Heat Stroke

Aka: Heat Stroke, Heatstroke

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II. Epidemiology

  1. Heat Stroke is the third leading cause of death among high school athletes
    1. Coris (2004) Sports Med 34(1): 9-16 [PubMed]

III. Risk Factors

  1. See Temperature Regulation
  2. See Heat Illness Risk Factors
  3. See Medications Predisposing to Heat Illness

IV. Types

  1. Nonexertional Heat Stroke (Classic Heat Stroke)
    1. Gradual environmental exposure and unable to transition to cooler environment
    2. Usually seen in elderly and debilitated patients with altered Thermoregulation
    3. Skin is often dry with Anhidrosis
    4. Associated with mild Coagulopathy, mild acidosis an milkd Creatinine kinase elevation
  2. Exertional Heat Stroke
    1. Rapid onset over hours
    2. Usually seen in young patients and in athletes or occupational heat exposure
    3. Skin is typically diaphoretic
    4. Associated Hypoglycemia, Rhabdomyolysis, Acute Renal Failure, Hypocalcemia, Lactic Acidosis

V. Pathophysiology

  1. Very high Body Temperatures (>105.8 F or 41 C) causes Proteins to denature with secondary multisystem organ damage
  2. Mental status changes are a result of decreased cerebral perfusion and secondary cerebral ischemia

VI. Precautions

  1. Heat Stroke is a time-sensitive, life threatening condition (treat aggressively as a code)
    1. First priority is to initiate definitive cooling without delay
    2. Perform the core Temperature immediately to prevent delays in definitive management
  2. Core Temperature may have decreased below discriminatory values by the time of patient presentation
    1. Have a high index of suspicion with neurologic signs, even when core Temperature <104 F (40 C)
  3. Neurologic changes from baseline may be difficulty to assess at extremes of age (very young and very old)

VII. Signs

  1. Includes Heat Exhaustion symptoms and signs
  2. Hyperpyrexia (Use rectal probe for core Temperature)
    1. Core Temperature exceeds 40 C (104 F) for Heat Stroke diagnosis
    2. Core temps may range as high as 44 C (111 F)
    3. Reports of Temperatures up to 47 C (116.6 F)
    4. Palpation of the chest on presentation can give an early indication of hyperthermia
  3. Significant neurologic changes
    1. Altered Level of Consciousness (Delirium to obtundation or coma)
    2. Slurred speech
    3. Ataxia
    4. Delirium
    5. Hallucinations
    6. Encephalopathy (associated with poor prognosis)
    7. Seizures (associated with poor prognosis)
  4. Systemic signs
    1. Anhidrosis
      1. Skin is typically dry in non-exertional Heat Stroke (classic Heat Stroke)
      2. However, in exertional Heat Stroke, patient may be diaphoretic in up to 50% of caseds
    2. Sinus Tachycardia
    3. Hypotension
      1. Especially common when core Temperature has exceeded 42 C (107.6 F)
      2. Shock results from heat-induced cardiovascular injury as well as systemic inflammatory response
    4. Tachypnea
      1. May indicate developing Acute Respiratory Distress Syndrome (ARDS)

VIII. Imaging

  1. Head CT
    1. May demonstrate cerebral edema (although CT Head is often normal)
  2. Chest XRay
    1. Acute Respiratory Distress Syndrome (ARDS) may complicate Heat Stroke

