Pre-induction skin-surface warming minimizes intraoperative core hypothermia

Study Objective: To test the hypothesis that only one hour of preinduction skin-surface warming decreases the rate at which core hypothermia develops during the first hour of anesthesia. Design: Randomized, prospective study. Setting: Operating theater of a university hospital. Patients: 16 ASA status I and II adult patients scheduled for laparoscopic cholecystectomy under general anesthesia. Interventions: Eight patients were assigned to receive forced-air warming for one hour before induction of anesthesia (prewarmed group); the other eight patients were covered only with a wool blanket during a similar preinduction period (control group). Measurements and Main Results: Tympanic membrane (core) and mean skinsurface temperatures were measured at 15-minutes intervals, starting one hour before induction of anesthesia. Mean skin temperature increased from 34.0 ± 0.1 °C to 37.0 ± 0.2 °C in the pre-warmed group ( p < 0.05), but remained unchanged at 34.7 ± 0.3 °C in the control group. Core temperature during the preinduction period did not change significantly in either group. Following induction of anesthesia, core temperature decreased at a rate of 1.1 ± 0.1 °C/hr in the control group, but only 0.6 ± 0.1 °C/hr in the pre-warmed group ( p < 0.05). After one hour of anesthesia, six of eight prewarmed patients had core temperatures of at least 36.5 °C, whereas only one of the eight control patients did ( p < 0.05). Conclusions: A single hour of preoperative skin-surface warming reduced the rate at which core hypothermia developed during the first hour of anesthesia. Preoperative skin surface warming is particularly helpful during short procedures because redistribution hypothermia is otherwise difficult to treat.