Hyperthermia

Hyperthermia

Hyperthermia. Hyperthermia results from an imbalance in heat production, dissipation. Predisposing factors include dehydration, chronic illness, old age, alcohol, alteration in skin function (scleroderma etc.), drugs including anticholinergics, phenothiazines, tricyclic antidepressants, MAO inhibitors, amphetamines, and succinylcholine. Think also of thyroid storm.


Malignant hyperthermia.
Causes: 1:20,000 in response to a muscle-relaxing agent (such as succinylcholine) or an inhaled anesthetic (such as halothane). Is hereditary. May also be secondary to physical or emotional stress.
Characteristics. Hyperthermia, muscle rigidity, tachycardia, acidosis, shock, coma, rhabdomyolysis.
Treatment includes IV dantrolene 1 to 10 mg/kg IV titrated to effect, management of acidosis and shock, peripheral cooling (see management of heat stroke below).

Neuroleptic malignant syndrome.
Cause. Neuroleptics (phenothiazines, etc.)
Characteristics. Same symptoms as malignant hyperthermia but generally develops over days instead of minutes.
Treatment. As per malignant hyperthermia.

Serotonin syndrome.
Cause. Serotonin excess. Generally secondary to combination of MAO and SSRI or rarely to excess SSRI ingestion.
Characteristics. Rapid development of fever, hypertension, muscle rigidity, decreased mental status. Much more rapid onset than neuroleptic malignant syndrome.
Treatment. Treat like malignant hyperthermia (above). Cyproheptadine, a serotonin antagonist, 4-8mg has been effective in case reports. Also diazepam in 5 mg aliquots IV for muscle spasm, intubation as needed, cooling blankets, acetaminophen. Treat hypertension as per malignant hypertension.

Heat cramps.
Cause. Strenuous physical activity.
Characteristics. Skeletal muscle cramps, profuse sweating, hyponatremia secondary to free water intake, normal body temperature.
Treatment. Rest, oral or IV rehydration.

Heat exhaustion.
Cause. Secondary to sweating, volume depletion, tissue hypoperfusion.
Characteristics. Fatigue, light-headedness, nausea, vomiting, headache, tachycardia, hyperventilation, hypotension, normal or slightly elevated temperature, profuse sweating.
Treatment. Rest, rapid IV fluid replacement (1 to 2 liters of NS or more).

Heat stroke.
Cause. Volume depletion, sweating, etc.
Characteristics. Hyperpyrexia (often >40 C [106 F]), Patient may be sweating or may be dry, and have loss of consciousness or alteration in mental status (hallucinations, bizarre behavior, status epilepticus, other neurologic symptoms).
Treatment. This is a true emergency. Check and follow labs including electrolytes, CBC twice a day, liver enzymes, CPK (may develop rhabdomyolysis), and clotting studies. Remove clothing; apply water to skin and fan to promote evaporative heat loss. (Avoid inducing shivering and peripheral vasoconstriction with ice. Shivering can be controlled with diazepam IV or chlorpromazine or meperidine.) Treat with fluids (but many do not have significant fluid deficits; be cautious), cooling blankets.