Altitude Sickness on the Everest Base Camp Trek: Prevention, Symptoms and Treatment

Introduction: 2am at 4,800 Metres. Is This Normal?

Picture this. You are lying in your sleeping bag in a teahouse somewhere above Dingboche. It is two in the morning. Your head is pounding with the kind of pressure that sits just behind your eyes and refuses to shift. Your heart is beating faster than it should at rest. The room is cold. Outside, the wind is pushing against the thin walls. You have had maybe three hours of broken sleep. You need to ask yourself an honest question: is this altitude sickness, or is this just what sleeping at 4,800 metres feels like?

The answer matters. Getting it right could save your trek. Getting it wrong could save your life.

Altitude sickness is the single most common reason trekkers do not complete the Everest Base Camp trek. Not blisters. Not bad weather. Not fitness. Altitude. Between 25% and 50% of all trekkers who attempt EBC experience some form of Acute Mountain Sickness during their trip. That is a significant number and it deserves a serious, honest guide.

Here is the reassuring part. The vast majority of altitude sickness cases on this route are mild. Most trekkers who experience headaches, poor sleep and lost appetite above Namche Bazaar are having a normal physiological response to rapid altitude gain, not a medical emergency. With one rest day and adequate hydration, most recover fully and continue to base camp. Only a very small percentage of EBC trekkers, roughly 1 to 3 per year among 30,000 plus annual trekkers, die from altitude related illness. And virtually all of those deaths involve either ignoring severe warning signs or ascending when clearly unwell.

The better news is that altitude sickness is largely preventable. With the right acclimatization schedule, the right preparation, and the willingness to act on symptoms early, you can reduce your risk significantly and give yourself the best possible chance of standing at 5,364 metres, staring up at the Khumbu Icefall with that enormous grin on your face.

This guide covers everything you actually need to know. We go through the science of why altitude makes you sick, the three types of altitude illness and how to tell them apart, a day by day symptom timeline for the EBC route, the Lake Louise Score system that guides and doctors use to assess severity, the golden rules of acclimatization, the medications that help (and the ones that do not), how to perform the walk test that can detect a brain emergency, when helicopter evacuation is necessary, and what happens at the Himalayan Rescue Association clinic in Pheriche that sits right on your path to base camp.

We have written this with one aim: to give you the knowledge to make good decisions on the trail. Because the mountain does not care how fit you are, how much you paid for this trip, or how long you saved to be here. It only responds to physiology. And physiology responds to preparation.

Why Altitude Makes You Sick: The Science

To understand altitude sickness you need to understand one core concept: the air at high altitude is not “thinner” in the sense that oxygen molecules disappear. The percentage of oxygen in air is constant at about 21% whether you are at sea level or at the summit of Everest. What changes is air pressure. And as pressure drops, so does the density of air molecules, meaning each breath you take delivers fewer oxygen molecules to your lungs.

At sea level, atmospheric pressure sits at approximately 1013 hectopascals (hPa). At this pressure your lungs receive a full complement of oxygen with each breath, your blood oxygen saturation (SpO2) runs between 95% and 100%, and everything works as designed.

By the time you reach Namche Bazaar at 3,440 metres, atmospheric pressure has dropped to around 660 hPa. Effectively you are breathing air with only about 65% of the oxygen density you had at sea level. Your body notices. Heart rate increases. Breathing deepens and quickens. Even at rest you may feel slightly breathless when you first arrive.

At Everest Base Camp at 5,364 metres, pressure has dropped to approximately 500 hPa, meaning you are working with roughly 50% of the oxygen available at sea level. At Kala Patthar, the high point of the standard EBC route at 5,545 metres, the pressure is lower still. This is the frontier of what the unacclimatized human body can sustain over time.

Your body responds to this hypoxic (low oxygen) environment with a cascade of adaptations. Your breathing rate and depth increase to pull more air through your lungs per minute. Your heart pumps faster to circulate the available oxygen more rapidly. Over three to seven days your bone marrow begins producing more red blood cells, increasing the blood’s oxygen carrying capacity. An enzyme called 2,3-DPG (2,3-diphosphoglycerate) increases inside red blood cells, helping hemoglobin release oxygen more readily to oxygen-hungry tissues. Your kidneys begin excreting bicarbonate to correct the blood chemistry shift caused by faster breathing. Over two to three weeks, full acclimatization at a given altitude becomes possible for most people.

