Altitude illness and Acclimatization; Thriving at high altitude

Altitude illness refers to the spectrum of diseases that occurs at high altitude (above 2,500 meters) as a result of failure to acclimatization. Altitude illness primarily involves following three syndromes:

  1. Acute Mountain Sickness (AMS)
  2. High Altitude Cerebral Edema (HACE)
  3. High Altitude Pulmonary Edema (HAPE)

Before jumping into these diseases per se let’s briefly recall some physics at high altitude. Basic physics says, with the gain in altitude the atmospheric/air pressure decreases but the percentage of the oxygen (21%) in the atmosphere remains constant. This results in decrease in the pressure exerted by the oxygen which is known as partial pressure of oxygen. As a result, the amount of the oxygen available for the exchange during ventilation decreases resulting in decrease in oxygen (hypoxemia) in the human body. This hypoxemia stimulates our body to make changes to adjust to this hypoxic environment. This is called acclimatization. And, the failure to acclimatize results in some form of altitude illness.

Acute mountain sickness (AMS):

AMS is a very common reversible condition that is characterized by headache plus any of these (fatigue, nausea/vomiting/loss of appetite, dizziness and sleep disturbance). These symptoms are similar to “HANGOVER“. Based on the severity of these symptoms it is classified as mild, moderate and severe.

Mild AMS can be treated in the same altitude with extra day or a couple of days to acclimatize along with treatment with acetazolamide and other supportive medications. However, moderate to severe form of disease needs immediate descent.

High altitude cerebral edema (HACE):

HACE is the swelling of the brain which is characterized by symptoms of AMS along with some form of neurological involvement like blurring of vision, irritability, confusion, disorientation, inability to walk in straight line, etc. This is potentially fatal form of altitude illness and requires immediate descent. If anyone looks like DRUNK then think of HACE!

High altitude pulmonary edema (HAPE):

HAPE is the swelling of the lungs which is characterized by the cough, non-exertional (at rest) breathlessness, fatigue, blood in sputum, chest pain, etc. This is also potentially fatal condition and requires immediate descent.

What causes altitude illness?

  • Rapid ascent to high altitude
    • Sleeping altitude >500 meters/day and lack of rest days after climbing >1000 meters
  • Over exertion
  • Dehydration
  • Past history of altitude illness

What to do if I get altitude illness?

  • Stop further ascend (Don’t use horse/donkey to climb up) and start to climb down if symptoms are worst
  • Start acetazolamide if you have any (250 mg)
  • Take painkillers for headache (Paracetamol/acetaminophen, ibuprofen)
  • Hydrate adequately

How to prevent altitude illness?

  • Slow and gradual ascend (300-500 meters) sleeping altitude every day with rest day after 1,000 meters climb
  • Avoiding over exertion
  • Adequate hydration
  • Avoid alcohol and sedatives

Listening to your body’s response, following the simple rule of slow and gradual ascend and giving adequate time to acclimatize is key to success in the mountains! Keep hydrated, fresh and make your trip to mountains memorable, joyful and spiritual.

Safe travels!

Dr. Santosh Baniya, MD (April, 2022)

Mythbuster; 10 Myths And Facts About Altitude Illness

In a sunny day with clear blue sky and the Annapurna range in the background I was having a tea chat with my good friend at Lakeside, Pokhara gazing the beautiful Fewa Lake. Few tables around us were occupied and everyone was busy talking and scrolling through their mobile phones. Out of nowhere I noticed very distinct voice saying “hya tension nali kta ho you lek lagne vaneko bidesi lai matrai ho” which translates “don’t worry guys only foreigners get this altitude illness”. This statement caught my attention but in the middle of everything I couldn’t do much but procced with our chat.

It was not the first time I have heard someone making statements like this. In fact, I have been dealing with situations which are much worse and illogical. I have encountered many educated youths make irrelevant & illogical hypothesis about altitude illness, ignoring the potential dangers in the mountains and promoting unsafe practices.

