ACUTE MOUNTAIN SICKNESS (AMS)
By Dr. Clare O'Leary and Pat Falvey.

Acute Mountain Sickness (AMS) is a self-limiting condition affecting previously healthy individuals who rapidly ascend to high altitude. After arrival, the individual may be well for 6-12hrs prior to development of symptoms, although in some cases, they may occur as early as 1hr after ascent.
 
SYMPTOMS OF AMS:

• headache
• loss of appetite
• nausea
• vomiting
• fatigue
• light-headedness
• sleep disturbance

Symptoms usually start gradually and peak by day 2-3; by day 4-5,
they have usually settled and do not recur at that altitude.
The incidence of AMS is dependant on the

• Altitude gained
• Speed of ascent
• Sleeping altitude
• Individual susceptibility

Following rapid ascent to 8,000-9,000 ft, 25% of individuals will have 3
or more symptoms and 5% will require bed rest. Ascent to 10,000-12,000 ft will result in symptoms in nearly everybody and about 10%
will be incapacitated.

• Physical fitness does not protect against AMS
• Men and women are equally affected by AMS, but women seem less
--susceptible to high altitude pulmonary oedema
• Young adults are more susceptible than those >50yrs
• Individual susceptibility
 
PREVENTION OF AMS:

• Rate of ascent: A slow rate of ascent is the best way to prevent AMS; --the generally accepted guideline is that above 3,000m, each night
--should be spent not more than 300m above the last, with a rest day
--(ie. 2 nights at the same altitude) every 2-3 days.
• Light activity
• Diet: High in carbohydrate, preferably taken in small frequent meals
--Avoid alcohol, codeine and sedatives
• Fluids: Enough fluids to prevent hydration should be taken; there is no --good evidence that excess fluids will prevent AMS.
• Drugs: Acetazolamide has been shown to reduce the incidence and --severity of AMS. The recommended dose is 125-250mg taken twice --daily, starting 24-48hrs before ascent and continued for 4-5days at the --final altitude. Acetazolamide has also been used and shown to be --beneficial in reducing altitude deterioration.
--The main side-effects of acetazolamide are frequent urination, and pins --and needles in the hands and feet.

Dexamethasone (a steroid) is also an effective prophylactic agent.
4mg 12hrly is the minimum effective dose. The combination of dexamethasone and acetazolamide is more effective than
acetazolamide alone. Side effects are common with steroids and use should be limited to specific conditions, eg failure to respond to other treatment / when oxygen is not available / descent is not possible. Steroids may cause a worsening of symptoms on withdrawal.

Ginkgo bilboa 80-120mg orally twice a day has been used in the prevention of AMS and appears to be effective. Further studies are needed.
 
TREATMENT OF AMS:

• Avoid further ascent until symptoms have resolved
• Limited activity or bed rest are advised
• Acetazolamide 125-250mg twice daily orally until symptoms resolve
• A single dose of Ibuprofen 400mg or 600mg is effective in ameliorating --or resolving high altitude headache
• Antiemetics are indicated for nausea and vomiting (Prochloperazine --10mg orally every 6-8hrs, or promethazine 25-50mg orally every 6hrs). --Promethazine may cause drowsiness.
• Acetazolamide also reduces periodic breathing and may be helpful for --insomnia. Sleeping tablets should be avoided in those with AMS --because of the risk of depressing breathing.

After acute mountain sickness has resolved, further ascent should be made with caution and acetazolamide prophylaxis considered.