Intervention
heat loss
COLD
Eligible patients were randomized 1:1 to either prewarming group or non-prewarming group using computer-generated numbers by a statistician not involved in patient screening or enrolment. Before entering the operating room, patients stayed at the preoperative waiting room for the intervention (prewarming vs. non-prewarming). The ambient temperature of the preoperative waiting room was thermostatically controlled being set at 25.0 °C at least 30 min before the patients' entrance. During the stay at the preoperative waiting room, non-invasive blood pressure, pulse oxymetry, and electrocardiography were monitored. Patients in prewarming group were covered from the neck to the feet by a disposable full-body forced-air blanket (Model 30000; 3M patient warming blanket, Eden Prairie, MN, USA). The blanket was tucked underneath the body to prevent direct leaking of forced-air to the ambient environment. They underwent forced-air warming during 30 min with the temperature of the forced-air being 43.0 °C using a dedicated warming device (Model 775; 3M Bair Hugger, St. Paul, MN, USA). Patients in non-prewarming group were covered by the same full-body forced-air blanket in the same way and a cotton blanket was additionally applied over it to prevent possible heat loss during the stay at the preoperative waiting room. They did not undergo active warming while the forced-air warming device was powered off. After the 30-min intervention, patients were immediately transferred to the operating room. The thermal comfort was assessed before and after the intervention in both groups with 11-point scale (0, worst imaginable cold; 5, identified thermal comfort; 10, worst imaginable hot)