top of page

Acute Mountain Sickness

Acute Mountain Sickness is a series of symptoms that can occur to people when traveling above 8,000ft elevation which left untreated can prove fatal. It is also known as Altitude Sickness, Hypobaropathy and Soroche. It is the most common form of altitude sickness that occurs to people that travel to areas of high elevation for recreation and professional sports like skiing, hiking, mountain climbing and biking and has become a great health concern. It is estimated that 1/4 of Colorado ski vacationers, 2/3 climbers to Mount Ranier, and 1/2 that flew to the Khumbu region of Nepal develop Acute Mountain Sickness. 
Normal Physiology when ascending-
As you ascend you may experience some symptoms associated with altitudes so it is important to understand what is normal and what is not normal since identifying an issue is key in treatment and for a complete recovery. 
Certain normal physiological functions occur when ascending-
-Hyperventilation (breathing harder, heavier and fast) 
-Increased urination as your body rids itself of alkalinity from                      hyperventilation.
-Shortness of breath during exertion (recovery should be quick when stopped).
-Changed breathing pattern at night. (body loses stimulus to breathe).
-Awakening frequently at night (follows periods of apnea from lack of stimulus).
     As one increases in altitude the rarity of oxygen molecules increases (stays at 21%) due to the decrease of barometric pressure. The body will breathe harder, deeper and faster as one exerts themselves and should resolve quickly upon rest. Increased breathing is critical to help maintain oxygen saturation levels even though levels will not return to normal at elevation. It is because of this that alcohol and drugs that interfere with oxygen saturation levels (narcotics, sleep aids) should be avoided. Hyperventilation over time decreases C02 levels which is key for the brain to stimulate breathing (high C02 levels stimulate breathing) without it low O2 levels will stimulate breathing (safety valve) even though it is a weaker signal.  This does not become an issue while awake but is a different story when going to sleep. A cycle of periodic breathing is balanced between the two stimulants to breathe. Periodic breathing are cycles of normal breathing which slows down to a period of apnea followed by a quick recovery of accelerated breathing. The apneic episode may last from 10-15 seconds and improves slightly with acclimatization. Descent to a lower elevation is the best remedy. A person can become anxious if they wake up during the apneic phase to the hyperventilation phase when waking up breathing fast. As your body increases repirations it lowers the acid levels and increaes the alkaline levels creating an imbalance of PH levels. One way your body attempts to return to normal Ph levels is though urination so it may become frequent unless dehydrated which is another reason to be hydrated. 
Primary Symptoms-
-Slight Headache
-Dizziness, Light Headedness, drowsiness
-Insomnia, lack of sleep, disturbed sleep
-Shortness of breath during exertion
-Nausea and Vomitting
-Lack of appetite
-Swelling of extremities
-General malaise
-Peripheal edema
-Persistent rapid pulse
These symptoms if not treated can lead to confusion, unstable walking, coma and finally death.  If anyone has a headache not relieved with over the counter drugs but increases in intensity when lying down, treat as HACE. Unable to walk a straight line (drunk walk), It is best to assume they are experiencing HACE and descending is critical to survival. 
Recognizing the symptoms to treat immediately is critical for their survival. It is believed that local response to lack of oxygen (hypoxia) resulting in greater blood flow thus greater capillary pressures, these pressures lead to fluid leaking out of the capillaries. This leaking leads to the swelling of the brain causing unstable walking (Ataxia), headache (increasing when lying down), drowsiness and confusion.
At higher elevations the air becomes thinner which makes availability of oxygen less even though the percentage of oxygen is the same (21%).  The percentage of oxygen remains constant up to 70,000 ft.  Dehydratjon from vapor lost at higher elevation is believed to also be a contributor. This is another reason  why keeping hydrated at elevation is highly recommended.  Rate of ascent, altitude attained, physical exertion at altitude, lack of acclimatization and susceptibility can also be contributing factors.
If you are experiencing or are witnessing anyone experiencing any of the symptoms I have already discussed, assume they have HACE and descend immediately. Time is critical and symptoms can progress quickly to death so don't wait until morning to descend (HACE often strikes at night). Here is a list of drugs that have proved helpful for treating symptoms as well as being used as a prophylaxis however, these should be used only when descent is not immediately possible (weather) or in conjuction with. Descending in elevation immediately is the best cure for AMS.
Dexamethasone (Decadron)-
This is a potent steroid that decreases brain edema. This steroid can prove to be a lifesaver in situations where the affected cannot climb to a lower elevation due to terrain or weather dangers. It is because of this feature that it makes for a good emergency drug when you need more time to descend.  Improvement can be as quick as 6 hours. It can also be used as a prohylaxis for those allergic to Acetazolamide (Sulfa drugs). It is not recommended to ascend if necessary for at least 18 hours after the last dosage of this drug. Dexamethasone can mask AMS symptoms. 



