High Altitude Sickness
PaO2 = 2/3rds at 10000ft (3050m)
PaO2 = 1/2 at 18000ft (5500m)
PaO2 = 1/3rd at 29000ft (8848m)
Degree and rapidity of hypoxic stress determines altitude illness. Age, gender, fitness does not have much effect. Ventilatory response is key.
Wilderness Medical Society recommends avoiding ascent > 9000ft (2800) in one day. And after arrival at 8-10000ft (2500-3000m), increase sleeping elevation < 1500ft (500m)/day as well as adding an extra day for every 3300ft (1000m).
Acute Mountain Sickness
Unacclimatized person > 8200ft (2500m)
1-2 days onset for AMS and 3-4d onset for HAPE
Headache + Additional symptom (loss of appetite, nausea, vomiting, dizziness, sleep disturbance, peripheral edema)
“Do you feel sick? Do you have a headache? Do you feel hung-over?”
Unusual below 1000m (3050ft)
Progression of CNS symptoms in someone with AMS or HAPE
Ataxia or acting drunk
Dypsnea at rest and weakness
Crackles first develop in right upper axilla
CXR shows R>L consolidations easily confused with PNA
For h/o AMS and ascent to >2800m in 1d
ascent > 2800m in 1d
ascent > 1600m/d over 10 000ft without acclimatization
>11 500ft in 1 day
For h/o HACE and HAPE
Acetazolamide 125mg – 250mg BID starting day before travel until d2-3 at altitude.
Dexamethasone 4mg BID or QID starting on ascent