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Perioperative hypothermia and postoperative opioid requirements

Background and objective Hypothermia may alter the disposition of opioids. Because opioids are commonly used as analgesics in the postoperative period, it is of clinical interest to clarify whether perioperatively developed hypothermia affects postoperative opioid requirements. Methods Fifty-nine patients undergoing subtotal hysterectomy were prospectively randomized and either treated intraoperatively with forced air warming, or served as controls covered with conventional blankets without active warming. Both groups received postoperative patient-controlled analgesia with the opioid ketobemidone. Total analgesic requirements, demands, analgesic requirements over 6-h intervals and pain scores were measured for 48 h. Core temperature at the tympanic membrane and ambient room temperature were measured during the perioperative period. Results There were no postoperative differences in analgesic requirements or pain intensity between normothermic and hypothermic patients. Patients treated with warm air had an up to 1°C higher core temperature from 0.5 h after anaesthesia induction until almost 2 h postoperatively. The actively warmed patients also had a lower intraoperative blood loss than the hypothermic patients (186 ± 27 mL vs. 308 ± 47 mL;P < 0.05). Conclusion In a clinical setting, opioid requirements do not seem to be affected by mild postoperative hypothermia after lower abdominal surgery.