DESCRIPTION

• High-altitude pulmonary edema (HAPE) is a form of noncardiogenic pulmonary edema that occurs after ascending to altitudes >8,000 ft:
  • Usually occurs in young, healthy persons who have quickly ascended to altitude and then engaged in physical exertion before they have become acclimated
  • Can also occur in persons who reside at high altitude and return home after a few days at lower altitude
• Systems affected: Pulmonary
• Synonym(s): Noncardiogenic pulmonary edema

EPIDEMIOLOGY

• Predominant age: Young adults
• Predominant sex: Males > Females
• Children more susceptible
• Upper respiratory tract infection or bronchitis may be precipitating factors.
• Recovery may be slower in the geriatric population

Incidence

Incidence ranges from 1/10,000 Colorado skiers to 1/50 climbers on Mt. McKinley.

Prevalence

In the U.S., occurs in 0.2–15% of the population, depending on factors such as age, sex, and rate of ascent.

RISK FACTORS

• Altitude achieved (increased incidence with higher altitude)
• Rate of ascent (increased incidence associated with more rapid ascents)
• Cold exposure
• Upper respiratory infection may increase risk
• Prior history of HAPE
• Women with low-risk pregnancies should experience no difficulties up to ~10,000 ft.
• Women with high-risk or late-term pregnancies should avoid high altitudes.

Genetics

Unknown

GENERAL PREVENTION

• Rate of ascent and altitude achieved are critical in development of HAPE:
  • Slow rate of ascent
  • Average increase in sleeping altitude 1,000–1,200 ft/day >8,000 ft
  • No ascent to higher altitude with symptoms of acute mountain sickness (AMS)
  • Descent when symptoms of AMS do not improve after a day of rest
• Limit activity for 1st 1–2 days:
  • Vigorous exercise should be avoided until acclimatized to altitude
• Diet high in carbohydrates may be beneficial.
• Avoid alcohol.
• Drink plenty of fluids.

PATHOPHYSIOLOGY

• Pronounced hypoxia-induced patchy pulmonary vasoconstriction may lead to overperfusion of the less obstructed portions of the vascular bed, leading to endothelial injury and pulmonary edema.
• Pulmonary edema is thought to be secondary to increased capillary permeability and increased pulmonary artery pressure without increased pulmonary capillary wedge pressure.

ETIOLOGY

Hypoxia (decreased inspired PO₂) plays a central role.

COMMONLY ASSOCIATED CONDITIONS

• Hypothermia
• Acute mountain sickness
• High-altitude cerebral edema

Outline

• Description
• Epidemiology
  • Incidence
  • Prevalence
• Risk Factors
  • Genetics
• General Prevention
• Pathophysiology
• Etiology
• Commonly Associated Conditions

History

• Symptoms begin within 2–5 days of a rapid ascent.
• Most cases are preceded by symptoms of AMS.
• Early symptoms:
  • Dyspnea
  • Fatigue
  • Decreased exercise tolerance
  • Weakness
  • Dry cough
• Late symptoms:
  • Confusion

Physical Exam

• Tachycardia
• Tachypnea
• Rales
• Pink-tinged frothy sputum
• Cyanosis
• Fever (usually <38.5°C)

DIAGNOSTIC TESTS & INTERPRETATION

Lab

• No specific diagnostic tests; diagnosis is made on clinical grounds.
• EKG:
  • Usually shows sinus tachycardia and may demonstrate RV strain, right-axis deviation, right bundle branch block, and P-wave abnormalities.
• No specific characteristic findings in common laboratory tests
• CBC: Frequent leukocytosis
• ABG: Respiratory alkalosis and low oxygen saturation

Imaging

CXR:

• Normal cardiac size
• Diffuse, peripheral patchy infiltrates, may be unilateral or bilateral
• Becomes more homogeneous in advanced cases and during recovery

Pathological Findings

Lung edema

DIFFERENTIAL DIAGNOSIS

• Viral or bacterial upper respiratory infection
• Pneumonia
• CHF
• Asthma
• Hyperventilation syndrome
• Mucus plugging
• MI
• Pulmonary embolus

Outline

• History
• Physical Exam
• Diagnostic Tests & Interpretation
  • Lab
  • Imaging
  • Pathological Findings
• Differential Diagnosis

