Shiver Suppression Using Focal Hand Warming in Unanesthetized Normal Subjects

Background: A decrease of 1 or 2 degreesC in core temperature may provide p rotection against cerebral ischemia. However, during corporeal cooling of u nanesthetized patients, the initiation of involuntary motor activity (shive r) prevents the reduction of core temperature. The authors' laboratory prev iously showed that focal facial warming suppressed whole-body shiver. The a im of the current study was to determine whether the use of hand warming al one could suppress shiver in unanesthetized subjects and hence potentiate c ore cooling. Methods: Subjects (n = 8; healthy men) were positioned supine on a circulat ing water mattress (8-15 degreesC) with a convective-air coverlet (14 degre esC) extending from their necks to their feet. 2 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 te mperature (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 in creased until it was widespread. After subjects reported whole-body shiver (SSL greater than or equal to 7), applied hand warming, in all cases, reduc ed shiver levels (SSL less than or equal to 3), decreased electromyographic root mean square amplitudes, and allowed core temperature to decrease from 37.0 +/- 0.2 to 35.9 +/- 0.5 degreesC (measured rectally). Conclusions: Focal hand warming seems to be valuable In minimizing or elimi nating the need to suppress involuntary motor activity pharmacologically wh en 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 cont raindicated.