Mountain Medicine
High Altitude Cerebral Oedema (HACE)
AMS is a spectrum of illness, from mild to life-threatening. At the "severely ill" end of this spectrum is High Altitude Cerebral Edema; this is when the brain swells and ceases to function properly. HACE can progress rapidly, and can be fatal in a matter of a few hours to one or two days. Persons with this illness are often confused, and may not recognize that they are ill.
The hallmark of HACE is a change in mentation, or the ability to think. There may be confusion, changes in behaviour, or lethargy. There is also a characteristic loss of coordination that is called ataxia. This is a staggering walk that is similar to the way a person walks when very intoxicated on alcohol. This loss of coordination may be subtle, and must be specifically tested for. Have the sick person do a straight line walk (the "tandem gait test") . Draw a straight line on the ground, and have them walk along the line, placing one foot immediately in front of the other, so that the heel of the forward foot is right in front of the toes behind. Try this yourself. You should be able to do it without difficulty. If they struggle to stay on the line (the high-wire balancing act), can't stay on it, fall down, or can't even stand up without assistance, they fail the test and should be presumed to have HACE.
HACE widely regarded as end stage of AMS
AMS HACE
Headache Alteration of consciousness
Vomiting Ataxia
Dizziness Focal neurological deficit
Anorexia Sign and symptoms of cerebral herniation, coma, death
Papiloedema, Retinal hemorrhage
Concomitant HAPE facilitates progression of AMS to HACE.