Overheating (Hyperthermia)

Hyperthermia (ICD-10-GM R50.9: Fever, unspecified; ICD-10-GM T88.3: Malignant hyperthermia due to anesthesia) is overheating that affects the entire body.

In this disorder, there is an overheating of the body against the control of the thermoregulatory center (in the hypothalamus area). The set point of the body temperature is normal to decreased, which distinguishes hyperthermia from fever.

Furthermore, unlike fever, hyperthermia is not triggered by pyrogens (“inflammatory substances”) and therefore does not respond to antipyretics (fever-reducing drugs).

Acute hyperthermia or heat exhaustion can occur in two different climates:

  • Dry hot climate (desert climate: average 25°C, maximum 30-45°C).
  • Warm and humid climate (annual average: 24-28 °C; humidity: about 70%; geographical location: within the tropics 23°N-23°S).

In countries with temperate climates, people with impaired thermoregulation (e.g., the elderly) and risk factors such as fatigue are particularly at risk for developing hyperthermia.

Exercise-induced hyperthermia typically occurs under punishing stress due to co-existing ambient heat. See also under classification “Etiological classification of heat shock“.

Malignant hyperthermia (MH; synonyms: malignant hyperpyrexia due to anesthesia, malignant hyperpyrexia, anesthetic hyperthermia syndrome, Ombrédanne syndrome; ICD-10 T88.3: malignant hyperthermia due to anesthesia) is a rare, life-threatening complication of anesthesia. The clinical picture is due to genetically determined dysregulation in the contraction-mediating calcium system (increased intracellular calcium); hypermetabolic metabolic derailment occurs.If predisposed, inhalation anesthetics (e.g., halothane) and/or depolarizing muscle relaxants lead to massive calcium release and subsequently to strong muscle contractions, resulting in an increase in core body temperature.

Hyperthermia can be a symptom of many diseases (see under “Differential Diagnoses”).

Course and prognosis: The earlier hyperthermia is treated, the more favorable the course. If the body temperature is lowered in time and there is no aggravation of existing diseases such as heart failure (cardiac insufficiency), hyperthermia usually has no consequences.

In the course of stress-induced hyperthermia, heat shock can occur, which is associated with a “multi-organ dysfunction syndrome” in approximately 75% of cases. The overall mortality (death rate) is between 20-60 %.

Malignant hyperthermia can progress to muscle rigor (muscle rigidity), metabolic acidosis (metabolic acidosis), hyperkalemia (excess potassium), renal and organ failure, leading to a lethal (fatal) outcome.