U.S. patent number 3,878,830 [Application Number 05/365,431] was granted by the patent office on 1975-04-22 for catheter system for blood gas monitoring.
This patent grant is currently assigned to Mediscience Technology Corporation. Invention is credited to Haim I. Bicher.
United States Patent |
3,878,830 |
Bicher |
April 22, 1975 |
Catheter system for blood gas monitoring
Abstract
A catherter system for blood gas monitoring comprising a
polarographic sensing means having a body, first and second
conductors supported by the body and each respectively having an
exposed conducting surface at a region of the body, electrolytic
material supported by the body at said region in contact with the
exposed surfaces at the first and second conductors, and a membrane
supported by the body extending over the region of said body
covering the electrolytic material. The membrane is pervious to
oxygen in the fluid system and semi-pervious to water. The
electrolytic material is anhydrous prior to use of the device and
is activated by immersing in a aqueous solution just before use.
The sensing means is at the end of a cable carrying the conductors
which cable has its other end joined to the connector end of a
terminal or transport unit. The end opposite the connector end of
the unit has a securing means for attaching the unit to the hub end
of a catherer through which the sensing means and cable are
receivable.
Inventors: |
Bicher; Haim I. (Charleston,
SC) |
Assignee: |
Mediscience Technology
Corporation (Collingswood, NJ)
|
Family
ID: |
23438895 |
Appl.
No.: |
05/365,431 |
Filed: |
May 31, 1973 |
Current U.S.
Class: |
600/360; 204/415;
204/403.13 |
Current CPC
Class: |
A61B
5/1473 (20130101); A61B 5/14542 (20130101) |
Current International
Class: |
A61B
5/00 (20060101); A61b 005/00 () |
Field of
Search: |
;128/2E,2L,2.1E
;204/195B,195P,195S,195W |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Niedrach, L. W. et al., Journ. of Assoc. for Advanc. of Med.
Instr., Vol. 6, No. 2, Mar.-Apr., 1972, pp. 121-125..
|
Primary Examiner: Howell; Kyle L.
Attorney, Agent or Firm: Trachtman; Jacob
Claims
What is claimed is:
1. A polarographic sensing means for a fluid system comprising a
body, first and second electrical conductors insulated from each
other and supported by said body and each respectively having an
exposed conducting surface at a region of said body, a deactivated
electrolytic material supported by said body at said region in
contact with the exposed surfaces of said first and second
conductors, and a membrane supported by said body extending over
the region of said body and covering said electrolytic material,
said membrane being pervious to oxygen in the fluid system and
semi-pervious to water.
2. The sensing means of claim 1 in which the electrolytic material
is anhydrous, and the electrolytic material of said sensing means
is activated by immersing said sensing means in an aqueous solution
prior to use.
3. The sensing means of claim 2 in which the electrolytic material
is crystalline potassium chloride.
4. The sensing means of claim 2 in which the membrane comprises a
layer of polyvinyl formal.
5. The sensing means of claim 2 in which the electrolytic material
is potassium chloride, the membrane is a layer of polyvinyl formal,
said first conductor providing an exposed silver surface in contact
with said electolytic material said second conductor providing a
silver chloride surface in contact with said electrolytic
material.
6. The sensing means of claim 4 in which said membrane includes an
outer layer of silicone over the layer of polyvinyl formal.
7. the sensing means of claim 6 in which said first and second
conductors are elongated wires encased in a flexible plastic
material and extending from said body to a terminal end.
8. The sensing means of claim 7 including a terminal unit having a
connector with a pair of contacts respectively electrically
engaging the said first and second wires at said terminal end.
9. The sensing means of claim 8 in which said body has a head of
substantially cylindrical configuration with an end providing a
flat surface, said wires extend through said body and have an end
providing said exposed conducting surfaces at said flat surface,
said electrolytic material being supported on the flat surface of
said head, and said membrane extending over the end of said head
and covering said electrolytic material.
10. The sensing means of claim 9 in which said terminal unit has a
first end and a second end and a cavity therein extending through
said first end, the connector of said unit being secured at its
second end with the wires of said first and second conductors
extending therefrom through the cavity and opening in the first end
of said unit to said head.
11. The sensing means of claim 10 in which the first end of said
unit includes securing means for attachment to the end of a
catheter through which the head and extending conductors are
receivable.
