Body morphology and the speed of cutaneous rewarming

Background: Infants and children cool quickly because their surface area la nd therefore heat loss) is large compared with their metabolic rate, which is mostly a function of body mass. Rewarming rate is a function of cutaneou s heat transfer plus metabolic heat production divided by body mass. Theref ore, the authors tested the hypothesis that the rate of forced-air rewarmin g is inversely related to body size. Methods: Isoflurane, nitrous oxide, and fentanyl anesthesia were administer ed to infants, children, and adults scheduled to undergo hypothermic neuros urgery. All fluids were warmed to 37 degreesC and ambient temperature was m aintained near 21 degreesC, Patients were covered with a full-body, forced- air cover of the appropriate size. The heater was set to low or ambient tem perature to reduce core temperature to 34 degreesC in time for dural openin g. Blower temperature was then adjusted to maintain core temperature at 34 degreesC for 1 h, Subsequently, the forced-ak heater temperature was set to high (approximate to 43 degreesC). Rewarming continued for the duration of surgery and postoperatively until core temperature exceeded 36.5 degreesC. The rewarming rate in individual patients was determined by linear regress ion. Results: Rewarming rates were highly linear over time, with correlations co efficients (r(2)) averaging 0.98 +/- 0.02. There was a Linear relation betw een rewarming rate (degreesC/h) and body surface area (BSA; m(2)): Rate (de greesC/h) = -0.59 (.) BSA(m(2)) + 1.9, r(2) = 0.74. Halving BSA thus nearly doubled the rewarming rate. Conclusions: Infants and children rewarm two to three times faster than adu lts, thus rapidly recovering from accidental or therapeutic hypothermia.