The problem is that “most people” is not everyone, and “two to three weeks” is not the timeline of a standard EBC trek. When the body cannot adapt fast enough, tissues that are highly sensitive to oxygen deprivation begin to suffer. The brain and lungs are the most vulnerable. The brain demands about 20% of the body’s oxygen supply despite being only 2% of body weight. When oxygen delivery falls short, brain cells become distressed, and the cascade that leads to Acute Mountain Sickness begins.

Risk Factors That Increase Your Susceptibility

Certain factors are known to increase your risk of developing altitude sickness. Ascending too fast is the single biggest one. Dehydration amplifies every symptom because it reduces blood volume and makes it harder for your cardiovascular system to compensate. Alcohol suppresses the respiratory drive that is actively helping you adapt, which is why drinks above 3,500 metres are particularly counterproductive if you are experiencing any symptoms. A prior history of AMS is a strong predictor of future episodes, since susceptibility appears to have a significant genetic component. Fatigue and poor sleep also raise your risk because your body’s compensatory mechanisms are less effective when you are exhausted.

One thing that does not protect you against altitude sickness is being young and physically fit. This surprises many trekkers. In fact, fitness can work against you because fit people often push harder and ascend faster than they should, triggering AMS precisely because their bodies feel capable of more. The mountains have humbled more than a few marathon runners and professional athletes on the approach to EBC. Physical condition gets you up the trail more comfortably, but it does not determine how well your brain and lungs handle low oxygen. That is determined by genetics and by how carefully you acclimatize.

Three Types of Altitude Sickness You Need to Know

Acute Mountain Sickness (AMS): The Common One

Acute Mountain Sickness is the early stage of altitude illness. It is what happens when your body is struggling to adapt and has not yet done so. On the EBC route, AMS most commonly first appears at or above Namche Bazaar at 3,440 metres, though susceptible individuals can experience symptoms as low as 2,000 metres. The standard altitude threshold where most people become vulnerable is 2,500 metres.

The medical community diagnoses AMS using the Lake Louise Score System. This gives you a headache score from 0 to 3 (none to severe), plus additional scores for gastrointestinal symptoms such as nausea or vomiting, fatigue and weakness, and dizziness or lightheadedness. A total score of 3 or above, with headache present, constitutes a diagnosis of AMS. We cover the full scoring table in a later section.

Mild AMS looks like this: a headache that is present but manageable, fatigue that seems disproportionate to the walking you did that day, reduced appetite, possibly mild nausea, disturbed sleep with frequent waking, and a vague feeling of heaviness or being unwell. Many trekkers describe mild AMS as feeling “flu-like” without the fever. These symptoms typically appear within six to twelve hours of arriving at a new altitude.

Moderate AMS escalates the headache to severe and difficult to relieve with standard painkillers, vomiting rather than just nausea, extreme fatigue where even sitting up feels like effort, and obvious coordination problems. If you or a trekking partner reach this stage, the day’s plan changes immediately. You do not continue upward.

How long does AMS last? Mild cases typically resolve in one to two days with rest at the same altitude and good hydration. If your symptoms are not improving after 24 hours at the same altitude, or if they are worsening at any point, the right response is to descend 500 metres and reassess. Only resume ascent when you have been symptom free for at least 12 hours.

High Altitude Cerebral Edema (HACE): The Brain Emergency

HACE is what happens when AMS progresses to actual brain swelling. Fluid accumulates inside the skull, putting pressure on brain tissue that has nowhere to go. This is a medical emergency with a narrow window for safe intervention.

The symptoms of HACE are not subtle once you know what to look for. A severe headache that does not respond to ibuprofen or paracetamol is the first alarm. Loss of coordination, known as ataxia, is the red flag that distinguishes HACE from severe AMS: the affected person cannot walk a straight line heel to toe without stumbling. Altered consciousness follows, ranging from confusion and disorientation to unusual behavior, emotional swings, and eventually drowsiness that progresses toward unconsciousness. A person with HACE may say strange things, become uncharacteristically aggressive or tearful, or simply seem “not themselves” in ways that their trekking companions notice before the person does.

HACE most commonly occurs above 4,000 metres and typically develops over hours rather than days, though it can accelerate rapidly. It often worsens at night, which is why many HACE deaths occur in sleeping bags. The person feels drowsy, goes to sleep, and does not wake up.

