Development and Internal Validation of a Risk Model to Estimate Probability of Intraoperative Hypothermia in Adult Surgical Patients

Intraoperative hypothermia is associated with various perioperative complications and an increased risk of mortality. This study aims to develop and validate a reliable risk model, the Intraoperative Hypothermia Risk Estimating Model (IHREM), for assessing the likelihood of intraoperative hypothermia in adult patients receiving different types of surgery and anesthesia. Data from 1815 surgical patients were collected, with 1521 used to develop the IHREM training set. Univariate logistic regression was utilized to evaluate the parameters included in the study. For the first time, parameters showing non-linear associations with the risk of intraoperative hypothermia were evaluated and then incorporated into a primary model using restricted cubic splines (RCS), based on the result of multivariate logistic regression. The final model was comprised of 12 risk factors, including body mass index (BMI), fasting time, preoperative heart rate, preoperative tympanic temperature, intravenous fluid administration volume, intraoperative irrigation volume, estimated blood loss, duration of anesthesia, surgical position, intraoperative warming, operation room temperature, and humidity. The IHREM model demonstrated satisfactory performance in the training set, exhibiting reliable discrimination, calibration, overall performance, and clinical utility. In the temporal validation set (<i>n</i> = 294), the c-index, calibration intercept and calibration slope, Brier score, and <i>R</i>² were determined to be 0.763 (95% CI, 0.710-0.819), 0.394 (95% CI, 0.118-0.680), 0.865 (95% CI, 0.638-1.114), 0.204 (95% CI, 0.180-0.229), and 0.236, respectively. Meanwhile, decision curve analysis and clinical impact curve showed that IHREM provides promising clinical value. In addition, RCS analysis indicated that maintaining the operation room temperature above 20°C is sufficient to prevent hypothermia while increasing or sustaining the preoperative core temperature to around 36.7-36.8°C significantly reduces the risk of hypothermia. IHREM holds promise as a valuable tool for identifying adult patients at risk of intraoperative hypothermia under various types of surgery and anesthesia, thereby supporting clinical decision-making.