High-Altitude Pulmonary Edema
High-Altitude Pulmonary Edema (HAPE)
High-Altitude Pulmonary Edema is a non-cardiogenic pulmonary edema that occurs in susceptible individuals after rapid ascent to high altitude, usually >2,500–3,000 m. It is one of the most serious forms of high-altitude illness and can rapidly become fatal if untreated.
1. Definition
HAPE is acute pulmonary edema caused by hypoxia-induced pulmonary hypertension and capillary leak at high altitude, occurring in individuals without primary cardiac disease.
2. Typical Altitude Risk
| Altitude | Risk |
|---|---|
| <2500 m | Rare |
| 2500–3000 m | Possible |
| >3000 m | Common in susceptible individuals |
| >4500 m | High risk |
Common locations:
- Mount Everest
- Ladakh
- Andes Mountains
- Himalayas
Pathophysiology (Key Exam Concept)
Hypoxia triggers uneven pulmonary vasoconstriction, leading to pulmonary hypertension and capillary stress failure.
Mechanism sequence
- Hypoxia at altitude
- Hypoxic pulmonary vasoconstriction
- Marked pulmonary artery pressure rise
- Regional over-perfusion of some capillaries
- Capillary stress failure → leak
- Protein-rich pulmonary edema
Important characteristics:
- Non-inflammatory
- Normal LV function
- Patchy edema
Hemodynamic Findings
| Parameter | Finding |
|---|---|
| Pulmonary artery pressure | Markedly elevated |
| Pulmonary capillary wedge pressure | Normal |
| Cardiac function | Normal |
| Edema fluid | Protein rich |
Risk Factors
Major risk factors:
• Rapid ascent
• Strenuous exercise
• Previous HAPE episode
• Cold exposure
• Male sex
• Young age
Medical predispositions:
- Pulmonary hypertension susceptibility
- Patent foramen ovale
- Reduced nitric oxide production
Clinical Features
Symptoms usually develop 2–5 days after ascent.
Early symptoms
- Reduced exercise tolerance
- Dyspnea on exertion
- Dry cough
- Fatigue
Progressive symptoms
- Dyspnea at rest
- Tachycardia
- Tachypnea
- Productive cough (pink frothy sputum)
Severe signs
- Cyanosis
- Altered mental status
- Severe hypoxemia
Physical Examination
Typical findings:
- Crackles (initially right middle lobe)
- Tachycardia
- Tachypnea
- Low oxygen saturation
- Mild fever
Imaging
Chest X-ray
Features:
- Patchy alveolar infiltrates
- Often perihilar
- Normal heart size
- Asymmetric edema
CT findings
- Ground glass opacities
- Patchy consolidation
Diagnostic Criteria (Lake Louise HAPE Score)
Diagnosis requires:
Symptoms
- Dyspnea at rest
- Cough
- Weakness
PLUS
Signs
- Crackles
- Central cyanosis
- Tachypnea
- Tachycardia
Management (Emergency)
1. Immediate descent (MOST IMPORTANT)
Descending 500–1000 m often improves symptoms rapidly.
2. Oxygen therapy
Target:
SpO₂ > 90%
3. Pharmacologic therapy
| Drug | Mechanism |
|---|---|
| Nifedipine | Pulmonary vasodilation |
| Tadalafil | PDE-5 inhibitor |
| Sildenafil | ↓ pulmonary pressure |
| Dexamethasone | Adjunct |
Preferred drug
Nifedipine SR 30 mg every 12 hr
4. Portable hyperbaric chamber
Used when descent is not possible.
Example:
- Gamow Bag portable altitude chamber
Prevention
Gradual ascent (most effective)
Rule:
Do not increase sleeping altitude >500 m/day above 3000 m
Add rest day every 3–4 days.
Drug prophylaxis for high-risk individuals
| Drug | Dose |
|---|---|
| Nifedipine SR | 30 mg BD |
| Tadalafil | 10 mg BD |
| Sildenafil | 50 mg TDS |
Important Differentials
| Condition | Key difference |
|---|---|
| Cardiogenic pulmonary edema | Elevated PCWP |
| Pneumonia | Fever, consolidation |
| Pulmonary embolism | Acute pleuritic pain |
10 NEET-SS Exam Pearls
- HAPE is non-cardiogenic pulmonary edema.
- Occurs >2500–3000 m altitude.
- Hypoxic pulmonary vasoconstriction is the primary trigger.
- Pulmonary capillary wedge pressure is normal.
- Chest X-ray shows patchy asymmetric infiltrates with normal heart size.
- Symptoms appear 2–5 days after ascent.
- Immediate descent is the most effective treatment.
- Nifedipine is the first-line drug.
- Oxygen therapy rapidly improves symptoms.
- Prior HAPE episode is the strongest risk factor.
1. Primary mechanism responsible for High-Altitude Pulmonary Edema is:
A. Hypoxia induced LV failure
B. Uneven hypoxic pulmonary vasoconstriction causing capillary stress failure
C. Cytokine mediated alveolitis
D. Autoimmune endothelial injury
Hypoxia causes heterogeneous pulmonary vasoconstriction → regional over-perfusion → capillary stress failure → protein-rich edema.