The only treatment for HACE is immediate descent of at least 500 to 1,000 metres. Not tomorrow. Not after one more hour of sleep. Immediately, even in darkness if you must. If descent is physically impossible for any reason, a Gamow bag (a portable hyperbaric chamber that simulates lower altitude) can buy time. These are kept at the Himalayan Rescue Association clinics. Dexamethasone, a powerful corticosteroid, can be given at 8mg as an initial dose followed by 4mg every six hours. This reduces brain swelling temporarily and is for emergencies only, not for routine AMS management or prevention. Dexamethasone buys time to descend. It is not a cure and it is not a substitute for descent.

HACE kills if untreated. It kills faster than most trekkers expect. Do not negotiate with it, and do not allow a trekking partner to talk you out of acting. If you see ataxia, you descend. Full stop.

High Altitude Pulmonary Edema (HAPE): The Lung Emergency

HAPE is the most common cause of death from altitude sickness. It occurs when fluid accumulates in the lungs rather than the brain, and it can deteriorate from uncomfortable to fatal within hours. It occurs most commonly above 3,000 metres but is far more frequent above 4,000 metres, which puts almost the entire upper half of the EBC route in its danger zone.

The early symptom of HAPE is breathlessness that seems greater than your exertion level justifies. You stop to rest after a short section of trail and find yourself gasping more than usual. At rest you notice you are still breathing harder than you should be. This progresses to a dry cough, then to a cough that produces a white or pink frothy sputum, which is fluid from the lungs. In the final stages, crackling sounds are audible in the lungs (a medical provider pressing a stethoscope to your back would hear something described as walking on dry leaves). Extreme fatigue, a feeling of suffocation especially when lying down, and cyanosis (blue coloring of lips and fingertips from oxygen deprivation) are late stage signs.

The critical thing to understand about HAPE is that it masquerades as many things. The early fatigue and cough can be written off as a chest cold, dehydration, or general altitude discomfort. This is how it kills people: they go to sleep expecting to feel better in the morning and they do not wake up.

Treatment is immediate descent. No delay. Even at night. Even in a snowstorm if the alternative is staying at altitude with worsening HAPE. If descent is genuinely impossible, supplemental oxygen should be administered and nifedipine at 30mg slow release can be given. Nifedipine is a calcium channel blocker that reduces pulmonary arterial pressure and is specifically indicated for HAPE when descent is delayed. It is not a routine drug and is not indicated for AMS or for prophylaxis except in people with a strong prior HAPE history, who should discuss it with their doctor before the trek.

AMS Symptoms Timeline on the EBC Trek

The EBC route rises through several distinct altitude bands, each with its own risk profile. Understanding where the danger zones are helps you pace your preparation and know what to watch for each day. The table below maps the standard itinerary against altitude risk. Actual symptoms depend on your individual physiology, the pace of your ascent, and your hydration and rest.

One note on Gorakshep: many trekkers find it the most difficult sleeping stop on the entire route. The altitude is severe enough that acclimatization is incomplete for most people. Expect the worst night of sleep on the trek. Bring ear plugs, accept the disrupted breathing, and know that you will feel better when you start descending.

The Lake Louise Score: Self-Assess Your AMS

The Lake Louise Score is the internationally accepted tool for diagnosing AMS. It was developed by a group of altitude medicine experts in 1991 at a meeting in Lake Louise, Canada, and has been updated since. Your guide should know this system. You should know it too, because you are the one who knows exactly what your head feels like.

AMS is diagnosed when the total score is 3 or higher AND a headache is present. A score without headache does not qualify as AMS by this scale, though individual symptoms should still be taken seriously.

How to use it: assess yourself each morning and evening. Score each symptom honestly. Total them up. A score of 3 to 5 with headache is mild to moderate AMS. A score of 6 or more is severe AMS and requires immediate action (stop ascending, consider descent). Scores do not capture everything: ataxia (coordination loss) or any change in mental status is a HACE red flag regardless of score and demands descent immediately.

A practical tip: do this assessment out loud with your trekking partner every evening before dinner. You can catch trends that way, such as a score that was 2 yesterday and is 4 today, which tells you something important even if neither number is alarming on its own.

The Golden Rules of Acclimatization

These are not suggestions. They are the framework that every reputable EBC guide company builds its itineraries around. Cutting corners on any of them raises your risk meaningfully.

Rule 1: Ascend Slowly

The standard guideline above 3,000 metres is to limit your sleeping altitude gain to 300 to 500 metres per day. This gives your body time to initiate and sustain its adaptive responses. The EBC itinerary from most reputable operators is designed around this principle. Any company offering you EBC in eight days is either cutting acclimatization days or expecting you to cover dangerous altitude gains in a single march. Neither is acceptable. When you are looking at companies, read about choosing a licensed EBC guide carefully and ask specifically about their acclimatization schedule before you book.

