HAPE is a noncardiogenic pulmonary edema caused by exaggerated hypoxic pulmonary vasoconstriction, typically developing 2–4 days after ascent above 2,500–3,000 m in unacclimatized individuals. It is the leading cause of death from high-altitude illness, with an estimated untreated mortality of 50%. [1-2] The pathophysiology involves abnormally high pulmonary artery and capillary pressures leading to noninflammatory, hemorrhagic alveolar capillary leak. [1][3]
The following figure illustrates the proposed pathophysiological cascade of HAPE, including the role of hypoxic pulmonary vasoconstriction and capillary stress failure:
1. History
- Key HPI questions: Altitude reached, rate of ascent, sleeping altitude, timeline of symptom onset, prior altitude exposure, history of previous HAPE episodes
- Symptom characterization:
- Early: decreased exercise performance, exertional dyspnea disproportionate to altitude/fitness, dry cough, fatigue, weakness, gurgling sensation in chest [1][4]
- Late: dyspnea at rest, cyanosis, cough productive of pink frothy sputum, respiratory distress [1-2]
- Timing: Typically onset on the 2nd night at a new altitude; rarely occurs after >4 days at a given altitude. Symptoms often worsen during sleep [2][5]
- Triggers: Rapid ascent, heavy exertion on arrival, cold exposure [2]
- Important negatives: Orthopnea is uncommon; frank hemoptysis is rare [2]
2. Alarm Features
- Dyspnea at rest or with minimal exertion
- Cyanosis
- Pink frothy sputum
- SpO₂ values of 50–70% (at least 10 points lower than healthy individuals at the same altitude) [6]
- Concurrent neurologic dysfunction (ataxia, confusion, altered mental status) → suggests concurrent HACE, present in 14% of HAPE cases [2]
- Failure of SpO₂ to improve to >90% within 5 minutes of high-flow O₂ → indicates severe HAPE requiring descent and possible hospitalization [2]
3. Medications
Treatment
- Supplemental O₂ (2–4 L/min) — first-line, reduces pulmonary artery pressure 30–50% [2]
- Nifedipine SR 30 mg q12h — adjunct in field settings when O₂ unavailable; primary therapy only if no other options [4][7]
- PDE-5 inhibitors (tadalafil, sildenafil) — unproven alternatives if nifedipine unavailable; do NOT combine multiple pulmonary vasodilators [4]
- CPAP — can be considered as adjunct to O₂ in hospital settings [4]
Prevention (for those with prior HAPE history)
- Nifedipine SR 30 mg q12h, starting day before ascent [6-7]
- Tadalafil 10 mg q12h (alternative) [7]
- Dexamethasone 8 mg q12h (alternative) [7]
Contraindicated/Not recommended
- Diuretics — no role in HAPE treatment [1][4]
- Acetazolamide — no established role in HAPE prevention or treatment [4][8]
- Beta-agonists — no established role [4]
- Dexamethasone has no established role in HAPE treatment unless concurrent HACE is suspected [4][9]
4. Diet
- Hydration: Maintain adequate oral hydration; dehydration is common at altitude due to increased insensible losses and decreased thirst
- Avoid alcohol — respiratory depressant, worsens hypoventilation during sleep at altitude [6]
- No specific dietary triggers for HAPE; general altitude advice includes avoiding heavy meals before exertion
5. Review of Systems
- Pulmonary: Cough (dry → productive), dyspnea (exertional → rest), chest tightness/gurgling, hemoptysis
- Neurologic: Headache, confusion, ataxia, altered mental status (screen for concurrent AMS/HACE — 50% of HAPE patients have AMS) [2]
- Constitutional: Fatigue, weakness, decreased exercise tolerance, insomnia
- GI: Nausea, vomiting, anorexia (may indicate AMS)
- Cardiac: Palpitations (tachycardia), chest pain
6. Collateral History and Family History
- Prior episodes of HAPE — recurrence risk is dramatically elevated (e.g., 60% recurrence when ascending to 4,500 m in 2 days) [1]
- Ascent profile details from travel companions
- Family history of HAPE susceptibility (individual susceptibility is a recognized factor)
- Pre-existing cardiopulmonary conditions: congenital heart disease (unilateral absent pulmonary artery, ASD/VSD), pulmonary hypertension [2]
- Social context: military deployment, search-and-rescue, trekking/mountaineering
7. Risk Factors
- Rapid rate of ascent — strongest modifiable risk factor [1-2]
- Higher altitude reached — unusual below 3,000 m [1]
- Prior history of HAPE — strongest individual risk factor [1]
- Heavy physical exertion on arrival [2]
- Cold exposure (increases pulmonary artery pressure via sympathetic stimulation) [2]
- Young age (children may be more susceptible) [2]
- Upper respiratory tract infection or bronchitis (especially in children) [2]
