The Immediate Effects of Respiratory Depression on Acid-Base Balance in Anesthetized Man1

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Abstract
The time course of alterations of acid-base balance was obtained on 25 patients before, during and after anesthesia induced with nitrous oxide, cyclopropane, ethylene, thiopental and/or regional block. The CO2 tension of 18 subjects became elevated 10 mm Hg or more during anesthesia. Respiratory acidosis was accompanied by a metabolic acidosis, measured as a reduction of buffer base exceeding 3 meq/l, which tended to be proportional to the extent of CO2 tension elevation. These changes subsided rapidly following termination of anesthesia. Although other investigators have reported a metabolic alkalosis to result from experimentally induced respiratory acidosis, it is concluded that the immediate response to elevation of CO2 tension resulting from depression of respiration in anesthetized man is a metabolic acidosis.