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BACKGROUND AND SUMMARY
Arterial blood for diagnostic testing in blood gas analyzers is commonly
collected by means of syringes, vacuum tubes, or capillary tubes, each of
which presents substantial disadvantages and difficulties. Syringes must
be airtight and, if formed of glass, usually require lubrication. The
entire dead space between the needle and the plunger must be filled with a
heparin solution, a procedure requiring considerable care to avoid small
air bubbles that may cling to the barrel or to the plunger and prevent
anerobic sampling. After collecting the blood, any residual air in the
syringe must be expelled to prevent the loss of carbon dioxide from the
blood by diffusion.
Although arterial blood can also be collected in heparinized vacuum tubes,
the requirement that such tubes be filled completely with blood (to avoid
a loss of pCO.sub.2 and an increase in pH) renders such a procedure
especially difficult. Also, there has been indications that utilizing a
vacuum for drawing blood samples may under some circumstances tend to
cause hemolysis.
The use of heparinized capillary tubes has the advantage over the other
techniques of avoiding the collection of excessively large samples, a
particularly important consideration in pediatric studies, but in other
respects the procedures used with such capillary tubes involve the same
problems of collecting, transporting, and delivering samples under
substantially anerobic conditions.
A main object of this invention therefore lies in providing a method which
greatly simplifies the procedures for sampling arterial (and venous)
blood, and for doing so in a way that minimizes risks of exposure to air
and increases the reproducibility and accuracy of test results. Another
object is to provide a relatively safe, uncomplicated, inexpensive, and
highly effective method for drawing micro samples of arterial or venous
blood and for storing, transporting, and delivering such samples to
suitable blood analysis equipment.
Briefly, the device includes a capillary tube, an adapter-handle detachably
connected to the tube, and a hypodermic needle detachably mounted on the
adapter-handle. A protective cover may extend over the needle, and at
least one end cap is provided to seal the end (or ends) of the capillary
tube after a blood sample is collected.
The adapter-handle is formed of resilient plastic material and has integral
body and tip sections. A bore extends longitudinally through both sections
with that portion of the bore within the body section tapering gradually
inwardly at an angle of approximately 2 to 6 degrees measured from the
axis of the adapter-handle. The tip of the adapter-handle has reduced
outside cross sectional dimensions and is tapered both internally and
externally. The external taper is that of a conventional Luer taper,
permitting the tip to be inserted and retained within the hub of a
standard hypodermic needle having a female Luer taper. The internal taper
of the tip extends inwardly at an angle in the range of about 1 to 3
degrees and is dimensioned to receive and sealingly engage the inlet tubes
of various models of commercially-available blood gas analyzers. Between
the Luer-tapered outer surface of the tip and the gererally cylindrical
outer surface of the body is a more sharply tapered surface of a
frusto-conical intermediate section, such surface being adapted to engage
and seal against the mouths of the inlet passages of other types of
available blood gas analyzers.
In use, the heparin-coated capillary tube, the resilient adapter-handle,
and the needle are assembled. A suitable artery or vein is punctured and
the capillary tube is filled by reason of arterial or venous pressure. The
free end of the capillary tube is then capped, thereby preventing blood
from escaping from either end of the capillary tube when the needle is
withdrawn from the puncture site. If analysis is to occur immediately,
then the user simply mixes the sample with the heparin within the tube,
detaches and discards the needle, couples the tip portion of the
adapter-handle to a blood analyzer, removes the cap, and allows the micro
sample to be drawn into the analyzer. If, on the other hand, any delay is
to be encountered before analysis, the user detaches (and discards) the
adapter-handle, replaces it with an end cap, and then, following mixing,
transit and/or storage, removes both caps, replacing one with a fresh
adapter-handle for delivering the sample to the inlet of a blood analyzer
in the manner already described.
Other advantages, objects, and features of the invention will become
apparent from the drawings and specification.
