Trekking at altitude holds a lot of appeal for hikers. It is only by going high that you can get close up to some of the most iconic and impressive mountains in the world.
I actually quite enjoy it, well most of it… the hard graft and the rewards that go with it.
It pays to give the altitude aspect of your trek some prior thought. At best, suffering mild altitude sickness may spoil your trip for a day or two. At worst it can be catastrophic, leading to death if untreated.
From sea level to 2000 metres you will likely not notice any difference. From 2000 metres and above however, the altitude will start to impact you. At sea level we have access to the 21% of effective oxygen that is in the air but when we reach 3000 metres we are only getting around 14% effective oxygen.
There is still the same amount of oxygen in the air as at sea level, we are just unable to access all of it because of the change in pressure. At 4000 metres there is 12.7% effective oxygen. This drops to 11% when we hit 5000 metres, almost half of what we have at sea level. It is no wonder that trekking feels so challenging the higher we go.
What happens to the body at altitude?
Our breathing rate increases in response to the low oxygen level. Heart rate increases too, helping to move the blood more quickly. Our blood starts to thicken with additional red blood cells. We also urinate more frequently. This is the process of acclimatisation, and if we give it time, our bodies can adapt to our new elevation. Once we are acclimatised it is safe to go higher again, allowing further time to acclimatise along the way.
Symptoms of altitude sickness
If we ascend too quickly or go too high, our body does not have time to acclimatise to this lower level of oxygen. This is where the problems begin. Some people acclimatise quicker than others but it is not uncommon for people to experience symptoms of altitude. AMS (Acute Mountain Sickness) is quite common and if treated should cause no serious problems. The symptoms are:
- Headache
- Nausea
- Fatigue
- reduced appetite
- Poor sleep
- Dizziness
The sympoms of mild AMS can be easily treated with simple things like rest, good hydration and standard painkillers. It is not uncommon though for people to downplay their symptoms. They worry that admitting to being under the weather may impact their trip. The irony is that by saying nothing they are pretty much guaranteeing that this illness WILL spoil their trip as it becomes more serious. Untreated AMS can become very severe and lead to life threatening illness.
I usually experience low grade headaches and reduced appetite once I reach 4000 metres. I manage myself by staying well hydrated and not over exerting (and therefore stressing my body even more). Sometimes I use painkillers to deal with headaches and I maximise rest when I can. If I take care of myself during this early acclimatisation stage I know that I will recover and feel better soon.
Acclimatisation profile
To aid acclimatisation when trekking in the mountains there is a recommended altitude profile to observe when over 3000 metres. There are variations of this and some may think this is a little conservative. Having led over 30 treks at high altitude I would say this is the gold standard.
- Sleep no higher than 300 metres at the end of each day
- For every 1000 metres gained, take a rest day – especially if you have had to sleep higher than the recommended 300 metres
- If you are feeling well, a rest day can include a hike to a higher elevation before returning for the night. If you are not feeling well but things are getting not worse, then rest some more.
Some travel companies offer shorter trips, maybe undercutting others on price. This really can be a false economy as your trip could be totally ruined if you do not have the time to acclimatise properly, and you could even end up being incredibly unwell.
If you are trekking independently it is worth planning your itinerary with this altitude profile in mind. It is not always possible to follow it to the letter. Your camps and water sources may be much higher than the ideal 300 metres per night, and that is fine. If you keep your eye on the bigger picture you can adapt and take acclimatisation days to accommodate this.
In some countries where maps are not so accurate it can be challenging to plan for altitude. I was on a trip a few years ago and had planned to camp at 4200 metres, well that’s what it said on the map. I felt really rough when we got there and so did my buddy. When I checked my altimeter I could see we were actually still up at almost 4600 metres and that the mapping was inaccurate. As we already weren’t feeling great we packed up and moved on, dropping into the valley as far as we could. To stay would have given us a poor night of sleep and potentially made us ill.
At altitudes above 3500 metres our bodies are under a lot of stress. There is an increase of pressure in our blood vessels and if we don’t allow enough time to acclimatise we can experience leaks and fluid build up in the lungs and/or brain. This is what causes the serious conditionss HACE (high altitude cerebral edema) and HAPE (high altitude pulmonary edema).
SYMPTOMS OF HACE
- AMS type symptoms
- Severe headache
- Change in behaviour, for example clumsy, confused
- Reduced level of consciousness
- Loss of physical coordination
SYMPTOMS OF HAPE
- Increased tiredness and fatigue
- A cough
- Breathlessness, even at rest
- Frothy sputum and maybe blood
If untreated, AMS, HACE and HAPE can be life threatening and HACE and HAPE are medical emergencies.
Lake Louise Score System
The Lake Lousie Score System is commonly used to evaluate whether or not someone is suffering AMS and the severity of it. On organised treks you may be asked to score yourself every day – this is really useful in setting a benchmark for your well being from the lowest elevation upwards. You may also use a pulse oxymeter too. Some people get hung up on the numbers but I would argue that generally, the numbers are less important than the pattern. If you are trekking independently I would advise tracking your score daily too. It really helps you see how you and your team are doing and helps in your decision making and management of your itinerary.
