Heat Related Emergencies

1. Mike McDonnell, MD Heat Related Emergencies

2. Scenario • HUSAR team gets deployed to the collapse of an office tower in downtown Toronto • people are trapped • mid August, 30ºC with Humidex feels like 40ºC • team member complains of cramps, stops working and drinks, goes back to work • later found sitting in corner, staring, mumbling about “mummy”

3. Objectives • physiology of heat transfer/cooling • heat related illnesses • types • Treatment • “on the pile” vs. “in the pile”

4. Physiology of Heat Transfer • “Supply” and “Demand” relationship • “Supply” (heat production) • BMR • without cooling, temperature increases 1.1ºC/hr • Increases up to 20X with strenuous exercise

5. Supply and Demand • “Demand” (heat loss) • Conduction • warm body to cooler surroundings (2%) • Convection • heat loss to air and water • better with loose clothing, higher wind velocity • Radiation • electromagnetic waves • great in cool temperatures, net gain when warm • Evaporation • conversion of liquid to gas • major factor – non-acclimatized – sweat 1 litre/hour • not effective when relative humidity >75%

6. Physiology of cooling We are like a water cooled car....

7. Heat Related Illnesses • Spectrum • Not so bad, bad, very bad

8. Not so bad • “Prickly Heat” • obstruction of the sweat gland pores, produces vesicles, sometimes ruptures, very itchy • can get superinfected/rupture • treated with chlorhexidine, antibiotic creams, loose clothing preventative

9. Not so bad • Heat edema • nonacclimatized individuals • standing for long periods of time • affects feet and ankles • treated with leg elevation

10. Not so bad • Heat Cramps • brief, intermittent, severe cramps in working muscles • early on in work in hot environment • heavy sweaters with hypotonic fluid replacement more at risk • usually after exertion • treatment • Rapid elevation of salt solutions: ½ tsp salt in quart of water, commercially available solutions taste better

11. Bad • Heat Syncope • vasodilation and venous pooling from standing • reduced circulating blood volume • volume loss makes it worse • elderly are more susceptible • treatment – fix causes/injuries

12. Bad • Heat Exhaustion • volume depletion under heat stress • two types: water and salt depletion • water: inadequate fluid replacement • salt: hypotonic fluid replacement

13. Heat Exhaustion • Signs and Symptoms • vague malaise, fatigue, headache    • core temperature often normal; if elevated, less than 40° C (104° F)    • mental function essentially intact; no coma or seizures    • tachycardia, orthostatic hypotension, clinical dehydration (may occur)    • other major illness ruled out    • if in doubt, treat as heat stroke

14. Heat Exhaustion - Treatment • rest    • cool environment    • assess volume status    • fluid replacement: normal saline to replete volume if patient orthostatic, replace free water deficits slowly to avoid cerebral edema

15. Very Bad • Heat Stroke • Hallmark: alteration in level of consciousness • thermoregulation is overwhelmed and fails • may be a prodrome, may be like heat exhaustion • rapid treatment is essential

16. Heat Stroke • Diagnosis • exposure to heat stress • signs of severe CNS dysfunction (coma, seizures, delirium)    • core temperature usually above 40.5° C (105° F), but may be lower    • dry, hot skin common, but sweating may persist   

17. Types • Classic and exertional

18. Treatment • cooling immediately is key to survival • use all methods of heat transfer • spraying atomized cool water (evaporation) combined with fans (convection) very effective • ice water immersion can be attempted • rapid but take out when body temp < 39ºC • ice packs/cooling blankets less effective

19. Complications • aspiration and seizures are common • airway control • tachyarrhythmias are common • usually resolve with cooling • don’t over hydrate (IV fluids) – pulmonary edema • agitation – benzodiazepines • shivering – chlorpromazine, Demerol?