The effects of forced-air warming on postbypass central and skin temperatures and shivering activity

Abstract

Study Objective: To test the hypothesis that forced-air skin-surface warming used prophylactically after hypothermic cardiopulmonary bypass (CPB) would: (1) decrease the incidence and severity of postbypass shivering, (2) rapidly increase skin-surface temperatures when compared with standard warmed cotton blankets, and (3) not contribute to excessive central temperature elevation. Design: Prospective, randomized, nonblinded comparison of two rewarming techniques. Setting: Multidisciplinary intensive care unit at a tertiary care, private teaching hospital. Patients: Following hypothermic CPB, 47 patients underwent postoperative rewarming by using either conduction (warmed cotton blankets) or convection (forced-air cover) techniques. Measurements and Main Results: Central and skin temperatures were measured at 30-minute intervals for 5.5 hours postoperatively. Four lead electromyographic recordings were used to objectively document shivering activity. Antihypertensives, opioids, sedatives, and muscle relaxants were administered per patient need and recorded. The forced-air cover markedly decreased the overall incidence, duration, and magnitude of significant shivering compared with the warmed cotton blankets. Forced-air therapy produced clinically significant increases in skin surface temperatures, but avoided excessive central temperature elevation when compared with passive rewarming with cotton blankets. Conclusion: Convection warming, when compared with conductive warming with cotton blankets, limited the incidence, magnitude, and duration of shivering following hypothermic cardiac surgery. This suggests an important role of cutaneous thermal input in the mediation of the shivering response. The central tissue compartment is buffered from the effects of skin-surface warming and, thus, forced-air therapy will not lead to excessive central temperature elevation in this patient population when compared with cotton blanket rewarming.