Altitude Sickness: AMS, HAPE, HACE

This information was gathered from various web sources and from personal experience. Recommendations are for adults. Hikers should do their own research and consult their doctor/s before hiking at altitudes greater than 6,000 feet (1,828.8m). Cold temperatures, low humidity, increased ultraviolet radiation, and decreased air pressure in high-elevation environments expose hikers to health challenges. The biggest concern is hypoxia (low levels of oxygen in body tissue), most pronounced while sleeping. 

Altitude sickness happens when your body doesn’t have time to adjust to lower oxygen levels at high elevations. It can happen to anyone regardless of physical fitness. Current thinking is that low oxygen in the air causes blood vessels in the brain to swell as they work to get more oxygen. Resultant headaches can be similar to migraines. Everyone ascending to high altitudes will have some swelling, but it’s more pronounced in people who develop altitude sickness. If you have hiked and camped at altitude without problems in the past, it doesn’t mean you won’t have them in the future.

Altitude sickness is often preventable and treatable. It usually resolves in 6-48 hours once your body has adapted to the higher altitude. Headache is the most common symptom. In some instances, altitude sickness can progress to more uncomfortable and even dangerous conditions requiring immediate medical assistance.

Altitude sickness is an umbrella term that refers to three conditions

• Acute mountain sickness (AMS) is the mildest and most common form of altitude sickness. AMS should not be confused with HAPE or HACE.
• High altitude pulmonary edema (HAPE) happens when lung blood vessels constrict causing fluid to leak to lung tissue and eventually into air sacs. HAPE typically occurs 2-5 days after ascending rapidly to altitudes greater than 8,200-9,842 feet (2,500-3,00m). It can be life-threatening. Immediate care is required. 
• High altitude cerebral edema (HACE) is the least common form of altitude sickness. Within 24 hours it can progress to brain herniation leading to coma and potentially death. HACE generally occurs after 2 days at altitudes above 13,123 feet (4,000m). Immediate care is required.

Risk factors for altitude sickness include

• Higher altitudes—the higher you go, the greater the risk of altitude sickness
• Speed of ascent
• History of AMS, particularly HAPE, and/or HACE
• Genetics
• Living at a low altitude, defined as below 5,000ft (1,500m)
• Obesity
• Current respiratory infection or other medical factor/s that affect breathing
• Alcohol use, especially 1st night at altitude
• Drug use

Climbing at altitude is not the time to quit caffeine if you regularly use it. Caffeine withdrawal can exacerbate AMS, and an accompanying headache could be confused with AMS.

Symptoms

Altitude sickness can produce a variety of symptoms that can vary in severity. Symptoms are sometimes described as feeling like an alcohol hangover. They normally appear within the first day or two of reaching a high altitude. Symptoms include:

• Headache—the most common symptom
• Nausea and vomiting
• Loss of appetite
• Fatigue, even when resting
• Feeling lousy
• Difficulty sleeping
• Dizziness or light-headedness
• Vision changes—rare and indicate more severe altitude sickness, caused by retina blood vessel rupture

HAPE and HACE 

HAPE and HACE can worsen quickly and require immediate medical attention. Be aware of the following symptoms, for yourself and others. Any of these symptoms may indicate HAPE or HACE:

• Shortness of breath at rest
• Chest tightness or pain
• Severe exhaustion or weakness
• Loss of coordination, difficulty walking straight
• Confusion
• Slurred speech
• Decreased consciousness

HAPE symptoms include nonproductive cough, difficulty breathing, decreased exercise tolerance, rales (lung rattling), and chest pain. Later symptoms include labored breathing at rest; cough that produces pink, frothy sputum or blood; wheezing; blue hands and feet; increased heart rate; and/or rapid, shallow breathing. 

HACE can be more rapidly fatal than HAPE. Its symptoms include loss of coordination (ataxia), intense exhaustion and/or weakness, and altered mental state (confusion, irritability, memory loss). 

Prevention, or reducing chances, of AMS:

• Talk to your doctor before traveling to high altitude destinations.
• Ascend slowly. 
• Tell traveling companions, especially guides, about your symptoms.
• Take rest days to acclimate.
• Because hypoxia is greatest during sleep, hike high, sleep low—sleep at a lower altitude than the highest you climbed that day. 
• Avoid alcohol and sleeping medications that contain benzodiazepine drugs as they suppress breathing resulting in lower blood oxygen. Sources consulted do not agree on the safety of using other sleep aids, e.g., Ambien or Lunesta.
• Stop using tobacco products. Tobacco use of any kind can affect oxygen levels.
• Preventative medications: acetazolamide (Diamox), most commonly used, and nifedipine can both prevent and treat altitude sickness. Phosphodiesterase (PDE) inhibitors, sildenafil and tadalafil, are also preventative. 
• Acetazolamide (Diamox) taken 24-hrs prior to arrival to altitude and the first 2 days at altitude is 75% effective in AMS prevention. Acetazolamide hastens acclimation, stimulates breathing, raises blood oxygen, and increases urination. 
• Drink plenty of water to avoid dehydration, and especially if you are taking acetazolamide.
• Gingko biloba is not fully tested and is contraindicated for several drugs and conditions. Be cautious.
• Monitor for HAPE and/or HACE.

Diagnosis

It is critical to monitor all potential symptoms of AMS, and to remember that some hikers experience symptoms at lower altitudes than do others. Confirmation of severe altitude sickness is best diagnosed by a healthcare provider who will check breathing, blood pressure, and heart rate. Hikers with AMS will probably be asked about how they feel, what they are experiencing. Coordination may be assessed. X-rays, EKGs, and MRIs may be used. 

