Basics
Description
- Range of progressively more severe illnesses due to increasingly overwhelming heat stress
- Begins with dehydration and electrolyte abnormalities and progresses to thermoregulatory dysfunction and multisystem organ failure
- Body temperature is maintained within a narrow range by balancing heat production with heat dissipation
- Oxidative phosphorylation becomes uncoupled and essential enzymes cease to function above 42 °C (108 °F)
Heat Stroke
- Core body temp >105 °F (40.5 °C)
- Failure of thermoregulatory function leads to severe CNS dysfunction and multisystem organ failure
- Classic heat stroke (nonexertional)
- Occurs in patients with compromised thermoregulation or an inability to remove themselves from a hot environment (e.g., extremes of age, debilitated)
- Develops over days to weeks, usually during heat waves
- Severe dehydration, skin warm and dry
- Exertional heat stroke
- Younger, athletic patients with combined environmental and exertional heat stress (e.g., military recruits)
- Develops over hours
- Internal heat production overwhelms dissipating mechanisms, often despite persistent sweating
Heat Exhaustion
- Core temp moderately elevated but usually <104 °F (40 °C)
- Fluid and/or salt depletion occurs secondary to heat stress
- Thermoregulatory function is maintained and CNS function is preserved
- Variable nonspecific symptoms including malaise, headache, fatigue, and nausea
- If left untreated, progresses to heat stroke
Etiology
- Pre-existing conditions that hinder the bodys ability to dissipate heat predispose for heat-related illness
- Age extremes
- Dehydration (incl. gastroenteritis, inadequate fluid intake)
- Cardiovascular disease (incl. CHF, CAD)
- Obesity
- Diabetes mellitus, hyperthyroidism, pheochromocytoma
- Febrile illness
- Skin diseases that hinder sweating (incl. psoriasis, eczema, cystic fibrosis, scleroderma)
- Pharmacologic contributors
- Sympathomimetics
- LSD, PCP, cocaine
- MAO inhibitors, antipsychotics, anxiolytics
- Anticholinergics
- Antihistamines
- β-blockers
- Diuretics
- Laxatives
- Drug or alcohol withdrawal
- Environmental factors
- Excessive heat/humidity
- Prolonged exertion
- Lack of mobility
- Lack of air conditioning
- Lack of acclimatization
- Occlusive, nonporous clothing
Children are at increased risk of heat illness due to increased body surface area to mass ratio and lower sweat production
Diagnosis
Signs and Symptoms
Heat Stroke
- Classic triad: Hyperthermia, CNS dysfunction, hot skin (often with anhidrosis)
- Core temp: >105 °F (40.5 °C)
- CNS:
- Severe confusion/delirium
- Lethargy or coma
- Seizure
- Ataxia
- CV:
- Tachycardia
- Wide pulse pressure
- Low peripheral vascular resistance
- Hypotension
- Conduction disturbances
- Pulmonary:
- Tachypnea
- Rales due to noncardiac pulmonary edema
- Respiratory alkalosis (may be substantial enough to cause tetany)
- Hypoxemia (due to aspiration, pneumonitis, pulmonary edema, and high metabolic demand)
- GI:
- Skin:
- Cutaneous vasodilation → Hot skin
- Usually dry, though sweating may be present if not dehydrated
- Acute oliguric renal failure due to dehydration +/- rhabdomyolysis
- Hepatic failure with elevation of transaminases in the tens of thousands
- Coagulopathy, including DIC (poor prognostic sign) → purpura, melena, hematochezia, hematuria, CNS hemorrhage
Heat Exhaustion
- Core temp moderately elevated, usually <104 °F (40 °C) and never >40.5 °C
- CNS:
- Frontal headache
- Fatigue/malaise
- Impaired judgment
- Vertigo
- Agitation
- No severe CNS dysfunction
- CV:
- Mild tachycardia
- Dehydration
- Pulmonary: Tachypnea
- GI: Nausea, vomiting
- Skin: Perspiration present, often profuse
Heat Cramps
- Cramps in heavily worked muscles after exercise
- Occurs after profuse sweating and rehydration with hypotonic fluid (i.e., water)
- Results in hyponatremia and hypochloremia without rhabdomyolysis or renal damage
- Treat with oral salt solutions if minor or NS IV if severe
Heat Edema
- Swelling of feet/ankles from environmental heat in nonacclimatized people
- Due to vasodilatation and orthostatic pooling and increased aldosterone
- Resolves after acclimatization. Treatment with elevation or compression stockings.