2. Pulmonary capillary wedge pressure in HAPE is typically:
A. >25 mmHg
B. Normal
C. Mildly elevated
D. Equal to pulmonary artery pressure
HAPE is a non-cardiogenic pulmonary edema; PCWP remains normal.
3. Earliest physiological abnormality in individuals predisposed to HAPE:
A. Exaggerated hypoxic pulmonary vasoconstriction
B. Decreased pulmonary vascular resistance
C. Hypercapnia
D. Left ventricular dysfunction
HAPE-susceptible individuals demonstrate markedly exaggerated pulmonary vasoconstriction when exposed to hypoxia.
4. Typical time of onset after ascent:
A. Within 6 hours
B. 12 hours
C. 2–5 days
D. 10 days
Symptoms usually appear after 2–5 days at altitude.
5. Drug of choice for pharmacologic prevention in HAPE-susceptible individuals:
A. Nifedipine
B. Acetazolamide
C. Dexamethasone
D. Furosemide
Nifedipine reduces pulmonary artery pressure and prevents HAPE.
6. Earliest symptom of developing HAPE:
A. Dyspnea on exertion
B. Orthopnea
C. Hemoptysis
D. Syncope
Reduced exercise tolerance and exertional dyspnea are earliest.
7. Most characteristic chest X-ray feature:
A. Patchy alveolar infiltrates with normal cardiac size
B. Kerley B lines
C. Cardiomegaly
D. Pleural effusion dominant
Radiology shows patchy asymmetric infiltrates without cardiomegaly.
8. Most important immediate treatment:
A. Rapid descent
B. Diuretics
C. Steroids
D. Antibiotics
Descent is the most effective life-saving intervention.
9. Genetic factor implicated in HAPE susceptibility:
A. Reduced nitric oxide synthesis
B. Excess prostacyclin
C. Increased surfactant
D. Elevated renin
Lower nitric oxide production contributes to excessive pulmonary vasoconstriction.
10. Portable treatment device used when descent is impossible:
A. CPAP chamber
B. Portable hyperbaric bag
C. Nitric oxide mask
D. ECMO capsule
Portable hyperbaric bags simulate descent by increasing ambient pressure.
High-Altitude Illness Rapid Revision
HAPE vs HACE vs AMS (NEET-SS Favorite Table)
| Feature | AMS (Acute Mountain Sickness) | HACE (High-Altitude Cerebral Edema) | HAPE (High-Altitude Pulmonary Edema) |
|---|---|---|---|
| Primary organ involved | Brain (mild cerebral edema) | Brain (severe vasogenic edema) | Lungs (non-cardiogenic pulmonary edema) |
| Altitude threshold | >2500 m | Usually >3500–4000 m | >3000 m |
| Onset after ascent | 6–24 hours | Usually 1–5 days | 2–5 days |
| Pathophysiology | Hypoxia → mild cerebral edema | Hypoxia → blood–brain barrier breakdown → vasogenic edema | Uneven hypoxic pulmonary vasoconstriction → pulmonary hypertension → capillary leak |
| Pulmonary artery pressure | Normal | Normal | Markedly elevated |
| PCWP | Normal | Normal | Normal (non-cardiogenic) |
| Key early symptom | Headache | Severe headache + ataxia | Dyspnea on exertion |
| Major symptoms | Headache, nausea, fatigue, dizziness | Ataxia, confusion, altered consciousness | Dyspnea, cough, exercise intolerance |
| Neurologic signs | None or mild | Ataxia (hallmark), confusion, coma | Usually absent |
| Respiratory signs | Normal lungs | Normal lungs | Crackles, tachypnea, hypoxemia |
| Chest X-ray | Normal | Normal | Patchy infiltrates with normal heart size |
| MRI brain | Usually normal | White-matter vasogenic edema | Not applicable |
| ABG | Mild hypoxemia | Moderate hypoxemia | Severe hypoxemia |
| Most important treatment | Rest ± acetazolamide | Immediate descent + dexamethasone | Immediate descent + oxygen |
| Drug of choice | Acetazolamide | Dexamethasone | Nifedipine |
| Portable chamber | Occasionally used | Often used | Often used |
| Mortality risk | Very low | High if untreated | High if untreated |
| Progression relationship | May precede HACE | Severe progression of AMS | Usually independent |
Key Exam Traps (NEET-SS)
1️⃣ Hallmark of HACE:
👉 Ataxia
2️⃣ Hallmark of HAPE:
👉 Dyspnea with crackles + normal PCWP
3️⃣ Drug prophylaxis differences
| Condition | Drug |
|---|---|
| AMS | Acetazolamide |
| HACE | Dexamethasone |
| HAPE | Nifedipine / Sildenafil |
Rapid Mnemonic
“HEAD–BRAIN–LUNG”
| Disease | Key Feature |
|---|---|
| AMS | Headache |
| HACE | Brain dysfunction (ataxia) |
| HAPE | Lung edema |
5 Super-High-Yield SS Pearls
1️⃣ Ataxia = HACE until proven otherwise.
2️⃣ Normal PCWP distinguishes HAPE from cardiogenic edema.
3️⃣ AMS can progress to HACE but rarely to HAPE.
4️⃣ HAPE chest X-ray shows patchy asymmetric infiltrates.
5️⃣ Immediate descent is the most important treatment in all three.
