MORPHOMETRIC INFLUENCES ON INTRAOPERATIVE CORE TEMPERATURE-CHANGES

Intraoperative core hypothermia develops in three characteristic phase s: 1) core-to-peripheral redistribution of body heat that is most prom inent during the first hour after induction of anesthesia; 2) subseque nt slow linear decrease in core temperature resulting largely from hea t loss exceeding metabolic heat production; and 3) core temperature pl ateau resulting when thermoregulatory vasoconstriction decreases cutan eous heat loss and constrains metabolic heat to the core thermal compa rtment. Accordingly, we tested the hypotheses that: 1) core cooling do es not depend on body fat (BF) or the ratio of weight-to-surface area (Wt/SA) during the initial redistribution phase; 2) the core cooling r ate is a function of the Wt/SA ratio during the second phase; and 3) t he rate of core cooling during the plateau phase (after vasoconstricti on) will be determined by the percentage of BF. In 40 patients undergo ing elective colon surgery, the amount of redistribution hypothermia w as inversely proportional to the percentage of BF (Delta T-C = 0.034.B F - 2.2, r(2) = 0.63) and the Wt/SA ratio (Delta T-C = 0.052.Wt/SA - 3 .35, r(2) = 0.66). The core cooled linearly during the second phase, a nd the cooling rate was inversely proportional to the Wt/SA ratio (rat e = 0.035.(Wt/SA) - 2.2, r(2) = 0.29). Thermoregulatory vasoconstricti on was effective in virtually all patients independent of their morpho logy, and produced a fourfold reduction in the core cooling rate. Thes e results indicate that patient morphometric characteristics substanti ally influence intraoperative core temperature changes, and that the e ffect depends on the hypothermia phase.