Acute mountain sickness (AMS)

Acute mountain sickness (AMS) is a condition that affects many travelers to high altitude. It is caused by a lack of oxygen and is especially common at heights above 2500m.

The symptoms of AMS are:
Headache
Loss of appetite
Nausea
Vomiting Lethargy
Anyone experiencing these symptoms within hours to days after arrival at high altitude should be regarded as having AMS unless proved otherwise.

The main risk for the development of AMS is ascending too quickly. A slow ascent lets your body Acclimatize to the altitude and avoids AMS. AMS occurs equally in males and females, the old and the young, the fit and the unfit.

Those who have experienced AMS on previous journeys to high altitude may be at increased risk for developing it again.

High Altitude Pulmonary Oedema (HAPE) & High Altitude Cerebral oedema (HACE)

The main danger with AMS is that it may progress to life-threatening forms of altitude illness, called high altitude pulmonary oedema (HAPE) and high altitude cerebral oedema (HACE). In HAPE, fluid Accumulates in the lungs, while in HACE, excess fluid causes the brain to swell.

The symptoms of HAPE are:

Shortness of breath (even at rest)
Cough (sometimes with production of blood stained phlegm)
Excessive tiredness
The symptoms of HACE are:
Worsening headache
Unsteadiness on the feet
Altered behavior
Hallucinations, disorientation, confusion *drowsiness, progressing to coma

Prevention:

AMS is best prevented by ascending gradually.

The usual recommendation when above 3000m is to:

ascend on average no more than 300m each day
stop for a rest day every 1000m or every three days
Some drugs have also been used to prevent AMS. The most widely used is acetazolamide (Diamox), which is normally given as one 250mg tablet twice a day from at least the day before ascending above 2500m.

Acetazolamide can make you pass more urine than usual, can cause a “pins and needles” feeling especially in the fingers and toes, and can make fizzy drinks taste flat.

Treatment:

The principles of treatment of AMS are as follows:

Stop further ascent
descend if there is no improvement or if the condition worsens
descend immediately if there are symptoms of signs of HAPE or HACE
do not leave anyone with AMS on their own
The best treatment for all forms of altitude illness is descent. However, in mild AMS rest alone may be sufficient. Anyone with symptoms of AMS must not ascend any further until the symptoms have disappeared.

Painkillers such as aspirin and paracetamol may be given for the headache. Acetazolamide may be useful (250mg every eight hours). People with moderate to sever AMS or whose symptoms of AMS are present despite rest for a day or two, should descend until symptoms have improved.