Thermal balance during cardiopulmonary bypass with moderate hypothermia in man

In six patients undergoing coronary vein graft operations under cardiopulmonary bypass and hypothermia, the temperatures of arterial and mixed-venous blood, nosopharynx, oesophagus, liver, rectum, deltoid and vastus lateralis muscles and 10 skin sites were recorded. Whole-body oxygen consumption was measured before cooling and twice during hypothermia. On average, a patient lost 1000 kJ of heat by the end of hypothermia, of which 84% was lost to the heat-exchanger and pump circuit. Evaporative and convective loss amounted to 380 kJ, while the patient's metabolism supplied 220 kJ. During rewarming, the pump returned 670 kJ to the patient. Nasopharyngeal temperature reflected accurately venous, oesophageal and hepatic temperatures in the steady state; however, it was slow to reflect changes. Compared with other sites, muscle remains warmer during hypothermia and cooler after rewarming.