Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + Download Section PDF Listen ++ For further information, see CMDT Part 37-14: High-Altitude Illness + Key Features Download Section PDF Listen +++ +++ 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 Download Section PDF Listen +++ +++ 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 + Diagnosis Download Section PDF Listen +++ +++ 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 + Treatment Download Section PDF Listen +++ +++ Medications +++ High-altitude–associated neurologic conditions ++ Acute mountain sickness Initial treatment involves oxygen administration to keep the pulse oximetry SpO2 > 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 + Outcome Download Section PDF Listen +++ +++ 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 + References Download Section PDF Listen +++ + +Jin J. JAMA patient page. Acute mountain sickness. JAMA. 2017 Nov 14;318(18):1840. [PubMed: 29136446] + +Luks AM et al. Wilderness Medical Society practice guidelines for the prevention and treatment of acute altitude illness: 2019 update. Wilderness Environ Med. 2019 Dec;30(4S):S3–18. [PubMed: 31248818] . + +Meier D et al. Does this patient have acute mountain sickness? The Rational Clinical Examination Systematic Review. JAMA. 2017 Nov 14;318(18):1810–19. [PubMed: 29136449] + +Nieto Estrada VH et al. Interventions for preventing high altitude illness: Part 1. Commonly-used classes of drugs. Cochrane Database Syst Rev. 2017 Jun 27;6:CD009761. [PubMed: 28653390]