(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2009/0240121 A1
`Bickoff
`(43) Pub. Date:
`Sep. 24, 2009
`
`US 20090240121A1
`
`(54) INTRAVASCULAR SENSOR AND INSERTION
`SET COMBINATION
`
`(75) Inventor:
`
`Charles Bickoff, Sharon, MA (US)
`
`Correspondence Address:
`MESMER & DELEAULT, PLLC
`41 BROOK STREET
`MANCHESTER, NH03104 (US)
`(73) Assignee:
`NOVA BIOMEDICAL
`CORPORATION, Waltham, MA
`(US)
`
`12/052,985
`
`(21) Appl. No.:
`1-1.
`(22) Filed:
`
`(51) Int. Cl.
`A6 IB5/00
`
`Mar. 21, 2008
`Publication Classificati
`DCOSSO
`
`(2006.01)
`
`(52) U.S. Cl. ........................................................ 6OO/309
`
`
`
`ABSTRACT
`(57)
`An intravascular sensor assembly insertable into an intrave
`nous 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 cath
`eter, a hub sealingly connected to the sheath proximal end, the
`hub adapted for removably coupling to the intravenous cath
`eter, 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 elec
`trode with a reagent matrix disposed thereon, the reagent
`matrix comprising an enzyme capable of catalyzing a reac
`tion 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 ele
`ments are exposed adjacent the sheath distal end, and a plu
`rality 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 plu
`rality of connector pads.
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`US 2009/0240121 A1
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`Sep. 24, 2009
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`INTRAVASCULAR SENSOR AND INSERTON
`SET COMBINATION
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`0001
`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 inten
`sive 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 con
`trol therapy reduced overall in-hospital mortality by 34 per
`Cent.
`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'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, undi
`luted 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 assem
`bly 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 test
`ing and monitoring a patient’s blood glucose level. A dispos
`able testing unit is carried by the patient's body and has a
`testing chamber in fluid communication with infusion lines
`and a catheter connected to a patient blood vessel. A revers
`ible 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, undi
`luted 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 solu
`tion 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 mea
`Surement apparatus. It is another object of the present inven
`tion 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 indwell
`ing 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 sensorsheath 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 assem
`bly is inserted into the catheter after removal of the insertion
`needle.
`0012. The sensor sheath contains a sensor having sensing
`elements disposed on a sensorshank adjacent a sensor distal
`end and electrical contacts at or adjacent a sensor proximal
`end. The sensorshank is sealingly embedded within the sen
`Sor sheath where the sensor elements are exposed at or adja
`cent the sensor distal end. The sensor sheath includes a hub
`configured formating with the luerlock 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 sensorshank.
`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 dos
`ing in tight glycemic control protocols. Although blood glu
`cose 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 insert
`ing 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
`
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`available IV catheters, no specially designed or customized
`insertion tools or devices are required to position the intra
`vascular sensor in the patient.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0015 FIG. 1 is a plan view showing the general installa
`tion 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 installa
`tion 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 inser
`tion 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.
`0.025
`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 embodi
`ment of the present invention showing the sensor assembly
`inserted into the intravenous catheter where the sensor ele
`ments 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 inven
`tion 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 makeup one embodiment of the intravascular sensor inser
`
`tion set 10 of the present invention. Additionally, other loca
`tional 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 moni
`tor 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 condi
`tioning electronics and radio unit 70' transmits electrical sig
`nals 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 assem
`bly 20 typically includes an insertion needle 24 disposed
`within a flexible catheter 22 and extends a predefined distance
`beyond a catheter distal end 22a. 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 assem
`blies 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 4.0a and a sheath proxi
`mal end 40b. Sheath proximal end 40b 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 60b
`that is received within hub 46 against a hub surface 48 along
`with a sensor cable proximal end 50b. Sensor 60 and cable
`proximal end 50b are fixedly retained within hub 46 by a
`pressure applying component 52 and a pressure cap 54. Pres
`Sure applying component 52 is optionally made from a resil
`ient material Such as a foam material that is placed over cable
`proximal end 50b to apply pressure between cable proximal
`end 50b and shank proximal end 60b. Pressure cap 54 pro
`vides 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
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`the circumference of hub surface 48. Perimeter wall 47 facili
`tates attaching pressure cap 54 when capturing sensor 60,
`cable proximal end 50b 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 62a and shank proximal end 62b. Shank
`proximal end 62b has contact ears 64 that have been orthogo
`nally 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 62b. 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 62a.
`Shank distal end 62a 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 ele
`ments are considered within the scope of the present inven
`tion.
