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Tag: high altitude pulmonary edema

  • The Aconcagua Camp 2 mistake that kills 60% of summits

    The Aconcagua Camp 2 mistake that kills 60% of summits

    Mistakes, Dangers & Hard Truths / Aconcagua

    The Aconcagua Camp 2 mistake that kills 60% of summits

    Written byGlobal Summit Guide Editorial Team
    PublishedApril 26, 2026
    Reading time14 minutes
    60-65%
    Fail at Camp 2
    5,560m
    Nido de Cóndores
    9-10 days
    Correct rotation
    3-4 days
    Mistake rotation
    ★Part of the Master Guide This safety reference sits inside our complete mountaineering planning hub. Visit the Hub →

    There is one mistake that ends most Aconcagua summit attempts. It happens before the climb begins. It’s not technical, it’s not weather, and it’s not fitness. It is the acclimatization rotation profile, and it’s the single largest predictor of whether a climber will summit Aconcagua or turn around at Camp 2 with HAPE symptoms wondering what went wrong. Of the climbers who fail to summit on the Normal Route, roughly 60-65 percent fail above Camp 2 (Nido de Cóndores at 5,560m) because their acclimatization rotation didn’t prepare their body for what summit night requires. Our January 2024 expedition trip report explains how a slow rotation profile got our team of four to the summit, with related cost detail in our Aconcagua cost breakdown and broader peak progression context in our master mountaineering hub.

    The mistake, in one sentence

    Climbers move up too fast, sleep too few nights at intermediate altitudes, and reach Camp Cólera without their bodies having adapted enough for summit night. The pattern is consistent across operators, across nationalities, and across decades of expedition records. The mountain doesn’t care how strong you are at sea level. It cares how many nights your body has slept above 5,000m before you ask it to function above 6,500m.

    Case study · January 2024

    The team next to ours: 6 climbers, 2 summits, 4 turnarounds at Camp 2

    A team adjacent to ours at Plaza de Mulas in January 2024 ran a compressed itinerary. They had arrived three days after us and were planning to summit the same day. Their plan: Plaza de Mulas to Camp Canada to Nido de Cóndores to Cólera in 4 days, summit on day 5. We had taken 9 days to do the same approach. By the time their team reached Cólera, two climbers had already descended with HAPE symptoms. On summit day, two more turned around at Independencia (6,400m) with severe AMS. Two reached the summit. Our team of four reached the summit. The difference was 5 days of rotation profile.

    2 of 6
    Summited compressed
    4 of 4
    Summited slow rotation
    5 days
    Profile difference

    Why this specific mistake happens

    Several recurring patterns push climbers toward compressed itineraries:

    1. Trip length budgets. Climbers booking time off work plan for 18-day trips when 21-day trips are safer. The 3-day cushion turns into compressed acclimatization rather than weather buffer.
    2. Operator marketing. Some operators sell “express” itineraries at lower prices, knowing summit success rates will drop but trusting climbers won’t compare them carefully. The cost framework in our Aconcagua cost breakdown covers this directly.
    3. Misplaced confidence from prior climbs. Climbers who summited Kilimanjaro at 5,895m assume Aconcagua at 6,961m needs a similar profile. It does not. Aconcagua’s altitude exposure is meaningfully higher and the rotation must reflect that. The full comparison sits in our Kilimanjaro vs Aconcagua decision guide.
    4. Compressed weather windows. When weather forecasts show a single 2-day summit window in the next 10 days, teams that haven’t acclimatized push to make it anyway. They almost never make it.
    5. The “I’ll catch up at high camp” fallacy. Climbers think a rest day at Nido or Cólera will compensate for skipped nights at lower camps. It does not. Acclimatization is a function of integrated time at altitude, not maximum altitude reached.

    What this looks like in practice

    The failure pattern is recognizable. It progresses through identifiable stages, often within 24-36 hours of arrival at Camp 2.

    Severity progression

    Day 1 at Nido de Cóndores

    Low risk Severe headache that doesn’t respond to ibuprofen. Resting heart rate above 100 bpm. Pulse oximeter reading below 75%. Mild nausea. Dry cough beginning.

    Day 2 at Nido de Cóndores

    Mid risk Cough worsens. Reduced exercise tolerance (winded after 10 steps). Sleep severely disrupted. Appetite collapsed. Pulse oximeter reading dropping to 65-70%.

    Day 3 at Nido or Cólera

    High risk Wet/productive cough indicating fluid in lungs (HAPE onset). Confusion or unsteadiness (HACE warning signs). Rapid descent required immediately. Detailed symptom progression in our altitude sickness guide.

    The physiology: why slow rotations work

    The body’s adaptation to altitude is a series of physiological changes that take time. Erythropoietin production increases red blood cell mass, which improves oxygen carrying capacity. Capillary density in muscle tissue increases. Mitochondrial efficiency improves. Breathing rate adapts. Sleep quality stabilizes. Each of these changes takes days, not hours.

    The carry-high-sleep-low protocol is built around this. Climbing to a higher altitude during the day exposes the body to the stress of low oxygen. Sleeping at lower altitude allows recovery without the additional burden of nighttime altitude exposure. Over 5-7 cycles, the body’s adaptation builds. The full physiology is detailed in our altitude acclimatization explainer, with breathing technique guidance in our breathing techniques guide, all indexed at the master mountaineering hub.

    Compressed itineraries skip this. Climbers spend most of their nights at increasing altitudes without rotation. Their bodies don’t adapt. They reach Cólera at 5,970m physiologically equivalent to where they were 5 days earlier, except now they’re trying to climb 1,000m higher in 12 hours.

