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High altitude pulmonary edema

Authors
Scott A Gallagher, MD
Peter Hackett, MD
Section Editor
Daniel F Danzl, MD
Deputy Editor
Jonathan Grayzel, MD, FAAEM

INTRODUCTION

Anyone who travels to high altitude, whether a recreational hiker, skier, mountain climber, soldier, or rescue worker, is at risk of developing high altitude illness. High altitude pulmonary edema (HAPE) is a life-threatening form of such illness that involves abnormal accumulation of fluid in the lungs, and in fact is the most common fatal manifestation of severe high altitude illness.

The pathophysiology, clinical presentation, treatment, and prevention of HAPE are reviewed here. Other forms of high altitude illness are discussed separately. (See "Acute mountain sickness and high altitude cerebral edema" and "High altitude illness: Physiology, risk factors, and general prevention" and "High altitude disease: Unique pediatric considerations".)

PATHOPHYSIOLOGY

High altitude pulmonary edema (HAPE) is the abnormal accumulation of plasma and some red cells in the lung due to a breakdown in the pulmonary blood-gas barrier, triggered by hypobaric hypoxia. This breakdown develops from a number of maladaptive responses to the hypoxia encountered at higher altitudes, including poor ventilatory response, increased sympathetic tone, exaggerated and uneven pulmonary vasoconstriction (pulmonary hypertension), inadequate production of endothelial nitric oxide, and overproduction of endothelin, many of which are genetically determined [1-3]. The end result is a patchy accumulation of extravascular fluid in the alveolar spaces that impairs respiration and can, in severe cases, prove fatal.

Genetics clearly play an important role in the risk of HAPE, as suggested by the marked variability in individual susceptibility, the higher rates of recurrence among some individuals, and the pathophysiological factors mentioned above. However, HAPE genetic studies are conflicting and clear conclusions are elusive. Genes associated with HAPE have included those in the pathways for nitric oxide, renin-angiotensin-aldosterone, hypoxia-inducible factor (HIF), heat shock protein (HSP 70), pulmonary surfactant proteins A1 and A2, and aquaporin-5 [4].  

High mean pulmonary artery (PA) pressure, in excess of 35 to 40 mmHg, appears to be the initiating event. Specific segmental and subsegmental capillary beds with relatively less vasoconstriction are disproportionately exposed to elevated microvascular pressures (>20 mmHg) that arise from the elevated mean PA pressure. This uneven vasoconstriction and regional overperfusion result in failure of the alveolar-capillary barrier and patchy pulmonary edema.

                                 

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Literature review current through: Nov 2016. | This topic last updated: Mon Sep 26 00:00:00 GMT+00:00 2016.
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