A  or the alternative surgical drain  130  shown in  FIG. 3B . The adhesive  108  may be a medical grade pressure sensitive adhesive (PSA) that is suitable for short-term or removable adhesion or implantation. The second surface  104  may be totally or partially covered by the adhesive  108  which may be a continuous coating, a web, or in discrete sections on the surface  104 . For a relatively short (e.g. 1-3 cm) probe length  101 , the second surface  104  may be totally covered with the adhesive  108 . For a relatively long (e.g. 4-6 cm) probe length  101 , only a proximal portion (i.e. closer to a protective jacket  114 ) of the second surface  104  may be covered with the adhesive  108 . For example, only the proximal 1-3 cm of the 4-6 cm long second surface  104  may be covered with the adhesive  108 . This partial coverage with the adhesive  108  may be preferred in instances where it is desirable to maintain the bending flexibility of the probe  100  when it is attached to the surgical drain  120 . 
     A protective release liner (not shown) may normally cover the adhesive  108  to prevent unintentional adherence to other surfaces or devices. This release liner may be peeled off or otherwise removed to expose the adhesive  108  just prior to the attachment of the probe  100  to other devices such as the surgical drain  120 , for example. 
     It is understood by one of ordinary skill in the art that alternative embodiments of means for attaching or mounting the probe to another body include hook and loop type fasteners (e.g., Velcro), fastening straps, tapes or other types of fasteners that attach the probe and the other body permanently or releasably. 
     The probe  100  includes a set of through-openings  112  extending between the first surface  102  and the second surface  104 . The openings  112  may be elongated in shape (e.g. rectangular slots) to facilitate and improve aperture coupling to drainage formations such as openings  122  of the surgical drain  120  as shown in  FIG. 3A  or to drainage formations such as grooves  132  of surgical drain  130  as shown in  FIG. 3B . Alternatively, the openings  112  may assume any other shape in their cross-section, including circular, elliptical, square, hexagonal, or rhombic. The relative positions of the openings  112  may be prearranged to match with the relative positions of the openings  122  of the surgical drain  120  on which the probe  100  is to be mounted. Alternatively, the relative positions of the openings  112  may be prearranged to match with the relative positions of the grooves  132  of the surgical drain  130  on which the probe  100  is to be mounted. 
     The openings may be arranged in a dual or multi-row configuration as shown for example in  FIGS. 3A and 3B  or in a single-row configuration as shown in  FIG. 3C  to reflect the drainage configuration of the corresponding surgical drain with which the probe is used. In the dual-row configuration, the openings  112  of the first and second rows may be symmetric about the long axis of the probe as shown for example in  FIG. 3B . Alternatively the openings  112  of the first and second rows may be asymmetric about the long axis of the probe as shown for example in  FIG. 3D . 
     In the single row configuration shown in  FIG. 3C , the probe  100 ′ having a single-row arrangement of the openings  112  may be attached to a surgical drain  140  with a centered draining groove  142 . In this configuration, the sensors  106  may be disposed on either side of the openings  112 . 
     The surgical drains  120 ,  130  and  140  have draining tubes  124 ,  134 , and  144  respectively extending from a proximal end of the drains. The draining tubes  124 ,  134 , and  144  may be exteriorized out of the body and connected to an external suction device or a drain bulb (reservoir) to suck out and collect the wound fluids. 
     The sensors  106  of the probe may be preferably of the fiberoptic type, however, they may be of any other type including electronic and hydraulic (e.g. for pressure measurements). Alternatively, the sensors may be a combination of the fiberoptic, electrical and hydraulic types. The cables (e.g. optical fibers, wires and/or tubes) of the sensors  106  may be bundled within a protective jacket  114  and guided from a proximal end of the probe to a connector  116  that connects the probe  100  to a monitoring unit  118  that drives the sensors  106 , processes measured data from the sensors, and/or displays physiological parameters obtained from the measured data to the user. 
