Partial Pressure of Oxygen in Arterial Blood of Patients

The partial pressure of oxygen in the arterial blood has been measured indirectly by interpolation of O₂ content on the oxyhemoglobin dissociation curve, and by estimation of solubilities of CO and O₂ in the subject's blood (Haldane), and directly by aerotonometry. The latter method has been used by Krogh 1 and by Barcroft and Nagahashi. 2 In this method of the latter authors some difficulty is experienced in keeping the equilibration pressure constant and in securing repeated samples of the small gas bubble for analysis. The present method avoids these two difficulties.

It has been customary to study anoxemic patients by determining the oxygen saturation of the arterial blood and to assume that the oxyhemoglobin dissociation curve is shifted only as changes in the pH take place. Barcroft 3 has studied the partial pressure of oxygen in a few such cases. However, it seemed that a simple, direct method for measurement of oxygen tension would permit a more exhaustive exploration of this field.

About 20 mil. of blood is drawn under anaerobic conditions from a femoral artery into an oiled syringe containing a bit of oxalate-fluoride and mercury, which facilitates mixing. About 10 mil. is then injected into the tonometer chamber in which 0.1 cc. of alveolar air has been placed by sticking the needle through the rubber tube (Fig. 1). The blood foams and mixture is easy with shaking. The remaining blood has its oxygen content and capacity determined in duplicate by standard methods on the Van Slyke manometric gas analysis apparatus.

Samples of the foam are withdrawn after about 10 minutes'shaking at 37.5°C. For this purpose the screw adjusted pipette shown in Fig. 1A is used. The pipette consists of a curved needle with adapter fitted into the bulb of an ordinary medicine dropper and adjusted by a screw clamp.