High-altitude pulmonary edema

High-Altitude Pulmonary Edema (HAPE)
Synonyms	High-Altitude Pulmonary Oedema
Classification and external resources
Specialty	emergency medicine
ICD-10	T70.2
ICD-9-CM	993.2
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High-altitude pulmonary edema (HAPE) (HAPO spelled oedema in British English) is a life-threatening form of non-cardiogenic pulmonary edema (fluid accumulation in the lungs) that occurs in otherwise healthy mountaineers at altitudes typically above 2,500 meters (8,200 ft). However, cases have also been reported at lower altitudes (between 1,500–2,500 metres or 4,900–8,200 feet in highly vulnerable subjects), though what makes some people susceptible to HAPE is currently unknown. HAPE remains the major cause of death related to high-altitude exposure, with a high mortality rate in the absence of adequate emergency treatment.

Physiological and symptomatic changes often vary according to the altitude involved.

The Lake Louise Consensus Definition for High-Altitude Pulmonary Edema has set widely used criteria for defining HAPE symptoms:

Symptoms: at least two of:

Signs: at least two of:

The initial cause of HAPE is a shortage of oxygen caused by the lower air pressure at high altitudes. The mechanisms by which this oxygen shortage causes HAPE are poorly understood, but two processes are believed to be important:

Although higher pulmonary arterial pressures are associated with the development of HAPE, the presence of pulmonary hypertension may not in itself be sufficient to explain the development of edema: severe pulmonary hypertension can exist in the absence of clinical HAPE in subjects at high altitude.

The standard and most important treatment is to descend to lower altitude as quickly as possible, preferably by at least 1000 metres. Oxygen should also be given if possible. Symptoms tend to quickly improve with descent, but more severe symptoms may continue for several days. The standard drug treatments for which there is strong clinical evidence are dexamethasone and nifedipine. Phosphodiesterase inhibitors such as sildenafil and tadalafil are also effective but may worsen the headache of mountain sickness.

The incidence of clinical HAPE in unacclimatized travelers exposed to high altitude (~4,000 m or 13,000 ft) appears to be less than 1%. The U.S. Army Pike's Peak Research Laboratory has exposed sea-level-resident volunteers rapidly and directly to high altitude; during 30 years of research involving about 300 volunteers (and over 100 staff members), only three have been evacuated with suspected HAPE.

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