     A reinforcement tensile member  110 , such as a wire, cable or woven or non-woven fiber, may be embedded within the probe  100  (or  100 ′), preferably within the perimeter of the probe  100 , and extends continuously through the protective jacket  114  between a distal end of the probe and the connector  116  as shown in  FIG. 2 . In the illustrated embodiment, the member  110  is a single, continuous fiber whose one end extends from the connector  116  and whose other end returns to the connector  116 . The reinforcement member  110  may serve to strengthen the structural integrity of the probe  100  (or  100 ′) especially when it is being pulled out of the body along with the surgical drain by, for example, the manual grabbing of both the protective jacket  114  and the draining tubes  124 ,  134 , or  144  of the surgical drains  120 ,  130  or  140 , respectively. 
     Although the probe  100  may be preferably rectangular in shape with a flat cross-section, it may assume other shapes including a C-shaped cross-section to enable its mounting on and/or attachment to rounded drains with circular cross-sections. 
     Prior to its application, the probe  100  may have an applicator  150  to facilitate its handling, calibration, and aligned attachment to the surgical drains.  FIG. 4A  illustrates an applicator  150  that may be used to attach the probe  100  to a surgical drain of the flat type as shown in  FIG. 3 . An embodiment of the applicator  150  may be a U-shaped plastic channel or tray member with a bottom  152  and two sides  156 ,  158  defining an opening  154  therebetween. The probe body  103  is lodged in the applicator  150  as shown in  FIG. 4 , with its first side  102  facing the bottom  152  of the applicator, and its second side  104  facing the opening  154 . The inner surface of the bottom  152  may include a calibration standard (not shown) to allow the calibration of the facing sensors  106  prior to the application of the probe  100 . The calibration standard may be an optically reflective material with known reflective characteristics (or spectrum) to be used in calibrating optical sensors of the reflective type. The sides  156  and  158  of the applicator may extend above or beyond the thickness of the probe  100  so the applicator can also receive within its U-shaped channel a surgical drain to which the probe  100  is to be attached. Outer surface of the sides  156  and  158  may have a grip impression (not shown) to facilitate the handling of the applicator  150 . 
     The applicator  150  may also include raised formations, for example, guide protrusions, prongs, nubs, teeth or pins  160 , as shown in  FIG. 4B  extending from the bottom side  152 . The guide pins  160  are configured in size and dimension to extend through the openings  112  of the probe  100  to facilitate the alignment of the openings  112  to the openings  122  of the surgical drain  120  (e.g. in the Jackson-Pratt type) as shown in  FIG. 3A  or to the grooves  132  of the surgical drain  130  (e.g. in the Blake type) as shown in  FIG. 3B . In a typical probe attachment procedure, the probe is inserted into the applicator with the first surface  102  facing the bottom  152  of the applicator  150  and the pins  160  extending through the openings  112  of the probe. Any release liner protecting the adhesive  108  on the second surface  104  of the probe facing the opening of the U-shaped channel of the applicator is removed to expose the adhesive  108 . The surgical drain  120  or  130  is then inserted into the opening of the U-shaped channel of the applicator to contact the adhesive  108  with the pins  160  also aligned with and inserted into the openings  122  or the grooves  132  of the drain as the applicator  150  holding the probe  100  and the surgical drain are pressed together. Attached to each other by the adhesive  108 , a resulting probe and drain assembly is removed from the applicator and ready for use inside a patient&#39;s body. The openings  112  are in communication with the openings  122  or grooves  132  of the drain and the sensors  106  remain exposed for monitoring the tissue or organ of interest. 
     The probe  100  may include discrete or unit sensors  106  to measure the physiological parameters of the tissue facing the sensor. Alternatively, the probe  100  may include an elongated or linear sensor  200  as shown in  FIG. 5 . The sensor  200  may be composed of a plurality of unit or discrete sensors to measure a physiological parameter along the length of the probe  100 . This configuration may be valuable in reducing site-dependency of the measurement and provide a more reliable spatially averaged measurement. Site dependency is the variation in the measured value of the physiological parameters depending on the sensor location on the tissue. 
     An embodiment of an optical reflectance elongated sensor  200  is shown in  FIGS. 6A ,  6 B and  6 C. The sensor  200  may be used to measure the spatially averaged optical reflectance characteristics of adjacent tissue  201 . The optical reflectance characteristics of the adjacent tissue  201  may be used to determine the percent saturation of tissue hemoglobin (tissue oxygenation), and the concentration of biological material (e.g. bile) and/or exogenous materials (e.g. drugs). 
