Mountain sickness
Background: At higher altitudes, there is less oxygen. For example, at 10,000 feet, the air is 14% oxygen while at sea level in NYC, we are breathing in 21% oxygen. Mountain sickness is the manifestation of the body’s response to hypoxia.
Clinical features:
Usually only occurs in altitudes greater than 8000 ft unless patients are particularly susceptible to hypoxia (COPD, anemia). This is also why when flying, airplane cabins are usually pressurized to 7-8000 ft. Patients who have experienced altitude sickness are more likely to have repeat episodes when returned to the same altitude. A quicker rate of ascent is also more likely to lead to mountain sickness. Most often presents the 1st night or 2nd night at higher elevations. The average duration of symptoms in cases that self resolve is one day (the body successfully acclimates).
Clinical criteria (most are CNS symptoms since the brain is most sensitive to hypoxia): An individual above 8000 feet presents with headache and one of the following
- GI symptoms
- Sleep disturbance
- Dizziness/lightheadedness
The feared complications of mountain sickness are High Altitude Cerebral Edema (HACE) & High Altitude Pulmonary Edema (HAPE).
Treatment & Prevention:
In mild mountain sickness, the patient can descend to a lower altitude (1000-3000 ft lower) or stop the ascent and acclimate for 12-36 hours. Acetazolamide (125-250 mg BID) can be used to speed up acclimation by increasing respiratory rate from the resultant metabolic acidosis. For patients who have moderate to severe mountain sickness, immediate descent 1000-3000 feet is indicated. Low flow oxygen, especially at night, can be helpful. Hyperbaric oxygen therapy can be considered. Lastly, besides acetazolamide, dexamethasone 4 mg q6 can be considered.
The best preventative measure is gradual ascent. Acetazolamide prophylaxis indicated in those who have previously experienced acute mountain sickness or anticipate a rapid ascent to altitude. Start 24 hours before ascent and continue until 48 hours after reaching final altitude. Dexamethasone can be started the day of ascent and likewise continued until the first two days at altitude. Ibuprofen also helps.
HACE
Severe and uncommon form of acute mountain sickness. Basically, it is a progression of acute mountain sickness resulting in AMS & ataxia from cerebral edema due to hypoxia. Treatment is immediate descent, supplemental O2, dexamethasone, & acetazolamide. Other treatments for increased ICP (mannitol etc…) are of undetermined benefit.
HAPE
Hypoxic pulmonary vasoconstriction led to pulmonary hypertension and eventual pulmonary edema due to elevated pulmonary artery pressures. Patients can have bilateral opacities on CxR and a better clinical appearance than their O2 saturations suggest. Immediate descent, minimizing exertion, supplemental O2, expiratory positive airway pressure mask (forces some PEEP in a non-intubated patient), nifedipine, & sildenafil (promotes pulmonary artery vasodilation) are possible treatment options.
https://www.ncbi.nlm.nih.gov/books/NBK430716/
https://wikem.org/wiki/High_altitude_pulmonary_edema
https://wikem.org/wiki/Acute_mountain_sickness
Imray C, Wright A, Subudhi A, Roach R. Acute mountain sickness: pathophysiology, prevention, and treatment. Prog Cardiovasc Dis. 2010 May-Jun;52(6):467-84. doi: 10.1016/j.pcad.2010.02.003. PMID: 20417340