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

Inhaled budesonide