Abstract:
An intravascular sensor assembly insertable into an intravenous catheter, the sensor assembly includes a sheath having a sheath proximal end and a sheath distal end wherein an outer diameter of the sheath is sized to be substantially equal to the outer diameter of an insertion needle of the intravenous catheter, a hub sealingly connected to the sheath proximal end, the hub adapted for removably coupling to the intravenous catheter, a sensor disposed within the sheath, the sensor having a sensor shank with a shank distal end and a shank proximal end, a plurality of sensor elements including a working electrode with a reagent matrix disposed thereon, the reagent matrix comprising an enzyme capable of catalyzing a reaction involving a substrate for the enzyme and a reference electrode, the plurality of sensor elements disposed adjacent the shank distal end, a plurality of connector pads disposed at the shank proximal end where the plurality of connector pads are contained within the hub and the plurality of sensor elements are exposed adjacent the sheath distal end, and a plurality of elongated conductive elements where each of the plurality of conductive elements electrically couples one of the plurality of sensor elements to one of the plurality of connector pads, and a cable electrically coupled to the plurality of connector pads.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to the field of medical devices. Particularly, the present invention relates to devices and methods for placing a sensor at a selected site within the body of a patient. More particularly, the present invention relates to an intravascular sensor and an insertion set therefor. 
         [0003]    2. Description of the Prior Art 
         [0004]    In the past, it was discovered that tight glycemic control in critically ill patients yielded statistically beneficial results in reducing mortality of patients treated in the intensive care unit for more than five days. A study done by Greet Van den Berghe and associates (New England Journal of Medicine, Nov. 8, 2001) showed that using insulin to control blood glucose within the range of 80-110 mg/dL yielded statistically beneficial results in reducing mortality of patients treated in the intensive care unit for more than 5 days from 20.2 percent with conventional therapy to 10.6 percent with intensive insulin therapy. Additionally, intensive insulin control therapy reduced overall in-hospital mortality by 34 percent. 
         [0005]    Attempts have been made in the past to monitor blood various analytes using sensors specific for the analytes being monitored. Most methods have involved reversing the direction of blood flow in an infusion line so that blood is pulled out of the patient&#39;s circulation at intervals, analyzed and then re-infused back into the patient by changing the direction of flow. A problem encountered in reversing an infusion line for sampling is determining how much blood should be withdrawn in order to be certain that pure, undiluted blood is in contact with the sensor. 
         [0006]    U.S. Pat. No. 5,165,406 (1992; Wong) discloses a sensor assembly for a combination infusion fluid delivery system and blood chemistry analysis system. The sensor assembly includes a sensor assembly with each of the assembly electrodes mounted in an electrode cavity in the assembly. The system includes provision for delivering the infusion fluid and measuring blood chemistry during reinfusion of the blood at approximately the same flow rates. 
         [0007]    U.S. Pat. No. 7,162,290 (2007; Levin) discloses a method and apparatus for periodically and automatically testing and monitoring a patient&#39;s blood glucose level. A disposable testing unit is carried by the patient&#39;s body and has a testing chamber in fluid communication with infusion lines and a catheter connected to a patient blood vessel. A reversible peristaltic pump pumps the infusion fluid forwardly into the patient blood vessel and reverses its direction to pump blood into the testing chamber to perform the glucose level test. The presence of blood in the testing chamber is sensed by a LED/photodetector pair or pairs. When the appropriate blood sample is present in the test chamber, a glucose oxidase electrode is energized to obtain the blood glucose level. 
         [0008]    Although Levin discloses a method of halting the withdrawal of blood at the proper time so that a pure, undiluted sample is presented to the sensor, the method uses an expensive sensor and risks the possibility of contamination by the infusion process. Additionally, infusion of the flush solution has a diluting effect of the blood in the vicinity of the intravenous catheter and presents a time dependent function as to the frequency at which blood glucose can be measured. 
         [0009]    Therefore, what is needed is a device that simplifies the measurement apparatus. What is also needed is a device that improves usability and limits the infusion fluid to the level required to clear the intravenous catheter site. What is further needed is a device that simplifies the procedures required of medical personnel to those closely related to existing accepted methods. 