12. The sensing means of claim 11 including a catheter having a
first end removably attached to the first end of said terminal unit
and a second end, said catheter having a longitudinal opening
therein communicating with the cavity of said unit and receiving
said head and extending conductors therewithin.
13. The sensing means of claim 12 in which said unit has a sealable
port communicating with its cavity for withdrawing fluid from and
infusing fluid into said fluid system through said catheter.
14. The sensing means of claim 12 in which the first end of said
unit has a cylinder containing said cavity and said second end
includes a piston received within said cavity and movable between a
first extended position and a second compressed position, said head
being positioned within the opening of said catheter when said unit
is in its extended position, while extending from the second end of
said catheter when said unit is in its compressed position, said
unit including locking means for securing said unit in its
compressed position.
15. The sensing means of claim 14 in which the head of said body is
made of epoxy material, and said catheter is an elongated plastic
tube.
Description
The invention relates to a catheter system for blood gas monitoring
and particularly a system for monitoring and measuring the partial
pressure of oxygen in the blood system which provides a sensing
head with a dry electrolyte for long shelf life which can be
activated prior to use by emersion in an aqueous solution.
The constant monitoring of respiratory gas tensions in the
circulating blood is vital for determining patient responses during
anesthesia, certain surgical procedures and the treatment of the
heart, pulmonary and metabolic diseases, as well as for assisting
positive pressure breathing and during many medical emergencies
including shock or trauma. Heretofore, no device has been available
for fulfilling such needs in a practical, reproducable, and
economical manner. The present invention provides such a catheter
system which is readily implantable and has a disposable catheter
and sensing means for determining gas tension in the blood,
particularly the partial pressure of oxygen and can be implanted in
the vein or artery, or in the tubing attached to a heart-lung
machine or to any similar profusion apparatus.
It is therefore a principal object of the invention to provide a
new and improved catheter system for blood gas monitoring which is
highly reliable and may easily be implanted in the region where the
blood system is to be monitored.
Another object of the invention is to provide a new and improved
catheter system which may be inexpensively produced and has a
disposable catheter and sensing unit.
Another object of the invention is to provide a new and improved
catheter system for monitoring the partial pressure of oxygen in
the blood system in-situ or at a selective point or location in the
circulatory system with desirable accuracy over an extended period
of time.
Another object of the invention is to provide a new and improved
catheter system for blood gas monitoring which provides a
relatively long shelf life and may be readily activated just before
use by immersion in an aqueous solution.
Another object of the invention is to provide a new and improved
catheter system for blood gas monitoring which allows a sensing
head to be threaded through a catheter or cannula already in place
in the patient without disturbing other catheter functions.
Another object of the invention is to provide a new and improved
catheter system for blood gas monitoring which may readily be
calibrated in-situ, provides for obtaining blood samples and for
infusing fluids therethrough without interfering with the
monitoring and measuring functions.
Another object of the invention is to provide a new and improved
catheter system for blood gas monitoring which includes a delivery
or transport unit for being secured with a catheter and controlling
the placement of the sensing head selectively within the catheter
or extending beyond the catheter into the circulatory system.
Another object of the invention is to provide a new and improved
catheter system for blood gas monitoring which permits the sensing
head to be implanted with the insertion of a catheter or after a
catheter has been implanted, and also allows the removal of the
sensing means without requiring the removal or disturbing of the
implanted catheter.
Another object of the invention is to provide a new and improved
catheter system for blood gas monitoring which is highly reliable
in operation, provdes good stability over an extended period of
time, and may readily be calibrated to provide accurate read-out
information.
The above and other objects of the invention are achieved by
providing a catheter system for blood gas monitoring which has a
polarographic sensing means or head comprising a body, first and
second conductors supported by the body and each respectively
having an exposed conducting surface at a region of the body,
electrolytic material supported by the body at said region in
contact with the exposed surfaces of the first and second
conductors, and a membrane supported by the body extending over the
region of said body and covering the electrolytic material. The
membrane is provided with an inner layer which is pervious to
oxygen in the fluid system and semi-pervious to water, and a gas
pervious outer layer which is compatible with the blood system into
which it is placed.
