Exertional Heatstroke

Curbside to Bedside

Intro

• Heat Stroke is broadly defined as a core temperature above 104 F with central nervous system abnormalities following strenuous exercise or environmental heat. - Wilderness Medical Society.
• Heat cramps, exhaustion, illness, stroke etc. are a spectrum of a single illness (systemic non drug related hyperthermia) rather than each being an individual entity.
• THE CARDINAL SIGN OF HEAT STROKE IS ALTERED MENTAL STATUS
  • Anhydrosis is not a reliable finding, and should not be used as a clinical guidepost.

Pathophysiology

• An increase in blood temp triggers hypothalamic thermoregulation it increase blood flow to the skin – cutaneous vasodilation – blood shunts the the periphery to facilitate heat loss through sweating.
• Renal and splanchnic perfusion is reduced.
• Heat stroke produces an inflammatory response similar to that seen in sepsis.
• Increased mucosal permeability from inflammatory mediators allows endotoxins from the gut to enter systemic circulation – leading to alterations in microcirculation, more endothelial and tissue injury, and impaired thermoregulation.

Prevention and Acclimatization

• Acclimatization may be likened to receiving a "heat vaccine" with small steady doses of exertion in hot environments provoking an adaptive response within the body.
• 1-2 hours of progressive, controlled, heat-exposed exertion per day for 10-14 days.
• This adaptation may persist up to a month.
• One bout of a heat stroke may reset thermoregulatory adaptations and increase risk for subsequent heat injury for months.
• Hyperhydration has no effect on heat tolerance.
• Forced hydration is ineffective and dangerous (hyponatremia risk).

Environmental Considerations

• Wet Bulb Globe Temperature
  • "Composite" temperature factoring humidity, sun angle, apparent temperature, wind speed, and solar radiation.
  • Generally considered more accurate than the Heat Index, which is a function of temperature and humidity in shaded areas.
• As the environmental temperature increases the body will incur a net heat gain through convective and radiative processes, leaving evaporative thermoregulation as the only cooling mechanism.
• Some activities enhance heat transfer: Cyclist, swimmers, etc.
• Increased metabolic demand and increased ambient conditions should lead to breaks in proportion to both.

Field Treatment Principles

• Rapid, often empiric, cold water immersion is the gold standard treatment.
• Rapid reversal of the condition is key: morbidity and mortality is directly associated with the duration of hyperthermia experienced by the patient.
• If a patient is hyperthermic and has AMS, empiric cooling should not be delayed to obtain a temperature – or if temperature is less than 104 F, it should not deter you from aggressive cooling measures.
• Naturally, manage ABCs as needed.
• Treatment on scene is preferred over rapid transport.

Cold Water Immersion Therapy

• CWIT is the gold standard of treatment, and usually involves placing a patient's entire body (with airway protection measures in place) in a tub or trough of cold water.
• CWIT is two times more effective in heat transfer than spraying cool water over the body.
• Hindrance of cooling in the setting of EHS due to shivering has been physiologically refuted.

Other Cooling Methods

• If CWIT is not available, repeated dousing of cold water over the patient is "next best".
• Ice Sheets placed over the patient's body and exchanged every 2-3 minutes is an approach often adapted by the military where carrying large troughs of ice water is not optimal.
• Axillary or inguinal placement of chemical cold packs or ice is not effective.
• Be creative! The goal is to get large volumes of water over the patient or place the patient in a body of water to maximize the effect of convective cooling.

Temperature Monitoring

• Rectal and/or esophageal temperature monitoring is the gold standard.
• Oral, axillary, or skin temperature readings are highly likely to be inaccurate.
• Temperature monitoring is not required to initiate therapy, but may be helpful to guide therapy or consider other differential diagnoses.