       SUMMARY OF THE INVENTION 
       [0010]    It is an object of the present invention to provide a device that simplifies the components needed for the measurement apparatus. It is another object of the present invention to provide a device that improves usability and simplifies the procedures to those closely related to existing accepted method known to medical personnel. 
         [0011]    The present invention achieves these and other objectives by providing an intravascular sensor and insertion set combination and method for the placement of an indwelling sensor within an inserted intravenous catheter. The present invention includes a sensor assembly configured for use with commercially available intravenous insertion devices. The sensor assembly includes a sensor sheath having a diameter substantially similar to a commercially available catheter insertion needle so that the sensor sheath sealingly engages the distal end of the catheter when the sensor assembly is inserted into the catheter after removal of the insertion needle. 
         [0012]    The sensor sheath contains a sensor having sensing elements disposed on a sensor shank adjacent a sensor distal end and electrical contacts at or adjacent a sensor proximal end. The sensor shank is sealingly embedded within the sensor sheath where the sensor elements are exposed at or adjacent the sensor distal end. The sensor sheath includes a hub configured for mating with the luer lock fitting on the catheter. A secondary seal is made at the luer fitting. The sensor may include one or more sensing elements on one side or on opposite sides of the sensor shank. 
         [0013]    The sensor signals are transmitted to a monitor by cabling or by radio waves. An optional signal conditioning electronics may be included to receive the sensor signals by way of electrical leads from the sensor. Either hard wiring or a radio link communicates the sensor signals to a monitor, which processes the sensor signals and displays analytical values, trends and other patient related data for the measured analyte. A typical analyte is blood glucose. Blood glucose measurements are commonly used to determine insulin dosing in tight glycemic control protocols. Although blood glucose is an important blood component, other analytes are possible to measure within the constructs of the present invention. 
         [0014]    One of the major advantages of the present invention is the combination with commercially-available IV catheters. This simplifies the procedure required of medical personnel since no additional special techniques are required for inserting the intravenous catheter. No highly specialized training is required since the procedures used by medical personnel to insert the intravascular sensor are closely related to existing accepted methods. Upon removal of the insertion needle, the sensor assembly of the present invention is simply inserted and locked into place using the luer lock fitting. Because the present invention is configured for use with commercially-available IV catheters, no specially designed or customized insertion tools or devices are required to position the intravascular sensor in the patient. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a plan view showing the general installation of the intravenous catheter and sensor on a patient in a direct connection to the monitor. 
           [0016]      FIG. 2  is a plan view showing the general installation of the intravenous catheter and sensor on a patient in a radio communication connection to the monitor. 
           [0017]      FIG. 3  is a perspective view of one embodiment of the present invention showing the intravascular sensor insertion set. 
           [0018]      FIG. 4  is an exploded view of the assembled sensor and cable of the present invention shown in  FIG. 3 . 
           [0019]      FIG. 5  is an end view of the cable end of the hub of the present invention showing the cross section of the sensor sheath. 
           [0020]      FIG. 6  is a perspective view of one embodiment of the sensor of the present invention showing contact wings. 
           [0021]      FIG. 7  is an enlarged perspective view of the contact wings shown in  FIG. 6 . 
           [0022]      FIG. 8  is an enlarged perspective view showing the sensor element end in one embodiment of the sensor. 
           [0023]      FIG. 9  is an enlarged end view of the hub of the present invention showing the connection between the cable and the connector end of the sensor. 
           [0024]      FIG. 10  is a perspective view of one embodiment of the present invention showing the sensor assembly inserted into the intravenous catheter. 
           [0025]      FIG. 11  is a cross-sectional view of the sensor inserted into the intravenous catheter. 
           [0026]      FIG. 12  is an enlarged perspective view of one embodiment of the present invention showing the sheath with a side opening/window exposing the sensor elements. 
           [0027]      FIG. 13  is an enlarged perspective view of another embodiment of the present invention showing the sensor and sheath end with the intravenous catheter where all sensor elements are on one side. 
