Abstract:
A system for administering negative pressure therapy to a wound includes a screen adapted to be positioned at the wound. A reduced pressure source is in fluid communication with the screen, and a blood gas transducer is exposed to a reduced pressure provided by the reduced pressure source. The reduced pressure supplied by the reduced pressure source induces hyperperfusion of a blood gas at the wound.

Description:
CROSS-REFERENCE OF RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 10/867,990, filed Jun. 15, 2004, which is a continuation of U.S. patent application Ser. No. 10/085,321, filed Feb. 28, 2002, now U.S. Pat. No. 6,856,821, which is a continuation-in-part of U.S. patent application Ser. No. 09/579,755, filed May 26, 2000, now abandoned, which claims the benefit of U.S. Provisional Application No. 60/136,293, filed May 27, 1999. All of the above-referenced applications are hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the monitoring of blood gases during vacuum assisted wound healing. More particularly, the invention relates to a method and system for the transcutaneous monitoring of blood gases wherein said monitoring is enhanced by application of a vacuum pressure in the region of skin under evaluation, and during which negative pressure therapy is being applied to an adjacent or proximal wound site. 
       BACKGROUND OF THE INVENTION 
       [0003]    Transcutaneous blood gas monitoring is known in the relevant arts as a method by which measurements of skin-surface gas pressures may be utilized to estimate arterial partial pressures of the gas of interest. In particular, skin surface oxygen or carbon dioxide pressure PO 2  or PCO 2 , respectively, is measured by a locally applied, electrochemically based device in order to develop an estimate of arterial partial pressure of oxygen or carbon dioxide PaO 2  or PaCO 2 , respectively. The obtained estimate is then made available to the clinician as an aid for the routine or emergency assessment of any of a variety of known cardiopulmonary functions. 
         [0004]    In practice, a condition of hyperperfusion is indicated in the region of skin adjacent the applied device in order to enhance the flow of arterial blood gases toward and through the skin surface. To date, this hyperperfusion condition has been established by local heating of the skin with an electrode in order to distend the arterial capillaries. Unfortunately, such local heating carries with it an increased risk for tissue injury—erythema, blisters, bums and skin tears being among the documented complications. In addition, some debate exists within the art as to whether the increased local metabolic rate concomitant the application of heat counteracts the intended perfusion effect. If so, false readings may result, which may ultimately lead to inappropriate treatment of the patient. 
         [0005]    The use of transcutaneous blood gas monitoring can be particularly advantageous when used in conjunction with negative pressure therapy for vacuum induced healing of open wounds or other tissue damage. Vacuum induced healing of open wounds has recently been popularized by Kinetic Concepts, Inc. of San Antonio, Tex., by its commercially available V.A.C.® product line. The vacuum induced healing process has been described in commonly assigned U.S. Pat. No. 4,969,880 issued on Nov. 13, 1990 to Zamierowski, as well as its continuations and continuations in part, U.S. Pat. No. 5,100,396, issued on Mar. 31 1992, U.S. Pat. No. 5,261,893, issued Nov. 16, 1993, and U.S. Pat. No. 5,527,293, issued Jun. 18, 1996, the disclosures of which are incorporated herein by this reference. Further improvements and modifications of the vacuum induced healing process are also described in U.S. Pat. No. 6,071,267, issued on Jun. 6, 2000 to Zamierowski and U.S. Pat. Nos. 5,636,643 and 5,645,081 issued to Argenta et al. on Jun. 10, 1997 and July 8, 1997 respectively, the disclosures of which are incorporated by reference as though fully set forth herein. Additional improvements have also been described in U.S. Pat. No. 6,142,982, issued on Nov. 7, 2000 to Hunt, et al. 
         [0006]    The use of transcutaneous blood gas monitoring in conjunction with V.A.C.® therapy allows for monitoring of blood gases within and around the wound bed. Blood gases can be an indicative factor of wound healing progression. Crucial information can be ascertained as to the progression of the wound without disturbing the wound dressing. 
