Practical evaluation of acid-base balance.

IDEALLY, THE EVALUATION of acid-base balance should be made from the determination of 002 content and pH on arterial plasma. Obtaining arterial blood is not, however, a routine clinical procedure. Hence, next in order of preference is the performance of these two determinations on plasma of arterialized blood which may be easily obtained by soaking the arm of the subject in a water bath at 40#{176} for 10 minutes and then drawing blood from the antecubital vein (1). This procedure, however, is not used in most clinical laboratories. Instead, quite satisfactorily, venous blood is used, and plasma 002 content and pH are determined. Frequently, the determination of CO2 content is performed alone and yields valuable information. Unfortunately, many hospital laboratories still employ the determination of 002 combining power. This determination was developed by Van Slyke and Cullen in 1917 (2). In 1920, Stadie and Van Slyke recommended that the determination of CO2 content should be used in place of the determination of CO2 combining power (3). This recommendation was confirmed in 1932 in Quantitative Clinical Chemistry, by Peters and Van Slyke (4), the authors pointing out that in their laboratories the 002 combining power procedure had not been used for some years. Nevertheless, this determination remains in widespread use. There are strong practical and theoretical objections to the determination of 002 combining power. Because it involves an equilibration with air containing 002 at a partial pressure of 40 mm., it is technically more difficult than the determination of CO2 content. From the standpoint of the physician, it is a poor measure of the in vivo bicar-