 |
Description  |
|
|
BACKGROUND
1. Field of the Invention
The present invention relates to cannulae and more particularly to
gas-sampling catheters and method for in vivo sampling of gases in
biological tissue.
2. The Prior Art
The use of gas-sampling catheters is becoming increasingly more important
as a diagnostic tool. Heretofore, gas determinations were made by
analyzing a blood sample in vitro. More recently, catheters have been used
to sample blood gases in vivo through an arterial or venous fistula.
Catheters for sampling gases in blood are well-known. See, for example,
U.S. Pat. Nos. 3,572,315 and 3,658,053. Historically, however, the
construction of conventional gas catheters has posed undesirable problems.
Generally speaking, gas-sampling catheters of the prior art fall into two
types. In the first type, a gas-permeable membrane is attached to a
portion of the catheter while the remainder of the catheter comprises
different material. This produces an undesirable joint presenting a
potentially dangerous fragmentation site and adversely affects both gas
sampling and sterility. Moreover, the joint tends to accelerate
undesirable clot formation when the catheter is exposed to blood.
In the second type an unbroken membrane is provided over the entire length
of the catheter. This type, however, has proved susceptible to
inaccuracies as a result of the migration of gases between the membrane
and the tube along the length of the catheter. For example, any portion of
the catheter remaining outside of the patient's body during in vivo
sampling would be adversely affected by atmospheric gases entering the
membrane exterior of the puncture site.
The problems suggested above have proved even more acute when measuring
gases in subcutaneous tissue other than blood. Further, until this present
invention, liquids have been universally used to calibrate gas-sampling
catheters. Liquids having known amounts of calibration gases are expensive
and difficult to store. No catheter assembly or method has been heretofore
devised to adequately calibrate the sampling portion of the catheter with
readily obtainable gases.
It would, therefore, be a substantial improvement in the art to provide a
gas-sampling catheter assembly and method overcoming the mentioned
obstacles.
BRIEF SUMMARY AND OBJECTS OF THE INVENTION
The present invention includes an in vivo gas-sampling catheter having an
unbroken exterior membrane for insertion into body tissues, the catheter
having a sampling tip of predetermined size and structure which prevents
undesirable migration of gases along the length of the catheter to the
sampling tip. Further, structure and method are provided for calibrating
the catheter by confining the sampling tip in a removable calibrating
chamber prior to use.
It is, therefore, a primary object of the present invention to provide an
improved catheter assembly.
It is another primary object of the present invention to provide an
improved method for calibrating and sampling gases.
It is another object of the present invention to provide an in vivo
gas-sampling catheter assembly having an unbroken exterior gas-permeable
membrane along the entire insertable length of the catheter.
Another valuable object of the present invention is to provide a
gas-impermeable barrier between the catheter tube and permeable membrane
to inhibit axial migration of gases along the catheter to the sampling
tip.
One still further object of the present invention is to provide improved
structure accommodating calibration of the catheter at the sampling tip.
One further object of the present invention is to provide means for
preserving the sterility of the catheter assembly.
These and other objects and features of the present invention will become
more fully apparent from the following description and appended claims
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is an elevational view of a preferred catheter assembly embodiment
shown partially in cross section.
FIG. 2 is an elevational view of the catheter assembly embodiment of FIG. 1
also shown in partial cross-section and illustrated with the membrane
catheter in a partially advanced position.
FIG. 3 is a fragmentary cross-sectional view of a membrane catheter
embodiment of the invention.
FIG. 4 is a fragmentary cross-sectional view of a catheter hub adapted to
be used with the catheter of FIG. 3.
FIGS. 5-16 are perspective elevations of various desirable catheter
sampling tip embodiments.
FIG. 12A is a cross-section taken along lines 12A--12A of FIG. 12.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
General
It has been found according to the present invention that the catheter
assembly described herein can be effectively used to sample biologically
significant gases such as anesthesia, carbon dioxide and others both in
vivo and in vitro. Of particular importance is the ability to aseptically
deliver the gas-sampling catheter subcutaneously adjacent a particular
muscle tissue site or directly intramuscularly to permit measurement
immediately at the tissue site.
The Assembly
Reference is now made to the Figures wherein like parts are designated with
like numerals throughout.
