Predictive variables of hypothermia in the early phase of general anesthesia

Core temperature decreases precipitously for 1 h and then decreases slowly for 2-3 h after the induction of general anesthesia. WE investigated the pr edictive variables of hypothermia by measuring peripheral skin temperature and total body fat (TBF). We studied 60 adult patients who required general anesthesia with isoflurane. The following variables were measured preopera tively: right palmar skin temperature by using an infrared thermometer and skin thickness at arm and scapula by using a standard caliper. TBF was calc ulated by using the regression equation of Durnin and Womersley. Rectal tem perature, taken to represent core temperature, was measured during the oper ation. The gradient of hypothermia induced by general anesthesia was divide d into two parts: 1) a precipitous decrease for the first hour and 2) a slo w decrease for the following 2-3 h. Preoperative palmar skin temperature ha d a significant linear relationship with the precipitous decrease in temper ature over the first hour (r = 0.69, P < 0.0001), and TBF had a significant linear relationship with the subsequent slow decrease in temperature (r = 0.63, P < 0.0001). By simple measurements, we can predict the extent of hyp othermia in the early phase of general anesthesia and prevent its onset by using body-warming techniques. Implications: After the induction of general anesthesia, palmar skin temperature had a Linear relationship with the pre cipitous decrease in rectal temperature over the first hour, and total body fat had a linear relationship with the subsequent decrease in temperature. Thus, by simple measurements, we can predict the extent of hypothermia in the early phase of general anesthesia.