Which is a feature of high altitude pulmonary edema?
High altitude pulmonary edema: High altitude pulmonary edema (HAPE) and High Altitude Cerebral Edema are most ominous forms of High altitude illness. Usually develops within the first 2-5 days after acute exposure to altitudes above 2500-3000 metres. It occurs in both unacclamatized and acclamatized inividual who ascends to high altitude from low. An excessive rise in pulmonary aery pressure preceding oedema formation is the crucial pathophysiological factor. Milder forms are; Acute mountain sickness Retinal hemorrhages Peripheral 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). Predisposing factors: HAPE is seen in unacclamatized healthy persons. Acclamatized high altitude natives may also develop this syndrome upon return to high altitudes after a relatively brief visit at low altitudes. HAPE generally occurs 1-4 days after rapid ascent to altitudes. This is common under the age of 25 years. HAPE is rare in infants and small children. Cold weather and physical exeion at high altitude are other predisposing factors. Pathogenesis: HAPE belongs to a spectrum of High altitude illness. The initial insult that causes HAPE is excessive hypoxia caused by the lower air pressure at high altitudes. The mechanisms by which this shoage of oxygen causes HAPE are poorly understood, but two processes are believed to be impoant: Increased pulmonary aerial and capillary pressures (pulmonary hypeension) secondary to hypoxic pulmonary vasoconstriction. An idiopathic non-inflammatory increase in the permeability of the vascular endothelium. Clinical features: HAPE presents within 2-5 days of arrival at high altitude Early symptoms of HAPE include exeional dyspnoea, cough and reduced exercise performance. As pulmonary oedema progresses, cough worsens and breathlessness at rest and sometimes ohopnoea occur. Gurgling in the chest and pink frothy sputum indicate advanced cases. The clinical features are cyanosis, tachypnoea,tachycardia and elevated body temperature. Investigations: Chest radiographs and computed,tomographic scans of early HAPE show a patchy,peripheral distribution of edema. Prevention and treatment: Slow ascent is the most effective method of prevention, can often be prevented by use of dexamethasone, calcium channel blocking drugs, or long acting inhaled beta-2 adrenergic agonists. Treatment includes Descent from altitude, Bed rest Oxygen Inhaled nitric oxide Nifidipine. Ref: Harrison's Principles of internal medicine, 17th Edition, Page 1707 ; Ganong, Review of medical physiology, 22nd Edition, Page 685
Associated with low cardiac output
Associated with pulmonary hypeension
Occurs only in unacclamatized persons
Exercise has no effect