Ann IM 2004;141:789; Nejm 2001;345:107

Cause:Acute change in elevation above at least 7000-8000 ft, by going up mountains, or in unpressurized airplanes (commercial airlines pressurized at 9000 ft); and usually w associated exertion

Pathophys:Cerebral edema from either cytotoxic vascular dilatation or change in blood–brain barrier permeability (Jama 1998;280:1920). Normal pulmonary capillary wedge pressures; increased atrial natriuretic factor; increased capillary permeability (Ann IM 1988;109:796)

Increased incidence with exercise and cold weather; increased in teenagers (Nejm 1977;297:1269), patients w patent foramen ovale (Jama 2006;296:2954), and patients with congenital aplasia of right pulmonary artery (Nejm 1980;302:1070). Inhabitants of high altitudes can get just with 1-2 d at low altitudes and return. Physical conditioning before ascent has no effect on acute mountain sickness, pulmonary edema, or cerebral edema incidence. 22% incid at 7000-9000 ft, 42% at 10 000 ft.

Sx: Onset in 6-48 h; headache (62%); fatigue (26%) and lassitude; anorexia (11%), nausea, and vomiting; insomnia (31%); dyspnea (21%); dizziness (21%)

Si:Dyspnea; dry cough; Cheyne-Stokes respirations, esp at night. Acute pulmonary edema (4% of nonacclimatized people at 12 000-14 000 ft) without warning si’s; cerebral edema w ataxia and confusion; asymptomatic retinal hemorrhages (Ophthalm 1992;99:739; Nejm 1970;282:1183)

Spontaneous resolution in 3-4 d

Lab: ABGs:Respiratory alkalosis (on Everest, pH 7.4-7.53, PaCO₂ as low as 13.3, PaO₂ as low as 24.6 mm Hg) (Nejm 2009;360:140)

Xray:MRI of head in cerebral edema type shows white matter edema, esp of corpus callosum

Rx:

Prevent

• By avoiding exertion for several days or acclimatize at 6000-8000 ft for 2-4 d
• O₂ at 4-10 L/min, hs and at 1st sx
• Acetazolamide 250 mg po bid-tid 24-48 h, decreases incidence by 50%
• Dexamethasone 4 mg po q 6 h before and during exposure; perhaps decreases cerebral edema (Nejm 1984;310:683) and mountain sickness but not the physiologic consequences, ie, it may mask the sx (Nejm 1989;321:1707)
• Sildenafil (Viagra) (Ann IM 2004;141:169) 50 mg po qd, or tadalafil (Cialis) 10 mg (Ann IM 2006;145:497), increases exercise capacity in hypoxic conditions by dcr pulmonary htn, helps prevent HAPE but not AMS (cerebral); adv effects: headache

of sx: most importantly, descend at least 1000 ft at 1st sx; O₂

of pulmonary edema: prophylactic nifedipine 20 mg SR po q 8 h; decrease PA pressures (Nejm 1991;325:1284), eg w nitric oxide 10% inhalations (Nejm 1996;334:624); morphine im to relieve anxiety and pool peripheral blood; rest and descend

of cerebral edema: dexamethasone 8 mg po/iv, then 4 mg q 6 h; O₂; immediate descent