Heat Related Illness

Aka: Heat Related Illness, Heat Illness, Heat Injury, Heat Tetany

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II. Epidemiology

  1. Climate change has resulted in global Temperature rise of 0.36 F (0.20 C) per decade (3x prior trends)
    1. For every 1.8 F (1 C) rise in hot Temperatures, Heat Related Illness morbidity increases 18%, mortality 35%
    2. Heat related deaths in the U.S. have increased 117% between 1999 and 2023
    3. Faurie (2022) Sci Total Environ 852:158332 +PMID: 36041616 [PubMed]
    4. Howard (2024) JAMA 332(14): 1203-4 [PubMed]
  2. U.S. High school athletes
    1. Incidence: 1.6 cases per 100,000 athletes (9000 cases per year)
      1. Kerr (2013) Am J Prev Med 4491):8-14 [PubMed]
    2. Third leading cause of death in high school athletes
      1. Coris (2004) Sports Med 34(1): 9-16 [PubMed]
  3. U.S. Military
    1. Overall Incidence: 1.41 per 1000 person years (2163 cases in 2017)
    2. Heat StrokeIncidence: 0.38 per 1000 person years (464 cases in 2017)
    3. (2018) MSMR 25(4):6-10 [PubMed]
  4. U.S. Emergency Departments
    1. Heat Illness represented 5 per 10,000 summertime visits (in the years 2006 to 2010)
    2. Heat Exhaustion: 75% of cases
    3. Heat Stroke: 5.4% of cases
    4. Mortality: 0.07% of cases (700 deaths per year in U.S.)
    5. Hess (2014) Environ Health Prospect 122(11):1209-15 [PubMed]

III. Physiology

  1. See Temperature Regulation
  2. Heat Illness results when metabolic heat production exceeds heat dissipation

IV. Types: Heat Related Symptoms

  1. Heat Rash (Miliaria Rubra, Sweat Rash, Prickly Heat)
    1. Papules, Pustules or Vesicles in in occluded areas of excessive sweating (esp. children)
  2. Heat Edema
    1. Benign swelling of feet, and ankles, and to a lesser extent hands
    2. Associated with salt or water retention from heat with cutaneous vasodilation
    3. Occurs in non-acclimitized patients (esp. elderly)
    4. Treated with leg elevation, Compression Stockings (avoid Diuretics)
    5. Resolves spontaneously over days with acclimitization or return to cooler environments
  3. Heat Syncope
    1. Dizziness or fainting with heat exposure immediately after completing Exercise or with prolonged standing
    2. Secondary to peripheral vasodilatation and venous pooling with secondary Postural Hypotension
    3. Seen in persons unaccustomed to extreme heat
    4. Move to cool, shaded environment, lie supine, and administer oral rehydration with salt containing solutions
    5. Higher risk in Sickle Cell Trait (as well as other Heat Illness Risk Factors)
    6. Consider Syncope differential diagnosis
      1. Exertional Syncope during Exercise is concerning (where as Syncope after Exercise is typically benign)
      2. Hypoglycemia
      3. Hyponatremia
  4. Heat Cramps
    1. Painful Muscle Contractions or cramps (esp. larger Muscle groups)
    2. Most commonly affected Muscles include abdominal, quadriceps and gastrocnemius Muscle groups
  5. Heat Tetany
    1. See Tetany
    2. Results from Hyperventilation during strenuous activity
    3. Carpopedal Spasm with Paresthesias (including perioral)
    4. Differentiate from Heat Cramps which involves proximal large Muscle groups
  6. 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
    3. Prevent with Carbohydrate-Electrolyte Beverages during Exercise and salty snacks

V. Types: Exertional Heat Syndromes (spectrum of increasing severity)

  1. Heat Stress
    1. Core Temperature unchanged (<38 C or 100.4 F) and associated with decreased Exercise tolerance
  2. Heat Exhaustion
    1. Core Temperature rises above 38 C (100.4 F) associated with systemic symptoms
  3. Heat Stroke
    1. Core Temperature rises above 40 C (104 F) asssociated with Altered Level of Consciousness

VI. Risk Factors

  1. See Heat Illness Risk Factors
  2. See Medications Predisposing to Heat Illness

VII. Management

  1. General Principles
    1. Rest (stop activity)
    2. Move to a cool, shaded area or indoor area
    3. Remove excessive clothing
    4. Initiate cooling (prompt cooling is imperative in Heat Stroke)
    5. Hydration
  2. Treat per degree of Heat Illness
    1. Heat Cramps
    2. Heat Exhaustion
    3. Heat Stroke

VIII. Associated Conditions

  1. Rhabdomyolysis

IX. Prevention

  1. See Heat Illness Prevention

X. References

  1. Czerkawski (1996) Your Patient Fitness 10(4): 13-20
  2. Sandor (1997) Physician SportsMed, 25(6):35-40
  3. Salinas and Ruttan (2017) Crit Dec Emerg Med 31(9): 3-10
  4. Zink (2020) Crit Dec Emerg Med 34(3): 19-27
  5. Barrow (1998) Am Fam Physician 58(3):749-56 [PubMed]
  6. Becker (2011) Am Fam Physician 83(11): 1325-30 [PubMed]
  7. Gauer (2019) Am Fam Physician 99(8):482-9 [PubMed]
  8. Gauer (2026) Am Fam Physician 113(4): 369-81 [PubMed]
  9. Glazer (2005) Am Fam Physician 71(11):2133-42 [PubMed]
  10. Hett (1998) Postgrad Med 103(6):107-20 [PubMed]
  11. Howe (2007) Am J Sports Med 35(8): 1384-95 [PubMed]
  12. Wexler (2002) Am Fam Physician 65(11):2307-20 [PubMed]

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