|Microsurgery: Transplantation and Replantation by Harry J. Buncke, MD, et al.
| Conduction. Conduction is heat loss from warm body surfaces in contact with colder surfaces. During anesthesia, conductive losses occur primarily from the infusion of cold intravenous fluids. All fluids entering the patient should be warmed to normal body temperature. Of course, if the patient develops a benign hyperthermia, cold intravenous fluids can help correct this situation. The use of warming blankets to maintain normal body temperature is a common practice. Except with very young children, however, we do not recommend using warming blankets. Although some authors believe that the conductive heat-saving measures of warming fluids and warming blankets are adequate in maintaining normal body temperature,8 more feel that temperature cannot be controlled in this manner3,9 and that the other mechanisms of heat loss require attention. Only about 30% of the body is in contact with the warming blanket. Also, the cutaneous vessels of the dependent areas may be compressed by the patient's weight and the relatively hard surface of the warming blanket.10 This compression could decrease heat exchange between the blanket and the patient's body and also increase the possibility of injury, thermal burn, or pressure necrosis. Heating blankets have also caused skin damage.11,12
Convection. Convective heat loss results when a cold air mass moves across exposed areas of the patient. Covering the patient as much as possible with blankets and maintaining an ambient room temperature of 21 to 24°C, can greatly reduce convective heat loss.7
Radiation. Normal radiation of heat into the atmosphere continues in the anesthetized patient and can be controlled by covering as much of the patient as possible with blankets. Benign hyperthermia occurs during the prolonged anesthetic. Prevention of convective heat loss, prolonged closed or semi-closed systems that increase heat and moisture from the carbon dioxide-soda lime reaction, malfunction or overuse of a humidifier, or even sepsis can result in an increase in body temperature. This increase is usually easily corrected (except in sepsis) by increasing fresh gas flow rates, uncovering the patient, removing humidifiers or heat-moisture exchangers, disconnecting fluid warmers, and decreasing the ambient temperature. Sepsis and malignant hyperthymia must always be considered and appropriate treatment instituted if these processes are identified.
POSITIONING THE PATIENT AND PREVENTION OF PRESSURE NECROSIS
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