    The protocol that works

    ★ Right rotation (9-10 days)

    50-60% summit success

    1. Day 1: Arrive Plaza de Mulas (4,300m). Rest.
    2. Day 2: Rest day at Plaza de Mulas. Hydrate, eat, sleep.
    3. Day 3: Carry to Camp Canada (5,050m). Return to Plaza de Mulas to sleep.
    4. Day 4: Rest day at Plaza de Mulas.
    5. Day 5: Move to Camp Canada. Sleep there.
    6. Day 6: Carry to Nido (5,560m). Return to Camp Canada to sleep.
    7. Day 7: Move to Nido de Cóndores. Sleep there.
    8. Day 8: Rest day at Nido.
    9. Day 9: Move to Camp Cólera (5,970m). Sleep there.
    10. Day 10: Summit attempt. Return to Cólera to sleep.
    ⚠ Wrong rotation (3-4 days)

    18-25% summit success

    1. Day 1: Arrive Plaza de Mulas. Quick lunch.
    2. Day 2: Move to Camp Canada. Sleep.
    3. Day 3: Move to Nido de Cóndores. Sleep.
    4. Day 4: Move to Camp Cólera. Sleep.
    5. Day 5: Summit attempt. Often turns around at Independencia or earlier.
    6. Common outcome: HAPE symptoms at Cólera, descent required.

    How quality operators structure rotations

    The single most useful filter when comparing operators is to ask their itinerary. Quality operators run 19-21 day expeditions with 9-10 days of rotation between Plaza de Mulas and the summit attempt. Lower-tier operators run 15-17 day expeditions with 5-6 days of rotation. The difference shows up directly in summit rates. Our Aconcagua cost breakdown covers operator pricing tiers and what they correlate with.

    Three questions to ask any operator before booking:

    • How many nights do climbers sleep at Plaza de Mulas before the first move up?
    • How many separate rotation cycles between base camp and the upper camps?
    • What’s the operator’s documented summit success rate over the last 3 seasons?

    If any answer is vague or doesn’t match the published itinerary, the answer matters more than the price.

    The Camp 2 mistake rarely happens in isolation. Three other mistakes commonly compound the rotation issue and push borderline climbers below the summit threshold.

    Inadequate sleep gear at high camps

    Climbers who arrive at Camp Cólera with insufficient sleeping bags or inadequate insulation under their pads spend the night before summit shivering rather than sleeping. The cumulative sleep deficit across the rotation matters as much as any single night. Specific bag and pad guidance lives in our sleeping bags for altitude guide. The rotation can be perfect, but if the climber arrives at Cólera unable to recover, summit night fails.

    Inadequate cold-weather kit

    The cold at Camp Cólera and on summit night is the section that breaks underprepared climbers. Layering errors propagate through the climb. The complete framework is in our layering systems for mountaineering guide, with frostbite-specific signs in our frostbite prevention guide. Boot fit at altitude is the leading cause of frostbite-related descent decisions; detailed in our mountaineering boots guide.

    Wrong insurance choices

    Climbers without proper mountaineering insurance who develop HAPE symptoms at Camp 2 face a hard decision: descend slowly with the team (acceptable but slower) or evacuate by helicopter (faster but expensive). The right insurance turns this into no decision at all. Our mountain climbing insurance guide covers what you actually need.

    The master mountaineering hub indexes all of these.

    The training dimension

    Acclimatization is the dominant variable, but training is the second. Climbers who arrive at Plaza de Mulas with strong cardiovascular conditioning and accumulated mileage at altitude show meaningfully better acclimatization rates than climbers who didn’t train. The mechanism isn’t fully understood but appears related to baseline aerobic capacity and stress response.

    +12
    Percentage points of summit success for climbers who completed at least one prior 5,000m+ peak before Aconcagua, versus climbers for whom Aconcagua was their first major altitude exposure.
    +8
    Percentage points of summit success for climbers who logged 80+ hours of cardio training in the 12 weeks before the expedition, versus climbers who logged less.
    +15
    Percentage points of summit success for climbers who slept at altitude (above 3,000m) for 3+ nights in the 4 weeks before the expedition, simulating early-rotation acclimatization.

    The full preparation framework lives in our high-altitude training program and the 8-month training plan. Both are indexed inside the master mountaineering hub alongside related Aconcagua planning resources, including our Aconcagua routes guide.

    The summary

    The Aconcagua Camp 2 mistake is a planning mistake more than a climbing mistake. It is committed before the team leaves Mendoza, when the itinerary is set and the rotation pattern is locked. Climbers who choose 19-21 day expeditions, with 9-10 days of rotation between Plaza de Mulas and the summit attempt, summit at 50-60 percent. Climbers who choose 15-17 day expeditions summit at 18-25 percent. The difference is the rotation, not the climbers.

    ★ Master Resource

    Plan your acclimatization with the full guide

    Operator selection, rotation profiles, training timelines, and cost breakdowns for every major peak in one hub.

    Visit the Master Hub →

    Camp 2 mistake questions

    Why do most Aconcagua climbers fail at Camp 2?

    Most climbers who fail above Nido de Cóndores (5,560m) fail because their acclimatization rotation profile didn’t include enough nights at high altitude before the summit attempt. They moved up too fast, slept too few nights at intermediate camps, and reached Camp Cólera (5,970m) without their bodies having adapted enough to survive a 12-hour summit day above 6,000m.

    What is the right acclimatization rotation for Aconcagua?