DRAWINGS
FIG. 1 is a side view of a device embodying this invention, the device
being shown with its needle cover removed (but with phantom lines showing
its attached position) for clarity of illustration.
FIG. 2 is an enlarged longitudinal side view, taken partly in section, of
the device.
FIG. 3 is a still further enlarged fragmentary view of an indicated portion
of FIG. 2 illustrating the functional relationship between the parts.
FIG. 4 illustrates a first step in the method during which blood is drawn
into the microcapillary tube.
FIG. 5 illustrates a further step in which the needle is removed and the
distal end of the capillary tube is capped.
FIG. 5A depicts a further step which may be used when access to a blood
analyzer is delayed.
FIG. 6 represents a further step of delivering the blood to an analyzer
having a female connector forming the inlet thereof.
FIG. 6A depicts the delivery step when the analyzer is provided with a male
connector at the inlet thereof.
DETAILED DESCRIPTION
Referring to the drawings, the numeral 10 generally designates a device
comprising an adapter-handle 11, a needle assembly 12, and a
microcapillary tube 13. Such components may be supplied to the user in
assembled form as shown, or they may be supplied as separate parts to be
assembled by the user. In either case, a suitable cover 14 should be
attached to the needle 12 to maintain sterility of the needle until use.
An end cap 15 may be fitted upon the distal end of the capillary tube, and
the entire assembly may be supplied in sterile condition within a suitable
wrapper (not shown).
The needle assembly 12, shown most clearly in FIG. 2, is conventional in
construction and includes a hollow needle 16 secured to a cup-shaped hub
17. In the illustration given, hub 17 is formed of rigid plastic such as,
for example, polystyrene, although it is to be understood that other
materials such as metals might be used. The open end of the hub provides
the entrance to a tapered cavity 18 dimensioned to receive and
frictionally engage the tip of adapter 11. The inward taper of the cavity
18 is commonly referred to as a standard Luer taper, meaning that the hub
will mate tightly with a tapered syringe tip identified by the name of its
originator. Such taper is described in Federal Specification GG-N-196 and
corresponds to an angle approximately 1.degree.43'6" measured from the
axis of the needle assembly 12 (or an included angle of about
3.degree.26'12"). In a preferred embodiment, the metal needle 16 should be
of relatively small gauge (No. 25 or less) and the opening at the mouth of
the cavity should be approximately 0.165 of an inch in diameter.
The tubular needle cover 14 is entirely conventional and serves simply to
protect the pointed hollow needle 16 as well as objects which the needle
might otherwise contact, and to help maintain sterility of the needle. The
cover may be formed of any of a variety of rigid or semi-rigid polymers
such as, for example, polypropylene or other polyolefins.
The microcapillary tube is also conventional, being formed of glass and
usually being of a standard length of 100 millimeters. Such a tube has a
through-bore which is precisely dimensioned to contain a sample of
predetermined volume, ordinarily either 100 or 200 microliters (.mu.l).
Color coded bands 19 and 20 indicate to the user both the capacity of the
tube and the fact that its interior surfaces have been heparinized to
prevent coagulation of a blood sample drawn into the tube.
End cap 15 is preferably formed of ethyl vinyl acetate, silicone rubber, or
some other suitable resilient plastic material and defines a tapered
cavity for snugly and sealingly receiving the end of glass capillary tube
13. While only a single end cap is needed in certain uses of the blood
collection device, a second identical end cap may be supplied to the user
where temporary sealing of the opposite end of the capillary tube is also
deemed necessary or desirable.
The adapter-handle 11 is also formed from a relatively soft resilient
elastomer such as ethyl vinyl acetate or silicone rubber and is composed
of integral body and tip sections 11a and 11b, respectively. A bore 21
extends through the adapter with that portion 21a of the bore within body
section 11a tapering gradually inwardly for receiving and frictionally
retaining one end of microcapillary tube 13. The gradual taper of bore
portion 21a and the resiliency of the material from which the adapter is
formed not only insure that a tight frictional seal will be formed between
the end of the capillary tube and the adapter but also permits the adapter
to form such engagement with standard capillary tubes of different
diameters and capacities. It will be noted from the enlarged view of FIG.
