Acute Mountain Sickness (AMS), Including HACE
AMS represents a clinical continuum of neurologic disease, of which high-altitude cerebral edema (HACE) is the most severe form.
Risk factors: rate of ascent, history of high-altitude illness, exertion
– Lack of physical fitness is not a risk factor.
– Exposure to high altitude within the preceding 2 months may be protective.
– Pts >50 years old may be less likely to develop AMS than younger pts.
Pathophysiology: Although the exact mechanisms remain unknown, hypoxic cerebral vasodilatation and altered permeability of the blood-brain barrier contribute to cerebral edema in AMS.
– Nonspecific symptoms (headache, nausea, fatigue, and dizziness) with a paucity of physical findings, developing 6–12 h after ascent to a high altitude
– HACE: encephalopathy whose hallmarks are ataxia and altered consciousness with diffuse cerebral involvement but generally without focal neurologic deficits
Retinal hemorrhages and, less commonly, papilledema may be seen.
Retinal hemorrhages occur frequently at ≥5000 m irrespective of the presence of symptoms of AMS or HACE.
Prevention: Gradual ascent with acclimation is the best measure to prevent AMS.
– At >3000 m, a graded ascent of ≤300 m each day is recommended.
– Taking an extra day for acclimation after 3 days of gain in sleeping altitude is helpful.
– Pharmacologic prophylaxis is warranted when the pt has a history of AMS or when flight to a high-altitude location is required.
Acetazolamide (125–250 mg PO bid) or dexamethasone (8 mg/d in divided doses), administered 1 day before ascent and continued for 2–3 days, is effective.
Gingko biloba is ineffective for prevention of AMS.
TREATMENT Acute Mountain Sickness
See Table 31-1.
TABLE 31-1MANAGEMENT OF ALTITUDE ILLNESS |Favorite Table|Download (.pdf) TABLE 31-1MANAGEMENT OF ALTITUDE ILLNESS
|Condition ||Management |
|Acute mountain sickness (AMS), milda ||Discontinuation of ascent |
Treatment with acetazolamide (250 mg q12h)
|AMS, moderatea ||Immediate descent for worsening symptoms |
Use of low-flow oxygen if available
Treatment with acetazolamide (250 mg q12h) and/or dexamethasone (4 mg q6h)c
|High-altitude cerebral edema (HACE) ||Immediate descent or evacuation |
Administration of oxygen (2–4 L/min)
Treatment with dexamethasone (8 mg PO/IM/IV; then 4 mg q6h)
Hyperbaric therapy if descent is not possible
|High-altitude pulmonary edema (HAPE) ||Immediate descent or evacuation |
Minimization of exertion while pt is kept warm
Administration of oxygen (4–6 L/min) to bring O2 saturation to >90%
Adjunctive therapy with nifedipinee (30 mg, extended-release, q12h)
Hyperbaric therapy if descent is not possiblea