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 approximate to43degreesC, and ( 3) face warming with 21 L/min of air at approximate to42degreesC at a relative humidity of 100%. Fluid at approximate to4degreesC was infused via a central venous catheter to decrease tympanic membrane temperature 1 degreesC/ h to 2 degreesC/ h; mean skin temperature was maintained at 31 degreesC. A sustained increase in oxygen consumption quantified the shivering threshold. Results - Shivering thresholds did not differ significantly between the control (36.7 +/- 0.1 degreesC), arm- warming (36.5 +/- 0.3 degreesC), or face-warming ( 36.5 +/- 0.3 degreesC; 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 degreesC ( 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.