From the Guidelines
Mount Everest climbers should undergo proper acclimatization, typically requiring several weeks of gradual ascent, to minimize the risk of altitude sickness, including acute mountain sickness (AMS), high-altitude pulmonary edema (HAPE), and high-altitude cerebral edema (HACE) 1.
Physiological Challenges
At high altitudes, such as Mount Everest, the body experiences hypobaric hypoxia, leading to an increase in respiratory rate and tidal volume, which promotes respiratory alkalosis, hypoxic diuresis, pulmonary vasoconstriction, and ultimately, pulmonary hypertension and pulmonary edema 1.
Adaptation Mechanisms
The body adapts to high altitude by increasing red blood cell production, heart rate, and respiration, but these adaptations have limits 1.
Prevention and Treatment
Medications like acetazolamide (Diamox) at 125-250mg twice daily can help prevent altitude sickness by increasing respiration rate and improving oxygen saturation 1.
- Proper hydration, nutrition, and physical conditioning are also crucial for survival in this extreme environment.
- Supplemental oxygen is typically used above 26,000 feet in the "death zone" 1.
Sex Differences
There may be sex differences in the risk of high-altitude illnesses, with women potentially being more susceptible to high-altitude pulmonary edema due to differences in pulmonary vascular resistance and PAP 1.
Key Recommendations
- Gradual ascent to allow for proper acclimatization
- Use of medications like acetazolamide to prevent altitude sickness
- Supplemental oxygen above 26,000 feet
- Proper hydration, nutrition, and physical conditioning
- Consideration of sex differences in the risk of high-altitude illnesses 1.
From the Research
Physiological Effects of High Altitude
- At high altitudes, such as Mount Everest, the human body is exposed to lower oxygen levels, which can lead to various physiological effects, including acute mountain sickness (AMS) and high-altitude pulmonary edema (HAPE) 2, 3.
- AMS is characterized by symptoms such as nausea, headaches, fatigue, and lightheadedness, while HAPE is a non-cardiogenic edema that can be life-threatening 4, 5.
Prevention and Treatment of Altitude-Related Illnesses
- Slow ascent is considered the most effective preventive measure for AMS and HAPE, as it allows the body to acclimatize to the higher altitude 3, 5.
- Acetazolamide, a carbonic anhydrase inhibitor, is commonly used for the prevention and treatment of AMS, and has been shown to be effective in reducing the incidence and severity of AMS 2, 4.
- Dexamethasone, a glucocorticoid, is also effective in preventing and treating AMS, but its use is limited due to side effects 2, 5.
- Nifedipine, a calcium channel blocker, is effective in preventing HAPE, but not AMS 5, 6.
Acetazolamide and HAPE Prevention
- While acetazolamide has been shown to reduce the incidence of AMS, its effectiveness in preventing HAPE is less clear, with some studies suggesting a reduction in HAPE incidence, but not to a statistically significant extent 6.
- A study found that acetazolamide reduced HAPE incidence by 35%, but this effect was not statistically significant, and was less than reductions achieved with other medications such as dexamethasone, tadalafil, and nifedipine 6.
Recommendations for Rapid Ascent
- For individuals ascending rapidly to high altitudes, such as military or emergency medical personnel, doses of 500-750 mg/day of acetazolamide within 24 hours of altitude exposure may be effective in minimizing symptoms of AMS 4.