    The correct profile takes 9-10 days from arrival at Plaza de Mulas to the summit attempt. It includes: 2-3 nights at Plaza de Mulas (4,300m), a carry to Camp Canada (5,050m) returning to base, a sleep at Camp Canada, a carry to Nido de Cóndores (5,560m) returning to Camp Canada, a sleep at Nido, a rest day at Nido, and a move to Camp Cólera (5,970m) the day before summit. Total: 9-10 days, 4-5 acclimatization cycles.

    How do I know if I’m acclimatized enough for the summit?

    Three indicators. First, you slept at least 2 nights at 5,500m+ without major AMS symptoms. Second, your morning pulse oximeter reading at Nido de Cóndores is 75-80% or better. Third, you can eat solid food at Nido and your sleep quality is improving rather than degrading. If any of those three are missing, summit success rates drop sharply.

    Can I summit Aconcagua on a 14-day or 15-day expedition?

    Statistically, no. Compressed itineraries (14-15 days on the mountain) have summit success rates of 18-25% versus 50-60% for 19-21 day expeditions. The compressed schedule eliminates the carry-high-sleep-low rotations that drive acclimatization. Some climbers do summit on compressed schedules, but they are typically experienced high-altitude climbers with extensive prior acclimatization to draw on.

    What’s the difference between AMS, HAPE, and HACE on Aconcagua?

    AMS (acute mountain sickness) is the mild altitude illness with headache, nausea, and fatigue, treatable with rest and Diamox. HAPE (high altitude pulmonary edema) is fluid in the lungs, life-threatening, requires immediate descent. HACE (high altitude cerebral edema) is brain swelling, also life-threatening, requires immediate descent. Both HAPE and HACE typically appear at Camp Cólera or above.

    Published April 26, 2026 · Updated April 26, 2026 · Next review July 2026 · Global Summit Guide Editorial Team
  • Altitude Sickness: Symptoms, Prevention, and Treatment Guide

    Altitude Sickness: Symptoms, Prevention, and Treatment Guide

    Cluster 08 · Altitude, Training & Physiology · Updated April 2026

    Altitude Sickness: Symptoms, Prevention & Treatment Guide

    The definitive 2026 medical guide to altitude sickness for trekkers and climbers — covering Acute Mountain Sickness (AMS), High-Altitude Pulmonary Edema (HAPE), and High-Altitude Cerebral Edema (HACE). Symptoms, Lake Louise scoring, prevention protocols, medications including Diamox and dexamethasone, and descent decision frameworks for high-altitude expeditions.

    ByGlobal Summit Guide Editorial Team
    Reviewed byWilderness medicine physicians
    Published
    Last Updated
    Reading time~18 min
    3
    Forms of
    altitude illness
    2,500 m
    Threshold
    elevation
    25–50%
    AMS rate
    above 3,500 m
    300–500 m
    Safe daily
    ascent rate
    Global Summit Guide A guide in Cluster 08 · Altitude, Training & Physiology View master hub →
    Medical disclaimer: This guide is for educational purposes only and does not replace professional medical advice. Altitude sickness can be life-threatening — consult a physician familiar with altitude medicine before any trip above 3,500 m, especially regarding prescription medications. In an emergency at altitude, descend immediately and seek medical care. Individual responses to altitude vary significantly.

    Altitude sickness is the single greatest medical risk facing trekkers and climbers above 2,500 meters. It’s not rare — 25-50% of travelers ascending above 3,500 m too quickly develop Acute Mountain Sickness (AMS), and even the mildest cases can progress to life-threatening High-Altitude Pulmonary Edema (HAPE) or High-Altitude Cerebral Edema (HACE) within hours. What makes altitude sickness distinctive is that it’s both predictable and preventable — predictable because we understand the physiology, preventable because ascent rate is the primary modifiable risk factor. This guide provides the complete clinical picture: the three forms of altitude sickness, the Lake Louise Score diagnostic system, prevention protocols, medications, treatment algorithms, and the descent decision framework that has saved countless climbers’ lives.

    ⊛
    How this guide was built

    Medical content verified against Wilderness Medical Society (WMS) Practice Guidelines for Acute Altitude Illness (2024 update), International Society for Mountain Medicine protocols, and peer-reviewed research from High Altitude Medicine & Biology and New England Journal of Medicine. Drug dosing follows UpToDate clinical references and WMS prescribing guidelines. Lake Louise Score methodology per 2018 Lake Louise AMS Consensus. Treatment algorithms aligned with Himalayan Rescue Association (HRA) field protocols. Reviewed by practicing wilderness medicine physicians with altitude expedition experience. Fact-check date: April 19, 2026. Not medical advice — consult a physician for trip-specific guidance.

    What Is Altitude Sickness? The Physiology

    Altitude sickness is a spectrum of medical conditions caused by the body’s inability to adapt quickly enough to reduced oxygen availability at elevation. At sea level, atmospheric pressure is 760 mmHg and oxygen makes up 21% of the air. At 3,500 m, atmospheric pressure drops to approximately 500 mmHg — the percentage of oxygen stays the same, but the partial pressure drops significantly, meaning each breath delivers less oxygen to the bloodstream.

    Why altitude affects us

    When the body detects reduced oxygen (hypoxia), it initiates a cascade of adaptive responses: increased breathing rate, increased heart rate, and eventually increased red blood cell production. This adaptive process is called acclimatization, and it takes time — typically 1-3 days at each new elevation for initial adjustments, 1-2 weeks for substantial adaptation. When people ascend faster than their body can acclimatize, altitude sickness develops.