IX. Labs

  1. Complete Blood Count (CBC) with Platelet Count
    1. Anemia may result from dilution and heat-induced red cell injury
    2. Platelet Count may decrease in first 24 hours
  2. Comprehensive Metabolic Panel (Chem18)
    1. Hyponatremia (or if no access to water, Hypernatremia)
    2. Renal Insufficiency is typical (due to prerenal Azotemia with BUN > Creatinine, as well as CPK in Rhabdomyolysis)
    3. Liver Function Test elevations (esp. AST, ALT) result from shock liver (see complications below)
      1. Peak at 48-72 hours after Heat Injury, and normalize by 14 days
      2. Transaminase increase in exertional and classic Heat Stroke (consider alternative diagnosis if absent)
  3. ProTime (PT)
    1. Typically elevated associated with liver dysfunction
  4. Partial Thromboplastin Time (PTT)
    1. Increased in Disseminated Intravascular Coagulation (DIC)
  5. Fibrinogen
  6. Venous Blood Gas (VBG)
    1. Metabolic Acidosis results from end organ ischemia and Protein breakdown
  7. Creatine Phosphokinase (CPK)
    1. Increased in Rhabdomyolysis
  8. Urinalysis
    1. Myoglobinuria (dipstick orthotoluidine positive for blood, but no Urine RBCs seen in freshly spun sediment)

X. Diagnostics

  1. Electrocardiogram (EKG)
    1. May demonstrate coronary ischemia (ST depression, T Wave Inversion) due to impaired Myocardium

XI. Differential Diagnosis (hyperthermia with Altered Level of Consciousness)

  1. See Medications Predisposing to Heat Illness
  2. Sepsis
  3. Meningitis or Encephalitis
  4. Cerebral Malaria
  5. Cerebrovascular Accident
  6. Brain Tumor
  7. Head Injury
  8. Intracranial Hemorrhage
  9. Status Epilepticus
  10. Withdrawal from abused substances
    1. Alcohol Withdrawal
    2. Benzodiazepine Withdrawal
  11. Malignant Hyperthermia
    1. Muscle rigidity will be present in Malignant Hyperthermia (and absent in Heat Stroke)
  12. Neuroleptic Malignant Syndrome
  13. Serotonin Syndrome
  14. Hyperthyroidism (Hyperthyroid storm)
  15. Pheochromocytoma
  16. Anticholinergic Poisoning
    1. Sweating absent
  17. Sympathomimetic Toxicity, Stimulant toxicity or Overdose (e.g. Methamphetamine)
    1. Sweating present
  18. Salicylate Overdose
  19. Venous Thromboembolism

