The facts

Altitude sickness, also known as acute mountain sickness (AMS), can occur in some people as low as 2,500m but serious symptoms do not usually occur until over 3,600m, even then it is not the height that is important, rather the speed at which you ascend to that altitude.

AMS is actually more common in fit young men because they are more likely to attempt a rapid ascent by racing up the mountain. As a general rule, it is far safer (and more enjoyable) to avoid altitude sickness by planning a sensible itinerary that allows for gradual acclimatisation to altitude as you ascend. Remember you can hurry back down as fast as you like!

What causes altitude sickness?

The percentage of oxygen in the air remains essentially constant at 21% up until about 21,330m, but the air pressure (and therefore the number of oxygen molecules) drops as altitude increases – consequently, the available amount of oxygen to sustain mental and physical alertness decreases above 3,050m. Altitude sickness usually does not affect persons travelling in aircraft because the cabin altitude in modern passenger aircraft is kept to 2,440m or lower.

Symptoms

Mild AMS

  • Headache
  • Nausea & Dizziness
  • Loss of appetite
  • Fatigue
  • Shortness of breath
  • Disturbed sleep
  • General feeling of malaise

Moderate AMS

  • Severe headache that is not relieved by medication
  • Nausea and vomiting, increasing weakness and fatigue
  • Shortness of breath
  • Decreased co-ordination (ataxia)

Severe AMS

  • Results in an increase in the severity of the aforementioned symptoms including: Shortness of breath at rest, inability to walk, decreasing mental status, fluid build-up in the lungs.

Potential consequences:

High Altitude Pulmonary Oedema (HAPO)

HAPO results from fluid build up in the lungs. This fluid prevents effective oxygen exchange. As the condition becomes more severe, the level of oxygen in the bloodstream decreases, which leads to cyanosis, impaired cerebral function, and death.

How to avoid altitude sickness

The only cure for altitude sickness is either acclimatisation or descent. Here are our top tips to keep you fit and well on the mountain:

  • Drink plenty of water. What you might think is altitude sickness might actually be dehydration, caused by the higher rate of water vapor lost from the lungs at higher altitudes. Avoid caffeine and alcohol, as these can increase the likelihood of dehydration. If it’s humid and you’re losing a lot of water through perspiration, maintain an electrolyte balance with sports drinks targeted specifically for this purpose.If you have a headache, drink one liter of fluid, and take some acetaminophen (brand name: Tylenol). If the headache disappears completely and rapidly, and you have no other symptoms of AMS you’re probably dealing with dehydration rather than altitude sickness.
  • A slow and steady ascent is vital to give your body enough time to get used to the rarefied air
  • Eat a high calorie diet while at altitude
  • Follow the “golden rule” – climb high, sleep low. Once you’ve made your way up past 3,000 metres (10,000 feet), do not ascend more than 300 metres (1,000 feet) per day to sleep. You can climb as high as you want, just make sure that you come back to a base camp that’s no more than 300 m (1,000′) higher than your previous night’s sleeping elevation. This is a useful guideline to keep in mind if you’re driving to a high altitude, as well.
  • Know the symptoms – if you spot any of the symptoms of altitude sickness, either with yourself or those around you, do NOT continue the climb. Stop and if necessary descend until the symptoms disappear.
  • Take it easy. The last thing you would want to do is to overexert yourself. It is harder to breathe at higher altitude and even if you are fit, you can still feel the effects if you push yourself too hard too quickly. Resting at the altitude at which you became ill is often the most effective remedy for altitude sickness (other than descent). You’ll usually feel better in 1-2 (or up to 4) days.
  • Avoid tobacco, alcohol and other depressant drugs including, barbiturates, tranquillisers, sleeping pills and opiates such as dihydrocodeine. These further decrease the respiratory drive during sleep resulting in a worsening of symptoms.
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