High Altitude Pulmonary Edema: Every Mountaineer's Nightmare
A study conducted between 1921 and 2006 by the British Medical Journal, says that out of the 8000+ mountaineers to venture on to Mount Everest, 212 died on the slopes of the great mountain. 17% of these deaths were on the way up, due to the high altitude, which caused pulmonary and cerebral edema. High Altitude Pulmonary Edema (HAPE) is a form of non-cardiogenic pulmonary edema which is life-threatening and occurs in perfectly healthy mountaineers. It is non cardiogenic because fluid accumulates in the lungs. Once a person crosses 2500 meters, he/she is at risk of HAPE. In the absence of adequate emergency medical aide, HAPE has a high mortality rate.
Signs and Symptoms of HAPE:
The symptomatic changes and physiological changes differ depending on the altitude the individual is at. The Lake Louise Consensus Definition for High Altitude Pulmonary Edema sets a widely used basis for HAPE symptoms:
Symptoms: At least two of the following:
- Dyspnea: difficult in breathing while at rest
- Decreased exercise performance and weakness
- Congestion or tightness in the chest
Signs: At least two of the following:
- Crackles or wheezing in at least one lung area
- Central Cyanosis: blue skin color
- Tachypnea: shallow and rapid breathing
- Tachycardia: rapid heartbeat
Intermediate Altitudes: 1500-2500 meters or 4900-8200 feet above sea level
At this height manifestation of clinical symptoms is unlikely and the blood oxygen level remains above 90%.
High Altitude: 2500-3500 meters or 8200-11500 feet above sea level
At this altitude clinical symptoms become common, and manifest after up to 3 days. The level of oxygen in the blood may drop below 90% and lower still during exercise. If prior acclimatization takes place, the symptoms may not be extremely severe, and it's possible to reverse the effect.
Extreme Altitude: an altitude of over 5800 meters or 19000 feet is considered Extreme Altitude
At this height even at rest the blood oxygen level is lower than 90%. And in spite of acclimatization the rate of deterioration is fast.
Causes of High Altitude Pulmonary Edema:
Initially High Altitude Pulmonary Edema is caused by a drop in the level of oxygen which is prevalent at high altitudes due to lower air pressure. All though exactly how low oxygen levels cause HAPE is not understood in entirety, two processes are important:
- An increase in pulmonary arterial and capillary pressures also called pulmonary hypertension which is secondary to Hypoxic Pulmonary Vasoconstriction.
- An idiopathic non-inflammatory increase in the permeability of the vascular endothelium.
Even though the development of HAPE has been associated with increased pulmonary arterial pressures, presence of pulmonary hypertension alone may not be sufficient to explain development of edema. Even in the absence of HAPE, people at high altitude can develop pulmonary hypertension.
In spite of extensive research, individual predisposition to HAPE remains unknown. A previous susceptibility to HAPE is the only reliable risk factor, and it has been postulated that a there is a genetic basis to the condition. Treatment:
The most important course of action in the case of high altitude pulmonary edema is to bring the patient down by at least 1000 meters as quickly as possible. If it is possible to give oxygen to the patient, it must be done. With descent, the severe symptoms improve very rapidly, but there is a chance that the less extreme symptoms stay for several days. Several prescription medications are also available, and are very helpful, but some of these may make the headache due to mountain sickness much worse than it already is. However rapid descent is the best treatment.