Hyperthermia and heat stroke
In hyperthermia the hypothalamic set-point is normal and heat load simply outstrips heat loss, so antipyretics have nothing to act on and physical cooling is the only disease-modifying treatment.
Definition
Hyperthermia is a rise in core temperature caused by excessive heat production or impaired heat dissipation while the hypothalamic set-point remains normal, which distinguishes it from fever. Heat-related illness runs from heat cramps through heat syncope and heat exhaustion to heat stroke, in which central nervous system dysfunction accompanies a high core temperature. Heat stroke is recognised clinically, in a hot or exertional context, and no UK guideline requires a temperature threshold to make the diagnosis.
First principles
Hyperthermia is not fever, and that decides the drug chart
Fever is regulated: pyrogens raise the hypothalamic set-point and the body defends the new level. In hyperthermia the set-point never moves, and heat production or environmental load simply beats heat loss. An antipyretic works by lowering a raised set-point, so in heat stroke it has no target. No UK guideline recommends paracetamol for heat stroke, and the Resuscitation Council UK treatment is cooling alone. Paracetamol also has its own ceiling: 4 g daily by mouth, and 3 g daily intravenously where there are risk factors for hepatotoxicity. Heat stroke injures the liver without any help.
This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.