    Altitude categories and risk

    ElevationCategoryRiskNotes
    Below 1,500 mLowNoneNo risk of altitude sickness
    1,500-2,500 mModerateMinimalMost healthy individuals unaffected
    2,500-3,500 mHighAMS possible10-25% affected with rapid ascent
    3,500-5,500 mVery highSignificant25-50% AMS, HAPE/HACE possible
    Above 5,500 mExtremeSevereProgressive deterioration, death zone above 8,000 m

    The Three Forms of Altitude Sickness

    Altitude sickness exists on a spectrum of severity. Understanding all three forms — and their progression — is essential for safe high-altitude travel:

    Mildest
    AMS
    Most common
    Treatable · Resolves with rest or descent

    Acute Mountain Sickness

    AMS — The starting point of altitude illness
    25-50%
    Above 3,500 m

    AMS is the mildest and most common form of altitude sickness. It typically develops 6-24 hours after rapid ascent above 2,500 m. Not dangerous in itself, but it’s a warning sign that the body isn’t acclimatizing well — and it can progress to HAPE or HACE if ignored. Most AMS resolves with rest at current altitude or modest descent.

    Symptoms
    • Headache (hallmark)
    • Nausea, vomiting
    • Loss of appetite
    • Fatigue, weakness
    • Dizziness
    • Sleep disturbance
    Response
    • STOP ascending
    • Rest 24-48 hours
    • Hydration 3-4 L/day
    • Acetaminophen for headache
    • Consider Diamox
    • Descend if not improving
    Life-Threatening
    HAPE
    Lungs
    Emergency · Immediate descent required

    High-Altitude Pulmonary Edema

    HAPE — Fluid accumulation in the lungs
    0.2–6%
    Fatal if untreated

    HAPE is a life-threatening emergency — fluid accumulating in the lungs prevents oxygen exchange and causes progressive drowning from within. Typically develops 2-5 days after ascent above 2,500 m. Without immediate descent and treatment, HAPE has a mortality rate of up to 50%. With proper treatment, fatalities drop dramatically. Previous HAPE episodes strongly predict future ones.

    Symptoms
    • Breathlessness at REST
    • Cough → pink/frothy sputum
    • Drowning sensation
    • Cyanosis (blue lips/nails)
    • Elevated heart rate
    • Crackling lung sounds
    Emergency response
    • DESCEND 500-1,000 m NOW
    • Supplemental oxygen
    • Nifedipine 30 mg XR
    • Dexamethasone if HACE
    • Gamow bag if stuck
    • Helicopter evacuation
    Life-Threatening
    HACE
    Brain
    Emergency · Can be fatal in hours

    High-Altitude Cerebral Edema

    HACE — Brain swelling from hypoxia
    0.5–1%
    Fatal if untreated

    HACE is a neurological emergency — brain swelling causes rapid deterioration of mental status and coordination. Usually follows AMS at altitudes above 4,000 m. HACE can progress from recognizable symptoms to coma within hours. The diagnostic test: ataxia (inability to walk heel-to-toe in a straight line) is the classic early warning. Frequently coexists with HAPE. Untreated HACE is nearly always fatal.

    Symptoms
    • Severe progressive headache
    • Confusion, disorientation
    • Ataxia (wobbly walking)
    • Slurred speech
    • Hallucinations
    • Loss of consciousness
    Emergency response
    • DESCEND IMMEDIATELY
    • Dexamethasone 8 mg initial
    • Supplemental oxygen
    • Continue 4 mg every 6 hrs
    • Gamow bag as last resort
    • Hospital evacuation
    !
    The ataxia test — HACE’s most important sign

    Ataxia — the inability to walk heel-to-toe in a straight line — is HACE’s most specific early warning sign. Any climber showing ataxia has HACE until proven otherwise. The test is simple: have them walk a 10-step straight line, placing each heel directly in front of the opposite toe. If they step off the line, sway, or cannot complete it, the diagnosis is HACE. Do not wait for more symptoms. Descent must begin immediately. This single test has saved more climbers’ lives than any other field diagnostic in altitude medicine.

    The Lake Louise Score: Standardized AMS Assessment

    Developed at the 1991 International Hypoxia Symposium in Lake Louise, Alberta, the Lake Louise Score (LLS) is the gold-standard diagnostic tool for Acute Mountain Sickness. The 2018 revision simplified the scoring to four symptom categories, each rated 0-3 points.

    The four scored symptom categories

    • Headache: 0 (none), 1 (mild), 2 (moderate), 3 (severe/incapacitating)
    • GI symptoms (nausea/vomiting): 0 (good appetite), 1 (poor appetite/nausea), 2 (moderate nausea/vomiting), 3 (severe vomiting, incapacitating)
    • Fatigue/weakness: 0 (none), 1 (mild), 2 (moderate), 3 (severe/incapacitating)
    • Dizziness/lightheadedness: 0 (none), 1 (mild), 2 (moderate), 3 (severe/incapacitating)

    AMS diagnosis requires: recent ascent above 2,500 m + headache present + total score of 3 or more.

    Score interpretation and clinical action

    0–2
    No AMS
    Normal / acclimatizing

    Continue with normal ascent protocol. Monitor for symptoms as elevation increases. Hydration and rest still essential.

    3–5
    Mild AMS
    Stop ascending

    Rest at current altitude 24-48 hours. Hydrate. Acetaminophen for headache. Consider Diamox. May resume ascent if resolved.

    6–9
    Moderate AMS
    Descend 300-1,000 m

    Descend immediately. Start acetazolamide 250 mg twice daily. Monitor for HAPE/HACE progression. Don’t delay.

    10–12
    Severe AMS
    Descend 500+ m now

    Descend immediately. Consider dexamethasone. Assess for HAPE/HACE. Evacuation may be needed. Never continue upward.

