High altitude hypoxia describes a condition resulting from reduced oxygen availability at higher elevations. As altitude increases, atmospheric pressure decreases, leading to a lower partial pressure of oxygen. This condition is a concern for individuals traveling to mountainous areas, as the body may struggle to adapt to the diminished oxygen supply.
How Altitude Affects the Body
As elevation increases, atmospheric pressure declines, reducing the partial pressure of oxygen (PO2) despite air still containing 21% oxygen. This means fewer oxygen molecules enter the lungs with each breath. For example, at 5500 meters, atmospheric pressure is roughly half that at sea level, and the partial pressure of oxygen is significantly lower.
The body responds to this hypoxia with immediate physiological adjustments. Breathing and heart rates increase to compensate for reduced oxygen intake and deliver more oxygen to tissues. Carotid bodies, which detect changes in oxygen levels, stimulate this increased ventilation.
Over several days, the body begins acclimatization, adapting to the lower oxygen environment. This involves physiological changes, such as the kidneys producing more erythropoietin, a hormone that stimulates red blood cell production to enhance oxygen transport. The body also adjusts fluid balance, initially increasing urination, which can lead to dehydration.
Types and Symptoms of Altitude Sickness
Altitude sickness manifests in various forms, from mild to severe. These conditions include Acute Mountain Sickness (AMS), High Altitude Cerebral Edema (HACE), and High Altitude Pulmonary Edema (HAPE).
Acute Mountain Sickness (AMS) is the most common and mildest form of altitude sickness. Symptoms appear within 6 to 24 hours of ascending and can resemble a hangover. Indicators include headache, fatigue, dizziness, nausea, vomiting, or sleep disturbances. These symptoms often resolve within one to three days as the body acclimatizes.
High Altitude Cerebral Edema (HACE) is a severe, life-threatening progression of AMS, where fluid accumulates in the brain. Symptoms include severe headache, confusion, and ataxia (loss of coordination making it difficult to walk in a straight line). Altered mental status, hallucinations, and drowsiness may also occur. HACE can progress to coma if not addressed rapidly.
High Altitude Pulmonary Edema (HAPE) is another severe, life-threatening condition involving fluid buildup in the lungs. Symptoms include shortness of breath (initially with activity, then at rest), a persistent cough that may produce frothy or blood-tinged sputum, and general weakness. Chest tightness and a rapid heart rate may also be present. HAPE can develop with or without AMS symptoms and requires immediate attention due to its rapid progression.
Preventing Altitude Sickness
Preventing altitude sickness involves allowing the body sufficient time to adapt to the reduced oxygen environment. A gradual ascent is the most effective strategy, especially above 8,000 feet (2,500 meters). Experts recommend ascending no more than 984 to 1,640 feet (300 to 500 meters) in sleeping altitude per day once above this elevation. Incorporating rest days every few thousand feet of ascent further aids acclimatization.
Adequate hydration is important, as increased breathing at higher altitudes can lead to greater fluid loss. Consuming plenty of water helps prevent dehydration, which can worsen altitude sickness symptoms. A diet rich in carbohydrates is also suggested, as carbohydrates are a more efficient energy source in low-oxygen conditions.
Avoiding alcohol and sedatives is advisable at high altitudes because these substances can depress respiratory function and hinder acclimatization. For individuals at higher risk or those planning a rapid ascent, a healthcare provider may suggest prophylactic medications like acetazolamide. This medication helps speed up acclimatization by affecting the body’s acid-base balance, encouraging increased breathing.
Managing Altitude Sickness
If altitude sickness symptoms develop, prompt action is important to prevent progression to more severe forms. The most effective treatment for all types of altitude sickness is immediate descent to a lower elevation. A descent of at least 984 to 3,281 feet (300 to 1,000 meters) often leads to rapid improvement in symptoms.
For mild symptoms, such as Acute Mountain Sickness, resting at the same altitude and avoiding further ascent can be sufficient. Hydration and over-the-counter pain relievers like ibuprofen or acetaminophen may help alleviate discomfort. Do not continue ascending until symptoms have completely resolved.
In cases of more severe symptoms, or if symptoms worsen despite rest, seeking medical attention is crucial. Supplemental oxygen can be administered if available, which helps increase oxygen saturation in the blood. Medications like dexamethasone may be used to reduce brain swelling in HACE, and nifedipine can be considered for HAPE. These medications are typically temporary measures to stabilize an individual until safe descent.