What are the physiological effects of high altitude on the human body at Mount Everest?

From the Guidelines

Climbing Mount Everest poses significant physiological challenges, and proper acclimatization, supplemental oxygen, and prophylactic medications like acetazolamide are crucial to prevent high-altitude illnesses and ensure a safe ascent. The extreme altitude of Mount Everest leads to severe hypoxia, with atmospheric oxygen levels dropping to about one-third of sea level, causing the body to respond through acclimatization 1. This response includes increasing respiratory rate and depth, elevating heart rate, producing more red blood cells, and enhancing oxygen-carrying capacity. However, high-altitude retinopathy (HAR) is a common condition that can occur in individuals who ascend beyond 4900 m above sea level, characterized by retinal oedema, haemorrhages, ischaemia, and optic disc swelling 1.

Key factors to consider when climbing Mount Everest include:

• Gradual ascent with rest days at intermediate elevations to allow for proper acclimatization
• Use of supplemental oxygen above 26,000 feet to prevent acute mountain sickness, high-altitude pulmonary edema, and cerebral edema
• Prophylactic medications like acetazolamide at 125-250mg twice daily to increase ventilation and reduce alkalosis 1
• Maintaining hydration and consuming high-calorie foods to support the body's increased energy demands
• Monitoring for symptoms like headache, nausea, and confusion, which can indicate high-altitude illnesses

The extreme cold, wind, and low humidity on Mount Everest also pose risks of frostbite and dehydration, requiring proper protective clothing and equipment. Furthermore, the physiological stress of high-altitude climbing can persist for weeks after descent, with complete recovery of oxygen-carrying capacity taking months. Proper preparation, including acclimatization, supplemental oxygen, and prophylactic medications, is essential to minimize the risks associated with climbing Mount Everest and ensure a safe and successful ascent.

From the Research

Physiological Effects of High Altitude on the Human Body

• At high altitudes, such as Mount Everest, the human body is exposed to lower oxygen levels, which can lead to a range of physiological effects, including acute mountain sickness (AMS) 2, 3, 4, 5, 6
• AMS can cause symptoms such as nausea, headaches, fatigue, and lightheadedness, and can be severe enough to require medical attention 2, 3, 5

Prevention and Treatment of Acute Mountain Sickness

• Acetazolamide is a commonly used medication for the prevention and treatment of AMS, and has been shown to be effective in reducing the incidence and severity of symptoms 2, 3, 4, 5, 6
• The optimal dosage of acetazolamide for prevention and treatment of AMS is still a topic of debate, but doses of 500-750 mg/day have been shown to be effective in minimizing symptoms 2
• Other medications, such as dexamethasone, have also been shown to be effective in treating AMS, but may have side effects that limit their use for prophylaxis 3, 5

Timing of Acetazolamide Pre-Treatment

• Pre-treatment with acetazolamide on the day before ascending to high altitude has been shown to reduce the incidence of AMS, but may not provide optimal protection until the second day of exposure 4
• Starting pre-treatment with acetazolamide at least two days before arrival at high altitude may be more effective in preventing AMS 4

Importance of Gradual Ascent and Descent

• Gradual ascent and descent are important for allowing the body to acclimatize to high altitudes and reducing the risk of AMS 6
• Resting at high altitude can also help to reduce the risk of AMS, but may not be as effective as gradual ascent and descent 6