Effects of cardiac surgery and intraoperative hypothermia on energy expenditure as measured by doubly labelled water.

Total energy expenditure (TEE) was measured over two 10-day periods, before and after operation in 16 patients undergoing coronary artery surgery and randomized to have cardiopulmonary bypass with an intraoperative blood temperature of either 28 or 20°C. TEE was measured with doubly labelled water containing stable isotopes of hydrogen and oxygen to allow calculation of TEE over fixed periods from the differential rate of excretion of the two isotopes. Results were available for eight patients in the 28°C group but for only seven in the 20°C group (one patient in this group was excluded as the temperature allocated was not achieved). The groups were similar with respect to body-weight and lean body mass. The 20°C group received more grafts than the 28°C group, resulting in an increase in cross-clamp and bypass times. Mean preoperative TEE was similar in both groups. The mean difference in fractional turnover rates of hydrogen and oxygen was not significantly different in the postoperative period. There was a non-significant increase in the mean 10-day postoperative TEE, calculated in total calories, of 4·7 per cent in the 28°C and 5·1 per cent in the 20°C group. When changes in postoperative TEE were calculated according to lean body mass, the mean increases were respectively 3·7 and 3·2 per cent. Cardiac surgery utilizing cardiopulmonary bypass and intraoperative hypothermia results in only a modest increase in postoperative TEE. In this study a more profound level of intraoperative hypothermia did not influence the change in postoperative TEE.