XII. Management

  1. ABC Management
    1. Intubation may be needed to protect airway
  2. Rapid cooling to Temperature under 101.4 F (38.6 C) or per some guidelines, <102.2 F (39 C)
    1. Best outcomes are associated when cooling is initiated within 30 minutes of heat-related injury
    2. Immediately remove from hot environment
    3. Monitor cooling with continuous rectal core Temperature
      1. Goal Temperature: 101-102 F
      2. Avoid targeting 98 F, as more likely to overshoot and result in Hypothermia
    4. EMS initiated cooling
      1. If effective cooling (e.g. water immersion) is available in field, then cool for 15 min before transport
      2. Otherwise, initiate temporizing cooling measures during transport
    5. Temporizing cooling measures until water immersion is available
      1. Air conditioned room cools patient at 0.03 to 0.06 C/min
      2. Evaporative Cooling with fans and misting (with patient uncovered to allow for evaporation)
        1. Mist with tepid water (15 C) with continuous fanning
      3. Ice sheets (wet sheets stored in ice cooler)
      4. Cool saline bags applied to neck, groin and axilla
    6. Water Immersion
      1. Temperate water immersion (68 F or 20 C)
        1. Alternative when cold or ice water immersion not available
        2. Body Temperature cooled at 0.11 C/min
      2. Cold water immersion (46 to 57 F or 8 to 14 C)
        1. Body Temperature cooled at 0.16 to 0.26 C/min
      3. Ice water immersion (35 to 41 F or 2 to 5 C, most effective measure)
        1. Body Temperature cooled at 0.12 to 0.35 C/min
        2. Place patient in body bag or tarp and fill bag with water and ice
        3. Associated with nearly 100% survival rate when used immediately in exertional Heat Stroke
        4. Casa (2007) Exerc Sport Sci Rev 35(3): 141-9 [PubMed]
    7. Avoid prolonged cooling beyond target core Temperature
      1. Risk of local cold injury with tissue ischemia and inflammation, as well as overshoot Hypothermia
      2. Goal Temperature <101 F (38.3 C), achieved typically within 20 minutes after cooling is initiated
        1. Stop water immersion immediately on reaching target Temperature
    8. Other initial measures to consider
      1. Benzodiazepines to reduce Agitation and shivering
    9. Measures not found effective (and with risk of Water Intoxication)
      1. Nasogastric lavage (Cold Gastric Lavage)
        1. Endotracheal Intubation for airway protection
        2. Place Orogastric Tube (OG)
        3. Instill 10 ml/kg iced saline (NS bag chilled in ice water) into OG tube, then suction out instilled fluid after 1 minute
        4. Repeat saline instillation via OG tube as needed
        5. Warrington (2023) Crit Dec Emerg Med 37(5): 22
      2. Peritoneal Lavage
      3. Ice water rectal enemas
    10. Other measures to avoid
      1. Avoid antipyretics (NSAIDs, Acetaminophen, Dantrolene) as ineffective and potentially harmful
      2. Hyperthermia is not Hypothalamus regulated and will not respond to antipyretics
  3. Same IV hydration as for Heat Exhaustion
    1. See Hypotension below
    2. Avoid Fluid Overload and observe closely for Pulmonary Edema
    3. Non-Exertional Heat Stroke may only require 1 Liter of crystalloid
    4. Exertional Heat Stroke may require 2-3 Liters of crystalloid
    5. Cold saline infusion (39 F or 4 C) may result in more rapid resolution
      1. Mok (2017) Curr Sports Med Rep 16(2): 103-8 [PubMed]
  4. Altered Level of Consciousness
    1. Treat as Delirium
    2. Check bedside Glucose
    3. Consider banana bag containing Thiamine
    4. Consider Naloxone
  5. Airway and Breathing Management
    1. Endotracheal Intubation is often required
    2. Rapid Sequence Intubation with Rocuronium for paralysis
      1. Rocuronium is not affected by Hyperkalemia (unlike Succinylcholine)
      2. Rocuronium will inhibit shivering for the 30-40 minutes (during the entire cooling process)
      3. Additional sedation with Benzodiazepines, which also reduces shivering
    3. Maintain a higher Minute Ventilation
      1. Increased Respiratory Rate will help to clear the Metabolic Acidosis
  6. Seizure
    1. See Status Epilepticus
    2. Administer Benzodiazepines
    3. Consider Hyponatremia, Hypoglycemia and other Seizure Causes
  7. Myoglobinuria
    1. Maintain Urine Output at 50 to 100 ml per hour
    2. Alkalinize urine and force diuresis with Mannitol
  8. Hypotension
    1. Start by treating as Distributive Shock (related to peripheral vasodilation)
    2. Heat Stroke patients are not uniformly volume depleted
      1. Non-Exertional Heat Stroke patients are not typically hypovolemic
      2. However, exertional Heat Stroke patients are typically hypovolemic
    3. Judicious rehydration (without overhydration especially in non-Exertional Syncope)
      1. Permissive Hypotension allows for the fluid redistribution that occurs with cooling
      2. Prevents pulmonary vascular congestion that otherwise occurs with aggressive rehydration
      3. If refractory Hypotension, increase fluid Resuscitation and consider Vasopressors
    4. Exercise caution with Vasopressors
      1. May provoke Dysrhythmias and decrease heat dissipation (due to Vasoconstriction)
  9. Disseminated Intravascular Coagulation (DIC)
    1. Fresh Frozen Plasma and Platelets as needed
  10. Shivering with rapid cooling
    1. Consider Muscle relaxants, Benzodiazepines or Neuroleptics (e.g. Chlorpromazine)
    2. However, avoid Anticholinergics, as these inhibit sweating
    3. Dantrolene is not effective in lowering core Temperature
      1. Bouchama (2002) N Engl J Med 346:1978-88 [PubMed]
  11. Disposition
    1. Nearly all patients will require hospitalization (typically ICU)
    2. Children should be admitted to pediatric ICU