         [0007]    It is therefore a primary object of the present invention to improve over the prior art by providing a method and apparatus for the transcutaneous monitoring of blood gases wherein local heating for hyperperfusion is eliminated, thereby eliminating a significant patient hazard and wherein the concomitant metabolic effects of local heating are likewise eliminated, thereby reducing the likelihood for misdiagnosis leading to inappropriate treatment regimen. 
         [0008]    Hyperperfusion through local heating also requires a prolonged warm up and stabilization time following electrode placement in order for equilibration and calibration of the electrochemical transducer. As a result, operator time is generally wasted in the administration of a transcutaneous blood gas evaluation. Additionally, transcutaneous blood gas monitors are either not available for emergency use or must be made available with an operated in a standby mode. Such a standby mode requires additional hardware and generally shortens the electrode lifecycle. 
         [0009]    It is therefore a further object of the present invention to improve over the prior art by providing a method and apparatus for the transcutaneous monitoring of blood gases wherein the apparatus is available for full operation on short notice without requirement for additional and/or lifecycle shortening hardware. 
         [0010]    It is still a further object of the present invention to provide a system and method that combines the advantages of a non-invasive blood gas monitoring device with the effectiveness of negative pressure therapy upon wounds, so as to further improve the efficacy of negative pressure therapy on the treatment of wounds and other tissue treatments. 
         [0011]    Finally it is still a further object of the present invention to improve over the prior art by providing a method and apparatus for the transcutaneous monitoring of blood gases wherein the above-described objects are implemented without sacrifice to patient safety or device efficacy, but wherein unnecessary hardware and software is nonetheless avoided, thereby conserving the ever more limited healthcare dollar. 
       SUMMARY OF THE INVENTION 
       [0012]    In accordance with the foregoing objects, the present invention—a method and system for the transcutaneous monitoring of blood gases and vacuum assisted wound closure—generally comprises a blood gas data acquisition device, a vacuum source and a blood gas transducer unit. The blood gas transducer is adapted for application to a patient&#39;s skin and administration of a local vacuum at the area of patient application. It further comprises an electrochemical blood gas transducer, well known to those of ordinary skill in the art, which is disposed entirely within the local vacuum at the area of patient application. The transducer may also be disposed within a wound site, or an area immediately adjacent a wound site that is being treated by negative pressure therapy. The use of negative pressure therapy may include a porous, semi-rigid screen placed within a wound bed, a cover for maintaining a negative pressure within the wound bed that is placed over the screen and wound bed, and a vacuum source in fluid communication with the screen. Additionally, a canister may be disposed between the screen and vacuum source, for the collection of fluids that may emanate from the wound during application of negative pressure by the vacuum source. A flexible tube or similar device is used to communicate between the screen and vacuum source. 
         [0013]    It is contemplated that the transducer may be incorporated within the screen, or alternatively placed as a separate element below the screen to be in direct contact with the wound bed, within a depression or cut-out of the screen, above the screen, or separate from the screen but immediately adjacent the wound bed. 
         [0014]    The blood gas transducer unit is in fluid communication with the vacuum source through an interposed vacuum hose and in electrical communication with the blood gas data acquisition device through an interposed electrical cable. The vacuum source, which comprises a vacuum pump operated by a pump motor is placed in fluid communication with the blood gas transducer unit in order to induce a condition of hyperperfusion in the locality of the electrochemical blood has transducer. Under the control of the microcontroller, or equivalent means, the blood gas data acquisition device is then utilized to capture this measure to arrive at an estimate of arterial partial pressure of oxygen or carbon dioxide, accordingly. Because vacuum induced perfusion produces the requisite condition of hyperperfusion without local heating and, therefore, without acceleration of the local metabolic function, the present invention results in more accurate than previously available estimates of partial blood gas pressures and does so while eliminating a significant risk for injury to the patient. 
         [0015]    The same vacuum source, or alternatively a second vacuum source, may be utilized to provide negative pressure at the wound site by communicating with the screen placed within the wound site, by means of a tube or similar device. 
