HACE (high-altitude cerebral edema) causes your brain to swell due to a lack of oxygen at high altitudes. It affects anyone, from expert climbers to first-time outdoor enthusiasts. Stop climbing and contact emergency services immediately if you feel tired, dizzy or confused while at high altitudes.
High-altitude cerebral edema, or HACE, is a life-threatening form of altitude sickness where your brain swells when you reach high altitudes. The oxygen level at high altitudes is less than what your body knows as normal. As a result, your brain reacts negatively to a lack of oxygen by swelling. Your skull contains your brain, so when your brain swells, there’s not a lot of room for it. The pressure of your brain against your skull is dangerous and affects how your body functions.
Common symptoms of HACE include difficulty with coordination, feeling weak, tired and confused.
HACE most often affects climbers, hikers or outdoor enthusiasts who travel to mountains or areas of the world where the elevation is significantly higher than sea level.
HACE affects less than 1% of people who reach an altitude above 4,000 to 5,000 meters or 2.5 to 3 miles above sea level. It’s the least common form of altitude sickness.
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Early symptoms of HACE include:
If you experience any of the following severe symptoms of HACE at high altitudes, seek immediate medical attention:
It’s common for the person who experiences HACE to not realize they’re ill. If you’re traveling with someone who experiences a sudden, unusual change to their general health and personality, take action. If it’s safe, move to a lower altitude and reach out for immediate medical help by calling 911 or your local emergency services number. Don’t continue climbing to higher altitudes.
Hypoxia causes HACE. Hypoxia is oxygen deprivation or a low level of oxygen in your body’s tissues. When your body doesn’t get enough oxygen, it affects how organs, like your brain, function. HACE hypoxia happens when your body isn’t used to altitudes where the oxygen level is lower than what your body perceives as normal.
You may be more at risk of developing HACE if you:
HACE can affect anyone at any age and any experience level of climbing. It usually happens to people who aren’t acclimated to high altitudes or who never spent time in an area of the world with high altitudes.
HACE, if left untreated, can lead to coma and death. Complications can happen within 24 hours after symptoms begin, due to brain herniation. Brain herniation is when pressure within your skull (intracranial pressure) pushes your brain against rigid tissue that divides each compartment of your brain. This pressure damages your brain and prevents blood flow to it.
Oxygen deprivation (hypoxia), which causes HACE, can lead to long-term effects on your body, including:
If treated quickly, your risk of developing long-term effects of HACE is low.
A healthcare provider will quickly diagnose HACE to treat it immediately. A diagnosis consists of a neurological examination and your provider reviewing your symptoms, medical history and travel history (to identify if you were at high altitudes).
While not always necessary to make a diagnosis, tests may include:
Treatment for HACE includes:
After treatment, you should feel better within a few days to a few weeks, depending on the severity of your condition. Most cases resolve within days rather than weeks.
The best way to prevent HACE is to acclimate yourself to high altitudes. Acclimation involves slowly letting your body adjust to changes in oxygen levels. Quickly reaching a high altitude that your body isn’t prepared for leads to HACE and other forms of altitude sickness.
You can acclimate yourself by climbing more gradually. For example, if you’re at an elevation of 2,500 meters above sea level (over 1.7 miles), limit your ascent (upward climb) to 300 to 500 meters (around a quarter of a mile) per day. This can be challenging because it requires a significant time commitment to safely reach your desired altitude.
HACE is a medical emergency that requires a quick diagnosis and treatment to prevent complications. It can affect anyone, from an experienced climber to a recreational hiker.
When you have a goal in mind, like reaching the peak of a mountain, your desire to complete the goal may prevent you from noticing your symptoms. You might think, “We’re almost to the top, so I can push through it.” This can be dangerous, as this worsens HACE, which can be life-threatening if left untreated.
If you or someone in your group start to feel tired, dizzy or develop a headache, don’t hesitate to stop your climb and move to a lower altitude if it’s safe to do so. Symptoms of HACE can get worse within hours, which is why it’s important to be aware of the signs and symptoms of HACE before you start your ascent.
HACE is a medical emergency. If you’re at a high altitude and feel ill, dizzy or tired, move when it’s safe to a lower altitude and contact emergency services.
HACE (high-altitude cerebral edema) is a rare but severe form of AMS (acute mountain sickness). HACE is also known as late or end-stage AMS. AMS is an illness that you experience when you rapidly climb to a high altitude. It includes symptoms like headache, nausea, lightheadedness and shortness of breath. Both conditions happen when your body doesn’t get enough oxygen at high altitudes.
It can feel exhilarating to reach the top of a mountain after a tough day of climbing. On your way up, take note of how you feel. As much as you might not want to stop, listen to your body and get yourself to a safe altitude if symptoms of HACE (high-altitude cerebral edema) set in. Leaving HACE untreated can be life-threatening within hours. Don’t delay. Take care of yourself and others you hike with when you start to notice altitude sickness.
Last reviewed by a Cleveland Clinic medical professional on 10/04/2023.
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