Figure 40-22 Relative effects of warming methods on mean body temperature (ΔMBT) as a function of time (upper portion) or administered fluid (lower portion). Mean body temperature is the average temperature of body tissues and is usually somewhat less than core temperature. The calculations assume an undressed 70-kg patient with a metabolic rate of 80 kcal/hr, in thermal steady state, and with a typical 21°C operating room environment. Only the changes resulting from specific treatments are shown; changes from combined interventions will be additive. a to d, Changes in MBT per liter of administered blood or crystalloid at various fluid temperatures; e, inspiring warmed, humidified gas; f and g, warmed or unwarmed blankets, with all skin below the neck covered; savings are similar with a single layer of other passive insulators; h, full-length circulating water mattress; i, full-length forced-air warmer. (Redrawn from Sessler AM, Sessler DI: Consequences and treatment of perioperative hypothermia. Anesthiol Clin North Am 12:425–456, 1994. See the original figure legend for equations and citations justifying the assumptions.)