So, let’s make some clarification about the myths of altitude illness and related topics which is very prevalent in the world.

Myth No 1: Altitude illness is disease of foreign travelers/mountaineers. Locals don’t get altitude illness!

Fact No 1: No-one is immune to altitude illness. Anyone can get altitude. Yes! High altitude residents and inhabitants are adapted to environment but they are also vulnerable to some form of altitude sickness like chronic mountain sickness, re-entry pulmonary edema, etc. 

Myth No 2: Altitude illness is caused by odor of certain flowers in the mountains.

Fact No 2: Altitude illness is caused by lack of oxygen (Hypobaric Hypoxia). After exposing to high altitude (>2,500 meters) if our body fails to acclimatize then we get one or other form of altitude illness. If you were to get altitude illness from odor of flowers then why don’t you get altitude illness when you climb down in the presence of same flower?

Myth No 3: I am physically too fit to get altitude illness.

Fact No 3: Everyone is susceptible to altitude illness regardless of the physical condition. Good physical condition definitely keeps you in shape and physically it would be easier to climb. But, keep in mind that we might increase the risk of getting altitude illness if you overexert in altitude. And, fit ones tend to ignore the early signs of altitude illness thinking they are too fit to get sick.

Myth No 4: Using garlic and ginger prevents altitude illness.

Fact No 4: Garlic and ginger doesn’t prevent altitude illness. Slow and gradual ascent prevents altitude illness. I don’t discourage you use garlic or ginger or any other food (except alcohol) but please take into consideration other proven methods like slow and gradual ascent, less exertion, etc for prevention of altitude sickness.

Myth No 5: Girls are more prone to altitude illness.

Fact No 5: There is no gender difference regarding altitude illness. Both are equally prone to it. Beside genetic predisposition, everyone is prone to getting altitude illness if you are not following the recommendations and listening to your body.

Myth No 6: Alcohol keeps you warm. So, drink rum when you are at altitude and it is cold.

Fact No 6: Alcohol in fact promotes heat loss and predisposes to get cold. You might feel like drinking hot rum keeps you warm but it’s not true. Please avoid alcohol (especially heavy drinking) if you are traveling to high altitude

Myth No 7: Drinking extra water prevents you from altitude illness.

Fact No 7: Drinking extra water won’t prevent altitude illness. We pee more frequently when we are exposed to altitude due to acclimatization but it is important to replace the fluid. And, signs of dehydration are similar to mild acute mountain sickness. So, it is important to keep well hydrated to replace the lost water and not confuse signs of dehydration with altitude illness. Don’t drink too much of water to avoid side effects of over hydration. Check you urine color!

Myth No 8: Don’t use caffeine at high altitude.

Fact No 8: Caffeine is a mild diuretics i.e. it makes you pee more but it won’t dehydrate. There is no any strong recommendation regarding use of caffeine at high altitude. In fact, caffeine is respiratory stimulant so it might help you with acclimatization. On the other hand, if you are heavy caffeine consumer and you stop taking at altitude then you will develop withdrawal symptoms like headache, palpitation.  So, there is no need to make specific change in the consumption of caffeine at high altitude.

Myth No 9: Elderly and Children are likely to suffer from altitude illness.

Fact No 9: Elderly are more likely to adhere to the “slow and gradual ascent profile”, they don’t overexert and notice & report the symptoms early so they are less likely to get altitude illness.

Similarly, there is no evidence to suggest children are more vulnerable to altitude illness. Yes, they are more likely to miscommunicate and report problems late. But, they are equally prone to getting altitude illness as adults are.

Myth No 10: Drugs like acetazolamide (Diamox) masks symptoms.

Fact No 10: Diamox doesn’t mask the symptoms. When used for prevention they help in acclimatization and it won’t cause any rebound symptoms. It is recommended to use for prevention if specific situations as suggested by your doctor.