Heat Syncope
- Unexplained syncope during heat exposure with prolonged standing, especially in elderly
- Cutaneous vessels dilate in an effort to dissipate heat → decreased central blood volume → syncope
- Self-limited illness. Resolves when the patient lays flat.
Prickly Heat
- Pruritic maculopapular/vesicular rash over clothed areas after profuse sweating in tight clothing
- Due to blockage of pores and secondary staphylococcus infection
Essential Workup
- Accurate core temperature
- History of heat exposure
- Heat exhaustion is a diagnosis of exclusion
- Core temperature >105 °F (40.5 °C) and CNS dysfunction required to make diagnosis of heat stroke
Diagnosis Tests & Interpretation
Lab
For Heat Stroke and Heat Exhaustion
- CBC
- Leukocytosis, hemoconcentration
- Electrolytes, BUN, Cr, glucose
- Hypernatremia with severe dehydration
- Hyponatremia can occur if drinking copious free water
- Acute renal failure
- UA
- Myoglobin present in rhabdomyolysis
- Blood and urine cultures to rule out septic etiology
- Toxicology screen
- Serum creatinine kinase to rule out rhabdomyolysis
- ABG
- Acidosis is common with exertional heat stroke, and lactate is usually elevated
For Heat Stroke
- PT/PTT/DIC panel - coagulopathy implies poor prognosis
- Liver function tests
- Troponin I - poor prognosis if elevated
- Consider lumbar puncture to distinguish from meningitis/encephalitis
Imaging
- EKG in elderly or patients at cardiac risk
- CT head for altered mental status
- CXR for ARDS, aspiration pneumonia, and to rule out septic etiology
Differential Diagnosis
- Febrile illness/sepsis
- Thyroid storm
- Pheochromocytoma
- Cocaine/PCP
- Anticholinergics
- MAO inhibitors
- Meningitis/encephalitis
- Cerebral falciparum malaria
- Delirium tremens
- Neuroleptic malignant syndrome
- Malignant hyperthermia
- Serotonin syndrome
Treatment
Pre-Hospital
- Initiate cooling measures for severe heat illness
- Remove from heat stress
- Disrobe patient
- Cover body with wet sheet
Initial Stabilization/Therapy
- ABCs
- Continuous core temperature monitoring with a rectal or esophageal probe
- Rapid cooling if temperature >104 °F (40 °C)
- Start with IV 0.9% NS 500 cc fluid bolus if hypotensive
- If altered mental status, administer glucose (or Accu-Chek), thiamine, naloxone
Ed Treatment/Procedures
Cooling Measures
- Initiate for body temperature >104 °F (40 °C)
- Evaporative cooling
- Extremely effective (0.05-0.3 °C/min)
- Spray disrobed patient with fine mist of warm water (prevents shivering)
- Airflow with fans blowing over patient
- Conductive cooling
- Ice packs to groin/axilla. Combine with evaporative cooling treatment above
- Iced or cold water immersion-effective but impractical
- Iced peritoneal lavage, cardiopulmonary bypass, or HD with cold dialysate for refractory cases - not well studied
- Stop cooling therapy at 102 °F (39 °C) to avoid overshooting and hypothermia
- Antipyretic agents are not helpful because underlying mechanism does not involve a change in the hypothalamus set point
- Avoid alcohol sponge baths. Toxicity can occur due to dilated cutaneous vessels.
