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Hyperthermia, Emergency Medicine

Basics

Description

- 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

- 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)

- 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

- 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)

- UA - Myoglobin present in rhabdomyolysis

- Initiate cooling measures for severe heat illness - Remove from heat stress - Disrobe patient - Cover body with wet sheet

- 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

  • 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 wavesSevere dehydration, skin warm and dry
  • Exertional heat strokeYounger, athletic patients with combined environmental and exertional heat stress (e.g., military recruits)Develops over hoursInternal 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 illnessAge extremesDehydration (incl. gastroenteritis, inadequate fluid intake)Cardiovascular disease (incl. CHF, CAD)ObesityDiabetes mellitus, hyperthyroidism, pheochromocytomaFebrile illnessSkin diseases that hinder sweating (incl. psoriasis, eczema, cystic fibrosis, scleroderma)
  • Pharmacologic contributorsSympathomimeticsLSD, PCP, cocaineMAO inhibitors, antipsychotics, anxiolyticsAnticholinergicsAntihistaminesβ-blockersDiureticsLaxativesDrug or alcohol withdrawal
  • Environmental factorsExcessive heat/humidityProlonged exertionLack of mobilityLack of air conditioningLack of acclimatizationOcclusive, 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/deliriumLethargy or comaSeizureAtaxia
  • CV:TachycardiaWide pulse pressureLow peripheral vascular resistanceHypotensionConduction disturbances
  • Pulmonary:TachypneaRales due to noncardiac pulmonary edemaRespiratory alkalosis (may be substantial enough to cause tetany)Hypoxemia (due to aspiration, pneumonitis, pulmonary edema, and high metabolic demand)
  • GI:
  • Skin:Cutaneous vasodilation → Hot skinUsually 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 headacheFatigue/malaiseImpaired judgmentVertigoAgitationNo severe CNS dysfunction
  • CV:Mild tachycardiaDehydration
  • 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

  • CBCLeukocytosis, hemoconcentration
  • Electrolytes, BUN, Cr, glucoseHypernatremia with severe dehydrationHyponatremia can occur if drinking copious free waterAcute renal failure
  • UAMyoglobin present in rhabdomyolysis
  • Blood and urine cultures to rule out septic etiology
  • Toxicology screen
  • Serum creatinine kinase to rule out rhabdomyolysis
  • ABGAcidosis 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 illnessRemove from heat stressDisrobe patientCover 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 coolingExtremely 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 coolingIce packs to groin/axilla. Combine with evaporative cooling treatment aboveIced 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 exhaustionInitial rehydration with 0.5-1.0 L 0.9% NSAggressive fluid resuscitation until BP >90/60 or central venous pressure (CVP) >12 mL H2OAvoid overhydration, which can contribute to pulmonary edema and ARDSPeds: Start with 20 cc/kg bolusPlace Foley catheter to monitor urine output for heat stroke victims and CVP monitor if feasible. Maintain UOP >2 mL/kg/hr if rhabdomyolysis is presentRehydrate 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 abnormalitiesRenal failure or evidence of rhabdomyolysisElderly

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)