Dr. Santosh Baniya, MD (April, 2022)

Headache in High Altitude

Headache is the most common symptoms travelers experience during travel to high altitude. It is found to be experienced by more than half of the travelers above 2,500 meters. And, probably almost all the travelers going to high altitude experience headache at least once in their lifetime.

At high altitude, headache is an abnormal response of body to the hypoxia and is manifested as an isolated symptoms called as “High altitude Headache” or a mandatory component of “Acute Mountain Sickness”. And, other headaches that are not-altitude-related (but occurring in altitude) are sinus headache, tension type headache, migraine, dehydration, environmental effect (d/t cold, light reflection), stroke and sometimes fatal “cerebral venous thrombosis” headache or subarachnoid bleed headache.

As headache is a very common symptom experienced anywhere, it usually is not taken too seriously and often ignored. Headache of non-serious origin in high altitude like headache due to dehydration, environmental effect & high altitude headache are benign and are easily treated with general measures. But, headache should never be ignored and other red-flag signs/warning signs should always be checked for.

Red Flag signs:

  • Sudden onset severe headache (Not experienced before)
  • Associated with fever, vomiting, seizure, weakness (paralysis), blurred vision
  • Personality change
  • Disturbed consciousness/confusion
  • Drowsiness

Distinguishing different types of headache:

  • High altitude headache:
    • Develops within 24 hours of ascent to high altitude (>2,500 meters) and subsides within 8 hours of descent
    • Isolated, mild to moderate intensity headache without other symptoms like nausea, poor appetite, fatigue, dizziness is classified at high altitude headache.
    • Caused by mild brain edema as a result of hypobaric hypoxia

  • Headache of Acute mountain sickness:
    • Headache associated with any of the following symptoms:
      • Poor appetite or nausea or vomiting, Dizziness, Fatigue and Poor sleep
      • Develops after 8 of ascent to high altitude (>2,500 meters)
    • Caused by the brain edema as a result of failure to acclimatize in hypobaric hypoxia.

  • Migraine headache:
    • Similar to character as in sea level but headache may not be typical “one-sided headache“. Often hard to distinguish from the headache of AMS but following characteristics are important to distinguish it from other headache:
      • Often unilateral but not necessarily. Moderate-Severe intensity pulsating headache lasting few to many hours and associated with “Photophobia
    • Migraine attacks are found to be aggravated by hypoxia at high altitude.

  • Sinus headache:
    • Often confused with migraine headache at altitude.
    • Typical features include
      • Pain, pressure and fullness in cheeks, brow or forehead
      • Worsening pain on bending forward or lying down
      • Stuffy nose
      • Achy feeling in upper teeth

  • Tension type headache:
    • Mild to moderate headache described as “feeling like a tight band around head“.
    • Typical features include:
      • Dull aching headache
      • Sensation of tightness or pressure across the forehead or on the sides and back of head
      • Tenderness in scalp, shoulder and neck muscles

  • Cerebral venous thrombosis:
    • This is clot of blood in the veins around the brain. Potentially fatal and often presenting with continuous headache with stroke like features.
    • Typical features include:
      • Unusual headache (not previously experienced) and associated with blurred vision, feeling/being sick, neurological loss, drowsiness or seizures.
      • Headache worsening on bending forward or lying down.

  • Subarachnoid bleed headache:
    • This is bleeding in the subarachnoid space (covering of brain).
    • Typical features include:
      • Very severe thunderclap headache (Worst headache of lifetime)
      • Often associated with neck stiffness and
      • Feeling/being sick

What should I do to treat headache?

You can always try some “over-the-counter” drugs like Paracetamol, Aspirin, Ibuprofen and take few more measures like keeping yourself warm and hydrating. But, if the headache is persistent and is accompanied by other red-flag signs then it’s the time to seek further medical help.

Always look for the red-flag signs of headache and watch out for symptoms of altitude illnesses. If headache is unusual and with red-flag signs then don’t hesitate to climb down and get consultation.

Safe Travels!

