Tissue Heat Content and Distribution During and After Cardiopulmonary Bypass at 17°C

We measured afterdrop and peripheral tissue temperature distribution in eight patients cooled to approximately 17°C during cardiopulmonary bypass and subsequently rewarmed to 36.5°C. A nasopharyngeal probe evaluated trunk and head temperature and heat content. Peripheral tissue temperature (arm and leg temperature) and heat content were estimated using fourth-order regressions and integration over volume from 30 tissue and skin temperatures. Peripheral tissue temperature decreased to 19.7 6 0.9°C during bypass and subsequently increased to 34.3 6 0.7°C during 104 6 18 min of rewarming. The core-to-peripheral tissue temperature gradient was 25.9 6 0.9°C at the end of cooling and 4.7 6 1.5°C at the end of rewarming. The core-temperature afterdrop was 2.2 6 0.4°C and lasted 89 6 15 min. It was associated with 1.1 6 0.7°C peripheral warming. At the end of cooling, temperatures at the center of the upper and lower thigh were (respectively) 8.0 6 5.2°C and 7.3 6 4.2°C cooler than skin temperature. On completion of rewarming, tissue at the center of the upper and lower thigh were (respectively) 7.0 6 2.2°C and 6.4 6 2.3°C warmer than the skin. When estimated systemic heat loss was included in the calculation, redistribution accounted for 73% of the afterdrop, which is similar to the contribution observed previously in nonsurgical volunteers. Implications: Temperature afterdrop after bypass at 17°C was 2.2 6 0.4°C, with approximately 73% of the decrease in core temperature resulting from core-to-peripheral redistribution of body heat. Cooling and rewarming were associated with large radial tissue temperature gradients in the thigh.