Referring now to FIG. 1, the catheter assembly generally designated 10
includes a catheter 12, a catheter hub 14, a base 16 and a calibration
chamber 18 as will now be more fully described.
The catheter 12 can be best understood by reference to FIG. 3. The catheter
12 includes an elongated metal tube 20 having a hollow interior 22. The
leading portion of the tube 20 has had a portion of its longitudinal
length collapsed as at 24 and is thereafter twisted to form a spiralling
core. This configuration presents a spirally configurated continuous
opening 26 which communicates with the hollow 22 of the tube 20. Other
suitable tip configurations are illustrated in FIGS. 5-16. The tube 22
terminates in a cylindrical collar 28.
Catheter 12 is covered with a gas-permeable membrane 30 along the entire
length of the catheter from the collar 28 to the base 16 (FIG. 1). It has
been found highly desirable to insure that the gas-permeable membrane
traverses the entire length of the catheter without breaks or seams which
tend to precipitate clot formation. In the presently preferred embodiment,
it has been found that the catheter of the present invention can be used
to measure tissue gases by inserting a substantial length of catheter (for
example, 2 to 4 inches) directly into the tissue of a patient to sample
gases therein. The continuous membrane 30 provides for facile insertion
and minimizes contamination.
The tip 32 of the catheter 12 is rounded to facilitate insertion in
biological tissue. In order to strengthen the tip 32 and prevent
inadvertent fracture of the membrane 30, a bulbous insert 34 is attached
adjacent the collar 28 and heat-sealed thereon to act as a forming mandrel
and support for the tip 32. Preferably, the bulbous insert is formed of
the same material as the membrane 30. While any suitable gas-permeable
membrane material could be used, Teflon is presently preferred.
Elongated catheters of the type used in the prior art have been found to be
adversely affected by ambient air. It has been found that even where the
gas-permeable membrane is tightly adhered to the underlying tubing, gas
tends to travel axially between the tube and the catheter. Thus, when a
portion of the catheter is inserted into biological tissue for sampling
purposes, the sample is distorted by ambient air travelling between the
catheter and the tube. According to the present invention, the axial
transference of gases is precluded by an annular barrier 36. The barrier
is preferably made of gas-impermeable material such as epoxy and is
heat-sealed directly to both the tube 20 and the gas-permeable membrane
30. Thus, the barrier 36 defines the trailing end of the sampling tip of
the catheter 12.
The trailing end of the catheter 12 is rigidly anchored within the base 16.
Preferably, the base 16 is formed of a gas-impermeable plastic material
and the tube 20, absent the membrane 30, projects rearward of the base 16
to permit tight coupling into a receiver (not shown) of a conventional
analyzer 38. The analyzer 38 can be of any suitable variety, one such
analyzer being the Perkin & Elmer Mass Spectrometer.
The catheter 12 normally passes through the catheter hub 14, best shown in
FIG. 4. The catheter hub 14 includes a body 40 having a forwardly tapered,
diametrally reduced male coupling 42 forming the leading end of the hub
14. The trailing end of the hub is defined by a diametrally enlarged
collar 44 mounted upon the body 40.
Interiorly, the hub 14 has a diametrally enlarged bore 46 which opens at
the upper surface 48 of the hub for the reason to be made subsequently
more apparent. A diametrally reduced bore 47 communicates coaxially with
the bore 46 and opens to the exterior of the hub 14 at the leading end of
the male coupling 42.
A tubular guide 50 is mounted in the bore 47 and projects into the bore 46
to the rear of the collar 44. Preferably, the guide 50 projects somewhat
beyond the end of the male coupling 42. As shown in both FIGS. 1 and 4,
the catheter 12 is telescopically disposed within the guide 50, the guide
50 at least at the leading tip being necked down and reduced thereby
exerting a slight frictional force on the catheter. The guide 50 also
prevents blood from moving through the hub 14 to contaminate the catheter
12.
Referring again to FIG. 1, the catheter is illustrated as enclosed within a
conduit 52 which is provided with a longitudinal slit 54 along its entire
length. The structure and operation of a suitable slit conduit can best be
understood by reference to U.S. Pat. No. 3,185,152.
The conduit 52, which circumscribes the catheter 12 also surrounds a
portion of the length of the guide 50 (FIG. 4) up to the ramp surface 49.
