High-altitude illness afflicts novices and experienced mountaineers alike. Acute mountain sickness (AMS), high-altitude pulmonary edema (HAPE), and high-altitude cerebral edema (HACE), usually occurring above 2,500 meters (8,202 feet), can lead to an epic. As a climber and nurse, I’ve encountered many ill climbers. Understanding altitude illness will reduce your risk for an emergency in the mountains.

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What is Altitude Illness?

High altitude starts at 1,500 meters (4,921 feet). At high altitudes, air pressure decreases (hypobaria), resulting in “thinner” air—that is, oxygen molecules spread farther apart. We take in less oxygen when breathing, resulting in less oxygen being absorbed in the lungs and delivered to the body. A low-oxygen state, whether in ambient air or in the body, is called hypoxia.

Hypobaric hypoxia causes multiple effects: Heart and respiratory rates increase immediately, improving oxygenation. Muscle fatigue, sleep apnea, changes in metabolism, altered hormone secretion, fluid retention, and swelling of the hands, feet, and face are common. Hemoglobin production and urination increase within two days at altitude as the body adjusts (acclimatizes). And weight loss may occur after about a week.

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Types of Altitude Illness

Experiencing some discomfort is normal at altitude, but symptoms may worsen to become illness. AMS, HAPE, and HACE typically start within 1–5 days of ascent without proper acclimatization. Contributing factors include living at lower altitudes, rapid ascent, higher sleeping altitude, exertion, possible genetic predisposition, and previous history of altitude illness. (Talk to your healthcare provider before traveling to altitude.)

AMS

AMS, the most common altitude illness, typically begins within 4–12 hours of ascent. Symptoms mimic a hangover, ranging from mild discomfort to debilitation. AMS is diagnosed by presence of a headache plus gastrointestinal disturbance (nausea, vomiting, loss of appetite), dizziness, difficulty sleeping, and fatigue. Most people improve within 1–2 days after they stop ascending. However, AMS may progress to life-threatening HAPE and/or HACE. If AMS is severe, not improving, or worsening after halting the ascent, immediately descend. Choosing to ascend with AMS may lead to serious illness, and the need for a rescue.

Common onset

>2,500 meters

Signs and symptoms

Headache

Nausea

Dizziness

Fatigue

Sleep disturbances

Treatment

Stop ascending

Acetazolamide

Ibuprofen

Dexamethasone

Anti-nauseants

Descent

HAPE

HAPE is the no. 1 killer among altitude illnesses, typically occurring abruptly on the second night above 2,500 meters. During HAPE, the lung’s arteries constrict, increasing pulmonary blood pressure; in turn, fluid leaks into the sacs of the lungs where gas exchange occurs, reducing oxygen absorption. Patients present with decreased exercise performance, shortness of breath at rest, and a dry cough. Because shortness of breath while exercising and cough are common at altitude, HAPE victims are often initially unaware they have it. Heart and breathing rates are elevated. As HAPE progresses, you may hear bubbling lung sounds, called rales. The patient may have bluish lips and nailbeds (cyanosis), and cough up pink, frothy sputum. Patients may have HAPE and HACE concurrently.

Common onset

>2,500 meters

Signs and symptoms

Shortness of breath at rest

Cough

Increased heart and breathing rate

Cyanosis

Rales

Treatment

Descent

Oxygen

Nifedipine

Gamow Bag

Evacuate

HACE

HACE involves brain swelling and is rare but life-threatening. HACE usually occurs within 1–2 days above 4,000 meters, but has occurred at 2,100 meters. Many, but not all, victims initially have AMS. HACE is a medical emergency that can progress to coma and death within 24 hours. HACE victims are withdrawn and lethargic, refusing to leave their tent. They lose coordination, becoming unable to “walk the line” heel-to-toe without stumbling. They may have slurred speech, confusion, or cognitive impairments, and be delusional or hallucinating. Judgment may be impaired, and on a mountain this could prove deadly.

Common onset

>4,000 meters

Signs and symptoms

Lethargy

Lassitude

Stumbling gait

Confusion

Personality changes

Treatment

Descent

Oxygen

Dexamethasone

Anti-nauseants

Gamow Bag

Evacuate

Prevention

Everyone reacts to altitude differently: Predicting susceptibility is difficult. Mountain preparedness includes anticipation of altitude illness. Study topos, altitude gains, weather patterns, and bail-out points before your climb.

Prevention includes pre-acclimatization. Despite common misconceptions, fitness does not enhance acclimatization. Hike and sleep at incrementally higher altitudes for 1–8 weeks before your trip. Frequent altitude exposure over long periods is optimal. A higher objective necessitates a longer, staged acclimatization. Acclimatization diminishes within 1–3 weeks of altitude exposure, so bagging a Fourteener two months in advance won’t help.

One time-tested strategy is “Climb high, sleep low.” Spend the first night below 2,000 meters. Ascend gradually, hiking higher each day and retreating lower to sleep. Include rest days, and be aware that you will move slower the higher you go. Once you reach a sleeping altitude of 3,000 meters, don’t increase sleeping altitude by more than 500 meters in a 24-hour period. Be aware that you will move slower the higher you go. Have a lower-altitude, backup objective.

Self-care is important. Avoid cold and dehydration by layering accordingly and drinking electrolyte beverages. Altitude reduces appetite so bring high-calorie foods. Avoid alcohol, respiratory depressants, and marijuana. Wear sunscreen, a hat, and UV-blocking sunglasses to avoid sunburn and photokeratitis (snowblindness).

Treatment

Only take medications to prevent or treat high-altitude illness under the guidance of a healthcare provider, who may direct you to take a few doses prophylactically prior to travel or if there are concerns about side effects or allergic reactions. Whether to use medication or oxygen at altitude is a personal decision and a valid ethical debate beyond the scope of this article. Many “purist” mountaineers carry altitude-illness medications “just in case.”

The most common medication for acclimatization is acetazolamide (Diamox), taken twice per day. This diuretic increases ventilation and improves sleep. Hydrate well while taking it. Acetazolamide may cause dizziness, nausea, tingling in fingers, toes, and lips, muscle weakness, and alterations in the taste of carbonated beverages. Nifedipine is first-line for HAPE prevention in those with a previous history; acetazolamide is also used. Dexamethasone, a steroid, may prevent AMS or HACE. One risk of steroid treatment is a potential cessation syndrome, so dexamethasone is reserved for severe AMS or HACE treatment.

When someone is sick above 2,500 meters, assume altitude illness until proven otherwise and stop ascending. A person with mild AMS may stop his ascent, or descend until symptoms abate, then re-ascend more slowly. Double the prophylactic dose of acetazolamide as a first-line treatment for AMS. Ibuprofen, acetaminophen, and anti-nauseants treat mild AMS, while dexamethasone treats more severe AMS. If you suspect HAPE or HACE, immediately descend at least 1,000 meters, exerting the patient as little as possible. Never abandon a patient with altitude illness—monitor pulse, respiratory rate, symptoms, and mental awareness throughout the descent. If descending is not possible under your own power, promptly call for help to evacuate the patient and, if possible, administer oxygen. Some expeditions bring portable hyperbaric chambers, such as a Gamow Bag, but you shouldn’t use this to delay evacuation or descent. Seek appropriate medical attention after the descent, as symptoms may require hospital care.

Wyoming-based nursing PhD student and climber Annie Wislowski studies high-altitude illnesses. She volunteers for the University of Colorado’s Altitude Research Center and Albany County Sheriff’s Search and Rescue. She has been known to boulder in Vedauwoo with her cat, Trixie.