         [0016]    Because the application of vacuum perfusion to the patient presents at least some risk for contamination of the vacuum source and blood gas data acquisition device, the preferred embodiment of the present invention further comprises a transducer interface module particularly adapted for the reduction or elimination of contamination risk. According to the invention, the transducer interface module comprises a male and female interface pair, wherein the male portion is adapted into the female portion and thereby establishes communication between the blood gas transducer unit and the vacuum source and blood gas data acquisition device. 
         [0017]    In implementing the male plug, a hydrophobic membrane filter—known to those of ordinary skill in the art—is interposed in the vacuum hose, thereby eliminating the opportunity for contaminants to pass from the patient to the vacuum source or blood gas data acquisition device. While the preferred embodiment of the present invention comprises a throw-away male plug, vacuum hose, electrical cable and blood gas transducer unit, those of ordinary skill in the art will recognize that each of these components can be made reusable with implementation of proper, known sterilization techniques. In this latter case, the hydrophobic membrane filter is preferably replaceable. 
         [0018]    Finally, many other features, objects and advantages of the present invention will be apparent to those of ordinary skill in the relevant arts, especially in light of the foregoing discussions and the following drawings and exemplary detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0019]    These and other features and advantages of the invention will now be described with reference to the drawings of certain preferred embodiments, which are intended to illustrate and not to limit the invention, and wherein like reference numbers refer to like components, and in which: 
           [0020]      FIG. 1  shows, in perspective view, the preferred embodiment of the transcutaneous blood gas monitoring apparatus of the present invention, as employed with a human subject; 
           [0021]      FIG. 2  shows, in schematic block diagram, details of the apparatus of  FIG. 1 ; and 
           [0022]      FIG. 3  shows, in schematic block diagram, a transcutaneous blood gas monitoring device utilized in conjunction with a negative pressure therapy device. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0023]    Although those of ordinary skill in the art will readily recognize many alternative embodiments, especially in light of the illustrations provided herein, this detailed description is exemplary of the preferred embodiment of the present invention, the scope of which is limited only by the claims that may be drawn hereto. 
         [0024]    Referring now to  FIG. 1 , the preferred embodiment of the transcutaneous blood gas monitoring system  10  of the present invention is shown to generally comprise a blood gas data acquisition device  11 , a vacuum source  12  and a blood gas transducer unit  13 . As shown in  FIG. 1 , the blood gas transducer unit  13  is adapted for application to a patient&#39;s skin  14 . In alternative embodiments, not shown, the blood gas transducer may be applied within a wound bed  30  or disposed within a screen  32  placed within the wound bed  30 . As will be better understood further herein, the blood gas transducer unit  13  is also adapted for administration of a local vacuum at the area of the patient application. Finally, the blood gas transducer unit  13  comprises an electrochemical blood gas transducer  15 , well known to those of ordinary skill in the art, which is disposed entirely within the local vacuum at the area of patient application. 
         [0025]    As also depicted in  FIG. 1 , the blood gas transducer unit  13  is in fluid communication with the vacuum source  12  through an interposed vacuum hose  16  and in electrical communication with the blood gas data acquisition device  11  through an interposed electrical cable  17 . Although those of ordinary skill in the art will recognize many substantial equivalents, the preferred embodiment of the present invention comprises a unitary hose and cable pair  18 . Such a unitary pair  18  serves to reduce clutter in the patient care environment, thereby reducing the likelihood of either the hose  16  or cable  17  becoming entangled with other tubes, cables or equipment. Further, and as will be better understood further herein, such a unitary pair  18  is especially adapted for use with the preferred embodiment of the novel transducer interface module  19  of the present invention. 
         [0026]    According to the preferred embodiment of the present invention, the vacuum source  12  comprises a vacuum pump  20  operated by a pump motor  21 . Those of ordinary skill in the art, however, will recognize many substantially equivalent embodiments for the vacuum source  12  including, for example, a central hospital vacuum or suction source or an integral pump and motor. In any case, all such equivalents are considered within the scope of the invention, which requires only a vacuum source  12  of the character otherwise described herein, and which is capable of providing suction in the range of about 50 mmHg through 250 mmHg. 