Prior to use of the sensing head, the electroytic material is
anhydrous or of crystalline form for providing long shelf life with
minimized deterioration. The electrolytic material is activated by
immersing the sensing head in an aqueous solution, which may be a
saline solution, prior to use. In the particular form illustrated,
the electrolytic material is potassium chloride, and the inner
layer of the membrane is made of polyvinyl formal with an outer
layer of silicone elastomer.
The pair of conductors of the head each comprising a copper wire
having a silver coating. One of the conductors is chlorinated to
provide a silver chloride, copper chloride surface in contact with
the postassium chloride electrolyte as one electrode, while the
other electrode is formed by the silver clad copper wire, also in
contact with the electrolyte. The pair of conductors of the sensing
head are provided by one end of a cable which has an insulating
coating of a flexible material such as "Teflon." The cable is
connected at its other end to a terminal or transport unit which
provides a connector for electrically detachably joining the wires
of the cable to read-out equipment which may digitally indicate
information derived from the sensing head, and also provide the
bias potential utilized for operation of the sensing head.
The transport unit also has a first end providing a connector for
threadedly engaging the hub of a cannula or catheter through which
the cable and sensing head are threaded, and a cavity for
communicating through the opening of the catheter to the
circulatory system. The terminal unit is also provided with a
plunger or piston which is received within the chamber and may be
longitudinally moved for extending the sensing head from within the
catheter to a position beyond the end of the catheter for making
measurements in-situ. The piston when it is in its retracted
position may be locked to avoid movement of the sensing head.
The terminal unit is also provided with a port communicating with
its chamber which allows the drawing of blood samples through the
catheter, and also for the infusion of fluids into the circulatory
system as may be required.
The method of making the sensing means of the invention includes
the steps of forming a body with first and second spaced electrodes
providing exposed surfaces at a region of the body, affixing an
anhydrous electrolytic material over the exposed surfaces of the
electrodes on the body, securing with the body a membrane which is
semi-pervious to water, enclosing the electrolytic material and the
exposed surfaces of the electrodes. The anhydrous electrical
material is affixed over the exposed surfaces of the electrodes by
applying a wet electrolytic material on the body over the
electrodes and allowing it to dry prior to enclosing the
electrolytic material by the membrane. The wet electrolytic
material is comprised of potassium chloride gel which is dried to
crystalline form. The membrane is formed by applying a solution of
polyvinyl formal to the body over the anhydrous electrolytic
material and drying same to form a coating which is semi-pervious
to water and pervious to oxygen in an aqueous solution. An outer
coating for the membrane is formed by the additional step of
applying a silicone solution over the polyvinyl formal coating and
allowing same to dry.
The method for forming the body of the sensing means with first and
second spaced electrodes includes providing a cylindrical mold
having an opening along its longitudinal axis and positioning in
spaced axial extending relationship therein the first and second
conductors, filling the opening of the mold about the conductors
with an epoxy material in unset form and permitting the epoxy
material to set and harden, severing the mold, the epoxy material
and conductors extending therethrough, along a plane perpendicular
to the longitudinal axis of the mold, providing the conductors with
an exposed surface at a flat surface region of the body, and
removing the remaining mold from about the body.
The method also includes the step of applying an aqueous solution
to the outside of the membrane for activating the electrolytic
material of the sensing means by passage of water through the
membrane, prior to the utilization of the sensing means for blood
gas monitoring.
The foregoing and other objects of the invention will become more
apparent when the following detailed description of the invention
is read in conjunction with the drawings, in which:
FIG. 1 is an elongated perspective view of a catheter system for
blood gas monitoring embodying the invention,
FIG. 2 is a sectional view of reduced size taken on the line 2--2
of FIG. 1,
FIG. 3 is an end elevational view taken on the line 3--3 of FIG.
2,
FIGS. 4, 5, 6, 7 and 8 are enlarged sectional views illustrating
the method of making the sensing head of the invention,
FIG. 8a is an enlarged portion of FIG. 8, and
FIG. 9 is an enlarged sectional view of the sensing head similar to
that shown in FIG. 8 after the electrolytic material has been
activated by immersing the head in an aqueous solution.
Like numerals designate like parts throughout the several
views.
