High altitude cerebral edema (HACE) is a potentially fatal diagnosis that can occur at high altitudes. It occurs when the brain swells from fluid leakage and results in a decrease in mental status. HACE can happen to anyone at any time, and it is important to be able to recognize the signs and symptoms so that you can get help as soon as possible.

Mild HACE is often called acute mountain sickness and is caused by a small amount of cerebral edema. Symptoms include headache, loss of appetite, and nausea. Treatment is symptomatic and includes pain medication, hydration, and avoidance of alcohol and narcotics.

Moderate HACE includes early mental status changes and vomiting, in addition to the symptoms of mild HACE. Treatment for moderate HACE includes supplemental oxygen and an immediate descent of at least 300 meters or 1,000 feet. If the patient is trapped at altitude, emergency treatment of corticosteroid medications can be used temporarily to reduce symptoms until evacuation can occur.

Severe HACE is rare below 4,000 meters or 13,000 feet in elevation. Common signs are ataxia (poor muscle control) and changes in level of consciousness and mental status. Severe HACE requires aggressive intervention, including all techniques from milder forms plus an immediate descent of 1,000 meters or 3,000 feet.

There is no guaranteed way to prevent HACE, but there are some things that you can do to decrease your risk. First, make sure to drink plenty of fluids and stay hydrated. Second, do not go too high too fast—give your body time to acclimatize by ascending slowly. Finally, pay attention to how you feel. If you start to experience any of the symptoms listed above, descend immediately.