Acute mountain sickness (AMS) is diagnosed clinically in a person who lives at low altitude but has recently ascended to high altitude (generally over 2000 M). Symptoms resemble those of an alcohol hangover: primarily headache often associated with fatigue, light-headedness, anorexia, nausea and vomiting, disturbed sleep, and mild shortness of breath with exertion. Onset of AMS is usually delayed for 6 to 12 hours following arrival at high altitude, but can occur as rapidly as one to two hours or as late as 24 hours.
Differential diagnoses include carbon monoxide poisoning, migraine, dehydration, exhaustion, hyponatremia, viral syndrome, alcohol hangover, bacterial infection, subarachnoid hemorrhage, stroke, and intracranial mass.
Further ascent can result in HACE (High Altitude Cerebral Edema), which includes encephalopathic symptoms and signs, including ataxic gait, severe lassitude, and progressive decline of mental function and consciousness. The mechanism is due primarily to increased cerebral vascular permeability.
- Conservative treatment: Patients with AMS should avoid further ascent, limit physical activity, avoid alcohol and other respiratory depressants because of the danger of exacerbating hypoxemia during sleep. Symptomatic treatment, such as basic analgesics for headache and antiemetics, is often helpful. With conservative treatment, most patients successfully acclimatize over 24 to 48 hours and symptoms resolve.
- Descent: Descent is always effective treatment for AMS, but it is not mandatory or even necessary except in the setting of intractable, or progressing symptoms
- Oxygen: Supplemental oxygen effectively relieves the symptoms of AMS and can serve as an alternative to descent.
- Hyperbaric therapy: Portable, lightweight, manually inflated hyperbaric chambers are can be used to decrease symptoms of AMS. By increasing barometric pressure, hyperbaric bags are capable of simulating a descent of 2500 m or more, depending upon the altitude where they are used. One hour of treatment in a pressurized chamber relieves symptoms, although they may return within 12 hours.
- Acetazolamide: Treatment with acetazolamide, a carbonic anhydrase inhibitor, accelerates acclimatization to high altitude. Acetazolamide 250 mg BID may be prescribed for one to three days while the patient remains at the same altitude.
- Dexamethasone: Dexamethasone alleviates the symptoms of AMS, but does NOT improve acclimatization. Dexamethasone 4 mg taken orally or intramuscularly, q 6 hours, for one to two days can be prescribed alone, in lieu of acetazolamide, or in combination with acetazolamide. Further ascent while taking dexamethasone alone is not recommended because of the risk of symptoms recurring or worsening when the drug is stopped.