Referring to the figures, the catheter system of the invention
comprises a sensing means 10 having a sensing head 12 at the end 14
of a flexible cable 16 including double parallel insulated lines 18
and 20 with wire conductors 22 and 24. The cable 16 may have an
outer insulating wall 26 of a plastic material which is compatible
with the blood system, such as that commercially known as Teflon.
The conductors 22 and 24, may be made of any suitable conducting
material, and in the specific embodiment disclosed comprises copper
wire which is silver plated. Such a cable having AWG size 36 wires
is commercially available from Phoenix Wire, Inc. as catalog number
36TDQ.
The conductors 22 and 24 at the other end 28 of the cable 16 are
secured with and electrically connected to the posts 30, 32 of a
male connector 34 which is located at the rear end 36 of a terminal
or transport unit 40. The front end 42 of the transport unit 40
provides an opening 46 and internal threads 44 for engaging the
connecting end or hub 48 of a catheter 51. The opening 46 of the
transport unit 40 communicates with a chamber 52 therewithin. The
chamber 52 communicates with the opening 54 of the catheter 51
which opening 54 extends from the connector end or hub 48 to the
distal end 56 thereof. The chamber 52 of the transport unit 40
extends in the longitudinal direction within a cylinder portion 58
of the transport unit 40.
The end 36 of the unit 40 is provided with a plunger or piston 60
which extends into the chamber 52 and is movable therein in the
longitudinal direction. The end of the piston 60 is provided with a
rubber seal 62 for preventing leakage of fluid from the chamber 52.
The cable 16 passes axially and in the longitudinal direction
through the center of the seal 62 and a central opening 64 in the
piston 60 to the connector 34. The cable 16 extends in the opposite
direction through the chamber 52 and out of the opening 46 of the
unit 40 to the sensing head 12 at its other end 14. The sensing
head 12 may be threaded through the opening 54 of a catheter 51
after which the connector end 48 of the catheter is threadedly
engaged with the end 42 of the unit 40 as illustrated in FIGS. 1
and 2.
As also illustrated in FIG. 1, when the unit 40 is in its extended
position, the head 12 is moved toward the end 42 of the unit, while
when the unit 40 is in its compressed condition with the piston 60
fully received into the chamber 52, the sensing head 12 is extended
away from the end 42 of the unit 40. This relative movement of the
head 12 may be seen from the illustrations of FIG. 1, which shows
the sensing head 12 within the opening 54 of the catheter 51, and
FIG. 2 which shows the sensing head 12 extending from the end 56 of
the catheter 51 so that it is positioned external to the catheter
51.
The terminal or transport unit 40 is provided with a radially
extending portion providing a port 68, proximate to its connector
end 42 which has a radially extending opening 66 communicating with
the chamber 52. The port 68 may be closed by a stop plug 70 when
not in use, as illustrated, and may be used for delivering or
removing fluid through the catheter 51 when such use is
desired.
The rear end 36 may be enlarged over the piston 60 to provide ease
of handling and a stop abutment when the piston 60 is fully
received into the chamber 52 of the cylinder 58. The unit 40 is
also provided with a locking means 72 in the form of a pin 74
extending radially from the piston 60 proximate to the rear end 36
and a J-shaped groove 76 in the cylindrical portion 58 for
receiving the pin in the axially direction and locking same by
relative rotation of the piston 60 and cylinder 58. Such locking
action is important for preventing the relative movement of the
piston 60 with respect to the cylinder 58 and in turn preventing
the movement of the sensing head 12, especially when the chamber 52
is subjected to high fluid pressure.
The head 12 at the end of the cable 16 provides a sensing means 12
of the polarographic type. The head 12 is produced at the end 14 of
the cable 16 in a manner illustrated by FIGS. 4 to 8 inclusive. The
end 14 of the cable 16 is placed into the end of a tube 78. The
tube 78 may be made of plastic material, such as polyethylene,
forming a casting mold as shown in FIG. 4. Epoxy material 80 in its
plastic state is placed within the opening of the tube 78 about the
end 14 of the cable 16. The positioning the epoxy 80 within the
tube 78 may be assisted by using a hypodermic syringe needle at the
rear of the tube to suck up the epoxy material. After the epoxy has
set and hardened and has dried for at least 8 hours, the tube 78,
epoxy material 80 and the cable 16 are severed along a plane
indicated by the dashed line 82 of FIG. 4. The plane along which
the cut is made provides a surface 84 which is perpendicular to the
extending direction of the cable 16.