Acetazolamide (Diamox®)-

This has become the go to drug for AMS with a proven track record of treating as well as preventing AMS. This drugs mode of action is to extcrete Alkali into the urine changing the PH levels to a more acidic level. Hyperventilation (fast breathing) blows off C02 making an alkaline environment. It is by creating a more acidic environment that stimulates breathing, paramount for acclimatization. Acetazolamide can be used as a prophylaxis if started one or two days before ascent and continued for three days once the highest altitude is reached. It is always better to ascend at a reasonable rate regardless if you are taking  any kind of altitude medicine or not. 



This is one drug I would highly recommend be in your pack because of its varied usefulness out in the field as well as being cheap and accessible to the public. This drug should be avoided for those allergic to NSAIDS as well as Aspirin (Cross reaction) and those with a history of Renal problems and stomach ulcers. This drug has shown to be effective as a prophylaxis as well as a treatment. Ibuprofen is an anti-inflammatory decreasing swelling and helping headaches as well as aiding the body in adjusting to an oxygen deprived environment. Ibuprofen helps climbers to get past those initial symptoms buying them time to acclimatize. It should be discontinued for at least 24 hours to help the body adjust and acclimatize when reaching and leveling off to the new higher altitude.


Ginko Biloba-

This natural herb has shown blood thinning properties. Pts are asked to discontinue this herbal remedy 2-3 weeks prior to surgery because of a bleeding potential. It is now showing promising results in the treatment and prevention of AMS although more studies need to be done to validate those results. Ginko Biloba is known for its ability to aid in cerebral perfusion as well as decrease blood pressure. I feel that more research should be done on herbals such as this one to validate its potential in safety and cost effectiveness as well as identify interactions with other drugs and contraindications.  



High Altitude Pulmonary Edema is a life threatening condition that can turn fatal in a short amount of time if treatment is not sought immediately. It is the primary cause of high altitude death with increased mortatlity in the absence of care. It is believed that the cause of this condition starts with high altitude hypoxia causing constriction of pulmonary capillaries shunting the blood through limited amount of blood vessels not constricted. This increases blood pressure into these vessels creating high presssure extravascular leaks into the lungs. Exertion and cold may also contribute to the onset as well as exacerbation of HAPE. 



Sometimes asthma/bronchitis can be confused for HAPE but  can be distinguished by the fact that in HAPE there is shortness of breath despite rest and severe fatigue. Asthmatics seem to do better at elevation than at sea level. If asthma is suspected then give asthmatic medications if symptoms persist then treat as HAPE.  Pneumonia is more difficult to distinguish from HAPE since both can have symptoms of fever and both can produce green or yellow sputum. HAPE will improve dramatically upon descent in elevation. If there is no improvement upon descent then consider giving antibiotics. HAPE is much more common at altitude and more dangerous than pneumonia. Many climbers have succumbed to HAPE because they were mistakenly treated for pneumonia. Here is a list of symptoms that might appear in HAPE. 


-Dyspnea at rest

-Chest tightness


-Crackels/wheezing (lung sounds of clicking/rattling, cellophane being              crumpled)




-Cough that produces a white or pink frothy sputum.



There are many treatment options (O2, Hyperbaric bag, drugs) however being in the high country limits your options. The best way to treat HAPE is by descending to a lower elevation at least to the last elevation remembered where the victim felt okay. Decending can be difficult since most need help descending. 