`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 50b. A portion of elec
`trical conductors 51 are exposed and overlay against electri
`cal contacts 65 of contact ears 64. As shown, cable proximal
`end 50b 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 50b. 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 proxi
`mal end 50b 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 50b.
`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 22b to form a leak-proof entity. A catheter distal end 22a
`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 22a between catheter distal end
`22a and sensor sheath 40. As FIG. 10 illustrates, a sheath
`distal end 4.0a containing sensing elements 67 extends
`beyond catheter distal end 22a 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 46a of the sheath
`hub 46 and the luer taper 27 of the luer lock fitting 23 of the
`intravenous catheter assembly 20. The threads 23a of the luer
`lock fitting 23 of the intravenous catheter assembly 20 thread
`ingly engages with the threads 46b 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 40b. Two sensor ele
`ments 67a, 67b on sensor shank 62 are disposed at side
`opening 44. In this embodiment, sheath distal end 40b has a
`sealed end 40c. Sensorsheath 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
`40b 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 sensorelements to mea
`sure a plurality of blood analytes.
`0042 FIG. 13 shows another embodiment of sensor
`assembly 30 where all sensorelements 67a, 67b, 67c, and 67d
`are on the same side of sensorshank 62. Sensorelements 67a,
`67b, 67c, and 67d 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 embodi
`ment 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 40b. 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 ele
`ments 67, sensorshank 62, sensor sheath 40, and catheter 22.
`0044 Because sensor 60 is positioned within sensor
`sheath 40, sensorshank 62 may have a characteristic of being
`rigid or flexible or any degree of rigidity/flexibility. Prefer
`ably, sensor shank 62 is flexibly resilient to provide less
`Susceptibility to damage during handling and use when con
`figured 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 PyraluxR). Pyralux(R) 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
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`light in a predefined pattern, and remove the unexposed areas
`to create a pattern for metal deposition. It should be under
`stood 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 refer
`ence 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 plati
`num, 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 elec
`trically 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 insu
`lation layer is preferably a flexible photoimageable coverlay
`available from E. I. du Pont de Nemours and Company as
`Pyralux(RPC. Pyralux(RPC 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 con
`ventional printed circuit exposure and development pro
`cesses. Unexposed areas can be developed off as explained in
`the technical information brochure provided by Dupont. For
`the present invention, Pyralux.R. 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 methacry
`late (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, accord
`ingly, the PHEMA membrane precursor solution for this elec
`trode additionally contains a glucose enzyme, preferably glu
`cose 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 elec
`trode, UV cure and dry. This optional step adds catalase that
`prevents release of hydrogen peroxide to the biological envi
`ronment, 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.
`
`What is claimed is:
`1. An intravascular sensor assembly insertable into an
`intravenous catheter, the sensor assembly comprising:
`a sheath having a sheath proximal end and a sheath distal
`end whereinan 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
`sensorshank with a shank distal end and a shank proxi
`mal end, a plurality of sensorelements including a work
`ing electrode with a reagent matrix disposed thereon, the
`reagent matrix comprising an enzyme capable of cata
`lyzing a reaction involving a Substrate for the enzyme
`and a reference electrode, the plurality of sensor ele
`ments disposed adjacent the shank distal end, a plurality
`of connector pads disposed at the shank proximal end
`wherein 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 wherein each of the plu
`rality 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.
`
`Page 13 of 14
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`US 2009/0240121 A1
`
`Sep. 24, 2009
`
`2. The sensor of claim 1 wherein the plurality of sensor
`elements and the shank distal end are exposed beyond the
`sheath distal end.
`3. The sensor of claim 1 wherein the plurality of sensor
`elements is exposed at an opening in the sheath adjacent the
`sheath distal end.
`4. The sensor of claim 1 wherein the plurality of sensor
`elements is exposed at orthogonal openings on opposite sides
`of the sheath adjacent the sheath distal end.
`5. The sensor of claim 1 wherein the sensor shank has a
`plurality of contact ears disposed Substantially perpendicular
`to the longitudinal axis of the sensor Shank and having the
`connector pads exposed thereon.
`6. The sensor of claim 5 wherein the contact ears are seated
`against a reference face within the hub at a base of the hub
`adjacent a sheath-hub interface.
`7. The sensor of claim 1 wherein the hub further includes a
`resilient component disposed within the hub against the cable
`and a pressure cap fixedly attached to the hub and sized to
`provide pressure on the resilient component causing the cable
`and the connector pads to remain in intimate electrical con
`tact.
`8. The sensor of cl