           [0028]      FIG. 14  is an enlarged cross-sectional view of the embodiment of the sensor assembly and intravenous catheter shown in  FIG. 13 . 
           [0029]      FIG. 15  is a perspective view of another embodiment of the present invention showing the sensor assembly inserted into the intravenous catheter where the sensor elements extend beyond the end of the sensor sheath. 
           [0030]      FIG. 16  is an enlarged perspective view of the sensor elements shown in  FIG. 15 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0031]    The preferred embodiment(s) of the present invention is illustrated in  FIGS. 1-16 .  FIGS. 1 and 2  illustrate the overall environment of the present invention connected to an arm  1  of a patient.  FIG. 1  shows, by way of example, a disposable sensor assembly  30  of the present invention inserted into the intravascular system of the patient, which has been inserted into a vein on the back of arm  1  above the wrist. A catheter assembly  20  (not shown) is preferably used with the present invention and together with the sensor assembly  30  make up one embodiment of the intravascular sensor insertion set  10  of the present invention. Additionally, other locational installations on the patient are possible and often used. 
         [0032]    As shown in  FIG. 1 , a sensor cable  50  emanates from the sensor assembly  30  and is attached to a conditioning electronics and a cable junction unit  70 . A monitor cable  72  electrically couples cable junction unit  70  to a monitor  4  mounted on a pole  6 . Such poles as pole  6  are often used to mount electronic equipment as well as intravenous drips and the like. Another common location for the monitor  4  is the bed rail. Monitor cable  72  and sensor cable  50  transmit electrical signals generated by the sensor assembly  30  directly to monitor  4  where the signals are processed and displayed for access by medical personnel. Cable junction unit  70  is shown for convenience, as it is possible for monitor cable  72  and sensor cable  50  to be a single entity. It should be noted that other mounting configurations other than mounting monitor  4  to pole  6  is possible. For instance, it is possible to mount monitor  4  to a bed rail, cart mount, or other convenient location and often desirable. 
         [0033]    Like the illustration in  FIG. 1 ,  FIG. 2  shows a sensor cable  50  emanating from the sensor assembly  30  and attached to a conditioning electronics and radio unit  70 ′. The conditioning electronics and radio unit  70 ′ transmits electrical signals generated by the sensor assembly  30  to the monitor  4  where the signals are processed and displayed for access by medical personnel. 
         [0034]    Turning now to  FIG. 3 , there is illustrated one embodiment of the intravascular sensor insertion set  10  of the present invention. Sensor insertion set  10  includes sensor assembly  30  and catheter assembly  20 . Sensor assembly  30  includes a sensor sheath  40  sealingly connected to a sensor hub  46  from which sensor cable  50  extends. Catheter assembly  20  typically includes an insertion needle  24  disposed within a flexible catheter  22  and extends a predefined distance beyond a catheter distal end  22   a.  Sensor assembly  30  is preferably constructed to be insertable into a commercially available intravenous catheter assembly  20  that are typically available from a variety of medical suppliers. Some examples of these commercially available intravenous catheter assemblies include intravenous insertion catheters sold under the trademarks Introcan (manufactured by B. Braun) and Insyte Autoguard (manufactured by Becton Dickinson). 
         [0035]      FIG. 4  is an exploded view of sensor assembly  30  shown in  FIG. 3 . Sensor assembly  30  includes sensor sheath  40 , sheath hub  46 , a sensor  60 , and sensor cable  50 . Sensor sheath  40  includes a sheath distal end  40   a  and a sheath proximal end  40   b.  Sheath proximal end  40   b  is sealingly affixed to sheath hub  46 . Sensor sheath  40  includes an internal channel  42  that extends substantially the entire length of sheath  40  and receives sensor  60 . Sensor  60  has a shank proximal end  60   b  that is received within hub  46  against a hub surface  48  along with a sensor cable proximal end  50   b.  Sensor  60  and cable proximal end  50   b  are fixedly retained within hub  46  by a pressure applying component  52  and a pressure cap  54 . Pressure applying component  52  is optionally made from a resilient material such as a foam material that is placed over cable proximal end  50   b  to apply pressure between cable proximal end  50   b  and shank proximal end  60   b.  Pressure cap  54  provides the mechanism for maintaining the applied pressure and is preferably permanently affixed to hub  46 . 
