The Spectrophotometric Determination of the Oxygen Saturation of Blood

ORDY AND DRABKIN (1) have described a simplified spectrophoto-metric procedure for the determination of oxygen saturation of whole hemolyzed blood. The described method of sampling by use of tonometers, although technically precise, is somewhat inconvenient for routine clinical use. In a note appended to the article, Marsh described a simpler mod-ification. He collects the samples in oiled, heparinized syringes and adds saponin solution directly by means of a syringe and three-way metal stopcock. A simple, open, 1 cm. absorption cell with a 9 mm. lucite plug, giving a light path of 1 mm., was substituted for the more complicated anaerobic cell of 0-ordy and Drabkin. We desired a method that would permit rapid handling of blood samples removed during cardiac catheterization or open heart sur-gery and that would make available aliquots for duplicate analyses or other analytical procedures such as hemoglobin or hematocrit estima-tions. We modified the technic described by Marsh in that a 1 ml. portion of the sample is transferred anaerobically to a 1 ml. tuber-culin syringe by means of a three-way stopcock. Hemolysing and reducing solutions may then be added through the same stopcock and mixed with the sample before transfer to an absorption cell. MATERIALS AND METHODS Blood samples are collected in the usual manner in heparinized 5 ml. syringes. To facilitate mixing, mercury is added to the samples in the following manner. The needle is removed and the mercury is injected from a syring