High-Altitude Illness

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

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

  • Dyspnea at rest

  • Chest tightness

• Later symptoms

  • Wheezing

  • Orthopnea

  • Hemoptysis

• Physical findings

  • Tachycardia

  • Mild fever

  • Tachypnea

  • Cyanosis

  • Prolonged respiration

  • Rales, wheezing, and rhonchi

  • Confusion or coma

  • May resemble severe pneumonia

Subacute mountain sickness

• Dyspnea and cough

• Dehydration, skin dryness, and pruritus

Chronic mountain sickness

• Somnolence

• Mental depression

• Chronic hypoxia

• Cyanosis

• Finger clubbing

• Right ventricular failure

Differential Diagnosis

• Migraine or tension headache

• Stroke or intracerebral bleed

• Heart failure

• Alcohol or drug intoxication

• Sepsis

Laboratory Tests

Acute high-altitude pulmonary edema

• Hypoxia

• Often mild leukocytosis, but the erythrocyte sedimentation rate is usually normal

• Elevated pulmonary arterial blood pressure; normal wedge pressure

Subacute mountain sickness

• Hypoxia

• Hematocrit may be elevated

Chronic mountain sickness

• Polycythemia; hemoglobin > 22 g/dL (hematocrit often > 75%)

• Pulmonary function tests usually disclose alveolar hypoventilation and elevated PaCO₂ but fail to reveal defective oxygen transport

Imaging Studies

Acute high-altitude pulmonary edema

• Chest film findings vary from irregular patchy infiltration in one lung to nodular densities bilaterally or with transient prominence of the central pulmonary arteries

Subacute and chronic mountain sickness

• Radiographic evidence of right-sided heart enlargement and central pulmonary vessel prominence

Diagnostic Procedures

Acute high-altitude pulmonary edema

• Transient nonspecific ECG changes, occasional right ventricular strain

Subacute and chronic mountain sickness

• May be ECG changes of right axis deviation and right atrial and ventricular hypertrophy

Medications

High-altitude–associated neurologic conditions

• Acute mountain sickness

  • Initial treatment involves oxygen administration to keep the pulse oximetry S_pO₂ > 90%

  • Acetazolamide, 250 mg orally twice daily

  • Dexamethasone

    • 4 mg orally every 6 hours

    • Should not be used for prophylaxis and should not be continued beyond 7 days

  • Both are recommended therapy for as long as symptoms persist and may be used together in severe cases

• High-altitude cerebral edema

  • Dexamethasone

    • 8 mg once then 4 mg orally every 6 hours

    • Should not be used for prophylaxis and should not be continued beyond 7 days

Acute high-altitude pulmonary edema

• Calcium channel blockers and selective phosphodiesterase type 5 (PDE5) inhibitors are effective for symptomatic relief

• Nifedipine, 60-mg slow extended-release daily, given in divided doses of 30 mg twice daily, or 20 mg three times daily

• Tadalafil, 10 mg orally every 12 hours

• Sildenafil, 50 mg orally every 8 hours

Chronic mountain sickness

• Medroxyprogesterone, 20–60 mg/day orally for 10 weeks

• Acetazolamide, 250 mg/day orally for 3 weeks

• Enalapril, 5 mg orally daily

Therapeutic Procedures

High-altitude–associated neurologic conditions

• Acute mountain sickness

  • Voluntary periodic hyperventilation, often relieves acute symptoms

  • Definitive treatment is immediate descent (essential if symptoms are persistent, severe, or worsening, or pulmonary or cerebral edema occurs)

  • 100% oxygen, 1–2 L/min, may relieve acute symptoms

  • If immediate descent not possible, portable hyperbaric chambers may provide symptomatic relief

  • Symptoms generally clear in 24–48 h

• High-altitude cerebral edema

  • Immediate descent of ≥ 610 m (2001 ft) until symptoms improve

  • Administer oxygen (100%) (2–4 L/min) by mask

  • If immediate descent impossible, use portable hyperbaric chamber

Acute high-altitude pulmonary edema

• Rest in semi-Fowler position (head raised) and administration of 100% oxygen by mask 4–6 L/min for 15–30 min; to conserve oxygen, use lower flow rates (2–4 L/min)

• Immediate descent ≥ 610 m (2000 ft) essential

• Recompression in portable hyperbaric bag will temporarily reduce symptoms if immediate descent not possible

• Treatment for acute respiratory distress syndrome may be required

Subacute mountain sickness

• Treatment: rest, oxygen administration, diuretics, return to lower altitudes

Chronic mountain sickness

• Phlebotomy, oxygen supplementation, respiratory training

• Almost all abnormalities disappear when patient returns to sea level

Prevention

• Persons with symptomatic cardiac or pulmonary disease should avoid high altitudes

• Slow ascent: 300 m per day

• Adequate rest the day before travel, reduced food intake, and avoidance of alcohol, tobacco

• Avoid unnecessary physical activity during travel

• A period of rest and inactivity for 1–2 days after arrival at high altitudes

• Prompt medical attention with rest and high-flow oxygen if respiratory symptoms develop may prevent progression to frank pulmonary edema

• Mountaineering parties at altitudes of 3000 m or higher should carry a supply of oxygen and equipment sufficient for several days

• An early descent of even 500 or 1000 m may result in symptomatic improvement

• Medication prophylaxis

  • Acetazolamide, 125 mg orally twice daily

  • Dexamethasone

    • 2 mg every 6 hours or 4 mg orally every 12 hours beginning on the day of ascent, continuing for 3 days at the higher altitude, and then tapering over 5 days, is an alternative

    • Higher doses (4 mg every 6 hours) may be considered in high-risk situations requiring immediate physical exertion (those airlifted to high altitudes for search and rescue or military)

  • Nifedipine, 30 mg extended-release orally every 12 hours started the day before ascent and continued through the 4th day at target elevation, or through the 7th day if the ascent rate was faster

  • Salmeterol

    • 125 mcg by inhaler every 12 hours beginning 24 hours prior to ascent

    • Use as adjunct to nifedipine but not as monotherapy

  • Phosphodiesterase inhibitors (tadalafil 10 mg orally twice a day or sildenafil 50 mg orally every 8 hours)

    • May be beneficial in the treatment of HAPE based on their physiologic effects of decreased pulmonary arterial pressures and pulmonary vasodilation

    • This class of drugs may be used if nifedipine is not available

    • Do not administer with nifedipine because the additive vasodilation effects may be increase the patient's risk of hypotension and cerebral hypoperfusion

When to Admit

• All patients with high-altitude pulmonary edema or high-altitude cerebral edema must be hospitalized for further observation

• Hospitalization must be considered for any patient who remains symptomatic after treatment and descent

• Pulmonary symptoms and hypoxia may be worsened by pulmonary embolism, secondary respiratory infection, bronchospasms, mucous plugging, or acute coronary syndrome