This is a more serious complication compared to AMS. Young subjects in apparently good health are more affected. It may manifest in newcomers and also in subjects acclimatized to high altitudes, if they ascend the height rapidly after periods of stay at lower altitudes. Altitudes above 2500 m can be harmful, but most of the cases occur at heights of 3050 to 4550 m. Heavy meal, physical exertion and too-rapid an ascent precipitate the condition. Symptoms start within 6 to 48 hours of reaching the station.
Though, pulmonary hypertension is invariably found as a consequence of hypoxia, only a small proportion of subjects develop acute pulmonary edema which tends to be patchy. The reason for the edema is not clear. Autopsy studies have revealed dilatation of pulmonary arteries and arterioles, congestion of capillaries, intravascular thrombi, perivascular hemorrhages, and alveolar edema. Cases of long duration may show hyaline membrane in the alveoli.
Clinical features: Many cases follow acute mountain sickness, but in some, pulmonary edema develops abruptly. Early symptoms are cough, tachypnea, dyspnea and chest pain. These are soon followed by hemoptysis, cyanosis, frothy expectoration, and intense chest discomfort. Oliguria may develop.
The course is variable. In some, the pulmonary edema worsens while in others, it may become subacute and persist for a few days. In severe cases, right sided heart failure may follow and this may precede death. Radiographic abnormalities include prominence of the pulmonary arteries, patchy edema which is more prominent in the upper and mid-zones and more marked on the right side. Electrocardiogram reveals acute right ventricular strain due to pulmonary hypertension.
Diagnosis: High altitude pulmonary edema should be anticipated in healthy subjects who develop vague cerebral and respiratory symptoms on reaching high altitudes. Early recognition and treatment are necessary to avoid rapid deterioration and death. Acute mountain sickness, respiratory infections, Cardiac failure, and malingering have to be differentiated from this condition.
Treatment: The patient should be hospitalized and administered oxygen. If oxygen is not available, the patient should be evacuated to a lower camp. Morphine, 15 mg and furosemide 40 mg should be given intravenously. In the majority of cases, there are enough to tide over an attack. Persistence of pulmonary edema is an indication for repeating furosemide. Physiological venesection by applying tourniquets proximately to the limbs, helps in reducing pulmonary edema. Precipitating factors such as respiratory infection have to be looked for and treated appropriately.
Prevention: proper training and conditioning for 1-2 weeks should be undertaken before reaching high altitudes. On reaching high altitudes all unacclimatized persons should avoid physical exertion for 48-72 hours. Furosemide 40 mg given orally daily for 2-3 days prevents the onset of acute pulmonary edema.
High altitude cerebral edema
This disorder is less common than pulmonary edema. Cerebral edema may follow acute mountain sickness several hours after reaching the high altitude. Pathological lesions consist of dilatation of cerebral vessels, cerebral edema and patchy hemorrhages. Early clinical features consist of lethargy, insomnia, dreamy state and irritability. Severe cases develop intense headache, confusion and coma before reaching the fatal end. Cheyne-stokes respiration may develop.
Treatment: The patient should be administered pure oxygen and evacuated to a lower camp. Dexamethasone given intravenously or intramuscularly in a dose of 4-8 mg gives relief.
Chronic mountain sickness-Monge's disease, chronic soroche, high altitude disease
Some persons living at high altitudes lose their acclimatization and develop symptoms. Most of such reports have come from South America. Males are affected more than females. The mechanism is not fully understood. Features are those of alveolar hypoventilation. Palliative measures are only of temporary benefit. Therefore it is advisable to remove affected individuals to low altitudes. The whole picture reverts tp normal on reaching low altitudes.
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