What is high altitude cerebral edema (HACE)?

From the Guidelines

High altitude cerebral edema (HACE) is a life-threatening condition that occurs when the brain swells with fluid due to rapid ascent to high altitudes, typically above 4500 m, and is associated with a 50% mortality when untreated. HACE represents the end stage of acute mountain sickness and requires immediate descent to lower altitude for treatment 1. It develops when the body fails to acclimatize properly to decreased oxygen levels at high elevations, causing increased cerebral blood flow and disruption of the blood-brain barrier. Symptoms include severe headache, confusion, ataxia (loss of coordination), hallucinations, altered mental status, and eventually coma and death if untreated.

Key Points

• HACE is a continuum of the cerebral form of high-altitude illnesses (HAIs) and is a life-threatening condition that requires immediate medical attention 1.
• The risk of HACE steeply rises when unacclimatised individuals are exposed to increasing altitude, affecting more than 50% of them at altitudes above 4500 m 1.
• Emergency treatment includes immediate descent (the most critical intervention), supplemental oxygen if available, and dexamethasone to reduce brain swelling.
• Prevention strategies include gradual ascent (no more than 300-500 meters per day above 3,000 meters), taking rest days, staying well-hydrated, and considering prophylactic medications like acetazolamide for those with previous history.

Treatment and Prevention

• Immediate descent to a lower altitude is the most critical intervention for HACE, as it helps to reduce the severity of symptoms and prevent further brain damage 1.
• Supplemental oxygen and dexamethasone can be used to reduce brain swelling and alleviate symptoms, but these treatments should only be used in conjunction with immediate descent.
• Gradual ascent, taking rest days, and staying well-hydrated can help to prevent HACE by allowing the body to acclimatize to the high altitude.
• Prophylactic medications like acetazolamide can be effective in preventing HACE, but individuals should be aware of potential side effects and have proper corrective measures in place 1.

From the Research

Definition of High Altitude Cerebral Edema (HACE)

• High altitude cerebral edema (HACE) is an uncommon and sometimes fatal complication of traveling too high, too fast to high altitudes 2.
• It is characterized by disturbances of consciousness that may progress to deep coma, psychiatric changes of varying degree, confusion, and ataxia of gait 2.
• HACE is distinguished by a perplexing array of both generalized and localized neurological symptoms and signs 3.

Clinical Features of HACE

• Symptoms of HACE are related to increased intracranial pressure (ICP), and death is from brain herniation 4.
• HACE is a potentially fatal illness characterized by ataxia, decreased consciousness, and characteristic changes on magnetic resonance imaging 5.
• The clinical features of HACE include a range of neurological symptoms and signs, such as confusion, psychiatric changes, and ataxia of gait 2, 3.

Pathophysiology of HACE

• The current leading theory of its pathophysiology is that HACE is a vasogenic edema; that is, a disruption of the blood-brain barrier 2.
• Causes of increased blood-brain barrier permeability might include mechanical factors, ischemia, neurogenic influences, and a host of permeability mediators 4.
• HACE could develop from a progression from cytotoxic swelling to ionic edema or permeation of the blood-brain barrier with or without ionic edema 6.

Relationship to Acute Mountain Sickness (AMS)

• HACE is most often a complication of acute mountain sickness or high altitude pulmonary edema 2.
• There is speculation regarding the exact etiology of both HACE and AMS and whether they share a common mechanistic pathology 6.
• Evidence is accumulating that established moderate to severe AMS is due to cerebral edema, but whether this is true for early AMS is unclear 4.