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For further information, see CMDT Part 37-14: High-Altitude Illness

Key Features

Essentials of Diagnosis

  • The severity of the high altitude illness is affected by the rate and height of ascent, and the individual's susceptibility

  • Prompt recognition and medical treatment of early symptoms of high altitude illness may prevent progression

  • Assessment must include other conditions that may coexist or mimic high-altitude illness (severe dehydration, hyponatremia, hypoglycemia, trauma, or infection)

  • Immediate descent is the definitive treatment for high altitude cerebral edema and high altitude pulmonary edema

General Considerations

  • High-altitude medical problems are due to hypobaric hypoxia at high altitudes (usually above 2000 m or 6560 ft)

  • Risk factors include increased physical activity with insufficient acclimatization, inadequate education and preparation, and individual susceptibility (preexisting medical conditions and medication use)

  • Presentations may be acute, subacute, or chronic disturbances that result from hypobaric hypoxia

  • Acclimatization to altitudes above 5500 m (18,045 ft) is incomplete or physiologically impossible, although individual differences in tolerance to hypoxia exist

  • Manifestations of altitude illness

    • High-altitude neurologic conditions (acute mountain sickness, high-altitude cerebral edema)

    • Acute high-altitude pulmonary edema

    • Subacute mountain sickness

    • Chronic mountain sickness (Monge disease)

High altitude–associated neurologic conditions

  • Acute mountain sickness: The severity correlates with altitude and rate of ascent

  • High-altitude cerebral edema

    • Appears to be an extension of the CNS symptoms of acute mountain sickness

    • Usually occurs at elevations above 2500 m (8202 ft)

    • More common in unacclimatized persons

    • Clinical findings are due largely to cerebral cellular hypoxia and cerebral vasogenic edema

Acute high-altitude pulmonary edema

  • Usually occurs at levels above 3000 m (9840 ft)

Subacute mountain sickness

  • Occurs most frequently in unacclimatized individuals at altitudes above 4500 m (14,764 ft)

Chronic mountain sickness (Monge disease)

  • Chronic hypoxia, polycythemia and sometimes pulmonary hypertension in residents of high-altitude environments

  • May be difficult to differentiate from chronic pulmonary disease

  • Uncommon condition

Clinical Findings

Symptoms and Signs

High altitude–associated neurologic conditions

  • Acute mountain sickness

    • Initial

      • Headache (most severe and persistent symptom)

      • Lassitude

      • Drowsiness

      • Dizziness

      • Chilliness

      • Nausea and vomiting

      • Difficulty sleeping

    • Later

      • Irritability

      • Difficulty in concentrating

      • Anorexia

      • Insomnia

      • Increased headaches (from cerebral edema)

    • More severe manifestations

      • Pulmonary edema

      • Cerebral edema

  • High-altitude cerebral edema

    • Altered mental status, ataxia, severe lassitude, and encephalopathy

    • Confusion, ataxia, urinary retention or incontinence, focal neurologic deficits, papilledema, and seizures

    • Symptoms may progress to obtundation, coma, and death

    • High-altitude retinopathy is separate but related effect of altitude; can include dilated vessels, retinal hemorrhage, vitreous hemorrhage, and papilledema

Acute high-altitude pulmonary edema

  • Early symptoms may appear within 6–36 h

    • Incessant dry cough

    • Shortness of breath disproportionate to exertion


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