         [0036]      FIG. 5  is an enlarged plan view of hub surface  48 . Internal channel  42  has a cross-section that is suitable for receiving sensor  60  and can be any desired shape. Hub  46  optionally has a perimeter wall  47  around a major portion of the circumference of hub surface  48 . Perimeter wall  47  facilitates attaching pressure cap  54  when capturing sensor  60 , cable proximal end  50   b  and pressure applying component  52 . Pressure cap  54  may be fixed to hub  46  by a snap fit, ultrasonic welding, chemical welding, or the like. Although cable  50  is shown as a flex circuit, it should be understood that other cable topologies are possible. 
         [0037]      FIG. 6  shows one embodiment of sensor  60  of the present invention. Sensor  60  has a sensor shank  62  with a shank distal end  62   a  and shank proximal end  62   b.  Shank proximal end  62   b  has contact ears  64  that have been orthogonally folded outward from sensor shank  62 . Contact ears  64  carry electrical contact pads thereon, which are more clearly illustrated in  FIG. 7 . Turning now to  FIG. 7  there is illustrated an enlarged view of shank proximal end  62   b.  Contact ears  64  have exposed thereon a plurality of electrical contact pads  65 . By optionally configuring contact ears  64  as shown, electrical contact pads  65  are all facing in one direction facilitating connection to a single-sided sensor cable  50  such as a flex cable.  FIG. 8  is an enlarged view of shank distal end  62   a.  Shank distal end  62   a  has one or more sensor elements  67 . Each of the one or more sensor elements  67  are electrically coupled to contact pads  65 , typically by embedding one or more electrically conductive pathways (not shown) within sensor shank  62  where the electrically conductive pathways are electrically isolated from each other. In this particular embodiment, sensor elements  67  of sensor  60  are on both sides. Other quantities of electrical contacts and sensor elements are considered within the scope of the present invention. 
         [0038]    Turning now to  FIG. 9 , there is illustrated an enlarged plan view of the electrical coupling assembly within hub  46 . Cable  50  has a plurality of electrical conductors  51  that terminate at cable proximal end  50   b.  A portion of electrical conductors  51  are exposed and overlay against electrical contacts  65  of contact ears  64 . As shown, cable proximal end  50   b  is preferably shaped to be captured within perimeter wall  47  of hub  46 . As previously disclosed, pressure applying component  52  (not shown) is positioned on top of cable proximal end  50   b.  In this embodiment, pressure applying component  52  has a thickness greater than the height of perimeter wall  47  so that pressure cap  54 , when installed, pushes pressure applying component  53  against cable proximal end  50   b  in order to maintain good electrical contact between electrical contacts  65  of contact ears  64  and the corresponding portions of exposed electrical conductors  51  at cable proximal end  50   b.    
         [0039]    Sensor assembly  30  positioned within catheter  22  is illustrated in  FIG. 10 . Catheter  22  includes a luer fitting  23  attached permanently and hermetically to a catheter proximal end  22   b  to form a leak-proof entity. A catheter distal end  22   a  is tapered so that a liquid tight seal is formed between the inside diameter of catheter  22  and insertion needle  24  (not shown). The diameter of sensor sheath  40  is selected to be substantially the same as the diameter of insertion needle  24  so that, when sensor assembly  30  is inserted into catheter  22  after removal of insertion needle  24 , a liquid tight seal is also formed at catheter distal end  22   a  between catheter distal end  22   a  and sensor sheath  40 . As  FIG. 10  illustrates, a sheath distal end  40   a  containing sensing elements  67  extends beyond catheter distal end  22   a  in order to expose sensing elements  67  to the sample fluid, i.e. the blood within the vein of the patient. 