Dr. Santosh Baniya, MD (November 2022)

Tips for successful travel in high altitude

No matter how exciting the travel is to the high altitude, it is always challenging and is never free of troubles. We have hundreds of stories of people loosing lives in mountains due to lack of preparation and making very minor and stupid mistakes in high altitude.

The summit/trek success depends on few very important things which should be followed properly and I recommend you to follow these as a “standard set of checklist” before you start your high altitude travel.


              Well organized pre-planned trip is the backbone of a successful trip to the high altitude and this is applicable from beginners to technical mountain summiteer. Pre-planning includes the following sets of planning:

  1. Appropriateness of travel destination:
    1. First and the foremost, make sure if the destination you choose is appropriate based on your physical fitness, past medical history and previous experience. If you are planning your first high altitude trek then it is better to have a short hikes in high altitude (2,500 meters -3,500 meters) to experience how it feels like to be in thin air.
  • Planning of itinerary:
    • A slow and gradual ascent profile is the key to successful acclimatization. Never ascent more than 500 meters of sleeping altitude per day and take a rest day after ascent of >1000 meters.
  • Health insurance plan:
    • Make sure the insurance plan covers all possible events during the travel. Check with your insurance company in advance and talk to them to make sure the policy covers altitude illnesses and other travel related illnesses.
  • Check weather forecast:
    • These days it is possible to check in advance the weather forecast. Prepare for the possible unexpected environmental changes and pack accordingly. Unexpected snow, rain, snowstorm, lightning, etc causes unexpected consequences if you are unprepared. So, preparation for possible unexpected events is vital for trouble free travel.
  • Medical Kit:
    • Make sure you have enough medical supplies for basic first aid. You can costumize your kit based on your expertise and experience/training. However, I recommend you to have following medications/items before you embark on your trip:
      •  Crepe bandages
      •  Gauze pieces/pads and band aids
      •  Betadine/antiseptics
      •  Ointments for burn, allergies and antimicrobials
      •  Painkillers (paracetamol, ibuprofen, aspirin, etc)
      •  Anti-emetics
      •  Acetazolamide

We can prepare you the first aid kit based on your need/demand and get it delivered at your doorsteps.

Get checked out:

              Before you start your trip to high altitude please get yourself checked up with your GP/Primary Care Physician. In fact, it is mandatory for people with pre-existing medical problems and follow doctor’s recommendations.

              You can book an appointment for pre-travel consultation here.

Get Fit:

              Physical fitness is not the predictor of altitude illness but it is important to be fit to endure in the high altitude. If you are physically fit then you have better chances of being more resilient and not get other injuries and illness.

              You can prepare physically by doing regular physical exercises like running, walking long distances, swimming, biking, weight training, etc.

Get Educated:              

Proper knowledge about altitude illnesses & its prevention, terrain, weather & topography, local culture, food, religion, clothing, foot wares and basic first aid is very important in making the trip successful. Experts agree that knowledgeable travelers are more likely to be safe and healthy.

Safe travels and stay safe!

Dr. Santosh Baniya, MD (June, 2022)

Level of difficulty in expedition

Trek/Expedition difficulty levels:

There is no specific classification on level/grades of difficulties for an expedition or trek. Please follow the following “Level of difficulty” which is prepared based on my experience and extensive literature reviews.