The tube 78 is now removed leaving an epoxy cast or plug 86 at the
end 14 of the cable 16 with a flat end surface 84. The end surface
84, as seen in FIG. 6, provides exposed perpendicular cross
sections of the conductors 22 and 24 of the cable 16 each of which
is respectively surrounded by an insulation layer 88, 89 which may
be of Teflon and bound to each other by the intermediate joining
plastic material 93 which may also be Teflon. Surrounding the cable
16 is the epoxy cast or plug 86. The plastic covering 88 of the
cable 16 may be provided with a red coloring to distinguish the
conductor 22 from the conductor 24 which is covered by a plastic
material 89 which is colored green or any other distinguisting
color.
The end 14 of the cable 16 with its cast epoxy body 86 and exposed
conductors 22, 24 is immersed in a 0.05 HCl aqueous solution for 2
minutes while an electrical potential of 1 volt is applied at the
other end of the cable 16 between the conductors 22, 24. The
positive potential is applied to the conductor 22, while the
negative potential is supplied to the conductor 24. This results in
providing a silver chloride coating at the silver plated surface of
the conductor 22 and copper chloride coating at the exposed copper
surface to form the reference electrode. The silver plated copper
conductor 24 is not affected by the chlorination operation thus
performed and provides the other electrode of the head 12. The flat
end surface 84 of the plug 86 is positioned to face upwardly and a
drop of wet electrolyte 90' is placed thereon making certain the
electrolyte 90' is not received over the cylindrical side wall 85
of the plug 86. The electrolyte 90' is allowed to dry to form a dry
electrolyte layer 90 for approximately 2 hours. The electrolyte 90'
applied is potassium chloride gel such as that commercially
available from Beckman Instruments, Inc. as PO.sub.2 Electrolyte
No. 326590.
Upon drying, the potassium chloride electrolyte crystallizes to
provide a layer of electrolyte on the surface 84 extending over and
between, and in contact with the exposed chlorinated end of the
conductor 22 and the exposed metallic end of the conductor 24 (see
FIG. 7).
The plug 86 is dipped into a solution of 0.25% "Formvar" in
ethylene dichloride. The Formvar utilized is Formvar 15/95E, a
polyvinyl formal which has an average molecualr weight of 24,000 to
40,000, a solution viscosity (15% by wt.) of 3,000 to 4,500 cp., a
resin viscosity of 37 to 53 cp., a specific gravity
(23.degree./23.degree.) of 1.227, a hydroxyl content expressed as %
polyvinyl alcohol of 5.0 to 6.0 (D1396-58), an acetate content
expressed as % polyvinyl acetate of 9.5 to 13.0 (D1396-58) and a
formal content expressed as % polyvinyl formal of about 82. This
product is sold by Monsanto Chemical Co. and is described in detail
in the Monsanto Technical Bulletin No. 6070A.
It has been found desirable to repeat the dipping process by double
dipping the plug 86 in the solution, at one minute intervals
between double dippings, and holding the plug 86 in the upward
direction and alternately in a downward direction between dippings.
The coated material is allowed to dry for from 5 to 10 minutes to
provide the inner layer 92 of the membrand 94. The layer 92 extends
over the entire outside surface 85 of the epoxy material 86 and
where the end surface 84 is covered by the dried electrolyte layer
90, it extends over and encloses the electroyte 90 as shown in
FIGS. 8 and 8a.
After the inner layer 92 is dried, the plug 86 is double dipped in
a solution of 0.2 gram of "Silastic" to each cc of xylene and
allowed to air dry for 24 hours. The Silastic used is commercially
available from Dow Corning Corp. as Silastic Medical
Adhesive-Sicicone, Type A, Stock No. 891. This forms a second or
outer layer 96 of the membrane 94. The outer layer 96 extends
completely over the inner layer 92 and provides a surface which is
compatible with the blood system into which the sensor head 12 is
to be received for making measurements.