     The reflectance sensor  200  is composed of at least one transmit optical communication apparatus, for example, wave guide, hollow optical guide, or optical fiber  202 , and at least one receive optical communication apparatus, for example, wave guide, hollow optical guide, or optical fiber  204 . Distal end apertures  206  and  208  of the optical fibers  202  and  204  are covered or coated by a reflective material  210  to minimize the loss of light in the fibers from escaping out of the end apertures  206  and  208  by reflecting light back into the fibers  202  and  204 , respectively. The optical fibers  202  and  204 , preferably of the plastic type, may be fixedly positioned on the probe at a preselected distance  212  ( FIG. 6C ) from each other. 
     Sides of the optical fibers  202  and  204  may be slightly indented at multiple equi-distant locations along the length of the fibers spanning the probe to create a series of micro mirrors (or reflectors, used interchangeably herein)  214  and  216 , respectively. The micro mirrors  214  and  216  may be cylindrical or convex in shape and are capable of emitting and collecting light at about 90-degrees to the axis of the optical fibers  202  and  204 , respectively. The micro mirrors may be thermo mechanically indented into the sides of plastic optical fibers and a cladding material and/or a reflective material may be applied on to the indentation sites. 
     Light passing through the transmit optical fiber  202  may be reflected by each micro mirror  214  to be emitted as light portion  215  ( FIG. 6C ) at about 90-degrees to the axis of the fiber  202 . Similarly, light portion  217  that is incident at about 90-degrees to the axis of the optical fiber  204  may be reflected by each micro mirror  216  into the optical fiber  204 . Therefore, the optical fibers  202  and  204  have a series of corresponding mirrors  214  and  216  that may respectively emit and collect light at about 90-degrees to the axis of the optical fibers  202  and  204 , respectively. 
     An optical isolator  218  may be placed between the optical fibers  202  and  204  spanning the length of the probe to minimize crosstalk or direct light transmission between the two fibers  202  and  204 . The optical isolator  218  may be an opaque absorptive wafer. A thin sheet  220  of transparent material such as medical grade transparent silicone may be used to cover the optical fibers  202  and  204  to isolate them from the adjacent tissue  201 . 
     The above elongated sensor  200  may be embedded in the probe  100  as shown in  FIG. 5 . In a typical application, with proximal portions of the fibers  202  and  204  extending through the protective jacket  114  between the probe and the monitoring unit  118 , a light source (not shown) in the monitoring unit  118  may transmit light into the transmit optical fiber  202  where it may be side-emitted as a light portion  215  by the mirrors  214  into the tissue  201  ( FIG. 6C ) adjacent to the first surface  102  of the probe  100 . The tissue  201  reflects some of the emitted light portion  215  back to the sensor  200  where it may be collected as light portion  217  by the mirrors  216  and channeled into the receive optical fiber  204 . The receive optical fiber  204  guides the reflected light to a spectrometer (not shown) in the monitoring unit  118  to measure its spectral characteristics. The spectral characteristics may be processed by a processor (not shown) in the monitoring unit  118  to obtain the value of the desired physiological parameters such as, for example, the percent oxygen saturation of the tissue. One advantage of using the sensor  200  is that it may allow the optical interrogation of an elongated segment of the tissue  201  rather than just a single location. This tends to decrease the site-dependency of the measurement and improve the reliability of the measured physiological parameters. 
     Alternative to the mounting of the probe to a surgical drain, the probe may be attached to a wound dressing with the adhesive layer facing the wound dressing and the sensors facing the tissue to be monitored. This configuration may be beneficial in monitoring superficial tissue grafts (e.g. skin) and burn wounds. For such application, the through-openings of the probe may be a network of holes that couples to the wound dressing and allow the absorption of tissue exudate into the fibers of the dressing. The method of application may include attaching the probe to the wound dressing, both placed on the tissue to be monitored, and the wound exudate seeping through the openings of the probe to be absorbed by the wound dressing. 
     Although the above detailed description describes and illustrates various preferred embodiments, the invention is not so limited. Many modifications and variations will now occur to persons skilled in the art. As such, the preceding description has been presented with reference to presently preferred embodiments of the invention. Workers skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structure may be practiced without meaningfully departing from the principal, spirit and scope of this invention. 
     Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and illustrated in the accompanying drawings, but rather should be read consistent with and as support to the following claims which are to have their fullest and fair scope.