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 predictive 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 preoperatively : right palmar skin temperature by using an infrared thermometer and skin thickness at arm and scapula by using a standard caliper. TBF was calculated by using the regression equation of Durnin and Womersley. Rectal temperature, taken to represent core temperature, was measured during the operation. The gradient of hypothermia induced by general anesthesia was divided into two parts: 1) a precipitous decrease for the first hour and 2) a slow decrease for the following 2-3 h. Preoperative palmar skin temperature had a significant linear relationship with the precipitous decrease in temperature 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 hypothermia 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 precipitous 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.