High altitude pulmonary edema

Background

• Also known as HAPE
• Noncardiogenic pulmonary edema due to increased microvascular pressure in the pulmonary circulation
  • Hypoxic pulmonary vasoconstriction leads to pulmonary hypertension
• Most lethal of the altitude illnesses
• Occurs in <1/10,000 skiers in Colorado; 2-3% of Mt. McKinley climbers
• Typical patient is strong and fit; may not have symptoms of altered mental status before onset of HAPE
• Most commonly noticed on the second night at a new altitude

Risk Factors

• Heavy exertion
• Rapid ascent
• Cold
• Excessive salt ingestion
• Use of a sleeping medication
• Preexisting pulmonary hypertension
• Preexisting respiratory infection (children)
• Previous history of HAPE

Clinical Features

• Early
  • Dry cough, decreased exercise performance, dyspnea on exertion, localized rales
  • Resting SaO2 is very low for the expected altitude but patients often appear clinically better than their saturation (aids in diagnosis)
  • Easily desaturates with exertion
• Late
  • Dyspnea at rest, marked weakness, productive cough, cyanosis, generalized rales
  • Cough generates pink, frothy sputum
  • Tachycardia and tachypnea correlate with severity of illness
  • Altered mental status and coma (from severe hypoxemia)

Differential Diagnosis

• Asthma
• Bronchitis
• CHF
• COPD
• MI

High Altitude Illnesses

• Acute mountain sickness
• Chronic mountain sickness
• High altitude cerebral edema
• High altitude pulmonary edema
• High altitude peripheral edema
• High altitude retinopathy
• High altitude pharyngitis and bronchitis
• Ultraviolet keratitis

Pulmonary Edema Types

Pulmonary capillary wedge pressure <18 mmHg differentiates noncardiogenic from cardiogenic pulmonary edema

• Cardiogenic pulmonary edema
• Noncardiogenic pulmonary edema
  • Negative pressure pulmonary edema
    • Upper airway obstruction
    • Reexpansion pulmonary edema
    • Strangulation
  • Neurogenic causes
    • Seizure
    • Head trauma
    • Subarachnoid hemorrhage
    • Electrocution
  • Iatrogenic fluid overload
    • Multiple blood transfusions
    • IV fluid
    • Inhalation injury
    • Pulmonary contusion
    • Aspiration pneumonia and pneumonitis
  • Other
    • High altitude pulmonary edema
    • Hypertensive emergency
    • ARDS
    • Flash pulmonary edema
    • Immersion pulmonary edema
    • Hantavirus pulmonary syndrome
    • Missed dialysis in kidney failure
    • Naloxone reversal

Evaluation

Chest x-ray of HAPE showing characteristic patchy alveolar infiltrates with right middle lobe predominance.

Workup

• ECG - right strain pattern
• CXR - Progresses from interstitial → localized-alveolar → generalized-alveolar infiltrates
• ABG - Hypoxemia with respiratory alkalosis

Evaluation

• Clinical diagnosis

Expected SpO₂ and PaO₂ levels at altitude

Altitude	SpO2	PaO2 (mm Hg)
1,500 to 3,500 m (4,900 to 11,500 ft)	about 90%	55-75
3,500 to 5,500 m (11,500 to 18,000 ft)	75-85%	40-60
5,500 to 8,850 m (18,000 to 29,000 ft)	58-75%	28-40

Management

High altitude management algorithm.

• Immediate descent is treatment of choice - minimize exertion
• If cannot descend use combination of:
  • Supplemental O2 - An oxygen concentrator is often used at high altitude ski resorts after the patient is titrated down to nasal cannula. A portable oxygen tank is used for ambulation. Can completely resolve the pulmonary edema within 36-72hr
  • Hyperbaric bag - (e.g. Gamow Bag). Should not delay descent, if possible.
  • Keep patient warm (cold stress elevates pulmonary artery pressure)
  • Use expiratory positive airway pressure mask
  • Nifedipine 30mg ER q12hr (or 20mg normal-release q8hr)
    • May consider the other medications listed below that are usually used for prevention

Disposition

• Admission
  • Warranted for severe illness that does not respond immediately to descent
• Discharge
  • Progressive clinical and X-ray improvement and a PaO2 of 60mmHg or SaO2>90%
• May re-ascend in 2-3 days if mild-moderate symptoms resolved that only required descent as the intervention

Prevention

• Nifedipine 20mg q8hr or 30mg ER q12hr while ascending is effective prophylaxis in patients with prior episodes of HAPE
• Tadalafil 10mg BID 24hr prior to ascent OR Sildenafil 50mg q8hr
• Salmeterol 125 mcg inhaled BID
• Acetazolamide 125mg BID for prevention of hypoxia

See Also

• High Altitude Medicine