High altitude medicine

Acute Mountain Sickness (AMS)

1. acetazolamide
   1. Start day before ascent 125- 150 mg BID or qhs for 2- 3 days while at altitude and then stop. Peds dose is 5mg/kg/day. Watch for sulfa allergy, paresthesias, diuresis.
2. Dexamethasone
   1. prevents as well as treats cerebral edema. 4mg BID- QID, day of ascent and taper off over several days. Can combine with acetazolamide.

Treatment

1. rest, descend 500- 1000m, acetazolamide 250- 500mg, dex 4mg with taper, Gamow bag (portable hyperbaric chamber)

High Altitude Pulmonary Edema (HAPE)

1. definition: two symptoms: dyspnea at rest, cough, weakness, chest tightness or congestion.
2. And
3. two signs: central cyanosis, crackles or wheezes, tachypnea, tachycardia.
4. most common medical cause of altitude related death.
5. >2500m, young males, usually second night of altitude or after 3- 4 days ascent.
6. recent URI predisposes
7. highest risk in mountain dweller who descends to sea level and then reascends- possibly due to pulm art muscle remodeling.
8. is noncardiogenic pulmonary edema with pulm hypertension and inflammation of capillaries and transepithelial water and sodium transport. Caused by combination of both pulm hypertension and increased cap permeability.
9. Nitric oxide (NO) inhalation decreases pulm art pressures and can improve oxygenation. Dz possibly due to NO deficiency?

Prevention

1. limit exercise for first 1- 2 days. Also limit ascent when over 2500m to 300- 350m/day.
2. Nifedipine 20mg TID or 30- 6- mg extended release qd- prevents HAPE but not pulm edema of exercise of AMS or HACE.

Treatment

1. descend, oxygen, nifedipine 10 mg po, CPAP mask, diuretics, GAMOW bag.
2. Can reascend in 2- 3days in needed but at increased risk for reoccurence.

High Altitude Cerebral Edema (HACE)

1. Acute Mountain Sickness plus altered mental status or ataxia. Of if mountain sickness not present, is ataxia with mental status changes.
2. occurs >4000m
3. due to increased brain water, not just volume. Get increased intracranial pressure.
4. initially get vasogenic edema- fluid and protein crosses BBB, Get reversible changes in white matter, especially corpus callosum.. Later get cytotoxic edema by toxins and ischemia. Mostly of gray matter and has poorer px.
5. Theories: angiogenesis model- hypoxemia causes macrophages to release cytokines and vascular endothelium growth factor. Basement membranes of capillaries are dissolved causing leaks and petechial hemorrhages. Inhibited by dexamethasone.
6. Other theory is due to unexpandable cranial vault. As brain volume increases buffering ability of CSF overcome and brain swells in closed nonexpanding space.
7. Prevent as with AMS

Treatment

1. descend, oxygen, dex 4- 8mg IV, then 4mg q6hr. If GAMOW bag available- 4-8 hr recompression may allow pt to walk down mountain (big help).