From the Guidelines
The recommended time frame for acclimatization to high altitude is generally 1-3 days for each 1,000 meters (3,300 feet) gained above 2,500 meters (8,200 feet). For optimal acclimatization, a gradual ascent is crucial, with experts suggesting the "climb high, sleep low" approach where you ascend slowly during the day but return to a lower elevation to sleep 1. If traveling to elevations above 3,000 meters (9,800 feet), plan to spend at least 24-48 hours at an intermediate altitude before going higher.
Key Considerations
- A slow ascent is effective and is the first-line preventive measure for high-altitude pulmonary edema (HAPE) 1.
- The incidence of HAPE increases with rapid ascent to altitudes above 2500 m, with an estimated incidence among visitors at 2 Colorado ski areas at 2500 to 3000 m between ≈0.1% and 0.01% 1.
- Medications like acetazolamide (Diamox) at 125-250mg twice daily, started 1-2 days before ascent and continued for 2-3 days at high altitude, can help speed acclimatization.
- Proper hydration, avoiding alcohol, and moderate physical activity during the first 48 hours also support the body's adaptation process.
Physiological Adjustments
- The body needs time to make physiological adjustments including increased breathing rate, production of more red blood cells, and changes in acid-base balance to compensate for the lower oxygen levels at altitude.
- These adjustments are critical to preventing altitude-related illnesses, such as HAPE and acute mountain sickness.
Prevention and Treatment
- Slow ascent is the most effective way to prevent HAPE, and medications like nifedipine, PDE5 inhibitors, and dexamethasone may be used as alternatives or in addition to slow ascent 1.
- Immediate descent to lower altitude and administration of supplemental O2 are the primary therapies for adults and children with HAPE 1.
From the Research
Acclimatization to High Altitude
The time frame for acclimatization to high altitude varies depending on several factors, including the altitude, individual susceptibility, and rate of ascent.
- At altitudes above 1,500 meters, sea level natives may develop acute mountain sickness (AMS), which can include symptoms such as nausea, headaches, fatigue, and lightheadedness 2.
- The risk of high-altitude-related illnesses, including AMS, high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE), increases with higher altitudes and faster rates of ascent 3, 4.
- To minimize the risk of AMS, it is recommended to ascend gradually, with a maximum increase in altitude of 500 meters per day 4.
- Acetazolamide, a carbonic anhydrase inhibitor, is a commonly used medication for the prevention and treatment of AMS, with doses of 500-750 mg/day appearing to be the most effective for minimizing symptoms during rapid ascents to altitudes above 3,500 meters 2.
Recommended Time Frame for Acclimatization
- The recommended time frame for acclimatization to high altitude is not strictly defined, but it is generally recommended to spend at least 2-3 days at an intermediate altitude (2,000-3,000 meters) before ascending to higher altitudes 3.
- Individual susceptibility to high-altitude-related illnesses can only be recognized in persons who have traveled to high altitudes in the past, and medical advice should be based on an assessment of the risk of illness in relation to the intended altitude profile of the trip 3.
- Slow ascent, rest, and hydration are also important factors in preventing AMS, and descent to a lower altitude is the most effective treatment for severe AMS 4.