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

  • Headache

  • Decreased exercise performance

  • Fatigue

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