EM@3AM – Altitude Sickness

Author: Erica Simon, DO, MHA (@E_M_Simon, EM Chief Resident, SAUSHEC, USAF) // Edited by: Alex Koyfman, MD (@EMHighAK, EM Attending Physician, UTSW / Parkland Memorial Hospital) and Brit Long, MD (@long_brit, EM Attending Physician, SAUSHEC, USAF)

Welcome to EM@3AM, an emdocs series designed to foster your working knowledge by providing an expedited review of clinical basics. We’ll keep it short, while you keep that EM brain sharp.

A 46 year-old male departs from southern Florida on a trip to Tanzania to summit Mt. Kilimanjaro. As the first day of his expedition comes to a close (base camp at 2400 m (7,874 ft)), the man notes a severe headache and nausea. Although he retires to his tent relatively early, the majority of the night he is restless. On day two, after ascending 600m, the male stumbles, falling to the snow-covered ground. He mumbles incoherently as the trail guide rushes to his side.

What do you suspect as a diagnosis? What’s the next step in your evaluation and treatment?

Answer: Altitude Sickness1-4

  • Precipitating Causes: Speed of ascent (leading risk factor), length of stay, residence at sea level, history of altitude sickness, physical exertion at high altitudes, persons with respiratory infections (baseline V/Q mismatch).1
  • Presentation:
    • Acute Mountain Sickness (AMS) – Most common; affects 22-50% of travelers to altitudes between 1850-4240 m (6,069-13,910 ft).2
      • Signs/Symptoms: headache, insomnia, anorexia, nausea, emesis.
    • High-Altitude Pulmonary Edema (HAPE) – Rare, but most lethal; occurs 2-4 days after reaching high altitude, may or may not be preceded by AMS.3
      • Signs/Symptoms: cough, dyspnea on exertion, physical exam demonstrating rales, crackles, tachypnea, central cyanosis, and hypoxia (portable pulse oximetry). Chest radiograph (if available): asymmetric alveolar infiltrates.3,4
    • High-Altitude Cerebral Edema (HACE) – may or may not be preceded by AMS.1,3
      • Signs/Symptoms: ataxia, altered mental status which untreated may progress to seizures or coma. Physical exam: papilledema, possible CN III or VI palsies secondary to increased ICP.3
  • Treatment:
    • AMS: Acetazolamide (250 mg PO q 12h).
      • Dexamethasone (4 mg PO/IV q 6h) is second-line and may lead to rebound AMS when discontinued.4
    • HAPE: Immediate descent; Gamow Bag and supplemental oxygen if present. Nifedipine (10 mg PO x1, then 20 mg ER PO q 8-12h). 4
    • HACE: Immediate descent; Gamow Bag and supplemental oxygen if present. Dexamethasone (8 mg IV x1, then 4 mg IV q 6hr) – continue until descent completed and symptoms resolved.4
  • Prevention:
    • Acetazolamide prophylaxis (125 mg PO q 12h): initiated one day prior to climbing and continued until acclimatization at the highest sleeping elevation.4
    • Gradual ascent – recommended that above 3000 m (9,842 ft) individuals increase their sleeping elevation no more than 300-500 m (984-1,640 ft) nightly.1
  • Pearls:
    • The differential diagnosis of AMS should include dehydration, hypothermia, hyponatremia, carbon monoxide poisoning, and pulmonary or cerebral infection.1
    • Focal neurologic signs in the setting of HACE are rare and suggest an alternative diagnosis.3
    • Brain MRI is the only imaging modality which reveals findings associated with HACE: increased T2 signal in the white matter of the corpus callosum.3
    • Acetazolamide is contraindicated in persons with sulfa allergies.4


  1. Luks A, Schoene R, Swenson E. High Altitude. In: Murray and Nadel’s Textbook of Respiratory Medicine. 6th ed. Philadelphia, Saunders Elsevier. 2016; 1763-1774.e.4.
  2. Honigman B, Theis M, Koziol-McLain J, et al. Acute mountain sickness in a general tourisk population at moderate altitudes. Ann Intern Med. 1993; 118: 587-592.
  3. Israeli R, Pearson R, Thompson A, Murray J, Bailey K. Altitude Sickness. 2012. First Consult. Elsevier, Philadelphia. PA.
  4. Fiore D, Hall S, Shoja P. Altitude illness: Risk factors, prevention, and treatment. Am Fam Physician. 2010; 82(9): 1103-1110.

For Additional Reading:

High-Altitude Pulmonary Edema:

High Altitude Pulmonary Edema: Diagnosis, Management, and Preventive Strategies

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