Altitude sickness kills campers every year. It's not an exotic mountaineering problem — it affects hikers and campers at elevations as low as 8,000 feet, which is the elevation of countless popular campgrounds in the Rockies, Sierra Nevada, and Cascades. This guide covers what happens to your body at altitude, how to recognize the three forms of altitude illness, and the protocols that prevent and treat them.
Important disclaimer: This guide is educational, not medical advice. Altitude illness can be fatal within hours. If you or someone in your group shows severe symptoms, descend immediately and seek emergency medical care.
At sea level, the partial pressure of oxygen (PaO2) in arterial blood is about 95-100 mmHg. At 8,000 feet, it drops to roughly 60 mmHg. At 12,000 feet, it's about 50 mmHg. Your body's oxygen saturation (SpO2) — normally 96-100% at sea level — drops to 88-92% at 8,000 feet for an unacclimatized person.
This isn't a small drop. Your brain and muscles are suddenly operating on 15-25% less oxygen than they're used to. The body compensates by increasing breathing rate (the hypoxic ventilatory response) and heart rate, and over days to weeks, by producing more red blood cells (erythropoiesis). But those adaptations take time, and going too high too fast is what triggers altitude illness.
| Condition | Onset Altitude | Key Symptoms | Time of Onset | Mortality if Untreated | Treatment |
|---|---|---|---|---|---|
| Acute Mountain Sickness (AMS) | 8,000+ ft (most common 10,000+) | Headache (throbbing, worse at night/bending over), nausea, fatigue, dizziness, poor sleep, loss of appetite | 6-12 hours after ascent | Low (but can progress to HAPE/HACE) | Stop ascent, rest, hydrate, descend if worsening; acetazolamide (Diamox) for symptom relief |
| High Altitude Pulmonary Edema (HAPE) | 10,000+ ft (rare below) | Extreme shortness of breath at rest, cough (initially dry, then pink frothy sputum), chest tightness, gurgling breath sounds, blue lips/nail beds | 2-4 days after ascent | ~50% without descent | IMMEDIATE descent (minimum 1,000-3,000 ft); oxygen if available; nifedipine; portable hyperbaric chamber (Gamow bag) |
| High Altitude Cerebral Edema (HACE) | 12,000+ ft (can occur lower) | Severe headache unresponsive to painkillers, confusion, loss of coordination (ataxia — cannot walk heel-to-toe), hallucinations, coma | 2-5 days after ascent | Very high without descent | IMMEDIATE descent (minimum 2,000-4,000 ft); dexamethasone; oxygen; Gamow bag; death can occur within hours |
AMS: Hypoxia (low oxygen) triggers increased cerebral blood flow as the brain tries to maintain oxygen delivery. This increases intracranial pressure, causing the hallmark headache. The exact mechanism of nausea isn't fully understood but is likely related to brainstem effects and gastrointestinal changes from hypoxia.
HAPE: Pulmonary artery pressure rises in response to hypoxia (hypoxic pulmonary vasoconstriction), but in HAPE, the response is exaggerated and uneven. Some lung capillaries constrict too much while others are over-perfused, causing capillary stress failure — essentially, the capillary walls leak fluid into the alveoli (air sacs), filling them with fluid. This is pulmonary edema — your lungs are drowning from the inside.
HACE: The same mechanism as AMS pushed to the extreme. Cerebral blood flow and capillary permeability increase to the point where the brain swells with fluid (vasogenic edema), compressing the brainstem against the skull. Coordination fails first (cerebellar ataxia) because the cerebellum is particularly sensitive to pressure.
Critical point: HAPE and HACE can occur together, and both can develop from untreated AMS. They are not separate diseases — they're points on a spectrum of hypoxic organ injury.
The single most effective prevention strategy is the "climb high, sleep low" method, derived from high-altitude mountaineering and validated by decades of use:
This protocol isn't always practical for weekend campers who drive from sea level to a 10,000-foot trailhead in 4 hours. If that's your situation, spend a night at an intermediate elevation (5,000-7,000 feet) if possible. Denver (5,280 ft) or Salt Lake City (4,226 ft) make good staging points before heading into the high country.
Acetazolamide (brand name Diamox) is a carbonic anhydrase inhibitor that acidifies the blood, which stimulates breathing (increases the hypoxic ventilatory response) and speeds acclimatization. It's FDA-approved for prevention and treatment of AMS.
Prophylactic dose: 125 mg twice daily, starting 24 hours before ascent and continuing for 48 hours after reaching maximum altitude. The 250 mg dose is also used but has more side effects with marginal additional benefit.
Side effects: Tingling in fingers/toes/lips (paresthesia — harmless but common), increased urination (it's a diuretic), and carbonated beverages tasting "flat" or metallic. It's a sulfa drug — allergic to sulfa antibiotics = contraindicated.
Important: Diamox is prescription-only in the US. You'll need to see a doctor or travel clinic before your trip. It does not eliminate the need for proper acclimatization — it helps, but it won't save you from ascending recklessly.
For altitude camping, having a Diamox prescription on hand even if you don't take it prophylactically is worth considering — it can be taken at first symptom onset of AMS to prevent progression. A pulse oximeter (available on Amazon for ~$20) lets you track SpO2 objectively; sustained readings below 80% at rest warrant serious attention.
If HAPE or HACE is suspected, there is exactly one priority: get the person to lower elevation as fast as possible. Everything else is secondary.
Fitness does not protect against altitude sickness. In fact, highly fit individuals may be at higher risk because they tend to ascend faster (feeling strong) and ignore early symptoms. Previous altitude illness is the strongest predictor — if you've had AMS or HAPE before, you are likely to get it again at similar altitude and ascent rate. Age is not protective; young adults get AMS at slightly higher rates than older adults, possibly for the same reason (faster ascent, ignoring symptoms).
If you're camping at altitude, also check your weather forecast — barometric pressure drops with storms, effectively increasing physiological altitude. A camp at 10,000 feet during a low-pressure storm system can feel like 11,500 feet.
Related: Best Camping Mess Kits
Medical Disclaimer: This article provides educational information based on current high-altitude medicine guidelines (Wilderness Medical Society, UIAA), not personal medical advice. Altitude illness can be fatal. Consult a physician before using prescription medications at altitude. If you suspect HAPE or HACE, descend immediately and seek emergency care.
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