Hyperthermia

Background

• Hyperthermia is an elevation in core body temperature due to failure of thermoregulation (distinct from fever, which is a regulated increase mediated by pyrogens)
• Core temperature >40°C (104°F) is generally considered severe hyperthermia
• The key distinction is: fever = hypothalamic set-point is raised (treat infection); hyperthermia = heat gain exceeds heat loss (active cooling required)
• Antipyretics (acetaminophen, NSAIDs) are ineffective in true hyperthermia because the thermoregulatory set-point is normal

Differential Diagnosis

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Fever

Infectious

• Critical
  • Sepsis
  • PNA with respiratory failure
  • Peritonitis
  • Meningitis
  • Cavernous Sinus Thrombosis
  • Necrotizing Fasciitis
• Emergent
  • PNA
  • Peritonsillar Abscess
  • Retropharyngeal Abscess
  • Epiglottitis
  • Endocarditis
  • Pericarditis
  • Appendicitis
  • Cholecystitis
  • Diverticulitis
  • Intra-abdominal abscess
  • Pyelonephritis
  • Tubo-ovarian abscess
  • Encephalitis
  • Brain abscess
  • Cellulitis
  • Abscess
  • Malaria
• Non-emergent
  • Viral syndrome
  • Otitis Media
  • Sinusitis
  • Pharyngitis
  • Influenza
  • TB
  • UTI
  • Epididymitis
  • Prostatitis

Non-infectious

• Critical
  • AMI
  • PE
  • Intracranial Hemorrhage
  • CVA
  • NMS
  • Thyroid Storm
  • Acute Adrenal Insufficiency
  • Transfusion Rx
  • Pulmonary Edema
  • Heat Stroke
  • Malignant hyperthermia
• Emergent
  • CHF
  • Dehydration
  • Recent Seizure
  • Sickle Cell Dz
  • Transplant rejection
  • Pancreatitis
  • DVT
  • Serotonin Syndrome
• Non-emergent
  • Drug fever (except as in NMS and Serotonin Syndrome)
  • Malignancy
  • Gout
  • Sarcoidosis
  • Crohn's Disease
  • Postmyocardiotomy syndrome
  • Sweet's syndrome

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Toxicologic causes of Hyperthermia

• Serotonin syndrome
• Neuroleptic malignant syndrome
• Excited delirium syndrome
• Sympathomimetic toxicity
• Anticholinergic toxicity
• Alcohol withdrawal/Delirium tremens
• Lithium toxicity
• Salicylate toxicity
• TCA toxicity
• Laundry detergent pod ingestion
• Malignant hyperthermia
• Dinitrophenol toxicity

Endocrine causes of Hyperthermia

• Thyroid storm
• Malignant hyperthermia
• Pheochromocytoma

Neurologic causes of Hyperthermia

• Anti-NMDA receptor encephalitis
• CVA
• Status epilepticus

Evaluation

• Core temperature (rectal or esophageal preferred; oral/temporal may underestimate)
• CBC, BMP, LFTs, coagulation studies, CK, lactate, urinalysis
• Consider blood cultures, LP, CXR if infectious cause not excluded
• Toxicology screen if ingestion or drug-related cause suspected
• Consider CT head if altered mental status

Management

• Active external cooling is the mainstay for all severe hyperthermia:
  • Ice water immersion (most effective for exertional heat stroke; target temp <39°C / 102.2°F within 30 min)
  • Evaporative cooling (mist and fan) if immersion not feasible
  • Ice packs to axillae, groin, neck
• Treat the underlying cause:
  • Heat stroke → aggressive cooling, IVF (see Heat stroke)
  • Malignant hyperthermia → dantrolene (see Malignant hyperthermia)
  • Neuroleptic malignant syndrome → dantrolene, bromocriptine (see Neuroleptic malignant syndrome)
  • Serotonin syndrome → cyproheptadine, benzodiazepines (see Serotonin syndrome)
  • Anticholinergic toxicity → physostigmine (see Anticholinergic toxicity)
  • Sympathomimetic toxicity → benzodiazepines, cooling
• Avoid succinylcholine if malignant hyperthermia or hyperkalemia suspected

Disposition

• Admit all patients with heat stroke, malignant hyperthermia, NMS, or serotonin syndrome
• ICU for altered mental status, organ dysfunction, or temperature >41°C (105.8°F)
• Mild heat-related illness (heat exhaustion, heat cramps) may be discharged after treatment with adequate follow-up

See Also

• Environmental heat diagnoses
• Heat stroke
• Heat exhaustion
• Malignant hyperthermia
• Neuroleptic malignant syndrome
• Serotonin syndrome
• Acute fever