A diagnosis of AMS is based on a recent rise in altitude, the presence of a headache and at least one other symptom. Typically, a score of 3 – 5 indicates mild AMS and anything higher is considered severe, with the likelihood of it worsening if action is not taken.
Sleep quality used to be included within the score but research indicated that disturbed sleep may not be a key factor and the system was reevaluated in 2018.
Treatment of altitude sickness
The treatment of mild AMS can be as simple as hydrating and resting. For more serious illness, drugs, descent and emergency evacuation to a medical facility may be required.
On an organised trek your leader should have appropriate experience, some quality first aid training, access to life saving medication, a PAC bag, also called a GAMOW bag and a sat phone with spare charged batteries.
Hydration
Do not underestimate how important hydration is at altitude. It is recommended that you drink around 3- 4 litres of water per day. This may sound a lot, but it is essential to your well being. It can be difficult to get into a good habit with this so you need to be proactive and prioritise it. My system looks like this:
- 2 cup of lemon and ginger tea in the morning
- 1 coffee at breakfast
- 2 litres of water on the trail, that I make sure I drink
- If I get to camp with water left in my bottles I drink it
- 1/2 – 1 litre of electrolyte in the afternoon/early evening
- fruit tea or hot chocolate in the evening
This may look a lot and it can be hard work but I quite simply prioritise it. I prefer to minimise my caffeine intake as if I drink a lot of coffee I feel my hydration passing through me more quickly. I enjoy a morning coffee then generally stick to water, fruit teas and electrolytes.
If you don’t prioritise hydration it is really easy to get dehydrated, it’s a cumulative thing. For a couple of days you feel OK and then the next you’re headachy, feeling sick and underperforming. BTW, these are symptoms of AMS too so if I know categorically that I’m well hydrated, I can put my energy and attention where it needs to go. I also know from experience that I feel better when I am hydrated and my body performs better and it is under less stress this way.
Rest
By resting you are allowing your body to acclimatise and avoiding putting it under any more stress. Rest might look like taking an afternoon nap. Or slowing your pace down and not over exerting is good too. It may look like not hiking on a rest day. It may also be necessary to stay an extra day and night at the same place to really help your acclimatisation. Your itinerary should have enough flexibility to accommodate rest days.
Descent
If altitude sickness is more than mild and rest and hydration aren’t cutting it and it is getting worse, then descent is the only real fix. By descending you instantly start to increase the oxygen available to you. The advised amount is 1000 metres of descent but even a few hundred metres should make a difference.
PAC or Gamow bag
If you are travelling as part of a trekking group I would expect a PAC (portable altitude chamber) or Gamow bag to carried with you as an an essential piece of safety kit. Back in the day a trek leader would get given a bottle of oxygen. Always of dubious origin and you’d never know how much was in it – not much use if you need to assist someone overnight before they can get evacuated in daylight.
The PAC bag is an amazing bit of kit. I have had to use it once, and it saved a life. It is like a super durable plastic sleeping bag. You slide someone in, zip the bag up and start to pump it up steadily with the foot pump. The air pressure inside the bag increases, simulating a lower elevation thus making more oxygen available. A valve prevents the bag over-inflating. Once you start this treatment, you will have to continue until evacuation occurs. You can pop an altimeter in and see it in action, it’s pretty awesome really.
Medicines
I am not a medical professional so I will keep this section brief. There are 3 main medicines available for the treatment of altitude sickness but quite simply if someone has or it is suspected they have HACE, HAPE or severe AMS, the drugs are only a temporary fix until they can be evacuated to hospital.
Acetazolamide aka Diamox is sometimes used preventatively. It does not mask symptoms and it helps the body acclimatise more quickly. If you have any idea that you might want to use it, or you intend to take it on an altitude trek ‘just in case’ I strongly recommend that you speak to a knowledgeable GP before your trek. Some people have a Sulfa allergy and may be unable to use it, although I have read of people trialling it home with their GP’s approval to make sure they have no adverse side effects.
Support crew
In some countries it is common to trek with the support of a local crew. It is often assumed that these local people are already and always acclimatised, either genetically or because of where they live. That is a really unhelpful assumption to make and we must all be aware that our local crew can be susceptible to altitude sickness in just the same way we can. Every year in mountainous regions local people die whilst working because of altitude sickness. For this reason I think it’s really important to offer the same duty of care to people working on treks as the people who are paying to trek.
Further reading
There is a small booklet created by MedEx that is really informative and well worth a read prior to a trip at altitude. For some reason their site is currently down but the download is here:
If you are looking for more general remote first aid and altitude info then this book First aid and wilderness medicine pocket guidebook | Cicerone Press is also a great choice.