  • Level 1:
    • Fitness level: Low fitness level/regular daily activities
    • Technicality: No technical skills required
    • Total duration of trip: 3-7 days
    • Duration of hike/trek: 3-5 hours/day
    • Altitude: Below 3,000 meters
    • Terrain: Well-maintained path with frequent exposure with locals/villages
    • Past experience: Not required
    • Accommodation: Tea house/lodges/hotels
  • Level 2:
    • Fitness level: Medium/1-2 days of cardio exercise/week
    • Technicality: No technical skills required
    • Total duration of trip: 7-14 days
    • Duration of hike/trek: 4-6 hours/day
    • Altitude: 3,000-5,000 meters
    • Terrain: Steep hills, usually rough trails, occasional encounter with horses/mules with less frequent exposure with locals/villages
    • Past experience: Previous hiking, camping or level 1 trekking experience required
    • Accommodation: Tea house/lodges with camping (optional)
  • Level 3:
    • Fitness level: Good/3-4 days of cardio exercise/fitness training per week
    • Technicality: Basic skills on crampons, knots and ice axe required
    • Total duration of trip: 12-21 days
    • Duration of hike/trek: 5-8 hours/day
    • Altitude: 3,000-5,500 meters
    • Type of trail: Steep hills, mostly rough trails, a couple of passes, exposure with snow & glacier, occasional exposure with locals/villages
    • Past experience: Previous exposure to high altitude trekking required
    • Accommodation: Tea house/lodges plus camping (mostly)/semi-expedition style
  • Level 4:
    • Fitness level: Good and above average/Regular daily exercise
    • Technicality: Efficient with crampons, ropes, knots and ice axe
    • Total duration of trip: 2-4 weeks
    • Duration of hike/trek: 5-8 hours/day
    • Altitude: 5,000-6,000 meters
    • Type of trail: Steep hills, rough trails, high passes, glacier and snow crossing and rare exposure with other people
    • Past experience: Previous level 3 trekking experience required
    • Accommodation: Mostly camping/expedition style

Dr. Santosh Baniya, MD (April, 2022)

Travelers diarrhea; A complete guide to avoid the illness

What is Travelers’ diarrhea?
It is the gastrointestinal infection occurring in the travelers within 10 days of travel as a result of
virus, bacteria or parasites. It particularly occurs if someone has travelled to an area with poor hygiene
and sanitation.
Travelers’ diarrhea is the most common and most predictable illness among the travelers.

How do I get traveler’s diarrhea?

  • It is acquired by eating food or drinking water containing any bacteria, virus or parasites. The
  • water and food is contaminated and ingested due to one of the following reasons:
  • No proper had hygiene is maintained (hand washing/use of sanitizer)
  • Drinking unsterilized/unpurified water or water of unknown source (contaminated) or
  • beverages.
  • Tap water and ground water in Nepal are all assumed contaminated!
  • Eating unsafe street food or food not properly stored and handled in buffet restaurants
  • Eating raw, uncooked, unwashed vegetables and fruits
  • Eating improperly handled meat, poultry products, dairy products, etc

What are the symptoms of travelers’ diarrhea?

Sudden onset (within 10 days of travel) of bothersome symptoms that ranges from mild to severe symptoms as follows:

  • Loose stools
  • Abdominal cramps
  • Nausea/Vomiting
  • Fever
  • Blood in stools
  • Bloating
  • Lethargy
  • Tiredness
  • Dizziness and sweating

Symptoms lasts based on the origin of the diarrhea. Viral diarrhea usually lasts 2-3 days, bacterial diarrhea lasts 5-7 days and parasitic diarrhea persists for weeks to even months without treatment.

How do I treat travelers’ diarrhea?

Milder form of disease can be treated at home/hotels by replacing the fluids (preferably WHO
standard ORS) and with supportive care.
Severe form of disease need in-hospital management with intravenous fluids, antibiotics and
necessary supportive care.

What can be done to prevent travelers’ diarrhea?

The classic golden rule is “Cook it, Boil it, Peel it or Forget it”. You have to be cautious with not just
what you eat but where you eat as well. Following measures can be taken to minimize the chances
of not getting diarrhea:

  • Following proper hand hygiene
  • Avoid restaurants and pubs/bars that looks unclean and you are not confident about the
  • hygiene
  • Avoid using unpurified water. Say NO to tap/ground/unbottled water in Nepal. Even “Jar
  • water” are not always purified as per the standards.
  • Never eat street foods
  • Always wash your fruits and vegetables with clean water or peel it
  • Don’t eat green salads and raw vegetables.
  • Don’t put regular ice in your drinks at bars/pubs/restaurants
  • Don’t eat food from unknown sources
  • Don’t always get your mouth in direct contact with utensils. Use straws instead of directly
  • drinking from glass.

