Heat related illnesses are characterized by hyperthermia (a core temperature over 40°C) and central nervous system disturbances that can lead to life-threatening conditions. They can be considered a form of systemic inflammatory response that affects multiple organ systems, which in many ways resembles sepsis. These illnesses can be categorized into three groups: heat cramps, heat exhaustion, and heat stroke.
Note: this guideline is intended to assist paramedics and EMRs/FRs in managing heat from exogenous sources. It is not to be used to manage fever.
Heat cramps are painful muscle spasms due to hyponatremia associated with strenuous activity. Patients have a normal body temperature with no evidence of dehydration.
Heat exhaustion develops over hours to days and is associated with fluid and electrolyte losses due to sweating with inadequate fluid replacement. Patients have a normal mental status, though they may be light-headed, nauseated, tachypneic, and experiencing a headache. Body temperature is normal, or slightly elevated. Hypotension can be present and may cause tachycardia.
Heat stroke can be divided into two sub-types:
Classic (non-exertional) heat stroke occurring in the elderly with high ambient temperature. Can develop over hours to days from passive fluid losses by sweating. Classic heat stroke carries a high mortality rate. Mortality correlates with the degree of temperature elevation, time to initiation of cooling measures, and the number of organ systems affected.
Exertional heat stroke develops due to extreme environmental conditions combined with high metabolic rates of heat production to overwhelm the body’s ability to lose heat. Generally seen in fit populations during exertional activities (e.g., long distance runners, firefighters, soldiers) especially when high humidity limits heat loss. Occurs when the body’s thermoregulation defences are exhausted and is a true medical emergency.
Heat stroke can present with altered mental status, irritability, seizures, ataxia, hallucinations, hypotension, tachycardia, and coma. Patients may stop sweating in either case and is a late sign of heat stroke. Rhabdomyolysis may complicate management.