Trips to high elevations, which include popular destinations in the Andes, Himalaya, Rocky Mountains and other areas, can cause problems for travelers due to the effects of reduced oxygen. Known as hypoxia, this reduction in oxygen can result in Acute Mountain Sickness (AMS). This can be inconvenient, resulting in lost opportunities to enjoy a trip, or life-threatening, depending on the severity of symptoms.
At moderate elevations of eight or nine thousand feet, people commonly experience headache, shortness of breath, loss of appetite, sleeplessness and other mild symptoms. At higher elevations, such as 11,000-foot Cusco, Peru, 12,100-foot Lhasa, Tibet, or 19,300-foot Kilimanjaro some people will experience more severe symptoms. These can include serious, potentially life-threatening signs of High Altitude Pulmonary Edema (HAPE, characterized by a productive cough or bloody sputum) or High Altitude Cerebral Edema (HACE, characterized by confusion or unsteady gait), requiring immediate descent or evacuation. A noticeable but less severe issue is peripheral edema which may exhibit as puffy eyes or swollen hands and feet. Another condition associated with high altitude above 14,000 feet is retinal hemorrhage in the back of the eye, which can result in temporary or, rarely, permanent vision changes.
Fortunately, there are some simple steps travelers can take to reduce the likelihood of developing altitude sickness though there is no way to eliminate the risk altogether. The AMS incidence rate is 20-25% at 8,200 ft., increasing to 40-50% and higher at 13,100 feet, depending on the speed of ascent. There is no specific altitude that triggers AMS and the level can be different for different people. That being said, one of the best predictors of AMS is having had AMS previously, although those who have never had problems before can develop AMS with no warning.
Experts agree that the best way to prevent AMS is to spend some time acclimating. All it takes is a little planning.
One recommendation is to acclimate by staying at a moderate altitude (i.e. 8,000-9,000 feet) before proceeding higher. A good strategy is to follow the adage “hike high, sleep low” and avoid increasing the sleeping altitude by more 1,600 feet in a day once above 9,000 feet. Avoiding alcohol and vigorous exercise the first day or two will help, as well as drinking enough fluid to stay adequately hydrated.
Mild symptoms of AMS can be managed with time, rest and over-the-counter medications such as ibuprofen for headache. More severe symptoms mean that ascent must be halted, allowing time for symptoms to resolve. If symptoms do not improve or worsen further descent is necessary. Often, descending 1000 feet is all that is required. Symptoms of HACE and HAPE, which are not common, must be addressed immediately by descending 1000-3000 feet to avoid tragic consequences unless medical resources, including oxygen and medications, are immediately available. Many hotels around Cusco, Peru offer oxygen upon request.
If AMS symptoms appear it doesn’t mean the trip is over; if symptoms subside the traveler can try resting for a day or descending to a lower altitude. Once symptoms have resolved the visitor can attempt to go to a higher altitude and see how it goes. For moderate AMS symptoms a rest day with light activity, which is better than either no activity or strenuous exercise, may do the trick.
Drug and Non-Drug Therapy
One drug, acetazolamide (Diamox) has been proven to speed acclimatization. Travelers should talk to their physician before the trip to see if acetazolamide, which is a prescription drug, is appropriate. Many physicians are not trained in managing AMS so it’s a good idea to do some research using the resources listed below. Specifically, some physicians prescribe a higher dose than is recommended by experts, which can lead to increased side effects and lower compliance. The recommended dose of acetazolamide for prevention of AMS is 125 mg twice a day. To find out more about what the experts recommend for prescription and non-prescription therapies for prevention and treatment see “Additional Resources” below for links to the Centers for Disease Control (CDC), Wilderness Medicine Society (WMS) and Institute for Altitude Medicine websites that summarize evidence-based recommendations. Many of the same physicians are authors on all three of these sources so there is general consistency among them.
On the internet all sorts of unproven remedies are routinely suggested, ranging from just needing to be in shape (not true–AMS can strike anyone, even the most fit), simply staying hydrated (dehydration can complicate the picture and slow acclimatization, but hydration by itself won’t prevent AMS in susceptible individuals) to various dietary or herbal supplements. Some supplements show some promise, including gingko biloba, but conflicting results have been reported from different studies. One difficulty in studying herbal remedies is assuring a consistent dose of whatever the active ingredient might be. Since the industry is unregulated it is impossible to know what, or how much of the active ingredient, is being ingested.
The best approach is to educate oneself and confer with a doctor about which remedies are appropriate. Several medications, including acetazolamide and dexamethasone, have proven benefit, but are also associated with side effects.
Lake Louise Score
The Lake Louise Score (LLS) is a quick, easy-to-use scoring system that can be understood by anyone, with or without medical training. It can be printed and included in a first aid kit or scanned into a smartphone using an application such as Evernote. The LLS uses an elevation gain in the last four days plus the presence of headache as a foundation, requiring at least one other symptom and a total score of 3 to confirm AMS. Each of the following symptoms is scored on a scale of 1-3 with specific criterion for each symptom:
- GI symptoms
- Fatigue and/or weakness
- Difficulty sleeping
A score of 3-5 indicates mild AMS while a score of 6-9 is severe AMS; 15 is the highest score possible.
Being aware of the Lake Louise Score can assist travelers in assessing their symptoms.
Many people do fine at altitude but for those who experience difficulties related to altitude it’s important to have access to reliable and accurate information. Mild to moderate AMS symptoms may resolve on their own or with over-the-counter medication while severe conditions like HAPE and HACE must be addressed immediately. Being familiar with the Lake Louise scoring system and strategies to manage AMS can save a life or at least a trip.
Altitude Illness, Centers for Disease Control (CDC) Yellow Book
Institute for Altitude Medicine
Wilderness Medicine Society Consensus Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2014 Update,
Altitude Acclimatization Facebook Group