Heat Stroke

OVERVIEW

• Heat stroke is hyperthermia with neurological dysfunction due to the failing thermoregulatory system
• rectal temperature exceeds 40.6°C (definition varies between authors — in practice, don’t be too strict especially if prehospital cooling performed)
• Classical heat stroke is non-exertional e.g. elderly patients during a heat wave
• Exertional heat stroke results from physical activity e.g. young soldiers exercises in hot conditions

Other forms of heat-related illness:

• Heat syncope is fainting due to peripheral vasodilatation secondary to high ambient temperature.
• Heat cramp refers to muscular cramping occurring during exercise in heat, which is related to salt deficiency and is usually benign.
• Heat exhaustion occurs when an individual develops salt and/or water depletion, dehydration and hypovolaemia from heat stress.  Nausea, vomiting, fatigue and excessive sweating are typical. Core temperature may or may not be raised and tissue damage does not occur.

PREDISPOSING FACTORS

• age (extremes of age, athletes)
• environmental (high ambient temperature, humidity, heat waves, poor ventilation)
• behavioural (lack of acclimatisation, salt and H2O deprivation)
• underlying conditions (many)
• drugs (anticholinergic, neuropsychiatric, sympathomimetic)

CLINICAL FEATURES

• neurological dysfunction
• hyperthermia
• lack of sweating (may be present, especially in exertional heat stroke)
• complications

EFFECTS

• hyperthermia
• warm skin (or cool if shocked)
• sweating often absent, but not always
• CNS depression/excitation, focal neurology
• vasodilatory shock decompensates as ongoing dehydration occurs
• ATN causing renal failure
• atraumatic rhabdomyolysis
• electrolyte abnormalities: hyperglycaemia, low phosphate, high CK

INVESTIGATIONS

• FBC – leukocytosis, thrombocytopaenia
• UEC – hyperkalaemia, hypophosphataemia, hyperglycaemia
• LFT – elevated
• INR, APTT, fibrinogen
• CK – high
• Urinalysis with myoglobin

MANAGEMENT

• rest in a cool, well-ventilated area
• unlimited salted foods with cool water if drinking

Resuscitation

• A – obtain definitive airway if obtunded
• B – ventilate
• C – risk of shock state from dehydration and decreased myocardial function, fluid boluses 20mL/kg + maintenance, inotropes, ECMO
• D – glucose management to normoglycaemia
• E:
  • monitor core and skin temperature
  • eliminate cause of hyperthermia
  • remove clothes
  • active cooling to < 40 C (cool environment, ice water packs, ice water lavage, cold IV fluids, fans, dialysis)
  • anti-pyretics useless
  • may require sedation and paralysis

Rhabdomyolysis

• maintain UO >2-3mL/kg/hr
• crystalloid infusion
• consider frusemide infusion 1mg/kg/h
• consider mannitol 0.25-0.5g/kg
• early RRT
• maintain normal potassium, calcium and phosphate levels

OUTCOME

• mortality > 60%
• permanent neurological deficit – 7-15%
• factors associated with poor prognosis:

(1) high core temperature
(2) high SAPS II score
(3) heat stroke @ home
(4) prolonged INR
(5) vasoactive therapy within 24 hrs
(6) no air conditioning in ICU

References and Links

• CCC — Hyperthermia

Journal articles

• Bouchama A, Dehbi M, Chaves-Carballo E. Cooling and hemodynamic management in heatstroke: practical recommendations. Crit Care. 2007;11(3):R54. PMC2206402.
  Grogan H, Hopkins PM. Heat stroke: implications for critical care and anaesthesia. Br J Anaesth. 2002 May;88(5):700-7. PMID: 12067009
• Hadad E, Cohen-Sivan Y, Heled Y, Epstein Y. Clinical review: Treatment of heat stroke: should dantrolene be considered? Crit Care. 2005 Feb;9(1):86-91. PMC1065088.
• Leon LR, Helwig BG. Heat stroke: role of the systemic inflammatory response. J Appl Physiol. 2010 Dec;109(6):1980-8. PMID: 20522730.
• Walter E, Venn R, Stevenson T. Exertional heat stroke  — the athlete’s nemesis. JICS 2012;13(4) 304-308.