Preparation for travel to high elevations is possible and often determines the success and safety of a trip. High altitude is generally defined as elevations above 8,000 feet (about 2,438 meters), where the environment presents a significant challenge to the human body. The fundamental issue is not a change in the percentage of oxygen in the air, which remains constant at about 21%, but rather the substantial drop in atmospheric pressure. This lower pressure means that each breath delivers fewer oxygen molecules to the lungs and blood, leading to oxygen deprivation known as hypoxia. Effective preparation focuses on strategies to mitigate this reduced oxygen availability and accelerate the body’s natural acclimatization process.
Understanding Altitude Illness
The body’s inability to adapt quickly enough to the low-oxygen environment results in acute altitude illness. This illness is categorized into three main syndromes of varying severity: Acute Mountain Sickness (AMS), High Altitude Cerebral Edema (HACE), and High Altitude Pulmonary Edema (HAPE). The underlying cause for all three is hypobaric hypoxia, which triggers a maladaptive response in some individuals.
Acute Mountain Sickness is the most common and mildest form, comparable to a severe hangover, and typically resolves with rest at the same elevation. HACE represents the most severe progression of AMS, involving brain tissue swelling that can be fatal if not immediately treated. HAPE is a distinct, potentially deadly condition characterized by fluid accumulation in the lungs, which severely impairs oxygen exchange.
Pre-Trip Medical and Physical Preparation
Preparation begins weeks or months before traveling, focusing on optimizing health and securing preventative measures. Consulting a physician is advisable, particularly for individuals with pre-existing heart or lung conditions, as altitude can aggravate these issues. A medical professional can assess individual risk factors, such as a prior history of altitude sickness or living at a low elevation.
The most common pharmaceutical preparation involves the prescription drug acetazolamide (Diamox). This medication works by promoting a mild metabolic acidosis, which stimulates the respiratory drive, causing faster and deeper breathing. This accelerated ventilation increases the amount of oxygen in the blood, speeding up the body’s natural acclimatization process. The drug is generally started 24 hours before ascent and continued for the first few days at altitude.
For those unable to take acetazolamide, the steroid dexamethasone can be prescribed, though it is typically reserved for shorter trips or for treatment due to potential side effects. General physical fitness is beneficial for the exertion of a high-altitude trip but does not directly prevent altitude sickness, as susceptibility is genetic. Some travelers may pursue simulated altitude training, such as sleeping in a hypoxic tent, to pre-acclimatize, though this method is often expensive and less accessible.
Essential Strategies for Safe Ascent
The most effective prevention strategy is a controlled, gradual ascent that allows the body sufficient time to acclimatize naturally. This requires careful planning to limit the daily increase in sleeping elevation. Above 10,000 feet (about 3,048 meters), the sleeping elevation should not increase by more than 1,000 to 1,600 feet (300 to 500 meters) per day.
A rest day, where travelers remain at the same altitude, should be incorporated every three to four days of ascent. Following the “climb high, sleep low” principle is also recommended: hike to a higher elevation during the day but descend to sleep at a lower altitude. This practice stimulates acclimatization while allowing rest in a more oxygen-rich environment overnight.
Hydration is a major factor, as the dry air at high altitudes leads to increased fluid loss through breathing. Travelers should drink a significantly increased volume of water, ensuring their urine output remains copious and clear. It is important to avoid depressants like alcohol and certain sleeping pills during the initial days, as these can suppress breathing and worsen the effects of hypoxia.
Identifying and Managing Symptoms
Recognizing the early signs of altitude illness is important for safety, as mild symptoms can progress quickly. Acute Mountain Sickness typically presents as a headache combined with one or more other symptoms, such as nausea, dizziness, fatigue, or difficulty sleeping. If these mild symptoms occur, the immediate action is to stop ascending and rest at the current elevation. Symptoms should resolve within 24 to 48 hours, and ascent can only be continued once the person is completely symptom-free.
The more dangerous forms, HACE and HAPE, require an immediate response because they are life-threatening. Warning signs for HACE include a severe headache unresponsive to medication, confusion, or a loss of coordination (ataxia), which can be tested by attempting to walk a straight line heel-to-toe. Symptoms of HAPE include severe shortness of breath even while resting, a persistent cough that may produce white, watery, or frothy fluid, and chest tightness.
In the event of HACE or HAPE symptoms, the most important action is immediate descent to a lower altitude. A minimum descent of 1,000 to 3,000 feet (300 to 1,000 meters) is generally necessary, and the affected person should exert themselves as little as possible during the evacuation. Supplemental oxygen and specific medications like dexamethasone for HACE or nifedipine for HAPE can be used if available, but they are temporary measures to stabilize the patient until descent is achieved.