Traveling to high elevations presents a unique challenge to the human body, but proper preparation can significantly minimize the risks associated with altitude-related illness. High altitude is generally defined as elevations above 8,000 feet (about 2,500 meters), where the air is noticeably thinner. Understanding how the body reacts to less available oxygen and implementing proven acclimatization strategies will greatly reduce the chance of developing acute mountain sickness.
How Altitude Affects the Body
The atmosphere’s oxygen percentage remains constant at about 21% regardless of elevation. However, as altitude increases, the barometric pressure—the weight of the air above—decreases. This drop in pressure means the partial pressure of oxygen (PO2) also decreases, resulting in fewer oxygen molecules being pushed into the lungs with every breath. This state of reduced oxygen availability, known as hypobaric hypoxia, triggers immediate physiological responses. The primary reaction is hyperventilation, where breathing becomes faster and deeper to increase oxygen intake, and the heart rate increases to boost blood flow and oxygen delivery to tissues. These short-term adjustments begin the process of acclimatization.
Long-Term Health and Planning
The most effective strategy against altitude illness is a slow and gradual ascent schedule. Avoid ascending to a sleeping altitude above 9,000 feet (about 2,750 meters) in a single day. Once above 10,000 feet, the sleeping elevation should not increase by more than 1,000 to 1,600 feet (300 to 500 meters) per day.
Allowing rest days is a necessary part of the itinerary, requiring an extra night for acclimatization for every 3,300 feet (1,000 meters) of altitude gain. Even high cardiovascular fitness does not prevent altitude sickness, so all individuals must follow a slow ascent schedule. Pre-existing conditions, particularly heart or lung issues, increase the risk of severe altitude illness, making a consultation with a healthcare provider before the trip necessary.
Consulting a physician can secure a prescription for prophylactic medications like Acetazolamide (Diamox). This medication is often taken the day before ascent and for the first few days at altitude. Acetazolamide speeds up the acclimatization process by encouraging the kidneys to excrete bicarbonate, which helps balance the blood’s pH level. Travelers with a history of altitude illness or those planning a rapid ascent should consider this preventative drug.
Immediate Acclimatization Tactics
Upon arrival at a higher elevation, the first 24 to 48 hours should involve minimal physical exertion. Starting slow allows the body to focus on initiating the acclimatization process rather than recovering from strenuous activity. Avoiding heavy loads or intense hiking immediately after arrival is prudent, even if you feel well.
Maintaining adequate hydration is paramount, as the increased respiratory rate causes greater water loss through breathing. Dehydration is compounded by the kidney’s natural increase in urination during acclimatization. Aiming for three to four liters of water daily can help counteract this fluid loss and prevent symptoms like headache.
Certain substances can interfere with the body’s ability to acclimatize and should be avoided or limited. Alcohol and sedatives can suppress the respiratory drive, particularly during sleep, which is dangerous at altitude. Caffeine and tobacco should also be avoided, as they can exacerbate symptoms or interfere with the body’s natural response to hypoxia. A beneficial strategy is to “climb high and sleep low,” meaning you ascend to a higher point during the day for activity but descend to a lower altitude to sleep.
Recognizing, Managing, and Treating Altitude Sickness
Altitude illness manifests in three forms, beginning with Acute Mountain Sickness (AMS), the most common type. AMS symptoms resemble a bad hangover and include headache, nausea, fatigue, loss of appetite, and disturbed sleep. Mild AMS can often be managed by resting at the current altitude, staying hydrated, and taking over-the-counter pain relievers.
The two severe and life-threatening forms are High Altitude Cerebral Edema (HACE) and High Altitude Pulmonary Edema (HAPE). HACE is a progression of severe AMS involving brain swelling, leading to symptoms like confusion, severe headache, and loss of coordination (ataxia). The inability to walk a straight line is a sign of HACE and constitutes a medical emergency.
HAPE involves fluid accumulation in the lungs and can occur without prior AMS symptoms. Symptoms include a persistent, dry cough that may progress to frothy sputum, severe breathlessness at rest, and chest tightness. For both HACE and HAPE, the most effective treatment is immediate and rapid descent of at least 1,000 to 3,300 feet.
For severe cases, a physician may prescribe Dexamethasone, a steroid that treats brain and lung swelling and is often used alongside descent. Acetazolamide can also be used as an adjunct treatment for AMS and HACE. Any worsening of symptoms while at the same altitude, despite medication, requires immediate descent.