In operation, the sensor head 12 is activated just prior to its use
by immersing it in an aqueouos solution, which may be a saline
solution. With the passage through the membrane 94 of water, the
crystallized potassium chloride electrolyte 90 is transformed into
the electrolyte 91 in its active liquid state. This transformation
causes the expansion of electrolyte 90 to provide the wet
electrolyte 91 as shown in FIG. 9. In the expanded form, the member
94 is stretched to provide the configuration illustrated in FIG. 9,
and the sensing head 12 is now in condition for measuring tension
or partial pressure of oxygen in the fluid system under
consideration.
In the form illustrated, the sensing means 10 provides a
intra-arterial catheter with a polarographic head 12 for measuring
in-vivo, the partial pressure of oxygen in the blood. The sensing
head 12 is provided with an outside diameter of 0.5 mm so that it
may easily fit through a 20 gauge Teflon arterial canulla. The
sensing head 12 may be placed in an artery by utilizing a catheter
which had previously been implanted in the subject, or by
positioning an arterial canulla or catheter with its implanted end
at the location at which in-vivo measurements are to be taken.
Thus, for example, with the catheter 51 positioned in the artery as
required, the cable 16 with the head 12 at its leading end 14 is
threaded through the opening 54 of the catheter 51 by entering its
terminal end or hub 48. At this time, the transport means 40 is
positioned with its plunger 60 in its withdrawn or extended
condition as shown in FIG. 1. After the cable 16 has been fully
threaded through the catheter 51, its sensing head 12 is positioned
as indicated by the dashed lines in FIG. 1 and the end 42 of the
transport unit 40 is proximate to the threaded end or hub 48 of the
catheter 51. The end 48 of the catheter 51 and the end 42 of the
transport unit are threadedly engaged so that the protruding male
portion 45 of the transport unit 40 is received into and securely
sealed with the catheter 51 to provide communication between its
chamber 52 and the opening 54 of the catheter 51.
The end 36 of the transport unit 40 may now be moved to its
contracted position shown in FIG. 2 and locked. The inward movement
of the piston or plunger 60 results in the advancement of the
sensing head 12 so that it extends out of the end 56 of the
catheter 51 and into the blood system in which measurements of
partial pressure of oxygen are to be obtained and monitored. An
electrical measuring apparatus (not shown) is electrically joined
to the connector 34 of the terminal 36 and provides a bias voltage
potential to the conductors and electrodes 22, 26 of the sensing
head 12 of 0.6 volt.
Since the membrane 94 is pervious to oxygen in the blood system,
the oxygen passes therethrough to the electrolyte 91 resulting in
polarographic action. As well known, the presence of oxygen at the
polarographic sensing head 12 produces a current which may be
calibrated to show the partial pressure of oxygen. Such current
flow is delivered to an indicating means (not shown) providing
output readings which may be calibrated by reference to
measurements taken of blood samples by means of a conventional gas
analyzer.
The catheter system for blood gas monitoring has been most
effective and useful during and after major cardiovascular and
pulmonary operations by providing continuous indications of oxygen
tension in the blood correlated to within 12% of the values
obtained by conventional gas analyzers. Such indications have
followed faithfully stepwise changes in oxygen tension of inspired
gas. It has been found that the catheter system could be left
in-situ in patients for periods of 24 hours and more, proving the
system to be of value for monitoring arterial partial oxygen
pressure during and after major cardiovascular and pulmonary
surgery and providing helpful information for the controlling of
artificial ventilation.
The system provides a great advantage over prior art, by having a
polarographic sensing head with an extended shelf life. This is
achieved by providing the head with its electrolyte in a dry
condition when not in use, while the head may be readily activated
for use by placing same in a saline solution. The sensing head 12
can also be activated by placing same in the blood system, although
the preactivation by immersion in the saline solution is
preferred.
The in-situ calibration is also advantageous in that it permits
making allowance for flow, temperature, and positioning artifacts.
Calibration is readily accomplished by withdrawing blood samples
through the catheter 51 by a syringe attached to the port 68 of the
transport unit 40. In addition to removing such blood samples,
other desirable fluids may be infused through the port 68, so that
the catheter system does not interfere with other functions which
are to be accomplished by use of the catheter, which may have
previously been implanted for such purposes, and is utilized by the
catheter system.
It will be obvious to those skilled in the art that the invention
disclosed may find wide application with appropriate modification
to meet individual design circumstances, but without substantial
depature from the essence of the invention.
* * * * *