Arterial blood sampler

[57] ABSTRACT

A blood sampler with an arterial needle and a collapsed flexible blood pouch that snaps into inflated condition with arterial blood pressure but not with venous blood pressure. This provides a visual indication that an artery and not a vein has been punctured.

Claims, 6 Drawing Figures

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PATENTED JAN 151974

3.785.3B7

SHEET 1 OF 2

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PATENTED»'Sim

3.7Θ5.36Τ

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3,785,367

ARTERIAL BLOOD SAMPLER

BACKGROUND

In diagnosing a patient’s illness, blood samples are often taken and analyzed in a laboratory. By far the most common blood sample taken is a “venous” blood sample. This sample is usually taken with an evacuated vial connected to a hypodermic needle or with a hypodermic syringe. The vacuum in these devices sucks the blood from the patient into the vial or syringe.

Recently, it has become more prevalent to also take an “arterial” blood sample for testing blood gases and pH, etc. When taking an arterial blood sample it is very important to know that the blood sample is from an artery and not a vein. The medical parameters of arterial blood, such as the partial pressures of oxygen and carbon dioxide are often sufficiently different from those of venous blood so as to cause erroneous test results if venous blood is sampled by mistake.

In the past, arterial blood has been taken with glass syringes with precision ground barrels and plungers. Because the arterial blood pressure was significantly greater than the venous blood pressure, only the arterial pressure would push the plunger rearwardly in a glass syringe. This gave a visual indication of whether an artery or vein had been punctured. The precision ground glass syringes were very costly and for this reason they were washed and resterilized after each arterial blood sampling.

Inexpensive disposable plastic syringes with rubber stoppers failed to give the visual indication that the needle was in the patient’s artery. This was because arterial pressure could not overcome the frictional drag of the rubber stopper in the disposable plastic syringe.

SUMMARY OF THE INVENTION

Our invention overcomes the problem of taking arterial blood samples present in previous glass syringes and disposable plastic syringes. We have provided an inexpensive disposable arterial blood sampler that gives a quick and accurate indication that an artery and not a vein has been punctured. Our invention has a collapsed flexible blood reservoir that snaps into an inflated position with arterial blood pressure but not with venous blood pressures. In a first version of our invention an elongated collapsed blood pouch resists inflation by venous pressure but will snap into an inflated balloon-like position when arterial pressure is applied. A second version of our invention includes a resilient cup member that inverts with arterial pressure but not with venous pressure.

THE DRAWINGS

FIG. 1 is a side elevational view, partially in section, of a first embodiment of our arterial blood sampler, showing the elongated collapsed blood pouch being inserted into a rigid protector housing;

FIG. 2 is a side elevational view, in section, of the first embodiment showing the action of the pouch when the hypodermic needle is in a vein;

FIG. 3 is a side elevational view, in section, of the first embodiment, showing the action of the pouch when the hypodermic needle is in an artery;

FIG. 4 is a side elevational view, in section, of a second embodiment, showing a resilient cup as the collapsed blood pouch;

FIG. 5 is a side elevational view, in section, of the second embodiment showing how arterial blood pressure causes the resilient cup to invert; and

FIG. 6 is a side elevational view, in section, of the second embodiment showing how the blood sample is forced out of the blood sampler and into testing equipment.

DETAILED DESCRIPTION

In FIG. 1, the first embodiment of the invention is shown as including an arterial needle 1 that includes a cannula 2 and a hub 3. This needle is connected to a hollow adapter 4 which in turn is connected to a collapsed flexible pouch 5. A ring 6 attached to the pouch’s rearward end is used to pull the pouch into a rigid protector sleeve 7 and seat the adapter to the sleeve. A passage extends through the cannula, hub, adapter and pouch for passage of blood when a patient’s artery is punctured with the cannula.

Once assembled as described above, the arterial blood sample is ready for use. In FIG. 2, when a nurse or physician punctures a vein with hypodermic needle 3 the flexible pouch 5 will resist inflation by the venous blood pressure, equivalent to approximately 110 mm of H₂O (8 mm Hg). Even though collapsed flexible pouch 5 may expand very slightly to receive a small amount of venous blood it is readily apparent to an operator that the needle is not in an artery. When this occurs, the needle is withdrawn from the patient’s vein and another puncture made.