- Abnormalities of cardiopulmonary circulation (e.g., congenital absence of a pulmonary artery, patent foramen ovale) [2]
- Re-entry phenomenon: high-altitude residents returning after brief stay at low altitude [4]
8. Differential Diagnosis
Per the Wilderness Medical Society (WMS) 2024 guidelines, consider: [2][4][6]
- Pneumonia — fever, purulent sputum, focal consolidation; HAPE can also cause low-grade fever (up to 38.5°C) and leukocytosis, making distinction difficult
- Pulmonary embolism — pleuritic chest pain, unilateral leg swelling, risk factors for VTE
- Cardiogenic pulmonary edema / heart failure — orthopnea (uncommon in HAPE), elevated JVP, cardiomegaly on CXR (HAPE has normal heart size)
- Myocardial infarction — chest pain, ECG changes, troponin elevation
- Asthma / bronchospasm — wheezing, history of reactive airway disease
- Pneumothorax — sudden pleuritic pain, absent breath sounds
- Viral upper respiratory tract infection — rhinorrhea, sore throat, milder hypoxemia
- Mucous plugging — focal atelectasis
Key distinguishing feature of HAPE: Hypoxemia disproportionate to altitude, patchy infiltrates with normal heart size on CXR, and the specific clinical context of recent ascent [2][4]
9. Past Medical History
- Previous episodes of HAPE or other altitude illness
- Known congenital heart disease (especially left-to-right shunts, absent pulmonary artery)
- Pulmonary hypertension
- Chronic lung disease (COPD, asthma)
- Coronary artery disease or heart failure
- Prior high-altitude travel history and tolerance
10. Physical Exam
- Vital signs: Resting tachycardia and tachypnea (worsen with progression); low-grade fever up to 38.5°C is common; SpO₂ markedly low (50–70%) [2][6]
- Lungs: Rales — classically begin in the right axilla and become bilateral as illness progresses; wheezing may be present [2]
- Cyanosis — central and peripheral, especially lips and nail beds
- Neurologic exam: Assess for ataxia, confusion, altered mental status (concurrent HACE)
- Cardiac: Prominent P2 (pulmonary hypertension); no S3 or elevated JVP (noncardiogenic)
- Extremities: Peripheral edema is not a feature of HAPE itself (unlike cardiogenic edema)
- Orthopnea is uncommon — helps distinguish from cardiogenic pulmonary edema [2]
11. Lab Studies
- Pulse oximetry — essential; SpO₂ disproportionately low for altitude is the hallmark diagnostic finding [4][6]
- ABG — respiratory alkalosis with alarmingly low PaO₂ and hemoglobin saturation [5]
- CBC — WBC count is usually elevated (nonspecific) [5]
- BNP/NT-proBNP — useful to rule out cardiogenic pulmonary edema (expected to be low/normal in HAPE)
- Troponin — to exclude MI
- BMP — baseline renal function, electrolytes
- Procalcitonin/CRP — may help distinguish from pneumonia if clinical uncertainty exists [10]
12. Imaging
- Chest X-ray (first-line in well-resourced settings):
- Normal-sized heart with full pulmonary arteries [2]
- Patchy alveolar infiltrates — confined to right middle and lower lobes in mild cases; bilateral in severe cases [2]
- Central interstitial edema, peribronchial cuffing, ill-defined vessels [11]
- Absence of cardiomegaly, Kerley B-lines, and pleural effusions helps distinguish from cardiogenic edema
- Lung ultrasound (field setting): B-lines are sensitive but nonspecific; no accepted threshold for diagnosis [4]
- CT chest: Generally only warranted when initial evaluation is unrevealing or alternative diagnoses remain high on the differential [4]
- Echocardiography: Not routinely needed; consider if concern for underlying cardiac pathology or pulmonary hypertension [4]
13. Special Tests
- Lake Louise Acute Mountain Sickness Score — useful for diagnosing concurrent AMS (headache + GI symptoms, fatigue, dizziness); does not specifically diagnose HAPE
- Point-of-care ultrasound (POCUS): Lung B-lines for pulmonary edema; cardiac views to assess RV dilation/strain and rule out pericardial effusion
- Portable pulse oximetry — critical field diagnostic tool; SpO₂ at least 10 points below expected for altitude strongly suggests HAPE [6]
14. ECG
- Sinus tachycardia — most common finding [2]
- Right ventricular strain pattern [2]
- Right axis deviation [2]
- Right bundle-branch block [2]
- P-wave abnormalities (P-pulmonale) [2]
- ECG is recommended in well-resourced settings to evaluate for MI and arrhythmia [4]
15. Assessment
HAPE is a life-threatening, noncardiogenic pulmonary edema that occurs in unacclimatized individuals ascending above 2,500–3,000 m. It is the most lethal form of acute altitude illness.