• High-flow oxygen to maintain oxygen saturation above 90%
• Nifedipine SR 30 mg every 12–24 hr, only necessary when supplemental oxygen is unavailable and descent is impossible:
  • Contraindications: Refer to manufacturer’s literature.
  • Precautions: Reflex tachycardia, peripheral edema, rare hypotension

ADDITIONAL TREATMENT

General Measures

• Immediate improvement in oxygenation is the treatment of choice:
  • Descent is critical, at least 3,000 ft as soon as possible
  • Supplemental oxygen at 2–6 L/min to keep oxygen saturation above 90%
  • If descent not feasible, use a hyperbaric bag to simulate descent
  • May benefit from continuous positive airway pressure mask if available
• Salmeterol:
  • 125 mg inhaled b.i.d.
  • Good adjunct to nifedipine
  • May increase alveolar fluid clearance

IN-PATIENT CONSIDERATIONS

Admission Criteria

• Required for patients unable to maintain saturations above 90% with supplemental oxygen
• Patients with concomitant high-altitude cerebral edema also should be hospitalized.

Discharge Criteria

• If patient can maintain oxygen saturation above 90%, discharge on home oxygen with next-day follow-up.
• Must have reliable person with them to observe for worsening condition

Outline

• Additional Treatment
  • General Measures
• In-Patient Considerations
  • Admission Criteria
  • Discharge Criteria

FOLLOW-UP RECOMMENDATIONS

Patient Monitoring

Pulse oximetry to monitor arterial oxygen saturation

PATIENT EDUCATION

• Persons with history of HAPE are at increased risk of recurrence.
• Nifedipine 20 mg q8h or 30 mg of sustained release q12–24h in patients with history of HAPE
• Rate of ascent and altitude achieved are critical in development of HAPE:
  • Slow rate of ascent
  • Average increase in sleeping altitude 1,000–1,200 ft/day >8,000 ft
  • No ascent to higher altitude with symptoms of acute mountain sickness (AMS)
  • Descent when symptoms of AMS do not improve after a day of rest
• Limit activity for 1st 1–2 days:
  • Vigorous exercise should be avoided until acclimatized to altitude

PROGNOSIS

• Mild cases show improvement in symptoms within hours and complete recovery within 2–3 days.
• Untreated and unable to descend, mortality rate >50%
• Severe, advanced cases may require prolonged hospital course.

COMPLICATIONS

Death, arrhythmias, cardiac arrest

Outline

• Follow-Up Recommendations
  • Patient Monitoring
• Patient Education
• Prognosis
• Complications

CODES

ICD9

• 411.89 Other acute and subacute forms of ischemic heart disease, other
• 518.4 Acute edema of lung, unspecified
• 993.2 Other and unspecified effects of high altitude

SNOMED

• 233707008 high altitude pulmonary edema (disorder)
• 413439005 acute ischemic heart disease (disorder)

CLINICAL PEARLS

• Persons who ascend quickly to altitudes >8,000 ft, and participate in vigorous exercise before becoming acclimated are at risk of developing HAPE. Other risk factors include a history of prior high-altitude illness and a concurrent upper respiratory tract infection. Physical fitness does not appear to be protective against high-altitude illness.
• The incidence of HAPE can be reduced by reducing the rate of ascent (limiting increases in sleeping altitude to 1,000–1,200 ft/day at altitudes >8,000 ft) and limiting vigorous physical activity for 1–2 days post ascent.
• The key to treating HAPE is in treating the hypoxia that causes the pulmonary vasoconstriction and pulmonary edema. This is best done with supplemental oxygen and/or descent to a lower altitude.

Outline

• Codes
  • ICD9
  • SNOMED
• Clinical Pearls

ADDITIONAL READING

• Hackett PH, Roach RC. High-altitude illness. N Engl J Med. 2001;345:107–114.
• Luks AM, Swenson ER. Medication and dosage considerations in the prophylaxis and treatment of high-altitude illness. Chest. 2008;133:744–755.
• Stream JO, Grissom CK. Update on high-altitude pulmonary edema: Pathogenesis, prevention, and treatment. Wilderness Environ Med. 2008;19:293–303.
• West JB. The physiologic basis of high-altitude diseases. Ann Intern Med. 2004;789–800.

Gerald A. Charlton