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CARDIOVASCULAR ANESTHESIA

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

Angela Rajek, MD^*, Rainer Lenhardt, MD^§,||, Daniel I. Sessler, MD^,§,||, Martin Grabenwöger, MD, Johannes Kastner, MD, Peter Mares, MD^*, Ursula Jantsch, MD^*, and Eva Gruber, MD^*

Departments of *Cardiothoracic and Vascular Anesthesia, Anesthesia and General Intensive Care, and Cardiothoracic Surgery and §Outcomes Research^TM, University of Vienna, Vienna, Austria; and ||Department of Anesthesia and Perioperative Care, University of California—San Francisco, San Francisco, California

Address correspondence and reprint requests to Daniel I. Sessler, MD, Department of Anesthesia and Perioperative Care, 374 Parnassus Ave., 3rd Floor, University of California, San Francisco, CA 94143-0648. Address e-mail to sessler{at}vaxine.ucsf.edu

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 ± 0.9°C during bypass and subsequently increased to 34.3 ± 0.7°C during 104 ± 18 min of rewarming. The core-to-peripheral tissue temperature gradient was -5.9 ± 0.9°C at the end of cooling and 4.7 ± 1.5°C at the end of rewarming. The core-temperature afterdrop was 2.2 ± 0.4°C and lasted 89 ± 15 min. It was associated with 1.1 ± 0.7°C peripheral warming. At the end of cooling, temperatures at the center of the upper and lower thigh were (respectively) 8.0 ± 5.2°C and 7.3 ± 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 ± 2.2°C and 6.4 ± 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 ± 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.