When do I seek medical attention?

It is very important to look for medical attention if you have any of the signs/symptoms as

  • Bloody diarrhea
  • FeverSevere abdominal pain
  • Signs of dehydration (dry mouth, sunken eyes, dry tongue, decreased urine formation)
  • You are not getting better in a couple of days
  • You are not sure if your home remedies is helping you and
  • You have significant past medical problems

Don’t just go to any hospitals you see. Travel clinics with doctors experienced in handling travelers is
required. Diarrhea in local population is different to travelers’ diarrhea so, there are chances you won’t
get proper care and updated treatment. So, always visit the travel clinic or doctors experienced in travel


Dr. Santosh Baniya, MD (April, 2022)

Unaware and Ignorant Pilgrims

Pilgrims in the Himalayas have been travelling to high altitude pilgrimage sites since ages with absolutely different mind-set, in comparison to other (usually younger) travelers. The aim here is to gain spiritual connection with the god, to wash the sins by taking a holy dip or bath and find a path to salvation following various methods and processes. In fact, this group of population is the first ones to get to the mountains who actually identified and opened the pathway to this heaven. However, strikingly they are the ones who are least informed and are unaware about the potential dangers of exposing to this extreme environmental conditions.

I have been dealing with this group of population in high altitude since 2012 and I have always been amazed with the way they have been dealing with all sorts of situations in the mountains. Every now and then I attend these pilgrims with some sort of problem either in the mountains or in my emergency room.

Recently I attended a female patient of 65 years age in my emergency room who was rescued down from Muktinath (3,800 meters) after she developed severe acute mountain sickness (AMS) and high altitude pulmonary edema (HAPE). Detailed interview with the patient and her husband revealed that she was resident of Kathmandu (1300 meters) and she started her journey from Pokhara (800 meters) to Jomsom (2,743 meters) on flight and went to Kagbeni (2,804 meters) via jeep on first day of travel. Next day, she went to Muktinath (3,750 meters) and developed symptoms (headache, vomiting, extreme fatigue, dizziness, cough, shortness of breath at rest). Then she was brought down to Jomsom and was treated for altitude illness and later evacuated to Pokhara at Western Regional Hospital.

This case is just a representative of many other similar and even more dangerous cases I have been witnessing.

Anyone who is used to travelling in high altitude and is keen to keep him/herself healthy in that environment must know how to plan the ascent, what to do and what not to do in the altitude. Here, I have shortlisted a few very important things one should be aware of and should not ignore when travelling to the high altitude destinations (especially focused for pilgrims!):

  • Plan the ascend profile; “Slow and gradual ascent” a 300-500 meters of sleeping altitude every night followed by a rest day after 1000 meters ascent above 2,500 meters.
  • Adequate hydration (drink plenty of water/fluids, oral rehydration solutions)
  • Avoid fasting (as much as possible)
  • Avoid overexertion
  • Report the early signs of altitude sickness like headache, weakness/fatigue to the partner/friend or medical personnel if possible and plan for decent if necessary!
  • Avoid exposure to cold
  • Use proper footwear, clothing including caps/hats and sunglasses
  • Use proper skin care products (sunscreen, lip balms)
  • Consult with your doctor if you have pre-existing illnesses like hypertension, diabetes, cardiac diseases, blood disorders, endocrine disorders, etc
  • Use medications for prevention in cases of unavoidable rapid ascent as per the prescription from experts in mountain medicine.
  • Pre travel consultation with your GP/Primary care physician with mountain medicine expertise

I wish you your upcoming journey to the religious sites of Himalayas to be full of spirituality and wish you to gain more sweetness and happiness to your life and into this world.

