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High Altitude Sickness What is high altitude sickness? Understanding High Altitude Sickness The ups and downs of mountain travel. Learn about altitude’s effects on the body to combat mountain sickness. High-altitude illness afflicts novices and experienced mountaineers alike. Acute mountain sickness (AMS), high-altitude pulmonary oedema (HAPE), and high-altitude cerebral oedema (HACE), usually occurring above 2,500 meters (8,202 feet), can lead to an epic. As a climber and nurse, I’ve encountered many ill climbers. Understanding altitude illness will reduce your risk of an emergency in the mountains. High altitude starts at 1,500 meters (4,921 feet). At high altitudes, air pressure decreases (hypobaria), resulting in “thinner” air—that is, oxygen molecules spread farther apart. We take in less oxygen when breathing, resulting in less oxygen being absorbed in the lungs and delivered to the body. A low-oxygen state, whether in ambient air or in the body, is called hypoxia. Hypobaric hypoxia causes multiple effects: Heart and respiratory rates increase immediately, improving oxygenation. Muscle fatigue, sleep apnea, changes in metabolism, altered hormone secretion, fluid retention, and swelling of the hands, feet, and face are common. Haemoglobin production and urination increase within two days at altitude as the body adjusts (acclimatises). And weight loss may occur after about a week. Types of High Altitude Sickness. Experiencing some discomfort is normal at altitude, but symptoms may worsen to become an illness. AMS, HAPE, and HACE typically start within 1–5 days of ascent without proper acclimatisation. Contributing factors include living at lower altitudes, rapid ascent, higher sleeping altitude, exertion, possible genetic predisposition, and previous history of altitude illness. (Talk to your healthcare provider before travelling to altitude.) AMS AMS, the most common high altitude sickness, typically begins within 4–12 hours of ascent. Symptoms mimic a hangover, ranging from mild discomfort to debilitating. AMS is diagnosed by the