Neither arm nor face warming reduces the shivering threshold in unanesthetized humans.

BACKGROUND AND PURPOSE Hand warming and face warming, combined with inhalation of heated air, are reported to suppress shivering. However, hand or face temperature contributes only a few percent to control of shivering. Thus, it seems unlikely that manipulating hand or facial skin temperature alone would be sufficient to permit induction of therapeutic hypothermia. We tested the hypothesis that focal arm (forearm and hand) warming or lower facial warming, combined with inhalation of heated and humidified gas, only minimally reduces the shivering threshold (triggering core temperature). METHODS We studied 8 healthy male volunteers (18 to 40 years of age) on 3 days: (1) control (no warming), (2) arm warming with forced air at approximately 43 degrees C, and (3) face warming with 21 L/min of air at approximately 42 degrees C at a relative humidity of 100%. Fluid at approximately 4 degrees C was infused via a central venous catheter to decrease tympanic membrane temperature 1 degrees C/h to 2 degrees C/h; mean skin temperature was maintained at 31 degrees C. A sustained increase in oxygen consumption quantified the shivering threshold. RESULTS Shivering thresholds did not differ significantly between the control (36.7+/-0.1 degrees C), arm-warming (36.5+/-0.3 degrees C), or face-warming (36.5+/-0.3 degrees C; analysis of variance, P=0.34) day. The study was powered to have a 95% probability of detecting a difference of 0.5+/-0.5 degrees C (mean+/-SD) between control and either of the 2 treatments at alpha=0.05. CONCLUSIONS Focal arm or face warming did not substantially reduce the shivering threshold in unanesthetized volunteers. It thus seems unlikely that these nonpharmacological modalities will substantially facilitate induction of therapeutic hypothermia.