    ◆
    When to use the Lake Louise Score

    The Lake Louise Score should be assessed daily at all elevations above 3,500 m. The evening — after the trekking day but before sleep — is the most useful assessment time. Trek leaders commonly assess entire groups. Self-assessment requires honest reporting: downplaying symptoms is dangerous. Any ataxia or confusion overrides the Lake Louise Score entirely — treat as HACE regardless of numerical score. The score complements but doesn’t replace clinical judgment. Pulse oximetry (SpO2 below 80% at 4,000 m is concerning) provides objective data alongside the Lake Louise Score.

    Prevention: How to Avoid Altitude Sickness

    Altitude sickness prevention is the safest and most effective approach — treatment is always a backup to good prevention. The core principle: ascent rate is the primary modifiable risk factor.

    The ascent rate rules

    • Below 3,000 m: Generally safe to ascend rapidly.
    • 3,000-4,000 m: Ascend no more than 300-500 m per day for sleeping elevation.
    • Above 4,000 m: Strictly follow 300-500 m/day rule for sleeping elevation.
    • Every 1,000 m gained: Spend 2 nights at same elevation (rest day).
    • “Climb high, sleep low”: Hike to higher altitude during day, return to lower elevation for sleeping.

    Non-medication prevention

    • Hydration: 3-4 liters daily at altitude. Dehydration mimics and worsens AMS.
    • Arrival acclimatization: 2-3 days at moderate altitude (2,500-3,500 m) before higher ascents.
    • Avoid alcohol in first 48 hours at altitude.
    • Avoid sleeping pills — they suppress breathing.
    • Maintain carbohydrate-rich diet.
    • Avoid smoking — worsens altitude effects.
    • Active rest days — short higher hikes with descent to sleep.

    Medications for prevention

    The two main prevention medications are acetazolamide (Diamox) and dexamethasone. Both require prescription — consult a travel medicine physician:

    • Acetazolamide (Diamox): 125-250 mg twice daily. Start 1-2 days before ascent above 2,500 m, continue first 2 days at target altitude. Gold-standard preventive — reduces AMS incidence by ~50%. Side effects: tingling, frequent urination, altered taste.
    • Dexamethasone: 2 mg four times daily or 4 mg twice daily. Reserved for high-risk situations or previously affected climbers.
    • Ibuprofen: 600 mg three times daily may reduce AMS incidence (studies mixed).

    Who should consider prevention medication

    • Previous history of AMS, HAPE, or HACE.
    • Rapid ascent profile unavoidable (flying to La Paz at 3,640 m, Lhasa at 3,650 m).
    • Known individual susceptibility from prior trips.
    • Essential travel above 3,500 m.
    • Short trip duration preventing gradual acclimatization.

    For deeper acclimatization science and practical ascent protocols, see our acclimatization explained guide.

    Treatment: When Altitude Sickness Strikes

    Treatment protocols depend entirely on severity. The golden rule across all altitude sickness: when in doubt, descend.

    AMS treatment (mild-moderate)

    • STOP ascending — never continue upward with active AMS.
    • Rest 24-48 hours at current elevation.
    • Hydration: 3-4 liters fluid daily.
    • Acetaminophen 500-1,000 mg for headache (avoid aspirin).
    • Anti-nausea medication (ondansetron 4-8 mg) if needed.
    • Acetazolamide: 250 mg twice daily (treatment dose).
    • If symptoms improve: Resume slow ascent after 24-48 hours.
    • If symptoms persist or worsen: Descend 300-1,000 m.

    HAPE treatment (emergency)

    • IMMEDIATE DESCENT at least 500-1,000 m — this is essential.
    • Supplemental oxygen if available.
    • Nifedipine: 30 mg extended release every 12 hours (reduces pulmonary artery pressure).
    • Sildenafil or tadalafil — alternative pulmonary vasodilators.
    • Acetazolamide 250 mg twice daily as adjunct.
    • Dexamethasone 4 mg every 6 hours if HACE also present.
    • Gamow bag (hyperbaric chamber) during evacuation if available.
    • Helicopter evacuation when conditions permit.

    HACE treatment (emergency)

    • IMMEDIATE DESCENT — life-saving and non-negotiable.
    • Dexamethasone: 8 mg initial dose, then 4 mg every 6 hours.
    • Supplemental oxygen.
    • Gamow bag if descent delayed.
    • Hospital evacuation mandatory once safely at lower altitude.
    ▲
    Dexamethasone warning

    Dexamethasone is extraordinarily effective at reducing cerebral edema and altitude symptoms — but this creates a serious hazard. Dexamethasone masks altitude sickness rather than curing it. Climbers who feel better on dexamethasone may be tempted to continue ascending, which can rapidly lead to catastrophic deterioration. Dexamethasone is a descent medication, not an ascent medication. Anyone who has required dexamethasone must descend, regardless of how good they feel. This rule has no exceptions. The drug buys time for descent — it does not cure the underlying hypoxic injury.

    Treatment tools

    • Gamow bag (portable hyperbaric chamber): Inflatable pressurized bag simulating descent of 1,500-3,000 m. Used when physical descent is impossible. Rented at major expedition bases.
    • Pulse oximeter: Measures SpO2. Below 80% at 4,000 m indicates severe altitude illness.
    • Oxygen cylinders: Available at major trekking camps and hotels.
    • Satellite communication (InReach, satellite phone): Essential for evacuation coordination.

    For pre-trip preparation that reduces altitude illness risk, see our high altitude training program.

