II. Epidemiology
- Most common Heat Related Illness for which patients seek treatment
III. Mechanisms
- See Heat Illess
- Strenuous Exercise in excessive heat exposure
- Electrolyte loss
- Exercise-induced Respiratory Alkalosis
-
Dehydration
- Although variable depending on degree of Fluid Replacement with activity
IV. Risk Factors
V. Precautions
- Heat Exhaustion is a precursor for Heat Syncope
- Immediately stop Exercise, move to cool, shaded area, external cooling and administer hydration
VI. Symptoms
- Fatigue
- Malaise
- Irritability
- Weakness
- Nausea and Vomiting
- Dizziness, Light Headedness or Presyncope
- Palpitations
- Myalgias
- Headache
- Dyspnea
- Excessive sweating
- Excessive thirst
VII. Signs
-
Temperature increased between 100.4 F (38 C) to 104 F (40 C)
- Body Temperature may be low or normal on presentation
- Sinus Tachycardia
- Hypotension or Orthostasis
- Syncope
- Sweating
- Cutaneous Flushing
- Decreased Urine Output
- Mild neurologic changes (typically transient)
- Minimal Incoordination
- Minimal confusion
- Irritability
- Mental status not seriously impaired
- Contrast with Heat Stroke
VIII. Labs
-
General lab testing
- Complete Blood Count (CBC)
- Comprehensive metabolic panel
- Creatinine phosphokinase
- Urinalysis
- Some guidelines recommend coagulation studies, myoglobin
- Evaluate for Electrolyte and renal abnormalities
- Evaluate for Rhabdomyolysis
- Urine blood positive on dipstick (but negative microscopy) suggests myoglobin
- Creatinine phosphokinase increased
- Normal Liver Function Tests (contrast with Heat Stroke)
- AST Normal
- ALT Normal
- LDH Normal
IX. Management: General
- External cooling (initiate as soon as possible)
- Move patient to cool environment
- Remove excessive clothing
- Lay patient supine with legs elevated
- Spray lukewarm water on body
- Cool with fans
- Gradual rehydration
- Manage Hypernatremia or Hyponatremia if present
- Manage Rhabdomyolysis if present
- Oral rehydration (Mild cases)
- Cooled, slightly hypotonic oral Electrolyte solutions (better absorbed)
- 1 Liter per hour over several hours
- Intravenous Rehydration
- Initial isotonic Fluid Replacement (NS or LR) with 20 ml/kg bolus
- Replace 50% total water deficit in first 3-6 hours
- Replace remaining 50% deficit over 6-9 hours
- Disposition: Predictors of hospitalization
- Nearly all Heat Stroke patients will require hospitalization (typically ICU)
- Age over 65 years old
- Comorbities (esp. cardiovascular disease, mental illness)
- Male gender
- Low socioeconomic status
- Pillai (2014) J Community Health 39(1): 90-8 [PubMed]
X. Complications
- Rhabdomyolysis
- Electrolyte abnormalities (e.g. Hypernatremia, Hypokalemia)
- Acute Kidney Injury
XI. Management: Playing field sideline
- See Marathon Medical Care
- Cease Exercise
- Remove excess clothing
- Move to shaded environment
- Place supine with legs elevated
- Encourage oral fluids with Electrolyte solution
- Obtain Vital Signs (be alert for Tachycardia or Hypotension)
- Persistent symptoms or signs >20 minutes should prompt emergency department care
XII. Prevention
XIII. References
- Czerkawski (1996) Your Patient Fitness 10(4): 13-20
- Salinas and Ruttan (2017) Crit Dec Emerg Med 31(9): 3-10
- Sandor (1997) Physician SportsMed, 25(6):35-40
- Zink (2020) Crit Dec Emerg Med 34(3): 19-27
- Barrow (1998) Am Fam Physician 58(3):749-56 [PubMed]
- Gauer (2019) Am Fam Physician 99(8):482-9 [PubMed]
- Hett (1998) Postgrad Med 103(6):107-20 [PubMed]
- Wexler (2002) Am Fam Physician 65(11):2307-20 [PubMed]