Influence of surface cooling and rewarming on whole-body oxygen supply-demand balance

The influence of moderate hypothermia induced by surface cooling was studied on haemodynamic variables and whole-body oxygen consumption in a 43-yr-old female undergoing clipping of multiple cerebral aneurysms. Decreasing oesophageal temperature to 32 degrees C lowered the whole-body oxygen consumption by about 40%. The decrease in oxygen consumption was matched by a proportional decrease in cardiac output. During the rewarming phase, there was a progressive increase in oxygen consumption, which was matched by a proportional increase in cardiac output. This resulted in a constant oxygen extraction ratio, as evidenced by oxyhaemoglobin saturation which remained constant at different body temperatures. While the temperature-corrected PVO2 decreased progressively with cooling, the temperature-uncorrected PVO2 remained constant at all body temperatures. Thus the use of temperature-uncorrected PO2 during hypothermia may simplify clinical interpretation because of our familiarity with normothermic PO2 values and the normothermic oxyhaemoglobin dissociation curve.