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Effect of Paco₂ on O₂ Consumption During Cardiopulmonary Bypass in Man

*Professor of Anesthesiology, Department of Anesthesiology, The Center for the Health Sciences, UCLA School of Medicine, University of California, Los Angeles, California 90024.

Abstract

Under conditions of anesthesia with controlled respiration, the changes in the state of the circulation due to altered Paco₂ are often overlooked or attributed to the anesthetic agent. During cardiopulmonary bypass when cardiac output is kept constant, change in fluid level of the extra corporeal reservoir reflects overall change in the circulatory beds.

Following an hour on total bypass for stabilization of all parameters, a change in the oxygenator ventilating-gas mixture was induced to increase or decrease the Paco₂ an average of 11 torr in 40 patients. A reduction in Paco₂ from 37 to 25 torr increased mean arterial blood pressure (MAP), central venous pressure (CVP), and the volume of blood stored in the extra corporeal circuit, signifying an overall reduction in the intra vascular capacity. This was associated with a decrease in total O₂ consumption (o₂). An abrupt increase of Paco₂ from 26 to 37 torr produced a decrease in MAP, in CVP, and in the reservoir blood level, signifying blood "take up" by the patient. There was also an associated increase in o₂.

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