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HYPERTHERMIA SYNDROMES-1

“Heat not the furnace for your foes 
So hot that it do singe yourself”
                                  -William Shakespeare

 Human body normally generated enough heat to increase body temperature by 1˚ C every hour, however hypothalamic thermoregulatory system (thermostat), tightly regulates core body temperature to a precise set point of around 37˚C, with a fluctuation of about 0.5-1.0˚C. This is achieved through negative feedback mechanism regulating thermostat, and by dissipating excess heat from body, by conduction, convective, radiation and evaporation (sweating).

Evaporation is the most effective method of heat dissipation. It involves water vaporization from skin and lung.

The exact mechanism that determines, the absolute threshold body temperature, is not known, but it appears to be mediated by norepinephrine, dopamine, serotonin, acetylcholine, prostaglandin, and neuropeptides.

FEVER VS HYPERTHERMIA- Elevation in body temperature could be due to fever or hyperthermia. There is fundamental difference between fever and hyperthermia.

Fever is the result of normal thermoregulatory system operating at higher set point, while hyperthermia is due to failure of thermoregulatory system, where excessive heat production is not effectively dissipated. Therefore antipyretic medication are not effective in hyperthermia.

HYPERTHERMIA leads to increased oxygen consumption, metabolic rate and CO2 production, resulting in tachypnea, hyperpnoea and tachycardia. Temperature above 42ºC (108ºF), leads to uncoupling of oxidative phosphorylation and failed functioning of various metabolic enzymes. A cytokine-mediated systemic inflammatory response ensues.

Dehydration and intravascular volume depletion leads to hypotension which causes shunting of blood from the splanchnic circulation to the skin and other vital organ. It predisposes to gastrointestinal ischemia and increased permeability of the intestinal mucosa, resulting in translocation of bacteria.

Clinical manifesting of hyperthermia are flushing, diaphoresis (may be absent in heat stroke), neurologic dysfunction (agitation, coma, seizures), severe intravascular volume depletion with hypotension, mixed metabolic and respiratory acidosis, dyselectrolytemia, tachyarrhythmia, conduction abnormality, coronary ischemia, non-cardiogenic pulmonary edema, rhabdomyolysis, acute kidney injury, liver dysfunction and disseminated intravascular coagulation.

The resulting multiorgan failure may make it difficult to differentiate from sepsis.

Hyperthermia syndromes can be divided into, heat related hyperthermia and drug induced hyperthermia.

Heat related hyperthermia is due to prolong exposure of environment heat as in Heat Stroke.

Drug induced hyperthermia are Malignant hyperthermia, Neuroleptic malignant syndrome, and Serotonin Syndrome.


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