3 that slight deformation of the wall of the adapter takes place when the
end of a capillary tube is formed into the tapered bore portion 21a, such
deformation assisting in the frictional retention of the capillary tube
without danger of chipping or fracturing that tube. In addition, retention
of a capillary tube by the adapter is enhanced by the squeezing force
normally applied (in the direction of arrows 22 in FIG. 2) when the
resilient adapter is gripped between the fingers and used as a handle. The
angle of taper x (FIG. 3) measured from the longitudinal axis of the
adapter should fall within 2.degree. to 6.degree. and should encompass a
range of diameters of at least 0.08 to 0.10 of an inch. In a preferred
embodiment, an angle of taper of 4.degree. and a size range of
approximately 0.070 to 0.110 of an inch have been found effective for
coupling the adapter to standard microcapillary tubes.
In some cases it may be desirable to draw a larger sample of arterial or
venous blood and for that purpose the tapered bore of the body section 11a
may be stepped outwardly to provide an enlarged entrance portion 21b. Bore
portion 21b has a Luer taper similar to that of hub cavity 18 and,
consequently, is adapted to mate with the Luer tip of a standard syringe.
Like the cavity 18 of the needle hub, bore portion 21b should have a
maximum diameter at its mouth of approximately 0.165 of an inch.
The tip section 11b of the adapter is reduced in outside dimensions and has
a standard male Luer taper allowing the distal portion of the tip to be
received tightly within the cavity 18 of the needle hub. The angle of
taper of the tip's outer surface should match closely the angle of inside
taper of the hub with the maximum outside diameter of the tip at point 23
exceeding the inside diameter at the mouth of cavity 18. A differential of
at least 0.003 of an inch should be provided (0.005 preferred) to insure a
snug fluid-tight friction fit between the parts.
Beyond the Luer tapered outer surface, between point 23 and the generally
cylindrical outer surface of body section 11a, the tip is provided with a
flared or frusto-conical outer surface 24. The angle of that
frusto-conical surface, measured from the axis of the adapter, should fall
within the general range of 10.degree. to 30.degree., an angle of
approximately 20.degree. being found particularly effective. As described
hereinafter, the frusto-conical surface is not merely a transitional
surface between the Luer taper of the tip and the cylindrical surface of
the body; it provides an inclined stop for limiting the extent of
insertion of the adapter into the inlet port of a blood analyzer, and for
sealingly engaging that port when delivery of a sample to such an analyzer
takes place.
It will be noted that the internal and external longitudinal surfaces of
the tip section 11b are reversely tapered; that is, in addition to having
a Luer taper along its outer surface the tip has a reversely-tapered bore
portion 21c which gradually and progressively increases in size towards
the free end of the tip section. The angle of taper y (FIG. 2) should fall
generally within the range of 1.degree. to 3.degree. measured from the
longitudinal axis of the adapter, the preferred angle of taper being
approximately 2.degree.. At its mouth the bore portion 21c should have a
diameter of at least 0.08 of an inch, a preferred dimension being about
0.09 of an inch. As shown, bore portion 21c tapers smoothly and gradually
inwardly to merge with bore portion 21a of body section 11a.
For use, the device 10 may be supplied in assembled condition as shown in
FIG. 1. Alternatively, the device may be supplied in disassembled
condition, requiring interfitting of the major components by the user.