    Descent Decision Framework

    The decision to descend is often the most critical in altitude medicine — and frequently the hardest due to psychological factors. Use this structured approach:

    SituationActionDistance
    No symptoms (acclimatizing)Continue normal ascent rate—
    Mild AMS (LLS 3-5)Stop ascent, rest 24-48 hrsStay or descend 300 m
    Moderate AMS (LLS 6-9)Descend300-1,000 m
    Severe AMS (LLS 10-12)Descend immediately500+ m
    Any HAPE symptomsEMERGENCY DESCENT500-1,000+ m minimum
    Any HACE symptoms (especially ataxia)EMERGENCY DESCENT500-1,000+ m minimum
    SpO2 <80% at 4,000 mDescend500+ m
    Unable to descendGamow bag + medicationsSimulate descent
    ★
    Psychological factors that delay descent

    Understanding the psychological traps that delay descent helps climbers and trip leaders override them. The most common: sunk cost fallacy (“we’ve come this far…”), summit fever (goal-focused mentality), peer pressure (not wanting to hold the group back), denial (minimizing symptoms), cost considerations (expensive trip), and limited opportunity (may never return). Override all of these for any HAPE/HACE symptoms. The mountaineering saying applies: “Reaching the summit is optional; returning home is mandatory.” Summits can be attempted again. Mountains remain. People do not.

    Altitude Sickness FAQ: Your Common Questions Answered

    What is altitude sickness?

    Altitude sickness is a group of medical conditions developing when the body cannot adapt quickly enough to reduced oxygen at elevation — typically above 2,500 m (8,200 ft). Three forms of increasing severity: AMS (Acute Mountain Sickness) mildest and most common, symptoms headache plus nausea/fatigue/dizziness/sleep disturbance, onset 6-24 hours after rapid ascent, affects 25-50% above 3,500 m. HAPE (High-Altitude Pulmonary Edema) life-threatening fluid in lungs, symptoms severe breathlessness at rest, dry cough progressing to pink/frothy sputum, drowning sensation, blue lips, usually above 2,500 m within 2-5 days, affects 0.2-6% of climbers. HACE (High-Altitude Cerebral Edema) life-threatening brain swelling, symptoms severe confusion, inability to walk straight (ataxia), hallucinations, loss of consciousness, usually follows AMS above 4,000 m, affects 0.5-1% of climbers. Why altitude sickness happens: at sea level atmospheric pressure 760 mmHg with oxygen 21%. At 3,500 m pressure drops to ~500 mmHg. Percentage of oxygen remains same but partial pressure decreases significantly. Lower oxygen pressure means less oxygen per breath reaches bloodstream. Body cannot deliver sufficient oxygen — triggering physiological responses and symptoms. Who gets it: anyone regardless of age, fitness, or experience. Individual susceptibility varies enormously. Prior altitude sickness strongly predicts future episodes. Fitness does NOT prevent altitude sickness. Ascent rate is biggest modifiable risk factor. Altitude categories: low sea level to 1,500 m, moderate 1,500-2,500 m, high 2,500-3,500 m (altitude sickness begins), very high 3,500-5,500 m, extreme above 5,500 m.

    What are the symptoms of altitude sickness?

    Altitude sickness symptoms range from mild discomfort (AMS) to life-threatening emergencies (HAPE/HACE). AMS symptoms: headache hallmark (bilateral, worse with exertion), nausea with or without vomiting, loss of appetite, fatigue and weakness, dizziness, sleep disturbances (insomnia, vivid dreams, periodic breathing), irritability, Lake Louise Score ≥3 with headache diagnostic. HAPE symptoms: shortness of breath at rest (not just with exertion), cough initially dry progressing to pink/frothy sputum, drowning sensation, cyanosis (blue lips/fingernails), elevated heart rate, fever possible, crackling sounds in lungs, severe weakness. HACE symptoms: severe progressive headache unresponsive to medications, confusion, disorientation, behavioral changes, ataxia (unable to walk heel-to-toe), slurred speech, hallucinations, loss of consciousness possible, can follow AMS rapidly (hours), frequently coexists with HAPE. Red flag combinations requiring immediate descent: AMS symptoms NOT improving after 24 hours, AMS symptoms WORSENING despite staying, any HAPE symptom (especially breathlessness at rest), any HACE symptom (especially ataxia or confusion), peripheral oxygen saturation below 80% at 4,000+ m. Lake Louise Score for AMS diagnosis: headache 0-3 points, GI 0-3 points, fatigue/weakness 0-3 points, dizziness 0-3 points. Total ≥3 with headache = AMS. 3-5 mild, 6-9 moderate, 10+ severe. Early recognition essential — AMS can rapidly progress to HAPE or HACE. When in doubt, descend.

    How do you prevent altitude sickness?

    Prevention centers on controlled ascent rate plus proper acclimatization, with medications as supplementary support. Primary prevention: gradual ascent 300-500 m per day sleeping elevation above 3,000 m, rest day every 1,000 m, climb high sleep low (hike higher during day return to lower elevation for sleeping), arrival acclimatization 2-3 days at moderate altitude before higher ascents, hydration 3-4 liters daily, avoid alcohol first 48 hours, avoid sleeping pills (suppress breathing), maintain carbohydrate-rich diet, avoid smoking. Ascent rate rules: below 3,000 m generally safe rapid ascent, 3,000-4,000 m 300-500 m per day sleeping, above 4,000 m strictly 300-500 m/day rule, every 1,000 m gained spend 2 nights at same elevation, build in active rest days with minor higher hikes. Medication prevention: Acetazolamide (Diamox) gold-standard, 125-250 mg twice daily starting 1-2 days before altitude, continuing first 2 days at target altitude, reduces AMS by ~50%, side effects tingling, frequent urination, altered taste. Dexamethasone 2 mg four times daily or 4 mg twice daily, reserved for high-risk or known susceptibility. Ibuprofen 600 mg three times daily may reduce AMS. Who should consider medication: previous history of AMS/HAPE/HACE, rapid ascent unavoidable (flying to La Paz, Lhasa), known individual susceptibility, essential travel above 3,500 m. Pre-acclimatization strategies: hypoxic tents at home, 3-5 days at moderate altitude before trek, multiple shorter altitude exposures weeks before main trip, cardiovascular fitness training (doesn’t prevent AMS but improves performance). See our acclimatization science guide.