Dr. Santosh Baniya, MD (March, 2022)

Rapid ascent to high altitude: Fast, Fun but Fatal

Under clear blue sky, facing snowcapped towering mountains and enjoying the majestic view of the highest lake in the world, Lake Tilicho (4,919 meters) is probably in every trekker’s bucket list. But, I bet you it is not easy and which is why not everyone can do this. After the construction of the road from Besisahar (760 meters) through Chame (2,650 meters) to Manang (3,519 meters) and Khangsar (3,800 meters) recently more and more nature lovers and trekkers are now able to live their dream to see the majestic Lake Tilicho.

 “It was very easy for us to go Lake Tilicho and cross Thorong-La pass, and it was the best thing my eyes had ever witnessed. The only regret was, two of our friends could not make it because they got sick at Manang and had to turn back”, my younger brother (Sangam Baniya; an MBA student) shared his experience after his group completed the Annapurna circuit trek on November, 2016. My brother’s group started the trek from Besisahar (760 meters) in a jeep, went to Manang (3,519 meters) in a day and then started the trek next morning. Despite my strong recommendation to avoid the rapid ascent (climbing >500 meters sleeping altitude per day) to high altitude (Manang) on jeep, they did it their way. I had suggested a slower rate of ascent. So, the only help I could offer them as a doctor was to start them on prophylactic Diamox (acetazolamide) one day earlier before they started the trip, told them to watch out for the signs of altitude illness, and get adequately hydrated and pray for good health.

 “22,108 foreign tourists and around 8,392 domestic tourists trekked through the trails of Annapurna circuit in 2016”, said Babu Lal Tiruwa UCO officer of Annapurna Conservation Area Project (ACAP) Manang during a press meet at Himalayan Rescue Association (HRA), Kathmandu. “This figure was highest ever in the history of Annapurna region in both categories” he added. “Amongst the domestic trekkers majority were found to be young boys and girls aged 16-30 years and also the majority of them were found to take a jeep or motorbike from Besisahar to Manang or Khangsar”, said one of the lodge owners from Manang. The statistics from the Himalayan Rescue Association aid post in Manang from fall of 2016 has the alarming figures which show that more than half of the altitude sickness patients traveled to Manang by motor vehicle. The study on the rapid ascent using motor vehicle to Manang is under analysis and more results are yet to come. “Number of patients with severe form of altitude illnesses, that is high altitude cerebral edema and high altitude pulmonary edema in Nepali trekkers has dramatically increased in 2016 compared to previous years”, said Mr. Thaneswor Bhandari from HRA aid post in Manang.

With the gain in altitude there is decrease in atmospheric pressure and partial pressure of oxygen. However, the percentage composition of oxygen (21%) in the atmosphere remains the same irrespective of altitude. This state of reduced partial pressure of oxygen in high altitude (>2,500 meters) is known as hypobaric hypoxia. On exposure to the hypobaric hypoxia the human organ-system starts to undergo changes to cope up the reduced oxygen pressure. This is called acclimatization. During acclimatization the rate of breathing increases, heart rate increases and kidneys make more urine. These changes starts as soon as we are exposed to high altitude and it takes days for the human body to fully acclimatize. If we stay for longer duration then human body starts to make more red blood cells.

Altitude sickness is common pathological condition in high altitude because of our body’s inability to acclimatize properly. Altitude sickness includes:

  1. Acute mountain sickness (AMS)
  2. High altitude cerebral edema (HACE) and
  3. High altitude pulmonary edema (HAPE)

 Acute mountain sickness is common form of altitude illness affecting around 60% of trekkers travelling to high altitude (>2,500 m). The cardinal symptom is headache which is accompanied by nausea, poor appetite, dizziness, fatigue or poor sleep. Depending on the severity of the symptoms it can be mild or moderate-severe AMS.  The end spectrum of the AMS is high altitude cerebral edema (HACE) which means water in the brain. It is signified by the presence of symptoms like confusion, irritability, disorientation, lethargy, drowsiness, ataxia on walking in a straight line along with symptoms of acute mountain sickness. The collection of fluid in the lungs is known as high altitude pulmonary edema (HAPE) and is characterized by non-exertional breathlessness which is more on lying down and at night, cough which is usually dry than frothy and blood mixed, drop in exercise performance, fatigue, chest tightness and sometimes low grade fever. This usually occurs after 3-4 days of ascending to high altitude but it can also occur suddenly in rapid ascent profile.

