High altitude pulmonary edema

High altitude pulmonary edema (HAPE) is a life-threatening form of non-cardiogenic pulmonary edema that occurs in otherwise healthy mountaineers at altitudes above 2,500 meters (8,200 feet). Some cases however have been reported also at lower altitudes (between 1500 and 2500 m in highly vulnerable subjects), although what makes some people susceptible to HAPE is not currently known. HAPE remains the major cause of death related to high altitude exposure with a high mortality in absence of emergency treatment.

Etiology

The initial insult that causes HAPE is a shortage of oxygen which is caused by the lower air pressure at high altitudes. [cite web | author=Kenneth Baillie and Alistair Simpson | title=Barometric pressure calculator | url=http://www.altitude.org/calculators/altitudefacts/altitudefacts.htm | publisher=Apex (Altitude Physiology EXpeditions) | accessdate=2006-08-10 - Online altitude calculator] The mechanisms by which this shortage of oxygen causes HAPE are poorly understood, but two processes are believed to be important:
# Increased pulmonary arterial and capillary pressures (pulmonary hypertension) secondary to hypoxic pulmonary vasoconstriction. [cite journal | author = Bärtsch P, Maggiorini M, Ritter M, Noti C, Vock P, Oelz O | title = Prevention of high-altitude pulmonary edema by nifedipine | journal = N Engl J Med | volume = 325 | issue = 18 | pages = 1284–9 | year = 1991 | month = Oct 31 | pmid = 1922223]
# An idiopathic non-inflammatory increase in the permeability of the vascular endothelium. [cite journal | author = Swenson E, Maggiorini M, Mongovin S, Gibbs J, Greve I, Mairbäurl H, Bärtsch P | title = Pathogenesis of high-altitude pulmonary edema: inflammation is not an etiologic factor | journal = JAMA | volume = 287 | issue = 17 | pages = 2228–35 | year = 2002 | pmid = 11980523 | doi = 10.1001/jama.287.17.2228]

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. [cite journal | author = Maggiorini M, Mélot C, Pierre S, Pfeiffer F, Greve I, Sartori C, Lepori M, Hauser M, Scherrer U, Naeije R | title = High-altitude pulmonary edema is initially caused by an increase in capillary pressure | journal = Circulation | volume = 103 | issue = 16 | pages = 2078–83 | year = 2001 | pmid = 11319198 | url=http://circ.ahajournals.org/cgi/content/full/103/16/2078]

Incidence

The incidence of clinical HAPE in unacclimatized travelers exposed to high altitude (~4,000 m) 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.

Predisposing factors

Individual susceptibility to HAPE is difficult to predict. The most reliable risk factor is previous susceptibility to HAPE, and there is likely to be a genetic basis to this condition, perhaps involving the gene for angiotensin converting enzyme (ACE). Recently, scientists have found the similarities between low amounts of 2,3-BPG with the occurrence of HAPE at high altitudes.

Research

In order to help understand the factors that make some individuals susceptible to HAPE, the International HAPE Database was set up in 2004. [cite web | title=International HAPE database | url=http://www.altitude.org/hape.htm | publisher=Apex (Altitude Physiology EXpeditions) | accessdate=2006-08-10] Individuals who have previously suffered from HAPE can register with this confidential database in order to help researchers study the condition.

Treatment

The standard and most important treatment is to descend to lower altitude as quickly as possible, preferably by at least 1000 metres.cite journal |author=Luks AM |title=Do we have a "best practice" for treating high altitude pulmonary edema? |journal=High Alt. Med. Biol. |volume=9 |issue=2 |pages=111–4 |year=2008 |pmid=18578641 |doi=10.1089/ham.2008.1017 |url=http://dx.doi.org/10.1089/ham.2008.1017 |accessdate=2008-09-04] Oxygen should also be given if possible. Symptoms tend to quickly improve with descent, but less severe symptoms may continue for several days. Drug treatments that may be useful include nifedipine, acetazolamide, dexamethasone, salmeterol and sildenafil (Viagra). [NATO guide to emergency war surgery (3rd), Chapter 29: Environmental Injuries. US Department of Defence 2004.] cite journal |author=Fagenholz PJ, Gutman JA, Murray AF, Harris NS |title=Treatment of high altitude pulmonary edema at 4240 m in Nepal |journal=High Alt. Med. Biol. |volume=8 |issue=2 |pages=139–46 |year=2007 |pmid=17584008 |doi=10.1089/ham.2007.1055 |url=http://dx.doi.org/10.1089/ham.2007.1055 |accessdate=2008-09-04]

References

ee also

*Acetazolamide, a drug which speeds up acclimatization to high altitudes.
*Pulmonary Edema
*Altitude sickness
*High altitude cerebral edema (HACE)
*High altitude flatus expulsion (HAFE)