Rule 2: Climb High, Sleep Low

This is one of the most effective acclimatization techniques available and it is baked into the standard EBC itinerary at two key points. On your rest day in Namche (3,440m) you hike up to the Everest View Hotel area at approximately 3,880m, then return to sleep at Namche. Your body experiences the higher altitude during the day, begins its adaptation, and then recovers overnight at a lower sleeping altitude. You get the acclimatization stimulus without the risk of sleeping at the higher altitude before you are ready.

The same principle applies at Dingboche (4,410m) where the acclimatization hike takes you up toward Nagarjun Hill or the Chhukung valley to 5,000 metres or above, before returning to sleep at 4,410m. These day trips are not optional extras. They are medically important steps in the process.

Rule 3: Two Nights at Namche. Minimum.

This is the single most important piece of scheduling advice for EBC. Namche Bazaar at 3,440m is where the majority of trekkers first experience meaningful altitude. Spending two nights here (one for arrival and adjustment, one for the acclimatization hike) gives your body its first real opportunity to begin the process. Trekkers who rush through Namche on a single night almost always pay for it above Tengboche.

Rule 4: Never Ascend With AMS Symptoms

This rule is absolute. If you have a Lake Louise score of 3 or above, or any single symptom that is worsening rather than stable, you do not move to a higher sleeping altitude that day. You rest at the same altitude. If symptoms worsen over 24 hours despite rest and hydration, you descend 500 metres. You only resume upward progress when you have been entirely symptom free for at least 12 hours.

This rule is broken constantly on the trail, often with the encouragement of the trekker’s own group. “Push through it,” says the eager member of the team who is feeling fine. Do not listen. Ascending with AMS can escalate to HACE within hours.

Rule 5: Drink 3 to 4 Litres of Water Per Day

Dehydration at altitude amplifies every AMS symptom. It reduces blood volume, thickens the blood, and reduces the efficiency of oxygen transport to tissues. At altitude your kidneys are working harder, your breathing rate is elevated (losing moisture with each breath), and you may not feel thirsty as reliably as you do at sea level. Drink consistently throughout the day. Do not wait until you are thirsty. A simple rule: if your urine is not pale yellow, you are not drinking enough.

Rule 6: No Alcohol Above 3,500 Metres When You Have Symptoms

Alcohol suppresses the respiratory drive, specifically the body’s response to rising CO2 levels that keeps your breathing rate appropriately elevated at altitude. It also dehydrates you, interferes with sleep quality, and impairs the cognitive clarity you need to make good decisions about your own symptoms. A single beer in Namche on a good day is one thing. Drinking when you have a headache or at altitudes above Dingboche is genuinely harmful. The teahouse menu does not tell you this. We are telling you.

Rule 7: Eat Carbohydrate-Rich Foods

Your body is more efficient at extracting energy from carbohydrates than from fat at altitude. Carbohydrate metabolism uses less oxygen per unit of energy produced, which matters when oxygen is already limited. This is one reason dal bhat, the traditional Nepali meal of lentil soup over rice with vegetables, is genuinely the best food you can eat on the EBC trek. It is warm, calorie dense, carbohydrate rich, and available everywhere on the route. Eat it. Even when your appetite is poor, force something down. Calorie deficit worsens altitude illness.

Rule 8: Accept That Sleep Will Be Difficult

Above 4,000 metres, a phenomenon called periodic breathing or Cheyne-Stokes respiration becomes very common. Your breathing slows and becomes irregular during sleep, sometimes pausing for several seconds before resuming with a gasp. This is a normal physiological response to altitude and is not dangerous in most trekkers, but it produces deeply disturbed sleep. You will wake repeatedly. You will feel like you cannot catch your breath. Bring ear plugs (for the snoring of others in the teahouse dormitories, which will be impressive). Accept the disrupted sleep as part of the experience. It improves as you acclimatize, and it is not a reason to panic at 3am.

Diamox (Acetazolamide): Should You Take It?

Diamox is the most commonly used medication for altitude sickness prevention and the one most trekkers ask about. Understanding what it actually does, and what it does not do, is more useful than a simple yes or no answer.

Acetazolamide is a diuretic that works by inhibiting the enzyme carbonic anhydrase. This causes the kidneys to excrete bicarbonate in the urine, which slightly acidifies the blood. This acid shift stimulates breathing, particularly overnight when breathing naturally slows. The result is faster and deeper breathing, which speeds up the acclimatization process. It does not prevent AMS by eliminating the problem. It accelerates your body’s adaptation so that you reach a given altitude’s physiological equilibrium faster than you would without it.