         [0040]    Luer fitting  23  removably connects to hub  46  of sensor assembly  30  in a similar fashion as the standard luer-lock connections known to those of ordinary skill in the art.  FIG. 11  is a cross sectional view which particularly shows the luer lock interface between the luer taper  46   a  of the sheath hub  46  and the luer taper  27  of the luer lock fitting  23  of the intravenous catheter assembly  20 . The threads  23   a  of the luer lock fitting  23  of the intravenous catheter assembly  20  threadingly engages with the threads  46   b  of the sheath hub  46 . 
         [0041]    Turning now to  FIG. 12  there is illustrated an enlarged perspective view of one embodiment of the sensor elements  67  of sensor  60 . Sensor sheath  40  has a side opening  44 , i.e. window, near sheath distal end  40   b.  Two sensor elements  67   a,    67   b  on sensor shank  62  are disposed at side opening  44 . In this embodiment, sheath distal end  40   b  has a sealed end  40   c.  Sensor sheath  40  also includes a cross-drilled opening  45  to provide access for disposing a sealant around sensor shank  62  and sheath channel  42  at sheath distal end  40   b  to form a liquid tight seal. It should be noted that sensor sheath  40  may optionally include additional side openings or windows to accommodate additional sensor elements to measure a plurality of blood analytes. 
         [0042]      FIG. 13  shows another embodiment of sensor assembly  30  where all sensor elements  67   a,    67   b,    67   c,  and  67   d  are on the same side of sensor shank  62 . Sensor elements  67   a,    67   b,    67   c,  and  67   d  are positioned with sheath  40  to be located beneath sheath side opening  44 . Sheath  40  also includes cross-drilled opening  45  for applying sealant around sensor shank  62  and sheath channel  42  to form a liquid tight seal.  FIG. 14  is a cross-section view of the embodiment in  FIG. 13 .  FIG. 14  more clearly shows the relational detail of sensor shank  62 , sheath side opening  44  and cross-drilled opening  45 . 
         [0043]      FIG. 15  is a perspective view of another embodiment of the present invention. In this combination of sensor assembly  30  and catheter  40 , sensor elements  67  are not protectively disposed beneath a window in sensor sheath  40  but positioned on a portion of sensor shank  62  that extends beyond sheath distal end  40   b.    FIG. 16  is an enlarged detail view of the distal end of the embodiment in  FIG. 15 .  FIG. 16  more clearly shows the relational detail between sensor elements  67 , sensor shank  62 , sensor sheath  40 , and catheter  22 . 
         [0044]    Because sensor  60  is positioned within sensor sheath  40 , sensor shank  62  may have a characteristic of being rigid or flexible or any degree of rigidity/flexibility. Preferably, sensor shank  62  is flexibly resilient to provide less susceptibility to damage during handling and use when configured for any embodiment of the present invention. The following is one example for fabricating a sensor  60  of the present invention. 
         [0045]    Sensor Fabrication 
         [0046]    Step 1. Obtain a sheet of polyimide film, preferably with a thickness of about 0.002 inches. One option to obtain such a polyimide film is to remove the copper layer from a sheet of polyimide flexible laminate available from E. I. du Pont de Nemours and Company, Cat. No. AP8525 under the trademark Pyralux®. Pyralux® AP double-sided, copper-clad laminate is an all-polyimide composite polyimide film bonded to copper foil. Chemical etching is the preferred method for removing the copper layer. The polyimide sheet will become the polyimide support substrate for the sensor elements  67  of the present invention. 
         [0047]    Step 2. Apply liquid photoresist to both sides of the polyimide support substrate, expose the photoresist to UV light in a predefined pattern, and remove the unexposed areas to create a pattern for metal deposition. It should be understood that the preferred embodiment of the present invention has sensor elements  67  on both sides of the support substrate but that a single-sided sensor can also be made and is within the scope of the present invention. It is also understood that isolated electrically-conductive pathways are defined in the pattern between each sensor element  67  and a corresponding electrical contact  65 . A single sheet of polyimide support substrate provides a plurality of sensors  60 . Typically, one side contains the defined two electrodes per sensor (referred to as the top side) while the opposite side contains the reference and/or counter electrodes (referred to as the backside). 
