High altitude medicine
Acute Mountain Sickness (AMS)
- acetazolamide- 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.
- Dexamethasone- prevents as well as treats cerebral edema. 4mg BID- QID, day of ascent and taper off over several days. Can combine with acetazolamide.
- Treatment- rest, descend 500- 1000m, acetazolamide 250- 500mg, dex 4mg with taper, Gamow bag (portable hyperbaric chamber)
High Altitude Pulmonary Edema (HAPE)
- definition: two symptoms: dyspnea at rest, cough, weakness, chest tightness or congestion.
And
two signs: central cyanosis, crackles or wheezes, tachypnea, tachycardia.
- most common medical cause of altitude related death.
- >2500m, young males, usually second night of altitude or after 3- 4 days ascent.
- recent URI predisposes
- highest risk in mountain dweller who descends to sea level and then reascends- possibly due to pulm art muscle remodeling.
- 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.
- Nitric oxide (NO) inhalation decreases pulm art pressures and can improve oxygenation. Dz possibly due to NO deficiency?
- Prevention
- limit exercise for first 1- 2 days. Also limit ascent when over 2500m to 300- 350m/day.
- Nifedipine 20mg TID or 30- 6- mg extended release qd- prevents HAPE but not pulm edema of exercise of AMS or HACE.
- Treatment-
- descend, oxygen, nifedipine 10 mg po, CPAP mask, diuretics, GAMOW bag.
- Can reascend in 2- 3days in needed but at increased risk for reoccurence.
High Altitude Cerebral Edema (HACE)
- Acute Mountain Sickness plus altered mental status or ataxia. Of if mountain sickness not present, is ataxia with mental status changes.
- occurs >4000m
- due to increased brain water, not just volume. Get increased intracranial pressure.
- 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.
- 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.
- Other theory is due to unexpandable cranial vault. As brain volume increases buffering ability of CSF overcome and brain swells in closed nonexpanding space.
- Prevent as with AMS
Treatment- 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).