Environ

Heat Exhaustion

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Heat Exhaustion

  • Epidemiology
  1. Most common Heat Related Illness for which patients seek treatment
  • Mechanisms
  1. See Heat Illess
  2. Strenuous Exercise in excessive heat exposure
  3. Electrolyte loss
  4. Exercise-induced Respiratory Alkalosis
  5. Dehydration
    1. Although variable depending on degree of Fluid Replacement with activity
  • 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. Weakness
  3. Nausea and Vomiting
  4. Dizziness, light headedness or Presyncope
  5. Myalgias
  6. Irritability
  7. Headache
  8. Dyspnea
  9. Excessive thirst
  • Signs
  1. Temperature increased between 100.4 F (38 C) to 104 F (40 C)
  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. Incoordination
    2. 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. Hypernatremia
    2. Hypokalemia
    3. 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. 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: Predictors of hospitalization
    1. Nearly 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]
  • Complications
  1. Rhabdomyolysis
  2. Electrolyte abnormalities (e.g. Hypernatremia, Hypokalemia)
  3. Acute Kidney Injury
  • 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
  • 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. Barrow (1998) Am Fam Physician 58(3):749-56 [PubMed]
  5. Gauer (2019) Am Fam Physician 99(8):482-9 [PubMed]
  6. Hett (1998) Postgrad Med 103(6):107-20 [PubMed]
  7. Wexler (2002) Am Fam Physician 65(11):2307-20 [PubMed]