High-altitude cerebral edema

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at December 27, 2016
StartDiseasesHigh-altitude cerebral edema

High-altitude cerebral edema (HACE) is a serious medical condition in which the brain swells with fluid, and it is caused by physiological responses to high altitude. It can begin and become a medical emergency within a few hours. Because of the speed of onset, it is important for travelers to high altitudes to be aware of the symptoms, causes, and treatments, as well as ways in which one can avoid it altogether.


Definition & Facts

HACE is frequently a consequence of altitude sickness and becomes more common the higher in elevation a person goes. Altitude sickness can begin at elevations as low as 8,000 feet, although most cases of HACE are seen at elevations of 10,000 feet and above. 

The cerebral edema or swelling can cause the brain to lose function partially or completely, depending on the severity of the inflammation. It occurs in 0.5% to 1% of people who climb at elevations between 4,000 meters (13,000 feet) and 5,000 meters (16,000 feet).

Generally it occurs only in those who have remained at these elevations for longer than 48 hours, meaning it takes some time to occur. In extremely rare cases it has occurred at elevations as low as 2,500 meters (8,200 feet). 

Symptoms & Complaints

HACE symptoms are many and varied. Symptoms vary depending on which part of the brain is impacted. Most symptoms occur in a specific order, beginning with confusion, changes in behavior, and fatigue/exhaustion.

More serious symptoms set in progressively, such as difficulty speaking and ataxia, which is the loss of coordination and stumbling that resembles having had too much alcohol. This is typically the stage where the patient may become unaware of what is happening, but the symptoms will be very clear to those around them who remain unaffected. Symptoms become more serious with vomiting, which can lead to dehydration.


The primary cause of high-altitude cerebral swelling is lack of oxygen flow to the brain also known as hypoxia or cerebral hypoxia. Higher frequency of HACE is seen in those who engage in high exertion activities in a low-oxygen environment (which high altitude environments are) such as hikers and mountaineers. A decrease in blood plasma levels of carbon dioxide, also known as hypocapnia, can ensue.

The swelling of the brain itself seems to be caused by an increase in the permeability of the blood-brain barrier. This results in vasogenic cerebral edema. Low oxygen environments may cause the blood-brain barrier to have micro-hemorrhages. This essentially tears the barrier and allows for leaking; coupled with the increase in external pressure, fluids are forced in through the micro-tears. 

Another contributing factor seems to be the retention of body fluids at high altitudes. This is a common effect of high altitude that even those who do not suffer from altitude sickness experience. All the cells in the body seem to swell microscopically at high altitude, making the swelling of tissues more pronounced. 

With lack of oxygen and a decrease in carbon dioxide in the bloodstream, along with cellular fluid retention, brain swelling can set in. Impairment, varying in severity from minor to severe, sets in. Left untreated, a patient will die as the brain keeps swelling and eventually hemorrhages from the pressure of pushing against the skull.

Other factors that can cause HACE are ascending significant heights too quickly, ignoring symptoms of altitude sickness, and a prior history of altitude-related illness.

Diagnosis & Tests

Diagnosis is important for treatment, and if it is identified in time then the problems can be generally reversed as long as brain damage has not occurred. Generally, other serious symptoms of altitude sickness precede HACE, such as high-altitude pulmonary edema, which is when the lungs swell with fluid (pulmonary edema).

Other symptoms that lead to a diagnosis of HACE are vomiting, a headache that is not relieved by nonsteroidal anti-inflammatory drugs (NSAID's), and hallucinations (both auditory hallucinations and visual hallucinations).

For a proper diagnosis, as with any illness, other diseases and symptoms must be ruled out. In the case of HACE, medical conditions such as stroke, inebriation/intoxication, low blood glucose levels or high blood glucose levels, and psychosis and other mental disorders must be considered and possibly ruled out. 

The physician will perform a pulse oximetry which can reveal significant low levels of oxygen in the blood. Imaging studies may be performed to assess whether or not the patient has high-altitude pulmonary edema.

Ultimately, if the symptoms are serious then the patient needs to be evacuated from the high altitude and immediately moved to lower altitude regardless of what the diagnosis might be.

Treatment & Therapy

The treatment for HACE depends on how the brain was impacted by the swelling. Immediate treatment is rapid removal from high elevation. This may at times necessitate an evacuation. Sometimes the patient is unable to move and must be carried down a mountain, regardless of what time of day or night. Minutes count and can mean life or death in a serious HACE situation.

Providing oxygen through a breathing mask can also minimize damage and the swelling, as the brain receives fresh oxygen that it has been deprived of. This, however, is only a temporary solution and the patient must be brought down to lower elevation. Certain drugs such as diuretics (e.g. acetazolamide) can reduce edema and symptoms of HACE.

Prevention & Prophylaxis

With HACE, the best preventative measures include adequate acclimatization to altitude with frequent rest days at the same elevation. The maximum limit to ascending in one 24-hour period has been determined to be about 1,000 meters (3,300 feet). Anything more than that in one day and a person is at a higher risk for high-altitude cerebral edema, along with many other symptoms of high-altitude sickness.