While we may not see as many wilderness related injuries in the concrete jungle of NYC, they are important to know. Especially when you ski out west, tick off the bucket list item of trekking K2 or when it inevitable shows up on the boards. Today we will talk about acute mountain sickness (AMS) and high altitude cerebral edema (HACE).

Acute mountain sickness (AMS) and high altitude cerebral edema (HACE) are generally thought to represent a spectrum of the same disease. AMS usually occurs at 2000 to 3000m and has different incidences depending on elevation reached and rate of ascent.  The progression of AMS to HACE is fairly uncommon, with an incidence of 0.1 -2% at elevation between 3000 to 4000m.  HACE and high altitude pulmonary edema (HAPE) often go hand in hand, and it is uncommon for patients to have cerebral edema without pulmonary edema (stay tuned for tomorrow’s pearl for more info).

AMS is a clinical diagnosis and presents like a hangover: headache, fatigue, anorexia, nausea and vomiting. The diagnosis is made when a patient has headache in addition to one of the following: nausea, vomiting, fatigue, weakness, dizziness, lightheadedness or difficulty sleeping. Symptoms usually occur 6 to 12 hours after reaching high altitude, but generally resolve in one day if there is no further ascent.

The transition from AMS to HACE occurs when there is onset of encephalopathy or ataxia. The classic symptom of HACE is progressive decline in mental status, starting at irritability and confusion and moving toward drowsiness, stupor and coma.

Treatment of AMS is primarily symptomatic. You can use analgesics to control headaches, anti-emetics or supplemental O2. If symptoms are severe, descent below the altitude in which symptoms started will reverse AMS.  Acetazolamide can be used to prevent symptoms or used as treatment once symptoms appear. Similarly, dexamethasone can be used for both prevention and treatment. Dexamethasone is a second line prophylactic medication and usually reserved for severe cases as treatment, as it does not aid in acclimation and can cause rebound symptoms once stopped. The best prevention for AMS is to ascent with adequate time to acclimate.

Treatment of HACE is first and foremost, descent. Oxygen and steroids should also be used, but are not substitutes for descent. If a patient cannot descend immediately, they should be placed in a portable hyperbaric chamber (if available) and receive steroids and oxygen.

Stop by on Friday when the discussion continues with HAPE.


Hackett PH, Davis CB. “High Altitude Disorders.” Chapter 216. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide.

Schoene RB, Illnesses at high altitude. Chest 2008; 124:402.

June 2024