Understanding Altitude Sickness: Types, Signs, Treatment, and Prevention
A Comprehensive Guide to Recognizing, Managing, and Preventing High-Altitude Health Risks
When thinking about altitude sickness, it’s common to think of symptoms that are similar to being dehydrated (headache, dryness, dizziness), or having the flu (stomach problems and vomiting). What many don’t realize is that altitude sickness can actually be a life threatening illness, causing fluid buildup in parts of the body that can impair cognitive abilities (such as hallucinations and cause intense aggression) as well as impacting lung capacity, requiring immediate medical attention.
By definition, altitude sickness, also known as acute mountain sickness (AMS), occurs when you ascend to high altitudes too quickly, and your body struggles to acclimate to the reduced oxygen levels. It can affect anyone, regardless of age or fitness level. Understanding its types, symptoms, treatments, and prevention strategies can help ensure a safer adventure in the mountains.
Why does this happen?
Altitude sickness results from the body's inability to quickly adapt to lower oxygen availability in the environment. When oxygen levels drop, your body works harder to produce more red blood cells to move oxygen throughout the rest of the body to compensate. This is an adaptive response due to erythropotein secretions in the kidneys (from lack of oxygen in the tissues ) that act on the liver to increase erythrocyte (red blood cell) production.
First, your breathing speeds up, as the lack of oxygen is picked up by peripheral chemoreceptors, which causes the adverse effect of alkalosis due to increasing the rate by which carbon dioxide is removed from the body. This inhibits the respiratory system from enhancing the respiratory rate to meet the oxygen demands.
Then, the peripheral chemoreceptors cause sympathetic nervous system stimulation, which causes the heart rate to increase while stroke volume (the amount of blood ejecting from the heart’s left ventricle) decreases, and digestion is impaired. Shortness of breath is common, and urination increases.
The primary factor is the rate of the ascent and the altitude reached, not just physical fitness. Even highly trained athletes or healthy individuals can experience symptoms if they ascend too quickly or do not give their body enough time to acclimate.
As they say when climbing Kilimanjaro, “Pole, pole!” (slowly, slowly).
Types of Altitude Sickness
Acute Mountain Sickness (AMS):
The most common form, usually occurring above 8,000 feet (2,500 meters). Symptoms are mild but can worsen if untreated.High-Altitude Pulmonary Edema (HAPE):
A severe condition where fluid accumulates in the lungs, impairing breathing. Typically occurs above 9,000 feet (2,700 meters).High-Altitude Cerebral Edema (HACE):
The most serious form, involving swelling of the brain. It can develop rapidly and is life-threatening, often above 12,000 feet (3,700 meters).
Signs and Symptoms
For AMS (Acute Mountain Sickness):
Headache
Fatigue or weakness
Dizziness or lightheadedness
Nausea and vomiting
Loss of appetite
Sleep disturbances
For HAPE (High-Altitude Pulmonary Edema):
Persistent cough (often dry)
Shortness of breath even at rest
Chest tightness or congestion
Blueish lips or fingertips
An alpinist and ski mountaineer shared their experience with HAPE at 16,200 feet in Nepal, describing the terrifying feeling of “gurgling lungs.” HAPE may be fatal within a few hours if left untreated.
For HACE (High-Altitude Cerebral Edema):
Severe headache that does not respond to usual pain relief
Confusion or disorientation
Changes in behavior and demeanor (aggression, depression, elation)
Loss of coordination or balance (ataxia)
Drowsiness or lethargy
Feeling “very drunk,” as some have reported
Slurred speech
Visual disturbances or hallucinations
Weakness or numbness
While many HACE survivors recover within days or weeks, research indicates that HACE can leave lasting effects on the brain. Studies presented at the RSNA congress in Chicago found:
Brain microhemorrhages (microbleeds) were found almost exclusively in HACE survivors.
These microbleeds were primarily located in the corpus callosum.
More severe HACE cases correlated with more prominent microhemorrhages on MRI scans.
These microhemorrhages remained detectable years after the HACE incident.
It’s common for guides to put a hiker on a leash if they start experiencing more serious symptoms. HACE has been known to cause hikers to blackout and walk off cliffs. It can be extremely dangerous not only for the individual experiencing the illness, but difficult for those around them to keep them safe. All the more reason to never hike big mountains alone or without telling anyone where you are.
Treatment Options
For Mild AMS:
Rest and avoid further ascent
Hydrate well
Take over-the-counter pain relievers for headaches
Consider descent if symptoms worsen
For Severe Conditions (HAPE & HACE):
Immediate descent to lower altitude
Oxygen therapy if available
Medications such as dexamethasone (for HACE) or nifedipine (for HAPE)
Seek emergency medical care promptly
In all cases, stopping further ascent and giving the body time to acclimate are critical.
Preventative Measures
Gradual Ascent — “Climb High, Sleep Low”
In high-altitude mountaineering, the recommended daily altitude gain is typically limited to 300-500 meters (~1,000-1,600 feet) per night once above 2,500 meters (8,200 feet). Above 4,500 meters (14,764 feet), even more conservative rates of ascent are recommended, with extra rest days for every 1,000 meters gained. The "climb high, sleep low" strategy is crucial, where climbers ascend during the day but descend to a lower altitude to sleep.Pre-Acclimatization:
Spend extra days at intermediate elevations before reaching higher altitudes.Stay Hydrated:
Drinking plenty of fluids will help fight off altitude sickness symptoms and counteract the additional depletion of fluids from frequent urination. While climbing the Machame Route on Kilimanjaro, our guides insisted that we consume at least 3L of fluids daily.Medications:
Consider medications like acetazolamide (Diamox) as prophylaxis under medical supervision if you're at high risk.Watch for Symptoms:
Monitor yourself and your companions for early signs, and don't ignore symptoms. If you have a Garmin or smart watch, keep an eye on your blood oxygen levels and heart rate while ascending.
The time it takes for your body to fully adapt to altitude can be approximated by multiplying the altitude in kilometers by 11.4 days. For example, to fully adapt to 4,000 meters (13,000 ft.) of altitude would require 45.6 days of living at that altitude. Obviously climbing most mountain peaks, you operate under a more condensed timeframe to acclimatize and such lengthy time spent at altitude isn’t a requirement for reaching a high summit; it only will help reduce your chances of developing altitude sickness.
After high-altitude exposure, the increase in red blood cells in the body can last for weeks after, which can make high altitude training even more effective when returning to and operating at lower altitudes.
Safe travels and happy hiking!
