Physiological responses to convective-air blanket warming of women after 60 minutes of cool exposure

Abstract

Convective-air warming is frequently applied to postoperative patients, but the process of warming is not understood. Hence, the study purpose was to describe the rewarming process during convective-air warming in women, 40 to 60 years, after exposure.Methods. Eight reclining women were exposed to 5 minutes of 35$\sp\circ{\rm C}$ water, then 45 minutes of 300$\sp\circ{\rm C}$ water, then three 5 minute incremental increases with the final 5 minutes at 35$\sp\circ{\rm C}.$ The subjects transferred to a dry, reclining position. Warming consisted of a baseline interval with the subject covered by a deflated blanket and two cotton blankets, followed by a 50 minute active warming interval on high setting. The variables of interest were central temperature (esophageal temperature, Tes) using a thermistor, mean skin temperature (Quartermaster weighted mean temperature, Tqrec) using thermocouples, metabolic rate (oxygen consumption, VO2) using a metabolic cart, conductance (Thermal Circulation Index, TCI) calculated from environmental, central and skin temperatures, body size (body mass index, BMI, and skinfold thickness) using height, weight and a caliper (respectively), and vasoactivity (forearm blood flow, FBF) using plethysmograph, temperature gradient, and forearm temperature.Results. During cooling, all subjects experienced a decreasing Tes (mean 0.24 $\pm\ 0.19\sp\circ{\rm C}).$ During warming, all subjects experienced afterdrop (mean 0.18 $\pm 0.10\sp\circ{\rm C}).$ Tqrec and FBF increased during baseline and active heating with the greatest rise during active warming. VO2 decreased during active warming. TCI, BMI, skinfold thickness, and FBF correlation with change in Tes were r = 0.85, -0.45 -0.50, and 0.18, respectively. FBF to forearm-index finger correlation within subjects resulted in r-values of 0.70 to -0.90 and to forearm temperature in r-values of 0.60 to 0.90. Burton's three weighted skin sites are highly correlated with Tqrec.Discussion. All individuals experienced afterdrop which took up to 60 minutes for recovery. The convective-air blanket was an effective therapy, since Tes, Tqrec and FBF rose while VO2 decreased. BMI, skinfold thickness and duration of afterdrop are better predictors of change in Tes than FBF. Forearm temperature is a better predictor of FBF than forearm-index finger gradient.