The standard prophylactic dose is 125mg taken twice daily. Some doctors prescribe 250mg twice daily. The lower dose has a better side effect profile for most people, and research suggests it is nearly as effective. You should begin taking Diamox 24 to 48 hours before ascending to altitude, not as a last minute measure when you already feel unwell.

Side effects are common and worth knowing before you commit. The most universal is increased urination, which means more nighttime bathroom trips in already cold teahouse conditions. Tingling in the fingers, toes, and sometimes lips (paresthesia) occurs in a substantial proportion of users. Carbonated drinks taste flat or metallic. Some people experience mild fatigue or blurred vision. These side effects are unpleasant but not dangerous.

Diamox is contraindicated for anyone with a sulfa drug allergy (it belongs to the sulfonamide class), kidney disease, pregnancy, or Addison’s disease. If you take lithium, metformin, or certain other medications, check with your prescribing doctor for interaction risks.

The debate about Diamox within the trekking community is real. Some experienced guides argue that it allows trekkers to ascend faster than they should, effectively masking symptoms that would otherwise trigger a rest day or descent. Others argue that it genuinely helps borderline cases and allows people with mild susceptibility to complete the trek they have worked toward. Both positions have merit.

Our view: Diamox is worth considering if you have had AMS on a previous trip, if you are doing a shorter than standard itinerary, if your schedule gives you no room for rest days, or if your doctor identifies other risk factors. It is not a replacement for proper acclimatization, and it should not be taken as permission to skip rest days or push too fast. It is a tool in the toolkit, not the whole toolkit.

Before you trek, see your doctor. Get the prescription if it makes sense for you. Take a small test dose before you leave home to confirm you can tolerate the side effects. And pack it even if you decide not to start it prophylactically, because having it available if symptoms begin is a reasonable backup plan.

Other Medications for Altitude Sickness

Ibuprofen

Ibuprofen at 400 to 600mg every 6 to 8 hours is the most effective over the counter treatment for AMS headaches. Several studies have shown it is at least as effective as Diamox for headache relief, though it does not have Diamox’s acclimatization benefit. It reduces headache pain without masking the other symptoms that tell you AMS is worsening. Take it with food and plenty of water. Do not use it as a reason to keep ascending: a headache that goes away with ibuprofen is still a headache, and you still need to assess the full picture before moving up.

Paracetamol (Acetaminophen)

A lighter option for mild headache when ibuprofen is contraindicated or not available. Less effective than ibuprofen for moderate AMS headaches but safe and widely available on the route. The standard dose is 500mg to 1000mg every 4 to 6 hours as needed, not exceeding 4000mg in 24 hours.

Dexamethasone

A powerful corticosteroid reserved for HACE emergencies. As described in the HACE section, the dose is 8mg as an initial loading dose, then 4mg every 6 hours. This is not a routine altitude medication. It should not be taken to prevent AMS or to push through mild symptoms. It suppresses the immune system, can cause serious side effects with extended use, and masks symptoms in ways that can allow a person to feel deceptively well while the underlying brain swelling continues. Carry it in your group emergency kit. Use it only for genuine emergencies, ideally on the advice of a medical provider.

Nifedipine

A calcium channel blocker specifically indicated for HAPE when descent is delayed or impossible. The dose is 30mg of the slow release formulation. It works by reducing pulmonary arterial pressure, which decreases fluid accumulation in the lungs. Like dexamethasone, this is an emergency medication, not a prophylactic. It is available in Kathmandu pharmacies. If you have had HAPE previously, discuss carrying nifedipine with your doctor before your trek.

Ginkgo Biloba

Some studies have suggested a modest benefit from ginkgo biloba supplementation in reducing AMS symptoms. The evidence is mixed and the effect size is small. It is not a medication you can rely on. If you want to try it, 120mg twice daily starting five days before ascent is the protocol used in trials. It is not a substitute for any of the above and should not factor into your core prevention strategy.

What to Avoid

Sleeping pills such as benzodiazepines and related medications suppress the respiratory drive, the very mechanism your body is using to compensate for altitude. They can worsen nighttime oxygen desaturation significantly. Unless specifically recommended by a physician who knows you are trekking at altitude, do not use them. Alcohol has the same problem. Narcotic pain medications suppress breathing and should not be used for altitude headaches.

