Acute Mountain Sickness is what medical people call altitude or mountain sickness; 'acute' simply means that the onset is sudden. AMS symptoms do not last, and, if mild or moderate, may disappear if the victim rests or ascends no further; if they are severe, the victim must descend. Most people who attempt Kilimanjaro have invested a lot of time and money, so the stakes are high. Learn to recognise whether AMS is mild, moderate or severe.

Mild AMS
Mild AMS feels like a hangover and can affect people at any altitude above 7000 feet or even lower. Its commonest symptom is a headache (which should respond to aspirin, paracetamol or ibuprofen) combined with at least one of the following:

• feeling sick
• lack of appetite
• difficulty sleeping
• general malaise (feeling lousy, lacking energy).

Moderate AMS
Moderate AMS differs from mild in that:

• there is likely to be vomiting
• the headache does not respond to pain relief
• the victim may be very short of breath even when not exercising (eg after 15 minutes’ rest).
  

Mild AMS is bearable, and affects most people who attempt mountains such as Kilimanjaro to a greater or lesser extent. Moderate AMS can be seriously unpleasant, and some sufferers have to give up. Although symptoms may clear if there is no further ascent, very few Kilimanjaro trips have the flexibility to allow individuals prolonged rest or to postpone the summit attempt. In practice the choice tends to be simple: continue the ascent or descend.

Severe AMS
Severe AMS is different again:

• there is ataxia - the word medical people use to describe loss of muscular
• co-ordination and balance, as when somebody stumbles, staggers or falls (but see below)
• there may be altered mental states, such as confusion, aggression or withdrawal
• it may lead to fluid leakage into the brain and/or lungs (see Complications, below)

if untreated, it can cause coma followed by death.

However, there are many other causes of ataxia, such as extreme fatigue, hypothermia, dehydration and low blood sugar. Get the suspected victim to have a short rest, a drink, and a snack, and put on extra clothing if need be: this should take care of other possible causes. If they recover promptly, the ascent can continue. If symptoms persist, or if there is mental confusion and/or extreme shortness of breath while at rest, suspect severe AMS.

Severe AMS is avoidable and treatable, but only if you are aware of the possible risks and look out for yourself and others. Most of your group will have mild AMS at some stage of the walk, but anyone with moderate AMS should be monitored closely in case they worsen. Assess the sufferer's condition first thing in the morning: symptoms that persist after resting should be taken seriously. Severe AMS should be treated by immediate descent, oxygen and suitable drugs.

If you are unlucky enough to have moderate to severe AMS, you will probably feel so ill that you no longer care about reaching the summit. Occasionally, because the stakes are so high, some very determined individuals play down or even deny their symptoms and want to struggle on. The problem is that AMS has affected their judgement, and they do not realise how ill they have become. In such cases the guide or group leader may instruct them to descend, and his or her decision is final. If you are on the trip with a friend, you will know that person better than the group leader can, so you can help the decision process.