When the needle does enter an artery as shown in FIG. 3, the arterial pressure equivalent to approximately 90 mm Hg will quickly snap the flexible pouch 5 into an inflated condition against sleeve 7. Once the arterial blood sample has been taken the protector sleeve 7 can be removed and the sack squeezed to expel the arterial blood into blood testing equipment.

In FIGS. 4, 5 and 6 a second embodiment of the invention is shown. Referring to FIG. 4 the resilient collapsible blood pouch has a rubber cup-shaped member 10 with a mouth facing away from the needle in FIG. 4, and facing toward the needle in FIG. S. This cupshaped member fits inside a rigid housing 11 which has a partially closed forward end attached to a hollow tapered adapter 12. Arterial needle 13 fits on hollow tapered adapter 12. Connected to a rigid adapter 11 is a rigid barrel 14 which is secured to housing 11 to form a structure similar to a hypodermic syringe barrel. Within the barrel is an axially slidable conventional hypodermic plunger 15 with a rubber stopper 16.

A very important aspect of this second embodiment is a side vent 17 opening in rigid barrel 14. The vent opening 17 has an upstanding collar 18 surrounding it and as shown in FIG. 5 permits air to escape from the rigid barrel 14 as the resilient cup-shaped member inverts in response to arterial blood pressure. An annular space 17α between the barrel and cup-shaped member allows air to escape. Because of the vent no internal pressure is built up inside barrel 14 to resist inversion of the rubber cup. The arterial blood sampler of the second embodiment gives a very vivid visual indication of whether the sampler is in a vein (FIG. 4) or in an artery (FIG. 5).

Once the sample has been taken, the side vent 17 is closed off by a removable cap 19 which is attached to collar 18 surrounding the vent. The cap has an internal undercut groove that snaps over an external rib on the

3,785,367 collar. Forward motion of plunger 15 and stopper 16 then forces the arterial blood collected in resilient cupshaped member 10 out through arterial needle 13 and into blood testing equipment (not shown).

In both embodiments of this invention it is seen that the collapsed flexible blood collecting pouch has an exterior surface that is exposed to atmospheric pressure. During the arterial blood sampling there is neither suction nor pressure applied to this pouch. In the first embodiment the flexible collapsed pouch is preferably of a stretchable rubber-like material with predetermined stretch characteristics so as to not substantially inflate under venous pressure, 8 mm Hg, but readily inflate when subjected to arterial blood pressure, 90 mm Hg.

In the second embodiment the resilient cup-shaped member 10 can be of a rubber or rubber-like material and have a shape and wall thickness so as to remain in the FIG. 4 position with a convex outer surface facing the needle when subjected to venous pressures through arterial needle 13. However, when subjected to arterial pressures as in FIG. 5 the cup will rapidly invert as shown. Because venous and arterial pressures vary with patients it is desired to have the snap action of the pouch occur at approximately midway, 50 mm of Hg, between ranges of normal venous and normal arterial blood pressures. Venous pressure ranges from 3.7 to 8 mm Hg and arterial blood pressure ranges from 90 to 150 mm Hg. The arterial pressure is normally reported as being in units of mm of Hg, and venous pressure is usually measured in cm. of H₂O. However, for ready comparison the pressures throughout the application and claims have been expressed in mm Hg for both venous and arterial pressures.

In either embodiment, the flexible pouch can contain an anti-coagulant or other solution for treating the blood as soon as it flows from the patient into the pouch. In the first embodiment the adapter 4 and rigid sleeve are preferably made of a conventional thermoplastic material. Likewise in the second embodiment the rigid adapter 11, barrel 14 and cap 19 are also made of conventional thermoplastic materials. The flexible pouch is preferably sufficiently thin and sufficiently transparent or translucent to visibly show blood entering the pouch.

Throughout the specification and claims we have used the word “snap” to describe the quick inflation of the flexible pouch when subjected to arterial blood pressure. We intend this word to describe an action of the pouch that is significantly great in speed and volume of inflation so as to clearly distinguish an arterial puncture from a venous puncture with its slow seeping blood which does not substantially inflate the flexible pouch.

In the foregoing description we have used specific examples to describe our invention. However, it is understood that those persons skilled in the art can readily make certain modifications to these embodiments without departing from the spirit and scope of the invention.