Abstract
In the determination of blood gases it is frequently desired to obtain samples of plasma which have not been exposed to air. The following method has proven very satisfactory in our laboratory. It has the particular advantages that: (a) small samples can be handled in this way, and (b) the plasma samples can be readily freed from any trace of mineral oil which may be present.
Procedure. The apparatus consists of the following special pieces: (a) a tuberculin syringe (available in 0.25, 0.50, 1.0 and 2.0 ml sizes) in which the solid glass plunger has been broken at some predetermined point, and (b) a syringe cap made by cutting the needle portion from a hypodermic needle and sealing the opening with solder. The syringe and both portions of the broken plunger are well lubricated with mineral oil and a few drops of mineral oil are placed in the syringe cap. The syringe is rinsed with a few drops of heparin solution, and the excess is ejected. This leaves the lumen of the needle filled with mineral oil and heparin, and displaces the last trace of air. Though the plunger of the syringe is broken, if well lubricated with mineral oil, the plunger will perform as a unit even under reasonable negative pressures. As the volume of blood drawn into the syringe reaches the desired capacity (and the break in the syringe plunger comes to the end of the barrel) the outer end of the plunger comes off easily and is removed. It is usually found that the blood pressure of the animal will continue to force the inner portion of the barrel out slightly. After the sample of blood is drawn, the needle is removed and is quickly replaced by the oil-filled syringe cap.
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