• Pulse oximeters measure oxygen saturation levels in red blood cells; guides on extensive treks often carry them. 90-92% is a good number. Oximeters are readily available for purchase, but buyer beware—not all oximeters are accurate.
• The Lake Louise AMS scoring system was created as a research tool, but could be helpful in assessing AMS. See “Lake Louise AMS Score” below.

Treatment

The quickest way to feel better is to descend to a lower altitude. Descend 300-1,000 feet or to the last elevation experienced without symptoms. Stay there until symptoms are relieved. If immediate descent is not possible, or if the condition is not severe, altitude sickness may be addressed by the following:

• Stop, rest, eat something, drink water, acclimate.
• Take aspirin, ibuprofen, or acetaminophen.
• Take acetazolamide (Diamox). Dexamethasone (CDC says is the most effective) and nifedipine are used for moderate or severe altitude sickness. It is critically important to work with your doctor to make sure drug/s are not contraindicated with other medications or conditions. 
• If available, use supplemental oxygen or hyperbaric therapy (Gamow hyperbaric bags). Do not ascend until symptoms go away. If not better within 24-48 hours, descend to the last elevation without symptoms, especially while sleeping.

Photo: Beginning of Hike

Personal anecdotes 

I climbed Mt. Kilimanjaro (19,341 feet, 5895m) in February 2024 and took acetazolamide (Diamox) to prevent AMS. Because I often have dramatic reactions to drugs, several weeks prior to climbing I experimented with taking acetazolamide, 125 mg twice daily for three days. I experienced dizziness and tingling in my hands, feet, and mouth. A few weeks later, I tried half that dose, 62.5 mg twice daily for three days. This time I only experienced mouth tingling. I decided to go with the smaller dose.

Photo: Porters 

At the outset of our hike, I told our guide my acetazolamide 62.5mg plan, but he recommended 125mg twice daily. After taking 125mg that evening, I experienced heart palpitations during the night. I took the second 125 mg dose in the morning and additionally experienced dizziness. Still in the rainforest, and not yet at substantive elevation, I spoke with the guide, and we agreed that I reduce to 62.5mg twice daily. I continued to feel dizzy for the rest of the hike, but much less so, and the heart palpitations stopped completely. I did not experience headaches. I had some diarrhea, but that resolved quickly after taking ciprofloxacin. I cannot be sure if the intestinal distress was caused by altitude, water, or just the whackiness of travel and climbing. I also experienced appetite loss, which is very common.

Photo: Altitude Vista

Pulse oximeters were used in the morning and at night to measure oxygen saturation levels. I found that diaphragmatic (yoga) breathing quickly put my numbers in good shape. This underscored the usefulness of that breathing technique while hiking. 

Photo: Summit

We spent about 30 minutes at the Kilimanjaro summit with nobody else there. I was ready to descend—it was really cold! The entire hike was astoundingly beautiful. The guides and crew were professional, experienced, smart, skilled, unbelievably strong, and deeply kind. I could wax poetic, but will spare you. 

My brother experienced HAPE when climbing volcanoes in Ecuador. He was taking acetazolamide, but remains unconvinced of its efficacy. He summited a 16,500 foot volcano near Quito quickly with no problems. He descended to 14-15,000’, took off his pack and at that point experienced motor function abnormalities. He descended further and spent the night in a hotel. The following day, he hiked up to about 16,500’ where he spent the night. The next day, he got to a large, impassable crevasse at about 19,000’. While assisting another hiker descend, he experienced a fast HAPE onset. He had an acute cough with blood, and an oximeter measured his oxygen saturation at 52 (hypoxemia sets in at 60; values under 90 are considered low). He had to spend the night there, and hiked out the next day. He went to an oxygen station, available at stores there. Two days later he was hiking again, but with great difficulty primarily due to involuntary coughing. He fully recovered. He is very lucky.

Here’s to the next adventure!

Betsy Fisher 

Photo: Cool tree & Banner Photo: Kilimanjaro from Amboseli Park, Kenya

from https://my.clevelandclinic.org/health/diseases/15111-altitude-sickness:

*Roach RC, Hackett PH, Oelz O, B?rtsch P, Luks AM, MacInnis MJ, Baillie JK and The Lake Louise AMS Score Consensus Committee

(2018). The 2018 Lake Louise Acute Mountain Sickness Score. High Alt Med Biol 00:1-3. DOI: 10.1089/ham.2017.0164

This document is a derivative of “The 2018 Lake Louise Acute Mountain Sickness Score” by Roach, et al. used under the Creative Commons license by Rozier, Aksamit and Meyer.

Revision date: 12/26/18

Sources consulted:

https://my.clevelandclinic.org/health/diseases/15111-altitude-sickness; consulted 1 Feb. 2024

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3617508/; consulted 2 Feb 2024

https://www.ncbi.nlm.nih.gov/books/NBK430819/; consulted 2 Feb. 2024

https://www.mayoclinic.org/diseases-conditions/pulmonary-edema/multimedia/img-20097483; consulted 2 Feb. 2024

https://www.uptodate.com/contents/high-altitude-illness-including-mountain-sickness-beyond-the-basics/print; consulted 2 Feb. 2024

https://wwwnc.cdc.gov/travel/yellowbook/2024/environmental-hazards-risks/high-elevation-travel-and-altitude-illness; consulted 2 Feb. 2024

https://www.lung.org/lung-health-diseases/lung-procedures-and-tests/pulse-oximetry; consulted 2 Feb. 2024

Wilderness Medical Society, Practice Guidelines for Prevention and Treatment of Acute Altitude 

Illness: 2019 Update

https://journals.sagepub.com/doi/full/10.1016/j.wem.2019.04.006#:~:text=Unacclimatized%20individuals%20are%20at%20risk,as%20low%20as%202000%20m.