I “read” extensively about Acute Mountain Sickness (AMS) before my trip to Spiti. I understood that it can be very unpleasant at best and fatal at worst. But only when I reached Kaza, I actually “experienced” it. And yes, it was bad!

The experience spurred me to know more about AMS and understand why I experienced headache, nausea, breathlessness and mild fatigue despite having good oxygen levels in blood.

Here, I have interchangeably used the terms “mountain sickness”, “altitude sickness” and “AMS”. To the best of my knowledge, mountain sickness and altitude sickness are mild forms of AMS. AMS can worsen to High-altitude pulmonary edema (HAPE) and High-altitude cerebral edema (HACE). The purview of this post is only till AMS.

What causes AMS?

Atmospheric pressure and air density is high at sea level. This air pressure and density decreases as the altitude increases. Although the “percentage” of oxygen remains same in the atmosphere, less denser air means less “amount” of oxygen. Thus, the “effective oxygen” available in each breath decreases with increase in altitude. Read information on this page for more clarity. Also, temperature, humidity and various other factors affect air pressure and density. So even though two regions have similar altitude, AMS chances might be different.

Given some time and rest, our bodies can adjust to handle these changes. Body creates more red blood cells to transport oxygen more efficiently. This process of body getting adjusted to new conditions is called “acclimatisation”. But when a person gains altitude faster than the body can acclimatise, AMS sets in. Basically, these AMS symptoms are your body signalling you to STOP. If neglected, it can be fatal.

The problem is actually two-fold when you are gaining altitude:

  • Decrease in air pressure – At sea level, air pressure outside is higher than the pressure inside lungs. So it is much easier for lungs to pull in air. When air pressure decreases at high altitude, lungs have to work harder. It’s simple physics; air flows from high pressure regions to low pressure regions. Higher the pressure difference, easier and quicker the air flow. Lower the pressure difference, slower the air flow.
  • Decrease in oxygen – Again, lungs not only have to work harder to pull in air but in each breath, oxygen is lesser than usual.

Thus, the problem is actually compounded. It is a real challenge to all vital organs. The vital organs have to work harder to only get lesser oxygen than they are used to. Breathing becomes rapid and lungs pull in as much oxygen as they can. Heart beats faster and furiously pumps blood to brain and distributes the remaining meagre amount of oxygenated blood as quickly as it can to other vital organs. As a result, blood pressure increases. Basically, body concentrates only on distributing the hard-acquired oxygenated blood to vital organs that are essential for your survival. Vital organs are, brain, heart, lungs, kidneys and liver. At this point, rest of the organs and systems are all secondary.

Body goes into “reserve” mode. Body pushes limits to ensure that vital organs are kept going and has absolutely no interest in pumping precious blood to your muscles so that you can trek. This is why people experience symptoms such as breathlessness, fatigue, nausea, headaches, dizziness and loss of appetite. Body has its priorities after all! It’s almost survival vs trek/vacation.

I made an attempt to mathematically derive how much more efforts our body must exert to keep us going here.

What are the symptoms of AMS?

When you are above 2500mts altitude, attribute any physical discomfort to AMS first.

Do not deny or rationalise that it is not AMS. In fact, treat for and rule out AMS first.

It might look like you have a simple stomach upset but understand why your stomach got upset in the first place. The chances are pretty good that your body has diverted the much needed oxygenated blood from the digestive system to vital organs. So instead of digesting the heavy meal you just had, body finds it prudent or may be even absolutely necessary for your survival, to puke it off.

Some of the common symptoms are:

  • Dizziness
  • Fatigue
  • Shortness of breath
  • Headache
  • Nausea
  • Loss of appetite
  • Sleeplessness

If you experience even one of these symptoms in mountains, treat for AMS first.

How to prevent and treat AMS?

The best prevention is to gain altitude slowly and take ample rest.

  • Do not gain altitude of more than 500mts a day.
  • Take ample rest.
  • Sleep well upon reaching the higher altitude. This gives time for your body to create more red blood cells to transport oxygen more efficiently.
  • Do not ascend until the AMS symptoms have subsided.
  • Do not exert yourself. Do not run, jump or do anything that requires significant physical effort.
  • Stay hydrated by drinking small amounts of water frequently. Do not gulp down a lot of water quickly.
  • Do not eat oily heavy food. Eat simple food that can be easily digested. Carbs are your best bet.
  • Consume simple food in small quantities, just enough to satiate your hunger. Do not stuff yourself.
  • Do not drink alcohol. Alcohol makes it more difficult to acclimate.
  • Do not smoke.
  • If you are used to having caffeinated drinks, do not totally avoid them as caffeine withdrawal symptoms might set in and they are similar to AMS symptoms. You can also try switching to herbal teas.
  • Respect your body, give it time to adjust and pay close attention to any signs it may give.

Take one tablet of Diamox before you have started to gain altitude and have half tablet everyday as a prevention later on.

If these measures do not work and your AMS symptoms persist for more than 7-12 hours or get worse, descend IMMEDIATELY to lower altitude or rush to the nearest hospital. Usually, the symptoms should subside after taking a Diamox and having a good night’s sleep.

If you have any health issues, consult your doctor before planning a high altitude trek or vacation.

Misconceptions about AMS

  • Headache is the only symptom of AMS.
  • Young or fit people do not experience AMS.
  • If you have climbed mountains and have not experienced AMS, it means you won’t experience AMS again.
  • Exercise prevents AMS.
  • MOUNTAIN SICKNESS IS FICTION. Trust me, I freaked out when I heard this from some local drivers. Some of them think that mountain sickness is a figment of travellers’ imagination! I tried educating them but it was all futile.

2 thoughts on “What is altitude sickness and how to deal with it

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