    How do you treat altitude sickness?

    Treatment depends on severity. Golden rule: when in doubt, descend. AMS treatment (mild): STOP ascending immediately, rest 24-48 hours at current elevation, hydration 3-4 liters daily, acetaminophen or ibuprofen for headache (avoid aspirin), anti-nausea medication if needed, if symptoms improve resume slow ascent, if symptoms worsen descend. AMS treatment (moderate-severe): Acetazolamide 250 mg twice daily (treatment dose higher than prevention), Dexamethasone 4 mg every 6 hours (moderate-severe cases), descend 300-1,000 m (almost always relieves symptoms), supplemental oxygen, Gamow bag if descent impossible. HAPE treatment (life-threatening): IMMEDIATE DESCENT 500-1,000 m essential, supplemental oxygen, Nifedipine 30 mg extended release every 12 hours (reduces pulmonary artery pressure), Sildenafil or tadalafil alternative, Gamow bag during evacuation, Acetazolamide 250 mg twice daily adjunct, Dexamethasone 4 mg every 6 hours if HACE also present. HACE treatment (life-threatening): IMMEDIATE DESCENT life-saving, Dexamethasone 8 mg initial then 4 mg every 6 hours, supplemental oxygen, Gamow bag if descent delayed, evacuation to lower altitude hospital mandatory. Treatment tools: Gamow bag (hyperbaric chamber) simulates descent of 1,500-3,000 m portable device for emergencies. Pulse oximeter monitors SpO2 — below 80% at 4,000 m indicates severe. Oxygen cylinders at major trekking camps. Satellite phones/InReach essential for evacuation. When to call evacuation: any HAPE symptoms not improving with descent, any HACE symptoms, inability to descend, loss of consciousness, cyanosis, ataxia. Recovery timeline: mild AMS 24-72 hours, moderate-severe 24-48 hours after descent, HAPE 1-3 days lung clearance 2-4 weeks, HACE days to weeks.

    What is the Lake Louise score?

    The Lake Louise Score (LLS) is the standardized medical assessment tool for diagnosing and grading AMS. Developed at the 1991 International Hypoxia Symposium in Lake Louise, Alberta. Self-assessed questionnaire with 4 symptom categories. Each category scored 0-3 points. Total ranges 0-12. AMS diagnosis requires recent ascent above 2,500 m, headache present, total score ≥3. The 4 categories and scoring: Headache 0 none, 1 mild, 2 moderate, 3 severe/incapacitating. GI (nausea/vomiting) 0 good appetite, 1 poor appetite or nausea, 2 moderate nausea or vomiting, 3 severe. Fatigue/weakness 0 none, 1 mild, 2 moderate, 3 severe. Dizziness 0 none, 1 mild, 2 moderate, 3 severe. 2018 revision removed sleep disturbance as standalone category. Score interpretation: 0-2 no AMS (may not yet be acclimatized), 3-5 with headache mild AMS, 6-9 with headache moderate AMS, 10-12 with headache severe AMS. Clinical decision-making: 3-5 mild stop ascending rest and hydrate may resume in 24 hours if resolved, 6-9 moderate descend 300-1,000 m start acetazolamide, 10-12 severe descend 500+ m consider dexamethasone monitor for HAPE/HACE. Any ataxia or confusion overrides score — treat as HACE. When to use: daily self-assessment above 3,500 m, evening evaluation of trekking day, before descending from high camps, when any symptoms appear, group-wide assessments. Limitations: doesn’t assess HAPE or HACE directly, subjective, other conditions can mimic AMS, should complement not replace clinical judgment, pulse oximetry provides objective data alongside LLS.

    What medications help with altitude sickness?

    Several medications prevent and treat altitude sickness. Acetazolamide (Diamox) is most common for prevention, dexamethasone reserved for emergency treatment. All require physician prescription. Acetazolamide (Diamox) primary prevention: brand Diamox generic acetazolamide. Mechanism carbonic anhydrase inhibitor promotes bicarbonate excretion causing mild metabolic acidosis stimulating faster breathing — accelerating natural acclimatization. Prevention dose 125-250 mg twice daily starting 1-2 days before ascent above 2,500 m continuing first 2 days at target altitude. Treatment dose 250 mg twice daily. Reduces AMS incidence by ~50%. Side effects tingling in fingers/toes/face (paresthesia), frequent urination, altered taste (carbonated drinks taste flat), mild nausea. Contraindications sulfa drug allergy, kidney disease, liver disease, pregnancy. Dexamethasone emergency drug: brand Decadron. Potent corticosteroid reduces inflammation stabilizes cerebral edema in HACE. Prevention dose 2 mg every 6 hours or 4 mg twice daily. HACE treatment 8 mg initial then 4 mg every 6 hours. Moderate-severe AMS treatment 4 mg every 6 hours. Dramatic effect — reduces cerebral edema rapidly. Can mask serious illness — user must still descend. Side effects mood changes, GI upset, insomnia, increased urination. CRITICAL WARNING: NEVER continue ascending on dexamethasone — only masks symptoms, must descend after administration. Pulmonary vasodilators for HAPE: Nifedipine 30 mg extended-release every 12 hours reduces pulmonary artery pressure. Sildenafil (Viagra) 50 mg three times daily alternative. Tadalafil (Cialis) 10 mg twice daily alternative. Other: Ibuprofen 600 mg three times daily may prevent AMS headache. Ondansetron 4-8 mg for nausea. Acetaminophen safer for altitude headache than ibuprofen. Avoid aspirin, sleeping pills, strong opioids. All require physician prescription.