Recognizing the Walk Test for Ataxia

The tandem gait test, or walk test, is the single most important physical check your guide or trekking partner can perform when neurological symptoms are suspected. It is quick, requires no equipment, and is highly reliable at detecting the coordination loss that marks the onset of HACE.

The test: find a flat, straight section of ground or floor. Ask the person to walk heel to toe, placing one foot directly in front of the other with the heel of the front foot touching the toe of the back foot, for about four metres. A person without HACE or significant brain impairment can do this with minimal stumbling. A person with ataxia from HACE will stagger, grab for support, or be unable to complete the line at all.

Critical points about this test. First, do not test someone for the first time when you already suspect HACE, because you will not have a baseline to compare to. Practice the test with your trekking partner at sea level before you leave home so you know what their normal looks like. Second, the test should be performed on anyone who is showing neurological symptoms: confusion, unusual behavior, unusual drowsiness, or severe headache not responding to medication. Third, if the test is failed or even borderline, the response is descent. Not “let’s see how they are in the morning.” Descent.

Teach this test to your trekking partner before you arrive in Kathmandu. It takes thirty seconds to demonstrate and it could make the difference between catching HACE early and missing it entirely. If you are trekking with a guide from a licensed operator, your guide should already know this test. If they do not, that tells you something about the operator’s training standards.

What Happens at the Himalayan Rescue Association Clinic in Pheriche

At 4,371 metres, right on the trail between Dingboche and Lobuche, sits the Himalayan Rescue Association (HRA) post at Pheriche. This is one of the most important stops on the EBC route and not enough trekkers treat it as such.

The clinic is staffed during the spring season (approximately March to May) and autumn season (approximately September to November) by rotating volunteer doctors and medical professionals from Western countries. They come from hospitals and medical schools across the United States, Europe, and Australia, and they bring considerable expertise in altitude medicine. The clinic is basic by any urban hospital standard but it is fully equipped to assess AMS, HACE, and HAPE, administer emergency medications, and arrange helicopter evacuation when needed.

The HRA runs a free altitude sickness education talk every afternoon, typically at around 3pm. Every single EBC trekker should attend this talk. It covers exactly the information in this guide, but delivered in person by doctors who have seen HACE and HAPE cases that week, on the same trail you are walking. Their case examples are recent, their advice is current, and the talk takes about an hour. If you have any questions about your specific health situation, symptoms you have been experiencing, or medications you are considering, bring them to the clinic afterward for a free consultation.

The clinic can provide pulse oximetry readings, which give you a concrete measure of your blood oxygen saturation at altitude. Knowing that your SpO2 is 81% at Pheriche versus 88% for most other trekkers is genuinely useful clinical information. Do not skip Pheriche. Stop there, attend the talk, get your oxygen levels checked, ask your questions. It is free and it is potentially lifesaving.

To understand more about the villages you will pass through on the route, including the communities that host these clinics, see our guide to villages on the EBC route.

Helicopter Evacuation: When It Is Needed and What It Costs

Helicopter evacuation from the high EBC route is a real event, not a theoretical possibility. Dozens of trekkers are airlifted from the Khumbu region every season. Most of those evacuations are appropriate responses to HACE, HAPE, or injury. Some are unnecessary evacuations driven by panic or, in a small number of reported cases, by guides with financial incentives to call helicopters when descending on foot would have been equally safe and far cheaper. Knowing the legitimate indications for evacuation helps you make a clear headed decision under pressure.

A helicopter evacuation is necessary when: the trekker cannot walk (injury or advanced altitude illness), when the altitude of the incident is so high that walking down to safety would take too long given the severity of the illness, or when HACE or HAPE has been diagnosed and rapid evacuation to a low altitude hospital is needed. If a trekker with suspected HAPE is at Lobuche (4,940m) at night and cannot walk, a helicopter to Kathmandu is the right call.

A helicopter evacuation is not necessary for: a trekker with mild to moderate AMS who is walking normally and can descend on foot with guidance and support, a trekker who simply decided they do not want to continue, or a trekker who is uncomfortable and anxious but has no clinical signs of HACE or HAPE.

The cost of helicopter rescue from the EBC route ranges from approximately $3,000 to $10,000 USD, depending on the location of the incident and whether bad weather requires multiple attempts. This cost is entirely the trekker’s responsibility unless they have proper insurance. Your travel insurance must cover helicopter evacuation to a minimum of $5,000 USD and ideally to $10,000 USD. Confirm that the policy covers high altitude trekking specifically. Many standard travel insurance policies explicitly exclude altitudes above 3,000m or 4,000m. Read the fine print before you buy the policy, not after you need it.