Although HAFE (High Altitude Flatulance Expulsion) sounds more comical than clinical it has been published in credible journals. The high altitude has less pressure which allows for expansion of gases within the digestive tract which is expelled. I have gone to altitude with some people that are effected by this phenomenon more than others. No treatment is necessary unless socially unacceptable by the group then Simethicone is the treatment of choice. 


Putting it all together

-AMS is a culmination of symptoms from the effects of high altitudes of 8,000ft  and above but can be felt at even lower altitudes.  

-HACE AND HAPE are believed to originate from the response of low pressures  at altitude increasing capillary pressures which lead to extravascular leakage  and swelling. 

-Asthmatics will get relief with asthma medications and do not have difficulty  with breathing at rest. HAPE  you do.

-Pneumonia can easily be confused with HAPE, if descending does not resolve    problems then antibiotics should be considered. 

-If the victim is confused, headache that increases when lying down and unable  to walk a straight line (drunk walking) consider it as HACE and descend  immediately,     do  not wait for morning, most HACE events happen at night. 

-If the victim has difficulty breathing without exertion, strange lung sounds  crackles (sounds like  cellophane being crumpled), gurgling, rumbling in chest,  descend immediately.

-Severe cases of HACE can be accompanied by HAPE.

-If HACE or HAPE is suspected then descending should not be delayed.

-Many fatalities of HAPE were mistakenly treated as pneumonia.

-Acetazolamide can be used as a prophylaxis as well as a treatment.  Dexamethasone is   a strong steroid that can be used as a treatment and  adjunct as well as a prophylaxis   if Acetazolamide is contraindicated.  

-Ibuprofen can be used as an anti-inflammatory which is cheap, effective and  available   over the counter. If a headache continues after taking Ibuprofen  then HACE should be   suspected and descent is critical.

-Although it is not well understood as who is more suceptible, age and fitness    does not   identify physical susceptibility. It should be noted that young and  more fit can be more suscepitble since they are the population to acend  quickly. 

-Rapid ascent is the greatest predictor of AMS.

-Those who have had AMS are more likely to get it again. 

-Early recognition for early treatment (descent) have the best success rates.

-Decending in elevation is the best treatment. The sooner the better outcome.



Since the greatest predictor of AMS is rapid descent, it would be no surprise that you should ascend at a reasonable rate. Being aware of your physical status as well as your group members is also key in the prevention of AMS.  If HAPE or HACE is suspected then descend immediately since symptoms can turn deadly in a matter of hours.  Being physically fit does not make you immune to the effects of AMS.  Here is a list of other ways to prevent AMS.


-Keep hydrated

-Eat well

-Avoid driving or flying directly to high altitudes. 

-If you become symptomatic delay ascent.

-If symptoms get worse while ascending descend as quickly as possible. 

-Keep ascending rate under 1000ft per day when at 8000ft and above.

-Climb high Sleep low. Try to sleep at lower elevations at night to help avoid      AMS and  increase acclimatization.  (Hike up to a peak but sleep in the valley).

-People who ascend slower have less incidence of AMS.

-Ascending slowly gives your body more time to acclimatize.


     The Sierra Nevada Mountain Range high peaks and mountain views can be breath taking and also take your breath away....literally. I cannot stress enough the importance of recognizing and treating AMS.  The best way to treat AMS is by descending in elevation.  Most who venture into the high country do not carry O2 and Hyperbaric bags that only mimic the effects of descent. Drugs can be useful but are not as effective and safe as descent. In today's fast paced society with tight scheduling and limited vacation time, pressures of completing adventures as scheduled can prove treacherous. I find it quite curious how a group of people will head into the high country to escape the fast pace of societal pressures only to bring that same mentality into the wild with them. It is best to take your time as you ascend not only to give your eyes time to absorb all of the beauty of the Sierra Nevada Mountain Range but for your body to acclimatize to the increasing elevations. Be aware, work the problem, and if any doubt descend.



bottom of page