To the Editor.
—Studies with tonometered plasma and blood indicate that the pK' level varies with pH.1-3 These studies have remained as standards for several years although the values were derived from a relatively small sample population. Recent studies4-7 indicate that the pK' value is unaffected by protein abnormalities, water content, viscosity, fibrinogen, or the severity of the particular disease process. Recently we examined the effect of pK' on 65 blood samples with pH values ranging from 7.10 to 7.70. The patients involved in this study were for the most part acutely ill or in a preoperative or postoperative phase. They suffered from a variety of disease states which were of renal, cardiovascular, pulmonary, hepatic, gastrointestinal, or metabolic origin. Ten determinations were made on normal blood.Standard procedures for tonometry were used and the carbon dioxide pressure was calculated from the per cent value of the gas used.