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)

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)