         [0048]    Step 3. Coat both sides with one or more layers of electrically conductive materials by vacuum deposition. Acceptable electrically conductive materials include platinum, gold, and the like. Preferably, platinum with a layer of titanium deposited thereon is used for the present invention. 
         [0049]    Step 4. Remove the photoresist including the electrically conductive material on top of the photoresist surface leaving a pattern of electrically conductive material on the polyimide surfaces. 
         [0050]    Step 5. Apply an insulation layer to both sides of the modified polyimide sheet preferably by lamination. The insulation layer is preferably a flexible photoimageable coverlay available from E. I. du Pont de Nemours and Company as Pyralux® PC. Pyralux® PC is a flexible, dry film solder mask used to encapsulate flexible printed circuitry. The dry film can be used as a solder mask by patterning openings using conventional printed circuit exposure and development processes. Unexposed areas can be developed off as explained in the technical information brochure provided by Dupont. For the present invention, Pyralux® PC 1015 was used. Expose the insulation layer to UV light and wash out the unexposed portions of the insulation layer. Thermally cure the remaining insulation layer/dry film. The cured remaining insulation layer serves as not only an insulation layer but also forms the wells to confine and contain the dispensed layers disclosed below. 
         [0051]    Step 6. Remove the titanium in the areas exposed by the insulation layer using aqueous hydrofluoric acid, which also conveniently removes any surface contaminants from the previous process. 
         [0052]    Step 7. Deposit silver onto the electrodes defined by the electrically conductive material pattern on the backside of the polyimide support substrate, and subsequently convert a portion to silver chloride to create a Ag/AgCl electrode, which will serve as counter and reference electrode. 
         [0053]    Step 8. Deposit a semi-permeable membrane to the two electrodes per sensor defined on the top side (i.e. glucose electrode and blank electrode) by electropolymerization. 
         [0054]    Step 9. Deposit a hydrogel membrane onto the Ag/AgCl counter and reference electrode on the backside of the sheet by dispensing a predefined amount of hydrogel membrane solution, followed by UV curing and washing. 
         [0055]    Step 10. Deposit a poly-2-hydroxyethyl methacrylate (PHEMA) membrane precursor solution onto the two electrodes per sensor defined on the top side, UV cure, wash and dry. It should be understood by those skilled in the art that one of the two electrodes is a glucose electrode and, accordingly, the PHEMA membrane precursor solution for this electrode additionally contains a glucose enzyme, preferably glucose oxidase. 
         [0056]    Step 11. Deposit a composite membrane precursor solution onto the glucose electrode and the blank electrode, UV cure and dry. The preparation of the composite membrane precursor solution will now be described. Microspheres are prepared from a material having substantially no or little permeability to glucose but a substantially high permeability to oxygen. The microspheres are preferably prepared from PDMS (polydimethylsiloxane). The microspheres are mixed with a hydrogel precursor that allows the passage of glucose. While polyurethane hydrogels work, a PHEMA precursor is preferred. The ratio of microspheres to hydrogel determines the ratio of the glucose to oxygen permeability. Thus, one of ordinary skill in the art can easily determine the ratio that enables the desired dynamic range of glucose measurement at the required low oxygen consumptions. It should be noted that if a polyurethane hydrogel is used, the membrane is cured by evaporating the solvent instead of using ultraviolet light. 
         [0057]    Step 12. Optionally deposit additional PHEMA membrane precursor solution to the glucose and blank electrode, UV cure and dry. This optional step adds catalase that prevents release of hydrogen peroxide to the biological environment, reduces flow rate influence on sensor sensitivity and prevents direct contact of the microspheres surface to the biological environment. 
         [0058]    Step 13. Cut the polyimide sheet into individual sensors  60 . 
         [0059]    The individual sensors  60  are then assembled into the sensor sheath  40  according to the preferred embodiments previously described. 
         [0060]    Although the preferred embodiments of the present invention have been described herein, the above description is merely illustrative. Further modification of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the invention as defined by the appended claims.