Environ

Heat Exhaustion

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Heat Exhaustion

  • See Also
  1. Heat Illness
  2. Heat Edema
  3. Heat Cramps
  4. Heat Exhaustion
  5. Heat Stroke
  6. Temperature Regulation
  7. Heat Index
  8. Heat Illness Risk Factors
  9. Medications Predisposing to Heat Illness
  10. Heat Illness Prevention
  • Epidemiology
  1. Most common Heat Related Illness for which patients seek treatment
  • Pathophysiology
  1. See Heat Illess
  2. Key factors leading to Heat Exhaustion
    1. Peripheral vasodilation
    2. Relative circulatory insufficiency
    3. Mild thermoregulatory dysfunction
  3. Other contributing factors
    1. Strenuous Exercise in excessive heat exposure
    2. Electrolyte loss (esp. Hyponatremia)
    3. Exercise-induced Respiratory Alkalosis
    4. Hypovolemia (although variable depending on degree of Fluid Replacement with activity)
  • Risk Factors
  1. See Heat Illness Risk Factors
  2. See Medications Predisposing to Heat Illness
  • Precautions
  1. Heat Exhaustion is a precursor for Heat Syncope
    1. Immediately stop Exercise, move to cool, shaded area, external cooling and administer hydration
  • Symptoms
  1. Fatigue
  2. Malaise
  3. Irritability
  4. Weakness
  5. Nausea and Vomiting
  6. Dizziness, Light Headedness or Presyncope
  7. Palpitations
  8. Myalgias
  9. Headache
  10. Dyspnea
  11. Excessive sweating
  12. Excessive thirst
  • Signs
  1. Temperature increased between 100.4 F (38 C) to 104 F (40 C)
    1. Body Temperature may be low or normal on presentation
  2. Sinus Tachycardia
  3. Hypotension or Orthostasis
  4. Syncope
  5. Sweating
  6. Cutaneous Flushing
  7. Decreased Urine Output
  8. Mild neurologic changes (typically transient)
    1. Minimal Incoordination
    2. Minimal confusion
    3. Irritability
    4. Mental status not seriously impaired
      1. Contrast with Heat Stroke
  • Labs
  1. General lab testing
    1. Complete Blood Count (CBC)
    2. Comprehensive metabolic panel
    3. Creatinine phosphokinase
    4. Urinalysis
    5. Some guidelines recommend coagulation studies, myoglobin
  2. Evaluate for Electrolyte and renal abnormalities
    1. Exercise-Associated Hyponatremia
      1. Heat Related Illness associated with prolonged Exercise and excessive hypotonic Fluid Replacement
      2. Also associated with NSAID use which can increase ADH level
    2. Hypernatremia
    3. Hypokalemia
    4. Acute Kidney Injury (increased Serum Creatinine)
  3. Evaluate for Rhabdomyolysis
    1. Urine blood positive on dipstick (but negative microscopy) suggests myoglobin
    2. Creatinine phosphokinase increased
  4. Normal Liver Function Tests (contrast with Heat Stroke)
    1. AST Normal
    2. ALT Normal
    3. LDH Normal
  • Management
  • General
  1. External cooling (initiate as soon as possible)
    1. Move patient to cool environment
    2. Remove excessive clothing
    3. Lay patient supine with legs elevated
    4. Spray lukewarm water on body
    5. Apply cool towels or ice packs to skin
    6. Cool with fans
  2. Gradual rehydration
    1. Manage Hypernatremia or Hyponatremia if present
    2. Manage Rhabdomyolysis if present
    3. Oral rehydration (Mild cases)
      1. Cooled, slightly hypotonic oral Electrolyte solutions (better absorbed)
      2. 1 Liter per hour over several hours
    4. Intravenous Rehydration
      1. Initial isotonic Fluid Replacement (NS or LR) with 20 ml/kg bolus
      2. Replace 50% total water deficit in first 3-6 hours
      3. Replace remaining 50% deficit over 6-9 hours
  3. Disposition: Discharge Indications
    1. Complete recovery (typically within 2-3 hours)
    2. Normalization of Vital Signs
    3. Ambulatory without symptom recurrence
    4. Tolerating oral hydration
    5. Normal examination including neurologic status
  4. Disposition: Predictors of hospitalization
    1. All Heat Stroke patients will require hospitalization (typically ICU)
    2. Age over 65 years old
    3. Comorbities (esp. cardiovascular disease, mental illness)
    4. Male gender
    5. Low socioeconomic status
    6. Pillai (2014) J Community Health 39(1): 90-8 [PubMed]
  • Management
  • Playing field sideline
  1. See Marathon Medical Care
  2. Cease Exercise
  3. Remove excess clothing
  4. Move to shaded environment
  5. Place supine with legs elevated
  6. Encourage oral fluids with Electrolyte solution
  7. Obtain Vital Signs (be alert for Tachycardia or Hypotension)
  8. Persistent symptoms or signs >20 minutes should prompt emergency department care
  • Complications
  1. Rhabdomyolysis
  2. Electrolyte abnormalities (e.g. Hypernatremia, Hypokalemia)
  3. Acute Kidney Injury
  4. Hepatic dysfunction
  • Prevention
  1. See Heat Illness Prevention
  • 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. Zink (2020) Crit Dec Emerg Med 34(3): 19-27
  5. Barrow (1998) Am Fam Physician 58(3):749-56 [PubMed]
  6. Gauer (2026) Am Fam Physician 113(4): 369-81 [PubMed]
  7. Gauer (2019) Am Fam Physician 99(8):482-9 [PubMed]
  8. Hett (1998) Postgrad Med 103(6):107-20 [PubMed]
  9. Wexler (2002) Am Fam Physician 65(11):2307-20 [PubMed]