Severity stratification
- Mild: Exertional dyspnea disproportionate to altitude, dry cough, decreased performance; SpO₂ mildly reduced; rales in one lung field
- Moderate: Dyspnea with minimal exertion, bilateral rales, cyanosis
- Severe: Dyspnea at rest, pink frothy sputum, respiratory distress, SpO₂ <50–60%, concurrent neurologic dysfunction (HACE)
Atypical presentations: Some patients present primarily with CNS dysfunction (confusion, drowsiness) due to severe hypoxemia rather than classic respiratory symptoms — particularly those with poor ventilatory response to hypoxia. [6] Concurrent HACE is present in 14% of cases and found in 50% of fatal cases at autopsy. [2]
16. Treatment Plan
Initial stabilization
- Supplemental O₂ (2–4 L/min, titrate to SpO₂ >90%) — highest priority [2][4]
- Minimize patient exertion (exertion worsens pulmonary hypertension) [2]
- Keep patient warm (cold increases pulmonary artery pressure) [2]
Descent
- Descend at least 300–1,000 m (1,000–3,300 ft) while minimizing exertion [7]
- Descent is the definitive treatment in resource-limited settings [4]
Pharmacotherapy
- Nifedipine SR 30 mg q12h — field adjunct when O₂ unavailable or as add-on if O₂ alone insufficient [1][4]
- If nifedipine unavailable: tadalafil or sildenafil (unproven) [7]
- Dexamethasone — add only if concurrent HACE suspected (8 mg load, then 4 mg q6h) [9]
- No diuretics, no acetazolamide, no beta-agonists for HAPE treatment [4]
Well-resourced settings (ED/hospital)
- Supplemental O₂ and bed rest may be sufficient [1][4]
- CPAP can be considered as adjunct [4]
- Nifedipine added if failure to respond to O₂ alone [4]
Field settings (no O₂ available)
- Portable hyperbaric chamber (Gamow bag) [4]
- Nifedipine as primary pharmacotherapy [4]
17. Disposition
Admission criteria
- Severe HAPE (SpO₂ fails to improve to >90% with high-flow O₂ within 5 minutes) [2]
- Concurrent HACE (altered mental status, ataxia) [9]
- Worsening symptoms or oxygenation despite appropriate interventions [4]
- Hemodynamic instability
Discharge criteria
- SpO₂ >90% on supplemental O₂ with stable or improving trajectory [4]
- Adequate support system (family/friends), appropriate lodging, and access to supplemental O₂ [4]
- Mild HAPE at a facility with medical oversight
Observation indications
Specialist consultation triggers
- Failure to improve with O₂ and descent → consider alternative diagnosis
- Concurrent HACE
- Recurrent HAPE episodes → pulmonary/cardiology evaluation for underlying cardiopulmonary abnormalities [2]
18. Follow Up / Return Precautions
- Reascent: Only after symptoms have completely resolved and SpO₂ is stable at rest and with mild exercise off O₂ and vasodilators. Consider nifedipine prophylaxis upon resuming ascent [4]
- Follow-up timing: Within 1–2 weeks if treated and descended; sooner if symptoms recur
- Return precautions — seek immediate care for:
- Worsening dyspnea or cough
- Return of pink/bloody sputum
- Confusion, ataxia, or altered mental status
- Inability to maintain SpO₂ >90%
- Patient counseling:
- HAPE recurrence risk is high with future rapid ascent (up to 60%) [1]
- Future ascents should follow gradual acclimatization schedules
- Carry nifedipine for prophylaxis on future high-altitude trips
- Avoid heavy exertion in the first 1–2 days at altitude
- Expected recovery: with descent and O₂, clinical improvement typically occurs within hours; radiographic clearing within days [2]
References
1. Acute High-Altitude Illnesses. — Bärtsch P, Swenson ER. The New England Journal of Medicine. 2013.
2. High-Altitude Illness. — Hackett PH, Roach RC. The New England Journal of Medicine. 2001.
3. Early Hours in the Development of High-Altitude Pulmonary Edema: Time Course and Mechanisms. — Swenson ER. Journal of Applied Physiology. 2020.
4. Wilderness Medical Society Clinical Practice Guidelines for the Prevention, Diagnosis, and Treatment of Acute Altitude Illness: 2024 Update. — Luks AM, Beidleman BA, Freer L, et al. Wilderness & Environmental Medicine. 2024.
5. High-Altitude Pulmonary Edema: A Collective Review. — Rabold M. The American Journal of Emergency Medicine. 1989.
6. High-Altitude Travel and Altitude Illness. — Peter H. Hackett and David R. Shlim CDC Yellow Book. 2025.
7. Acute Altitude Illness: Updated Prevention and Treatment Guidelines from the Wilderness Medical Society. — American Academy of Family Physicians (2020). 2020.
8. Effects of Acetazolamide on Pulmonary Artery Pressure and Prevention of High-Altitude Pulmonary Edema After Rapid Active Ascent to 4,559 M. — Berger MM, Sareban M, Schiefer LM, et al. Journal of Applied Physiology. 2022.
9. Wilderness Medical Society Clinical Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2019 Update. — Luks AM, Auerbach PS, Freer L, et al. Wilderness & Environmental Medicine. 2019.
10. Differential Diagnosis in Patients With Both Features of Pneumonia and Pulmonary Edema on Chest Computed Tomography. — Lee HJ, Kim M, Seo CO, et al. Medicine. 2025.
11. Clinical and Radiologic Features of Pulmonary Edema. — Gluecker T, Capasso P, Schnyder P, et al. Radiographics : A Review Publication of the Radiological Society of North America, Inc. 1999.