General Consideration:
Acute high altitude illnesses are a spectrum of clinical syndromes occurring in non-acclimatized individuals traveling to altitudes greater than 8000 feet. The incidence and severity of illness increases with higher altitudes and rapid rates of ascent. The illnesses can be categorized as following:
a. Acute mountain sickness (AMS):
b. High altitude pulmonary edema (HAPE):
c. High altitude cerebral edema:(HACE)
The symptoms of high altitude illness start with in two to eight hours of ascent; This is important in our increasingly mobile society, in which a sea level resident may fly to a high altitude destination with in a few hours.
The partial pressure of oxygen decreases in the air as one ascends higher and higher. At high altitudes there is also temperature declines below freezing point and requirement of oxygen increases to keep the body at normal body temperatures.
Pathophysiology:
In a non-acclimatized person the partial pressure of oxygen in the blood decreases, if he reaches high altitudes suddenly, resulting in hypoxemia that consequently leads to an increased respiratory rate. This results in hypocapnia ( ed partial pressure of carbon dioxide in blood) and respiratory alkalosis. The heart rate increases with ascent to high altitudes and cardiac output is initially increased. Sinus tachycardia and sinus arrhythmia, premature atrial and ventricular beats can occur. These changes can be reverted to normal on descent from high altitudes. Hypoxia produces vasodilatation in the cerebral vasculature of the brain and hypocarbia (low concentration of carbon dioxide in the blood) induces vasoconstriction. The overall effect of these changes is believed to cause an increased cerebral blood volume and a variable increase in cerebral blood flow. Exercise tolerance is reduced at high altitudes and vigorous exercise clearly worsens resting hypoxemia.
Acclimatization begins after approximately 24 to 36 hours, when renal compensation for respiratory alkalosis cause a bicarbonate diuresis ( ed excretion of bicarbonate ions in the urine) and restoration of a more physiological pH reverses the symptoms.
Acute mountain sickness:
The symptoms usually occur within the first several hours of ascent and reach a peak at thirty-six hours, then gradually resolve over the next one t o two days. Symptoms usually occur at more than 8,000 to 10,000 feet. Symptoms include fatigue, dizziness, irritability, headache, vomiting, palpitations, and poor sleep.
High altitude pulmonary edema (HAPE):
It may occur, when an un-acclimatized person ascends more than 80000 feet. The symptoms of pulmonary edema are usually observed after approximately 48 to 96 hours after ascend. On physical examination, the person may be cyanotic (blue coloration of skin) and crepitations (crackling sounds heard by stethoscope on respiration) are heard on auscultation (hearing through stethoscope). Chest X-ray confirms the pulmonary edema.
High altitude cerebral edema (HACE):
It is defined as a progressive neurological syndrome occurring in patients with acute mountain sickness or high altitude pulmonary edema at elevations more than 12000 to 15000 feet. Symptoms are lack of concentration and coordination, headache, ataxia (uncoordinated gait), retinal hemorrhages (rupture of blood vessels in the retinal layer of eye). These symptoms are due to increased intracranial pressure eventually leading to coma and death.
Treatment:
Treatment of high altitude illness includes the following:
- Rapid descent.
- Oxygen therapy
- Hyper-baric (closed pressurized chamber) units.
Prevention:
- Proper acclimatization.
- Avoidance of rapid ascent.
- Prophylactic administration of tablet diamox (acetazolamide).
- Avoidance of alcohol and over exertion.
- Plenty of fluids
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