I. Signs and Symptoms
II. Mechanisms
III.Management
IV. Clinical Study
V. Perspective and Research Implications

• I. SIGNS AND SYMPTOMS
  High-altitude pulmonary edema, severe shortness of breath due to accumulation of fluid in air sacs of the lungs, may occur in young, healthy, susceptible adults who ascend rapidly to altitudes in excess of 2500 m. The first symptom is usually dyspnea on exertion and a reduced exercise tolerance greater than expected for the altitude. A dry and annoying cough later becomes productive with blood¬stained sputum. Symptoms typically occur in the first two to four days after arrival at these high altitudes.
• II. MECHANISMS
  Vasoconstriction of pulmonary vessels causes an increase in both alveolar capillary pressure and vascular fluid shear stress. Flooding of pulmonary capillaries and increased capillary permeability occur. Fluid and inflammatory cells leak into the air sacs that are normally dry. Pulmonary edema is caused by an imbalance between forces that drive water into the air sacs and the physiologic mechanisms that remove it.
• III. MANAGEMENT
  The best strategy to prevent pulmonary edema is to ascend gradually to allow sufficient time for acclimatiza¬tion. Descend to a lower altitude as quickly as possible and administer a high inhaled concentration of oxygen. Simulated descent with a portable hyperbaric chamber can be lifesaving.
• IV. CLINICAL STUDY
  Study question: Beta-adrenergic agonists upregulate the clearance of alveolar fluid and attenuate pulmonary edema in animal models. The study assessed effects of prophy¬lactic inhalation of salmeterol, a beta-agonist, on the incidence of high-altitude pulmonary edema.
• V. PERSPECTIVE AND RESEARCH IMPLICATIONS
  High-altitude pulmonary edema is preventable. Fortu¬nately, very few mountain climbers are susceptible, but those who are may have unpredictable recurrences when they are exposed to high altitudes. The susceptible individual must take prophylaxis including acetazolamide, nifedipine, inhaled salmeterol; ascend slowly; and avoid vigorous exertion. Considerable research is required in this area to further clarify the pathogenesis of high-altitude cerebral edema. This research would help refine more beneficial treatment. Natural products including Ginkgo biloba and garlic may be useful for the amelioration of benign symptoms of high-altitude illness. Drugs including sildenafil, which inhibits hypoxemia-induced pulmonary hypertension, may be useful in the management of high-altitude pulmonary edema and are being studied.
• BIBLIOGRAPHY
  Basnyat, B., and Murdoch, D. R. High altitude illness. Lancet, 361:1967–74, 2003.

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