Your insurance card and policy number should be accessible immediately, not buried in your checked luggage. Your guide should have a copy. The HRA clinic in Pheriche, teahouse owners, and the Sagarmatha National Park authorities all have contacts for rescue coordination. In an emergency, your guide is your first call. If you do not have a guide, contact the nearest teahouse owner immediately and tell them the situation.

Before finalising your booking, read about common EBC booking mistakes, where inadequate insurance is one of the most frequent and costly errors trekkers make.

Preparing Before You Go: Your Doctor Visit Matters

A pre-trek medical consultation is not bureaucratic box-ticking. For the EBC trek, it is genuinely important. Here is what to discuss with your doctor.

Your cardiovascular health matters at altitude because your heart will be working significantly harder for two weeks. If you have uncontrolled hypertension, arrhythmias, or a history of cardiac events, your doctor needs to assess whether high altitude trekking is safe for you. Some cardiac conditions are compatible with EBC with proper management. Others are not.

Your lung health matters because HAPE occurs in people with certain underlying pulmonary conditions more readily than in healthy individuals. If you have asthma, discuss whether cold dry high altitude air is likely to trigger it and what medications to carry.

Your prescription medications may interact with altitude or with altitude medications. Diuretics, beta blockers, and some antidepressants all have altitude related considerations your doctor should review.

Ask your doctor to prescribe the following for your emergency kit:

• Diamox (acetazolamide) 125mg if you decide to use it prophylactically, or to have on hand for therapeutic use if AMS begins
• Dexamethasone 4mg tablets for HACE emergency use
• Nifedipine 30mg slow release if you have any history of HAPE or high altitude pulmonary problems
• Ibuprofen 400mg tablets for headache management

Buy a pulse oximeter before your trip. These are available online for $20 to $40 and every EBC trekker should carry one. Measure your baseline SpO2 and heart rate at sea level before you travel. Then use it regularly on the trek to track where you are.

Normal SpO2 at sea level is 95% to 100%. At Namche (3,440m) an acclimatizing trekker might read 88% to 92%. At Dingboche (4,410m) readings of 82% to 88% are common and not necessarily alarming in the context of other normal symptoms. At Gorakshep (5,164m), readings of 75% to 82% are typical for an acclimatizing person, and at EBC itself most trekkers read between 75% and 85%. A reading below 70% at any altitude is a red flag that warrants a medical assessment. A reading below 60% is dangerous and requires immediate action.

The pulse oximeter does not make the clinical decision for you. A person can read 68% and feel fine, while another reads 78% and be developing HACE. Use the number in context. Use it as one input among several, including the Lake Louise Score, the walk test, and your own gut sense of how the person looks and feels.

A Note on Solo Trekking and Altitude Safety

If you trek solo or without a licensed guide, you carry a significantly higher risk in the event of altitude illness. The reasons are practical. A solo trekker who develops ataxia from HACE is not in a position to accurately assess their own coordination. Confusion from HACE actively impairs the judgment needed to recognize confusion from HACE. A solo trekker with worsening HAPE at 3am in a teahouse dormitory may not be discovered in time.

A licensed guide changes this equation completely. A good guide performs symptom checks every morning and evening. They know the walk test. They know the difference between “you have a headache so we rest today” and “you need to go down now.” They know which teahouse has a satellite phone and which trails are passable at night. They know the HRA contacts in Pheriche. They are, in altitude emergencies, often the difference between a bad day and a tragedy.

If you are committed to trekking independently, at minimum trek with at least one other person and agree before the trek begins that either of you has veto power to call for a rest day or descent at any point. No social pressure, no guilt, no “but we have already paid for the next teahouse.” Altitude sickness decisions are not group decisions. They are individual medical decisions that need to be respected.

Frequently Asked Questions

Can you die from altitude sickness on the EBC trek?

Yes, from HACE or HAPE that is ignored or unrecognized. Fatal outcomes do occur on the standard EBC route, at a rate of approximately 1 to 3 per year among 30,000 plus annual trekkers. That is a very low rate, but it is not zero. Virtually every fatal case involves clear warning signs that were ignored, descent that was delayed, or a situation where the trekker was alone or without proper guide support. With proper acclimatization, a reputable guide, and the willingness to descend when symptoms demand it, fatal altitude illness on EBC is extremely rare.

Will I definitely get altitude sickness?