Mild acute mountain sickness is usually harmless and can be treated by taking extra rest day, using diamox, and plenty of fluids and also pain killers like paracetamol or ibuprofen, may help. But, patients with, moderate-severe form of acute mountain sickness must be brought down to lower altitude and treated otherwise there is a high chance of developing high altitude cerebral edema. High altitude cerebral edema and high altitude pulmonary edema are potentially fatal condition and patients should be immediately evacuated from the high altitude. Descent, descent and descent is the only treatment of these severe forms of altitude illnesses. In situation where planned evacuation is not possible, due to for example bad weather, in the middle of night medical treatment can be done if resources are available. Oxygen using oxygen cylinder or concentrator and Gamow bag which is a portable altitude chamber can be used to buy time until the evacuation is planned.

Importantly, these altitude illnesses are preventable conditions and lives can be saved from potentially fatal conditions like HACE and HAPE if we stick to simple rules. First rule is making the ascent profile “slow and gradual” which means not increasing the sleeping altitude more than 500 meters per day compared to previous night’s sleeping altitude and taking a rest day after ascending 1,000-1,200 meters above 2,500 meters. Reducing the other risk factors like over exertion, dehydration, improper clothing is equally important in prevention. Thirdly, individuals with the past history of altitude sickness can be started in diamox half a tablet (125mg) morning-evening one day prior of trek to reduce the chance of getting altitude sickness.

Sticking to the rule of slow and gradual ascent (this doesn’t mean walking slowly but rather not excessively gaining sleeping altitude compared to previous night as described above), avoiding sudden gain in altitude by motor vehicle and trekking through the trails we can make our trip more memorable, enjoyable and also altitude illness free.

Dr. Santosh Baniya, MD (Jan, 2017)

(Note: Revised version of this article was published in “The Himalayan Times” with changed title and contents on Feb 8th 2017.)

Calculating oxygen capacity of cylinder and it’s lifespan

Supplementing oxygen through the oxygen cylinder either to thrive in extreme altitudes (>8,000 meters) to ascent peak or to treat hypoxia related illnesses is a very common practice. This has been in practice since decades. But, every time someone decides to use the oxygen cylinder, s/he faces the most difficult questions;

  1. How much oxygen is there in the cylinder? And,
  2. How long will it last?

Cylinder size and total oxygen capacity:

The oxygen capacity of the cylinder depends on the size of the cylinder and here is the common type of cylinder size and its capacity:

Cylinder sizeDEFGJ
Oxygen capacity (Liters)340680136034006800
Water capacity (Liters)2.3L4.7L17L39L47.2L

To calculate the oxygen capacity of any type of oxygen cylinder the formula is:

Cylinder Capacity (Liters) = Water capacity × 144

Longevity of the cylinder/Duration of oxygen supply:

              This depends on the flow rate, cylinder (tank) pressure, residual pressure and conversion factor of different cylinder size. And, this can be calculated using the following formula:

Time to runout a cylinder = (Cylinder pressure in PSI – 200) × Cylinder conversion factor ÷ Flow rate (Liter/min)

Residual pressure = 200 (constant)

Cylinder pressure = measured in the pressure gauze attached to the cylinder

Flow rate = desired flow rate adjusted in the flow meter

Cylinder sizeCylinder conversion factor

Cylinder conversion factor = depends on size of cylinder


Please calculate the time to rundown the oxygen cylinder (F-size) at given pressure and flow rate:

Gauze pressure = 2,000 psi

Residual pressure = 200 psi

Flow rate = 5 liter/min

Time duration = (2000-200) × 0.68 ÷ 5  

                      = 244.8 minutes or 4.08 hours

Safely used the oxygen delivery devices!

Dr. Santosh Baniya, MD (July, 2022)