HYPERTHERMIA AND FEVER

Hypothermia is by far the most common perianesthetic thermal perturbation. However, hyperthermia is more dangerous than a comparable degree of hypothermia. Hyperthermia is a generic term simply indicating a core body temperature exceeding normal values. In contrast, fever is a regulated increase in the core temperature targeted by the thermoregulatory system. Hyperthermia can result from a variety of causes and usually indicates a problem of sufficient severity that physician intervention is required.

Passive Hyperthermia and Malignant Hyperthermia

Passive intraoperative hyperthermia results from excessive patient heating and is most common in infants and children. It is especially frequent when effective active warming is used without adequate core temperature monitoring. Passive hyperthermia, by definition, does not result from thermoregulatory intervention. Consequently, it can easily be treated by discontinuing active warming and removing excessive insulation.

The increase in body temperature during malignant hyperthermia results from an enormous increase in metabolic heat produced by both internal organs and skeletal muscle. Central thermoregulation presumably remains intact during acute crises, but efferent heat loss mechanisms may be compromised by the intense peripheral vasoconstriction resulting from circulating catecholamine concentrations 20 times normal.^[193]