Some level of altitude-related symptoms is almost universal above 4,000 metres. A mild headache on the first night in Namche, disrupted sleep in Dingboche, and breathlessness on the approach to base camp are normal physiological responses, not illness. Clinically defined AMS (Lake Louise score 3 or above) affects somewhere between 25% and 50% of EBC trekkers at some point during the trek. HACE and HAPE are far less common, affecting a small fraction of that number. Most trekkers who start the route and follow a proper itinerary complete it without serious altitude illness.

Does physical fitness prevent altitude sickness?

No. This is one of the most stubborn misconceptions about EBC. Physical fitness helps you walk faster and recover more quickly from exertion. It does not protect your brain or lungs from the effects of low oxygen. In fact, very fit individuals are sometimes at higher risk because they feel physically capable of pushing further and faster than their physiology can safely support. AMS susceptibility appears to have a genetic basis that fitness does not override.

Should I go down if I get a headache?

Not necessarily and not immediately. A mild headache with no other symptoms, appearing on the first evening at a new altitude, can be monitored for 24 hours at the same altitude. Take ibuprofen, drink water, rest. If the headache responds to medication and does not return, and you have no other symptoms, you are likely experiencing mild acclimatization that your body will work through overnight. If the headache is severe, if it does not respond to ibuprofen, if it is accompanied by vomiting or fatigue, or if it is worsening rather than stable, those are reasons to take more decisive action: hold the altitude for another day, or descend 500 metres.

Can children get altitude sickness?

Yes. Children are equally susceptible to altitude illness as adults. The same physiological processes apply, and the same rules of acclimatization are necessary. Younger children may have more difficulty communicating their symptoms accurately, which puts a greater burden on accompanying adults to observe behavioral changes, energy levels, and appetite. The walk test applies equally to children. If you are planning to bring children on the EBC route, discuss it thoroughly with your pediatrician before departure.

Is there a blood test or genetic test that predicts altitude sickness?

Not reliably. Several genetic variants have been associated with increased AMS susceptibility in research settings, but no clinically validated predictive test is available to consumers. Pulse oximetry is useful for monitoring at altitude but does not reliably predict susceptibility in advance. The most reliable predictor of your response to altitude is a previous experience at high altitude. If you have had AMS before, you are more likely to have it again. If you have been to 4,500 metres without significant problems, that is a reasonable positive signal. If you have never been above 2,000 metres, you simply do not know yet.

What does a normal SpO2 reading look like at different points on the route?

At sea level: 95% to 100%. At Lukla (2,860m): 92% to 96%. At Namche (3,440m): 88% to 93%. At Dingboche (4,410m): 82% to 88%. At Gorakshep (5,164m): 75% to 82%. At Kala Patthar (5,545m): 70% to 78% during exertion is common. Values below 70% at any point are concerning. Below 60% requires immediate attention. These are rough ranges: individual variation is significant and a single low reading should be interpreted with clinical context, not in isolation.

Planning Your Trek with the Right Operator

The safest EBC treks are built around acclimatization, not convenience. A proper itinerary includes two nights in Namche, an acclimatization day hike from Namche, two nights in Dingboche with a day hike, and a return to lower altitudes immediately after visiting EBC and Kala Patthar rather than sleeping at Gorakshep for additional nights at high altitude. It does not cut corners to save money or shorten the trip by a day or two.

When you assess operators, ask specific questions. What is the exact sleeping altitude each night? How many acclimatization days are included? What emergency protocols does the guide have? Are guides trained in altitude illness assessment? Does the company carry Gamow bags, pulse oximeters, and emergency medications? Does the itinerary allow for genuine rest days, not just “acclimatization hikes” that are actually full days of trekking at altitude?

A licensed, reputable guide company answers all of these questions confidently and in detail. An operator that tells you “don’t worry, it will be fine” without specifics is one to avoid. If you are in the process of planning, start by reading about planning your EBC trek for 2026 or 2027 to understand the seasonal considerations and booking timeline.

The EBC route passes through some of the most dramatic terrain on earth. The villages on the EBC route from Phakding to Gorakshep are remarkable communities with deep Sherpa cultural traditions. The Himalayan Rescue Association and the teahouse network are a genuine safety net. But none of these systems replace the judgment of a good guide and the preparation of a well informed trekker.

Altitude sickness is manageable. HACE and HAPE are survivable when caught early and acted upon without hesitation. The EBC route sends the vast majority of its trekkers home safely with a memory they carry for the rest of their lives. What separates those trekkers from the small number who do not is preparation, knowledge, and the willingness to respect the mountain’s terms.