Supportive Measures
- Rehydration for heat stroke/heat exhaustion
- Initial rehydration with 0.5-1.0 L 0.9% NS
- Aggressive fluid resuscitation until BP >90/60 or central venous pressure (CVP) >12 mL H2O
- Avoid overhydration, which can contribute to pulmonary edema and ARDS
- Peds: Start with 20 cc/kg bolus
- Place Foley catheter to monitor urine output for heat stroke victims and CVP monitor if feasible. Maintain UOP >2 mL/kg/hr if rhabdomyolysis is present
- Rehydrate to hemodynamic stability with NS then slowly administer free water if needed for correction of hypernatremia
- Benzodiazepines for seizure, agitation, or to stop shivering
- Tachyarrhythmias can develop, which usually resolve with cooling. Avoid electricity or α-adrenergics until after the myocardium is cooled
- Heat cramps: Analgesics and oral or IV hydration with electrolyte-containing fluid
- Heat edema: Lower extremity elevation + compression stockings
- Prickly heat: Chlorhexidine cream/lotion +/- salicylic acid 1% TID
Medication
- Diazepam: 5-10 mg (peds: 0.2-0.4 mg/kg) IVP
- Lorazepam: 1-2 mg (peds 0.05-0.1 mg/kg) IVP
- Naloxone (Narcan): 2 mg (peds: 0.1 mg/kg) IVP
Follow-Up
Disposition
Admission Criteria
- Heat stroke - admit to the ICU
- Heat exhaustion - admit to general or monitored floor if:
- Severe electrolyte abnormalities
- Renal failure or evidence of rhabdomyolysis
- Elderly
Discharge Criteria
All patients except those with heat stroke or severe heat exhaustion may be discharged
Pearls and Pitfalls
- Cannot make diagnosis of heat stroke without temp >40.5 °C and severe CNS dysfunction.
- Management of heat stroke requires management of ABCs and rapid cooling.
- Continuous core monitoring with a rectal or esophageal probe is standard of care.
- Evaporative cooling is the cooling method of choice.
Additional Reading
- Hausfater P, Doumenc B, Chopin S, et al. Elevation of cardiac troponin I during non-exertional heat-related illness in the context of a heatwave. Crit Care. 2010;14(3):R99.
- LoVecchio F, Pizon AF, Berrett C, et al. Outcomes after environmental hyperthermia. Am J Emerg Med. 2007;25(4):442-444.
- Martin-Latry K, Gourmy MP, Latry P, et al. Psychotropic drugs use and risk of heat-related hospitalization. Eur Psychiatry. 2007;22(6):335-338.
- Marx JA, Hockberger RS, Walls RM. Heat Illness. Rosens Emergency Medicine: Concepts and Clinical Practice. 7th ed., Vol 2. Philadelphia, PA: Mosby Elsevier; 2010:1882-1892.
- Smith JE. Cooling methods used in the treatment of exertional heat illness. Br J Sports Med. 2005;39(8):503-507.
- Varghese GM, John G, Thomas K, et al. Predictors of multi-organ dysfunction in heatstroke. Emerg Med J. 2005;22(3):185-187.
Codes
ICD9
- 992.0 Heat stroke and sunstroke
- 992.2 Heat cramps
- 992.5 Heat exhaustion, unspecified
- 992.1 Heat syncope
- 992.3 Heat exhaustion, anhydrotic
- 992.6 Heat fatigue, transient
- 992.7 Heat edema
ICD10
- T67.0XXA Heatstroke and sunstroke, initial encounter
- T67.2XXA Heat cramp, initial encounter
- T67.5XXA Heat exhaustion, unspecified, initial encounter
- T67.1XXA Heat syncope, initial encounter
- T67.3XXA Heat exhaustion, anhydrotic, initial encounter
- T67.6XXA Heat fatigue, transient, initial encounter
- T67.7XXA Heat edema, initial encounter
SNOMED
- 52072009 Heat stroke (disorder)
- 95868006 Heat exhaustion (disorder)
- 87108006 Heat cramps (disorder)
- 89797005 Heat syncope (disorder)
- 12979003 Transient heat fatigue (disorder)
- 16209006 Anhidrotic heat exhaustion (disorder)
- 55017000 Heat edema (disorder)