• J M Hynson and D I Sessler.
• Department of Anesthesia, University of California, San Francisco 94143-0648 USA.
• J Clin Anesth. 1992 May 1; 4 (3): 194-9.

Study ObjectiveTo compare the effectiveness of three commonly used intraoperative warming devices.DesignA randomized, prospective clinical trial.SettingThe surgical suite of a university medical center.PatientsTwenty adult patients undergoing kidney transplantation for end-stage renal disease.InterventionsPatients were assigned to one of four warming therapy groups: circulating-water blanket (40 degrees C), heated humidifier (40 degrees C), forced-air warmer (43 degrees C, blanket covering legs), or control (no extra warming). Intravenous fluids were warmed (37 degrees C), and fresh gas flow was 5 L/min for all groups. No passive heat and moisture exchangers were used.Measurements And Main ResultsThe central temperature (tympanic membrane thermocouple) decreased approximately 1 degree C during the first hour of anesthesia in all groups. After three hours of anesthesia, the decrease in the tympanic membrane temperature from baseline (preinduction) was least in the forced-air warmer group (-0.5 degrees C +/- 0.4 degrees C), intermediate in the circulating-water blanket group (-1.2 degrees C +/- 0.4 degrees C), and greatest in the heated humidifier and control groups (-2.0 degrees C +/- 0.5 degrees C and -2.0 degrees C +/- 0.7 degrees C, respectively). Total cutaneous heat loss measured with distributed thermal flux transducers was approximately 35W (watts = joules/sec) less in the forced-air warmer group than in the others. Heat gain across the back from the circulating-water blanket was approximately 7W versus a loss of approximately 3W in patients lying on a standard foam mattress.ConclusionThe forced-air warmer applied to only a limited skin surface area transferred more heat and was clinically more effective (at maintaining central body temperature) than were the other devices. The characteristic early decrease in central temperature observed in all groups regardless of warming therapy is consistent with the theory of anesthetic-induced heat redistribution within the body.

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