XIII. Complications

  1. Disseminated Intravascular Coagulation (DIC)
    1. Complicates 50% of Heat Stroke cases
  2. Rhabdomyolysis
  3. Acute Renal Failure
    1. Secondary to prerenal Azotemia, as well as Rhabdomyolysis
  4. Adult Respiratory Distress Syndrome (ARDS)
  5. Compartment Syndrome
  6. Gastrointestinal Bleeding
  7. Hepatocellular necrosis (or shock liver)
    1. Liver is particularly susceptible to Heat Illness (highest heat generation and highest organ Temperature)

XIV. Prognosis: Short-Term

  1. Mortality: <10% (if treated appropriately)
    1. Mortality higher in some groups (e.g. firefighters)
  2. Indicators of Poor Prognosis
    1. Core Temperature exceeds 42 degrees Celsius
    2. Aspartate Aminotransferase (AST) >1000 in first day
    3. Prolonged coma exceeds 2 hours

XV. Prognosis: Long-Term outcomes for survivors

  1. Increased risk of Heat Stroke under same conditions
    1. Test heat tolerance 8-12 weeks post-episode
    2. Assess for residual injury in Thermoregulation
  2. Long-term neurologic or behavioral deficits
    1. Neurologic injury is permanent in 20% of cases
    2. Dematte (1998) Ann Intern Med 129:173-81 [PubMed]

XVI. Prevention

  1. See Heat Illness Prevention
  2. Guidance after discharge from Heat Stroke admission
    1. No Exercise for at least 7 days and until medically cleared for activity
    2. Follow-up in 1 week for repeat exam, labs
    3. When re-starting Exercise
      1. Perform in a cool environment
      2. Gradually advance duration, intensity and heat exposure over 2 weeks
    4. Clearing athletes for full competition
      1. Heat tolerance achieved after 2-4 weeks of full training
    5. Heat tolerance test indications
      1. Athlete unable to return to full, vigorous activity in expected time interval, or
      2. Recurrent symptoms with activity
    6. References
      1. O'Connor (2010) Curr Sports Med Rep 9(5):314-21

XVII. References

  1. Czerkawski (1996) Your Patient Fitness 10(4): 13-20
  2. Salinas and Ruttan (2017) Crit Dec Emerg Med 31(9): 3-10
  3. Sandor (1997) Physician SportsMed, 25(6):35-40
  4. Swadron, Herbert and Paquette in Herbert (2019) EM:Rap 19(6): 10-11
  5. Shoenberger and Swaminathan in Herbert (2021) EM:Rap 21(9): 1-2
  6. Zink (2020) Crit Dec Emerg Med 34(3): 19-27
  7. Barrow (1998) Am Fam Physician 58(3):749-56 [PubMed]
  8. Becker (2011) Am Fam Physician 83(11): 1325-30 [PubMed]
  9. Hett (1998) J Postgrad Med 103(6): 107-20 [PubMed]
  10. Howe (2007) Am J Sports Med 35(8): 1384-95 [PubMed]
  11. Epstein (1990) Med Sci Sports Exerc 22(1): 29-35 [PubMed]
  12. Gauer (2019) Am Fam Physician 99(8):482-9 [PubMed]
  13. Grafe (1997) Clin Sports Med 16(4):569-91 [PubMed]
  14. Jardine (2007) Pediatr Rev 28(7): 249-58 [PubMed]
  15. Wexler (2002) Am Fam Physician 65(11):2307-20 [PubMed]
  16. Yaqub (1998) J Neurol Sci 156(2):144-51 [PubMed]

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