The Everest Base Camp Medical Centre cautions against its routine use as a substitute for a reasonable ascent schedule, except where rapid ascent is forced by flying into high altitude locations or due to terrain considerations. The Centre suggests a dosage of 125 mg twice daily for prophylaxis, starting from 24 hours before ascending until a few days at the highest altitude or on descending; with 250 mg twice daily recommended for treatment of AMS. The Centers for Disease Control and Prevention (CDC) suggest the same dose for prevention of 125 mg acetazolamide every 12 hours. Acetazolamide, a mild diuretic, works by stimulating the kidneys to secrete more bicarbonate in the urine, thereby acidifying the blood. This change in pH stimulates the respiratory center to increase the depth and frequency of respiration, thus speeding the natural acclimatization process. An undesirable side-effect of acetazolamide is a reduction in aerobic endurance performance. Other minor side effects include a tingle-sensation in hands and feet. Although a sulfonamide; acetazolamide is a non-antibiotic and has not been shown to cause life-threatening allergic cross-reactivity in those with a self-reported sulfonamide allergy. Dosage of 1000 mg/day will produce a 25% decrease in performance, on top of the reduction due to high-altitude exposure. The CDC advises that Dexamethasone be reserved for treatment of severe AMS and HACE during descents, and notes that Nifedipine may prevent HAPE.There is insufficient evidence to determine the safety of sumatriptan and if it may help prevent altitude sickness.
While AMS and HACE occurs equally frequently in males and females, HAPE occurs more often in males. The earliest description of altitude sickness is attributed to a Chinese text from around 30 BCE which describes "Big Headache Mountains", possibly referring to the Karakoram Mountains around Kilik Pass. Signs and symptoms
People have different susceptibilities to altitude sickness; for some otherwise healthy people, acute altitude sickness can begin to appear at around 2,000 metres (6,600 ft) above sea level, such as at many mountain ski resorts, equivalent to a pressure of 80 kilopascals (0.79 atm). This is the most frequent type of altitude sickness encountered. Symptoms often manifest within ten hours of ascent and generally subside within two days, though they occasionally develop into the more serious conditions. Symptoms include headache, confusion, fatigue, stomach illness, dizziness, and sleep disturbance. Exertion may aggravate the symptoms.Those individuals with the lowest initial partial pressure of end-tidal pCO2 (the lowest concentration of carbon dioxide at the end of the respiratory cycle, a measure of a higher alveolar ventilation) and corresponding high oxygen saturation levels tend to have a lower incidence of acute mountain sickness than those with high end-tidal pCO2 and low oxygen saturation levels. Primary symptoms
Headaches are the primary symptom used to diagnose altitude sickness, although a headache is also a symptom of dehydration.