         [0027]    In operation, the vacuum source  12  is placed in fluid communication with the blood gas transducer unit  13  in order to induce a condition of hyperperfusion in the locality of the electrochemical blood gas transducer  15 . Under the control of a microcontroller  22 , or equivalent means, the blood gas data acquisition device  11  is then utilized to capture a measure of skin surface oxygen or carbon dioxide pressure. The microcontroller  22  can then utilize this measure to arrive at an estimate of arterial partial pressure of oxygen or carbon dioxide, accordingly. Because vacuum induced perfusion produces the requisite condition of hyperperfusion without local heating and, therefore, without acceleration of the local metabolic function, the present invention results in more accurate than previously available estimates of partial blood gas pressures and does so while eliminating a significant risk for injury to the patient. 
         [0028]    Because the application of vacuum to the patient presents at least some risk for contamination of the vacuum source  12  and blood gas data acquisition device  11 , the preferred embodiment of the present invention further comprises a transducer interface module  19  particularly adapted for the reduction or elimination of contamination risk. According to the invention, the transducer interface module  19  comprises a male  23  and female  24  interface pair, wherein the male portion  23  is adapted to plug into the female portion  24  and thereby establish communication between the blood gas transducer unit  13  and the vacuum source  12  and blood gas acquisition device  11 . 
         [0029]    In implementing the male plug  23 , a hydrophobic membrane filter  25 —known to those of ordinary skill in the art—is interposed in the vacuum hose  16 , thereby eliminating the opportunity for contaminants to pass from the patient  14  to the vacuum source  12  or blood gas data acquisition device  11 . While the preferred embodiment of the present invention comprises a throw-away male plug  23 , vacuum hose  16 , electrical cable  17  and blood gas transducer unit  13 , those of ordinary skill in the art will recognize that each of these components can be made reusable with implementation of proper, known sterilization techniques. In this latter case, the hydrophobic membrane filter  25  is preferably replaceable. 
         [0030]    Referring now to  FIG. 3 , a collection canister  34  may be interposed between the vacuum source  12  and the screen  32 . As suction is applied, fluids may be drawn from the wound  30  and collected in the canister  34 . A common vacuum source  12  may be utilized to provide vacuum perfusion to the blood gas transducer  13  and negative pressure to the wound site  30 . A seal  36  is adhered over the screen  32  in order to maintain negative pressure within the wound site  30 . The seal  36  may be comprised of an elastomeric material. The screen  32  is preferably comprised of poly-vinyl alcohol foam, or alternatively a polyurethane porous sheet. It is to be understood that any semi-rigid and porous material may be utilized as a screen  32  within the wound bed  30 . The tube  16  may be in direct fluid communication with the screen  32  (not shown), or connected to an adapter  38  that is adhered over an opening  40  in the seal  36 . It is preferable that the tube  16  is bifurcated at a position between the vacuum source  12  and the canister  34  so that fluids being drawn from the wound site  30  do not interfere with the vacuum perfusion of the blood gas transducer  13 . 
         [0031]    In an alternate embodiment, not shown, a separate vacuum source may be utilized to provide negative pressure to the wound site  30  and another vacuum source utilized to provide vacuum perfusion to the blood gas transducer  13 . 
         [0032]    While the foregoing description is exemplary of the preferred embodiment of the present invention, those of ordinary skill in the relevant arts will recognize the many variations, alterations, modifications, substitutions and the like as are readily possible, especially in light of this description and the accompanying drawings. For example, a membrane or other like switch pad  26  may be implemented for user control of the transcutaneous blood gas monitor  10  and/or a display, printer or other output device  27  may be provided for monitoring and/ or recording of estimated partial pressures. Likewise, a pressure transducer  28  may be, and preferably is, provided for monitoring and control of the vacuum applied to the patient  14 . In any case, because the scope of the present invention is much broader than any particular embodiment,, the foregoing detailed description should not be construed as a limitation of the scope of the present invention, which is limited only by the claims that may be drawn hereto.