Shiver suppression using focal hand warming in unanesthetized normal subjects

Background: A decrease of 1 or 2°C in core temperature may provide protection against cerebral ischemia. However, during corporeal cooling of unanesthetized patients, the initiation of involuntary motor activity (shiver) prevents the reduction of core temperature. The authors' laboratory previously showed that focal facial warming suppressed whole-body shiver. The aim of the current study was to determine whether the use of hand warming alone could suppress shiver in unanesthetized subjects and hence potentiate core cooling. Methods: Subjects (n = 8; healthy men) were positioned supine on a circulating water mattress (8-15°C) with a convectiveair coverlet (14°C) extending from their necks to their feet. A dynamic protocol was used in which focal hand warming was used to suppress involuntary motor activity, enabling noninvasive cooling to decrease core temperatures. The following parameters were monitored: (1) heart rate; (2) blood pressure; (3) core temperature (rectal, tympanic); (4) cutaneous temperature and heat flux; (5) subjective shiver level (SSL scale 0-10) and thermal comfort index (scale 0-10); (6) metabolic data (n = 6); and (7) electromyograms. Results: During cooling without hand warming, involuntary motor activity increased until it was widespread. After subjects reported whole-body shiver (SSL ≥ 7), applied hand warming, in all cases, reduced shiver levels (SSL ≤ 3), decreased electromyographic root mean square amplitudes, and allowed core temperature to decrease from 37.0 ± 0.2 to 35.9 ± 0.5°C (measured rectally). Conclusions: Focal hand warming seems to be valuable in minimizing or eliminating the need to suppress involuntary motor activity pharmacologically when it is desired to induce or maintain mild hypothermia; it may be used in conjunction with facial warming or in cases in which facial warming is contraindicated.