II. Epidemiology

  1. Most common Heat Related Illness for which patients seek treatment

III. 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

V. Precautions

  1. Heat Exhaustion is a precursor for Heat Syncope
    1. Immediately stop Exercise, move to cool, shaded area, external cooling and administer hydration

VI. 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

VII. 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

VIII. 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

IX. 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]

XI. 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

XII. Prevention

XIII. 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 (2019) Am Fam Physician 99(8):482-9 [PubMed]
  7. Hett (1998) Postgrad Med 103(6):107-20 [PubMed]
  8. Wexler (2002) Am Fam Physician 65(11):2307-20 [PubMed]

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Related Studies

Ontology: Heat Exhaustion (C0018839)

Definition (MSH) A clinical syndrome caused by heat stress, such as over-exertion in a hot environment or excessive exposure to sun. It is characterized by SWEATING, water (volume) depletion, salt depletion, cool clammy skin, NAUSEA, and HEADACHE.
Concepts Injury or Poisoning (T037)
MSH D006359
ICD9 992.5
ICD10 T67.5
SnomedCT 212941006, 157726006, 269277006, 241971009, 95868006, 52072009
English Exhaustion, Heat, HEAT EXHAUSTION, Heat Prostration, Prostration, Heat, Heat exhaustion, unspecified, Effects of heat exhaustion, unspecified, Heat Exhaustion, heat exhaustion (diagnosis), heat exhaustion, Heat exhaustion NOS, Heat prostration NOS, Heat Exhaustion [Disease/Finding], heat prostration, exhaustion heat, Heat: [exhaustion, unspecified] or [prostration NOS] (disorder), Heat: [exhaustion, unspecified] or [prostration NOS], Tropical heat exhaustion, Heat prostration NOS (disorder), Heat prostration, Heat exhaustion, Heat exhaustion (disorder), exhaustion; heat, heat; exhaustion, heat; prostration, Heat exhaustion, NOS, Heat prostration, NOS
German Hitzeermuedung, Hitzeerschoepfung, unspezifisch, Hitzeerschoepfung, Hitzeerschoepfung, nicht naeher bezeichnet, Hitzeprostration, Hitzeerschöpfung
Italian Esaurimento da calore, Esaurimento da calore non specificato, Prostrazione da calore, Collasso da calore
Dutch hitte-uitputting, hitte-uitputting, niet-gespecificeerd, hitte; uitputting, uitputting; hitte, warmte; uitdroging, Uitputting door warmte, niet gespecificeerd, hitte-afmatting, Hitte, uitputting door, Hittecollaps, Uitputting door hitte
French Epuisement par la chaleur, non précisé, Coup de chaleur, Epuisement dû à la chaleur, Prostration due à la chaleur, Épuisement dû à la chaleur
Portuguese Prostação pelo calor, Exaustão pelo calor NE, Exaustão pelo calor, Exaustão por Calor, Prostração Devida ao Calor
Spanish Insolación no especificada, Postración por calor, postración por calor, SAI, postración por calor, SAI (trastorno), agotamiento por calor (trastorno), agotamiento por calor, postración por calor, Agotamiento por calor, Agotamiento por Calor, Prostración por Calor
Japanese 熱疲労、詳細不明, ネツヒロウ, ネツヒロウショウサイフメイ, ネツバテ, 熱けいれん症, 熱疲憊, 熱痙攣症, 熱衰弱症, 熱性虚脱, 熱疲労, 熱虚脱症, 暑さへばり, 熱ばて
Swedish Värmeutmattning
Czech vyčerpání z tepla, tepelná exhausce, Vyčerpání z horka, Vyčerpanost z horka, Blíže neurčené vyčerpání z horka
Finnish Lämpöuupuminen
Korean 상세불명의 열탈진
Polish Wyczerpanie cieplne, Przegrzanie
Hungarian Hődepressio, Hőkimerülés, Nem meghatározott hőkimerülés
Norwegian Varmeutmattelse, Varmeprostrasjon