Original Article

Effect of Hypothermia on Arterial Versus Venous Blood Gases During Cardiopulmonary Bypass in Man

Department of Anesthesiology, Epidemiology and Biostatistics, American University of Beirut, Beirut, Lebanon

^* Address correspondence to: Anis Baraka, MD, Professor & Chairman, Department of Anesthesiology, American University of Beirut 850 Third Avenue, 18th floor New York, NY 10022 U.S.A.

Abstract

The effect of moderate hypothermia on arterial versus venous blood gases was investigated in 11 patients during cardiopulmonary bypass. The pump and oxygen flows were maintained at a constant flow of 2.4 L/m²/min throughout bypass. After going on bypass, the central venous blood temperature was dropped to 27.8 ± 0.6°C, and after surgery was completed the patients were rewarmed to 37.0°C. Arterial and venous blood gases were sampled simultaneously from the arterial outlet and the venous inlet lines of the oxygenator every two degrees of temperature change until37°C was reached. The effect of temperature changes on pCO₂ simulated the alpha-stat strategy of acid-base regulation; the temperature-corrected arterial and venous pCO₂ varied directly and the corrected pH varied inversely with body temperature, while the uncorrected pCO₂ and pH did not show a significant changE- with changes of body temperature. The arterial pO₂ whether corrected or uncorrected, as well as the venous oxygen saturation and the uncorrected venous pO₂, significantly increased with each increment decrease of body temperature. However, the corrected venous pO₂ did not significantly change with changes of body temperature. The report suggests that maintenance of constant perfusion and oxygen flows at normothermic levels during hypothermic cardiopulmonay bypass will maintain a constant carbon dioxide content and a constant corrected venous pO₂.