    At what altitude does altitude sickness begin?

    Altitude sickness can begin as low as 2,500 m (8,200 ft) though most cases develop between 3,000 m and 5,500 m. Exact threshold varies between individuals. Altitude thresholds: below 1,500 m low altitude no risk, 1,500-2,500 m moderate altitude low risk most healthy individuals unaffected, 2,500-3,500 m high altitude AMS begins (10-25% affected with rapid ascent), 3,500-5,500 m very high altitude significantly elevated risk (30-50% AMS HAPE/HACE possible), above 5,500 m extreme altitude no permanent human habitation progressive deterioration. Common destinations: Low/moderate (generally safe) Tour du Mont Blanc max 2,665 m low risk, Torres del Paine W Circuit max ~1,000 m no altitude issues. High altitude (AMS possible) Rocky Mountain Park Colorado up to 3,600 m some AMS, Machu Picchu 2,430 m mild effects, Atlas Mountains Toubkal 4,167 m moderate risk. Very high (significant AMS risk) Everest Base Camp 5,550 m Kala Patthar AMS common, Kilimanjaro summit 5,895 m HAPE/HACE possible with rapid ascent, Aconcagua 6,961 m high AMS risk, Manaslu Circuit 5,106 m max, K2 Base Camp 5,000 m. Extreme (acclimatization essential) 8,000 m peaks death zone oxygen typical, Everest 8,849 m, K2 8,611 m. Individual variation factors: genetics (susceptibility varies 10x between individuals), previous altitude experience, baseline fitness (doesn’t predict AMS), age (teens and young adults often MORE susceptible), prior AMS history strongly predicts future episodes, pre-existing cardiopulmonary conditions. Ascent rate vs absolute altitude: rapid ascent BIGGER risk than absolute altitude. Flying from sea level to 3,500 m (La Paz, Lhasa) causes more AMS than gradual ascent to 4,500 m. Key thresholds: 2,500 m AMS possible, 3,500 m Lake Louise assessments, 4,000 m mandatory acclimatization days, 4,500 m HAPE/HACE screening, 5,000 m extended acclimatization essential, 5,500 m short duration only for most climbers.

    Can fitness level prevent altitude sickness?

    No — cardiovascular fitness does NOT prevent altitude sickness. Persistent myth in mountaineering. Fit individuals are just as susceptible as unfit individuals. Why fitness doesn’t prevent altitude sickness: altitude sickness results from inability to acclimatize to reduced oxygen — physiological response unrelated to cardiovascular conditioning. Fitness improves oxygen utilization at current capability but doesn’t increase oxygen uptake beyond what body can extract from low-oxygen environment. Ability to acclimatize primarily genetic and not trainable through fitness. Some studies suggest fitter individuals may push harder and ascend faster — potentially INCREASING AMS risk. What fitness DOES help: endurance for long trekking days, recovery between trekking days, carrying pack weight, overall trip enjoyment and performance, cardiovascular health baseline reducing other risks, mental resilience during challenging conditions. What actually prevents altitude sickness: gradual ascent (300-500 m per day sleeping elevation), proper acclimatization schedule, hydration, appropriate medications (Diamox), individual susceptibility (genetic), recognition and response to early symptoms, climb high sleep low protocols. Common misconceptions: ‘I run marathons so altitude won’t affect me’ Wrong marathon runners get AMS. ‘Young people don’t get altitude sickness’ Actually younger people may be MORE susceptible. ‘I’m acclimatized from prior trips’ Acclimatization doesn’t persist more than 1-2 weeks after return to sea level. ‘Fit climbers can skip acclimatization days’ Common and dangerous mistake. Historical evidence: professional mountaineers still get altitude sickness. World-class climbers have died from HAPE/HACE. Elite Sherpa guides experience altitude effects. Military special forces affected at altitude. What trainable factors matter: previous altitude exposure (1-2 weeks benefit), hypoxic training, psychological preparation, skill at self-assessment, practiced response protocols. Don’t rely on fitness to skip acclimatization. Follow standard ascent rates regardless of fitness. Take Diamox if predisposed. Be prepared to descend even at peak fitness. See our training program guide.

    Authoritative Sources & Further Reading

    Content reflects authoritative altitude medicine sources:

    • Wilderness Medical Society (WMS) — wms.org — Practice Guidelines for Acute Altitude Illness (2024 update)
    • International Society for Mountain Medicine (ISMM) — ismm.org — Professional altitude medicine standards
    • Himalayan Rescue Association (HRA) — himalayanrescue.org — Nepal field protocols and aid posts
    • Lake Louise AMS Consensus (2018 revision) — Standardized scoring system
    • High Altitude Medicine & Biology journal — Peer-reviewed altitude research
    • New England Journal of Medicine — Altitude illness clinical reviews
    • UpToDate — Clinical decision support for altitude medications
    • CDC Yellow Book — Travel medicine altitude chapter
    • Reference texts: Going Higher: The Story of Man and Altitude by Charles Houston, Altitude Illness: Prevention & Treatment by Stephen Bezruchka
    Published: March 19, 2026
    Last updated: April 19, 2026
    Next review: July 2026
    Altitude & training resources

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