Assuming that the device is in the assembled condition of FIG. 1, the user
removes end cap 15, detaches the protective needle cover 14, and, holding
the device by means of the resilient adapter-handle 11, inserts the
sterile needle 16 into the blood vessel from which the sample is to be
taken. For blood gas analysis arterial blood is preferred. Such blood may
be obtained by inserting the fine-gauge needle 16 into an artery such as
the brachial, radial, femoral, or jugular arteries. FIG. 4 depicts the
sampling step, the outline of the patient's body being generally
represented by line 25 and the transparent collection tube shown to be
filled with blood taken from the patient. Entry of the needle into an
artery is confirmed by the pulsatile filling of the bore of the glass
capillary tube, such filling action generally being completed within three
seconds and occuring by reason of arterial (or venous) pressure. The user
then withdraws the needle and immediately caps the remote end of the
capillary tube with cap 15 (FIG. 5). Still holding the device by means of
the adapter-handle, the user detaches (and discards) the needle assembly
12. If the blood analyzing equipment is close at hand, the adapter is then
simply coupled to the inlet connector of the analyzer to allow the
collected blood sample to be drawn into the analyzer where it is tested
(FIGS. 6 and 6A).
After taking a sample, and before introducing that sample into an analyzer,
a user should make sure that the sample is thoroughly mixed with the
heparin salt coating the inside surfaces of the capillary tube. A suitable
magnetic stirrer, commonly referred to as a "flea", may be inserted into
the bore of the tube and reciprocated therein by means of an external
magnet. Particularly effective results may be achieved where end cap 15 is
formed and used as set forth in my copending U.S. Pat. application Ser.
No. 10,234, filed Feb. 8, 1979, the disclosure of which is incorporated by
reference herein, so that upon completion of the mixing step the flea may
be captured and removed by means of the cap, thereby preventing the
possibility that such a flea might be left within the capillary tube and
be drawn accidentally into the blood analyzer.
In FIG. 6 the numeral 26 generally designates that type of
commercially-available blood analyzer having an inlet port 27, the mouth
of which is engagable with the tip section of the adapter 11 to provide a
temporary seal as the blood sample is aspirated from the capillary tube
into the machine. The frusto-conical outer surface 24 of the adapter is
particularly effective in forming such a seal with the mouth of the
instrument and for limiting the extent of insertion of the resilient
adapter into the inlet.
FIG. 6A schematically depicts a different type of blood analyzer 26' in
which the inlet takes the form of a protruding nipple or tube 28 having an
outside diameter of approximately 0.08 of an inch. In delivering a blood
sample to such an analyzer, the user, holding the device by its resilient
adapter 11, simply fits the internally tapered tip section 11b on to the
inlet tube 28 and allows the blood sample to be drawn into the machine.
In those cases where the blood analyzer is remote from the collection site,
adapter-handle 11 may be removed from the filled capillary tube 13 and
replaced by a second end cap 15 (FIG. 5A). With both ends of the capillary
tube so capped, the collected sample may be mixed, transported, and
temporarily stored under refrigeration. Upon arrival at the blood
analyzer, one of the end caps is removed and replaced by a fresh adapter
11. The procedure represented in FIG. 6 or 6A is then performed with the
distal end cap 15 removed from the capillary tube to permit aspiration of
the blood sample into the analyzer.
It is believed evident from the foregoing that the adapter 11 is
constructed to perform a multiplicity of functions. In addition to its
coupling functions the adapter serves as a resilient handle. In the
operations depicted in FIGS. 4, 5, 6, and 6A, the user grips the sampling
device by holding the resilient adapter between his fingers. As already
described, the squeezing forces tend to assist in maintaining the
capillary tube and adapter in interconnected relation. In addition, the
danger of breakage of the fragile capillary tube, and the risks of
possible contamination of the user, are reduced. For example, should a
patient move suddenly during arterial or venous puncture, the resilient
handle provides limited articulation between the rigid glass tube 13 and
the needle assembly 12, thereby reducing the chances of breakage of either
rigid part, and, should such breakage happen to occur, the handle serves
as a protective sheath between the fractured tube and the user's fingers
to prevent injury and possible contamination.
While in the foregoing I have disclosed an embodiment of this invention in
considerable detail for purposes of illustration it will be understood by
those skilled in the art that many of these details may be varied without
departing from the spirit and scope of the invention.
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