Recommended practices for the prevention of unplanned perioperative hypothermia

AORN Journal,  May, 2007  

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4. The extent and severity of any patient burns should be considered.

Patients with extensive burns lose body heat readily by radiation from burned tissue and convection when tissue is exposed to air currents. Burned patients are at high risk for unplanned hypothermia. The threshold for physiologic response to external temperature is set higher in these patients, triggering a metabolic response to cold at higher ambient temperatures than in unburned patients. The set point is estimated to be 0.03[degrees]C higher for each percent of total body surface area burned (eg, 50% burn = 1.5[degrees]C higher set point). (9) The natural insulating effect of skin is also impaired. The higher set point, combined with the lack of insulation, places patients with severe burns at high risk for hypothermia.

5. The type and duration of planned anesthesia should be reviewed.

Hypothermia in the operating room results from impaired thermoregulation induced by anesthetic agents and exposure to the relatively cool environment. General or major regional anesthesia (eg, epidural, spinal) for periods longer than one hour induces hypothermia. General anesthetics inhibit tonic vasoconstriction and cause vasodilatation. This results in a shift of heat from the body's core to its periphery and a drop in core temperature of approximately 1.6[degrees]C over the first hour after induction. During the subsequent two hours of anesthesia time, core temperature continues to decrease an additional 1.1[degrees]C. (1) Epidural and spinal anesthesia decrease the vasoconstriction and shivering to a slightly lesser degree, depending on the level of the block. (28,29)

6. Perioperative registered nurses should be aware of factors influencing the severity of potential hypothermia in patients under general or major regional anesthesia. These factors include, but are not limited to,

* OLDER ADULTS. In a case control study of adult general surgery patients, increased age was found to be a predictive risk factor for perioperative hypothermia. (30) This has been found in patients receiving either general or epidural anesthesia, (31) or spinal anesthesia. (32) Older patients lose heat more rapidly than younger adults due to decreased fat or muscle mass and changes in vascular tone that inhibit vasoconstriction and decrease heat production. (32) Older patients' thermoregulatory defenses are also impaired more than younger patients by general (11) and neuraxial (33) anesthesia.

* BODY WEIGHT. Low body weight has been identified as a risk factor for perioperative hypothermia in general surgery patients. (30) Thin patients have a large body-surface-area-to-weight ratio and limited insulation to prevent heat loss. Obese patients have a high weight-to-body-surface ratio and maintain peripheral tissues at high temperatures due to high body fat and a consistent vasodilated state in the time prior to induction of anesthesia. These patients generally have low core-to-peripheral temperature gradients and little redistribution hypothermia. (34)