The ramp surface 49 guides the conduit 52 out of the hub 14 and
facilitates opening of the longitudinal slit 54 to separate the conduit
from the catheter 12 without violating asepsis. Thus, when the catheter is
advanced axially through the catheter hub from the FIG. 1 to the FIG. 2
position, the conduit 52 is automatically stripped away by the catheter
hub.
Prior to use in sampling gases from biological tissue, the sampling tip of
the catheter 12 is maintained within a calibration chamber 18 shown best
in FIG. 1. The calibration chamber has a tubular body 60 preferably formed
of plastic material and having an internal diameter sized so as to mate
snuggly with the male coupling 42 of the catheter hub 14. The body 60 is
provided with a discharge port 62 to permit the chamber 18 to be purged
with calibration gas as will be hereinafter more fully described. The
leading end of the calibration chamber 18 is mounted into a coupling 64
which defines an inlet port 66. In the illustrated embodiment, a filter 67
is located within the coupling 66 to remove contaminants from the
calibrating gas. Preferably, the filter 67 is a bacterial filter to assure
asepsis of the catheter 12 during calibration. While any suitable
bacterial filter could be used, a 0.45 micron filter has been found
acceptable. A filter (not shown) at the discharge port 62 may also be
employed if desired.
Calibration gas is conducted through the inlet port 66 to purge the
interior of the tube 60, the purged gases escaping at the discharge port
62. Because of the existence of the annular barrier 36 (FIG. 3) only the
sampling tip need be supplied with calibrating gas, the remaining length
of the catheter 12 being prevented from adversely affecting the sampled
gas because of the barrier 36. The calibration chamber 18 may also be used
for temperature stabilization of the catheter 12, when desired.
The Method
As has been heretofore pointed out, the catheter assembly of the present
invention may be used to sample gases in blood, both in vivo and in vitro
or, to sample gases subcutaneously adjacent selected tissues, such as
muscle.
In using the catheter assembly described herein, it is observed that the
sampling tip of the catheter 12 is aseptically preserved because of the
sampling chamber 18. Prior to removing the sampling chamber 18, a
calibration gas having a known concentration of the gas to be tested is
conducted through the inlet port 66 to the interior of the tube 60.
Asepsis is preserved through the filter 67. The tube 60 is purged through
the discharge port 62. Thus, the analyzer 38 can be calibrated to the
known gas composition. Oxygen, carbon dioxide, anesthesia, trace gases and
the like can all be sampled when the analyzer 38 is calibrated to measure
the gas.
Thereafter, the calibration chamber 18 is separated from the hub 14 and the
catheter 12 is inserted through a previously made incision subcutaneously
or intramuscularly adjacent the tissue to be sampled. Preferably, the
catheter 12 is inserted from between 2 to 4 inches into the tissue to
improve the reliability of the sample.
Alternatively, a fistula may be formed by cannulating an artery or other
blood vessel in the manner taught in U.S. Pat. No. 3,459,183 and inserting
the catheter 12 into the blood vessel through the fistula. It is pointed
out that the coupling 42 is provided with a standard Luer taper to
accommodate mating of the hub 40 with the trailing end of conventional
cannulas. Blood is prevented from migrating along the catheter 12 by the
reduced tip of guide 50, which acts as a check valve. Thus, contrary to
the requirements of prior art devices, in vivo blood sampling can be
accomplished without first sterlizing the patient's skin area at the
sampling site.
As the catheter 12 is advanced into the tissue, the conduit 52 is
automatically stripped away at the ramp surface 49 of the hub 14. The
guide 50 exerts just enough tension on the catheter 12 to permit the
catheter hub to be used to make the initial insertion and to properly
guide the catheter 12.
The catheter assembly and method described herein have been found to obtain
in vivo gas samples with surprising ease and facility. Moreover, the
catheter may be used equally well to sample in vivo blood or tissue gases.
Also, if desired, in vitro gases may be sampled because adverse
interference with sampling is prevented even though the catheter is
elongated because of the annular barrier 36.
The invention may be embodied in other specific forms without departing
from its spirit or essential characteristics. The described embodiment is
to be considered in all respects only as illustrative and not restrictive
and the scope of the invention is, therefore, indicated by the appended
claims rather than by the foregoing description. All changes which come
within the meaning and range of equivalency of the claims are to be
embraced within their scope.
* * * * *
|
|
 |
|
 |
Description |
|
