Hyperthermia is an increase in temperature of 2 °C/h or 0.5 °C/15 min. It is uncommon for a patient to become hyperthermic based solely on maneuvers to conserve body heat in the operating room. Therefore, any increase in temperature must be investigated. Hyperthermia and its accompanying hypermetabolic state produce an increase in oxygen consumption, cardiac work, glucose demand, and compensatory minute ventilation. Sweating and vasodilation may result in decreased intravascular volume and venous return.

1. Etiologies
   1. Malignant hyperthermia must be considered during any perioperative temperature increase (see Section XVII).
   2. Inflammation, infection, and sepsis with release of inflammatory mediators may cause hyperthermia.
   3. Hypermetabolic states such as thyrotoxicosis may cause hyperthermia.
   4. Injury to the hypothalamic thermoregulatory center from anoxia, edema, trauma, or tumor may affect temperature set points in the hypothalamus.
   5. Neuroleptic malignant syndrome (NMS) triggered by neuroleptics such as phenothiazines (eg, haloperidol); it is a rare cause.
   6. Sympathomimetics, such as monoamine oxidase inhibitors, amphetamines, cocaine, and tricyclic antidepressants, may produce a hypermetabolic state.
   7. Anticholinergics, such as atropine, may suppress sweating.
2. Treatment
   1. If malignant hyperthermia is suspected, dantrolene treatment must be initiated (see Section XVII).
   2. Severe hyperthermia can be treated by cooling exposed body surfaces (eg, skin) with ice, cooling blankets, and reduced ambient temperature or by performing internal lavage (eg, stomach, bladder, bowel, and peritoneum) with cold saline.
      1. Volatile liquids, such as alcohol, applied to the skin will promote evaporative heat loss.
      2. Conductive heat loss can be increased with vasodilators such as nitroprusside and nitroglycerin.
      3. Centrally active agents such as aspirin and acetaminophen can be given by nasogastric tube or rectally.
      4. Shivering can be prevented by maintaining neuromuscular blockade.
      5. When hyperthermia is profound, extracorporeal cooling can be used. Cooling should be stopped when the body temperature reaches 38 °C to avoid hypothermia.