High Altitude Illnesses - AMS HACE HAPE

Recognize, Treat and Manage High Altitude Illnesses

High Altitude Illnesses can range from mild to life-threatening. Luckily, the most common of which, is fairly mild. Altitude sickness (typically referred to as Acute Mountain Sickness or AMS) is brought on by climbing to a higher altitude too quickly without allowing time for your body to adjust to the changes in air pressure and oxygen level.

The air above 8,000 feet is “thinner” meaning that each breath you take contains less oxygen than what you’re used to. When your body doesn’t have time to adjust to the lower oxygen levels at higher altitudes, it increases its breathing rate in an attempt to boost the blood’s oxygen, though this is not enough to return it to normal levels.

There are three main (common) altitude illnesses: Acute Mountain Sickness (AMS), High Altitude Cerebral Edema (HACE), and High Altitude Pulmonary Edema (HAPE).


High Altitude Illnesses 101

Acute Mountain Sickness (altitude illness)

– Acute Mountain Sickness –

• Nausea + Vomiting
• Headaches + Dizziness
• Fatigue + Lassitude
• Lack of Appetite
• Nosebleeds

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High Altitude Cerebral Edema (altitude illness)

– High Altitude Cerebral Edema –

• Headaches + Dizziness
• Disorientation + Confusion
• Nausea + Vomiting
• Extreme Lethargy
• Lack of Coordination (Ataxia)

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High Altitude Pulmonary Edema (altitude illness)

– High Altitude Pulmonary Edema –

• Trouble Breathing
• Chest Pain
• Dry Cough
• Pink, Frothy Sputum
• Rapid Heart Rate

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Acute Mountain Sickness

Often simply called “Altitude Sickness,” Acute Mountain Sickness is a fairly common altitude illness that can manifest symptoms unpleasant enough to spoil your climb. Over 25% of people who go to high altitude (over 6000 ft elevation) present with symptoms of AMS. If one understands the cause of AMS then taking steps to avoid it or minimize its effects should be somewhat easy.

Atmospheric pressure and the oxygen content of the air decrease in an approximately exponential manner as altitude increases. This means that as you climb higher, the breath you take contains less oxygen. For most climbers, this effect can become apparent at an altitude of just 6,000-8,000 ft (3000 m) above sea level.

Acclimatization is the resetting of your physiological mechanisms which allows the body to return oxygen levels in the tissues to normal or near-normal. As this process is not instantaneous, and when your rate of ascent is faster than the body’s ability to adjust to the gain in altitude, AMS (and other altitude illnesses) occur. The symptoms of AMS can be unpleasant, serious, or in some rare situations, be fatal. It is therefore essential that the rate of ascent should allow for this adjustment.

Keep in mind that there is a lot of variation between individuals, but each person’s response to altitude is fairly constant on different occasions, given similar conditions and speed of ascent. Luckily, preventing altitude illness is relatively easy and is recommended for everybody headed to altitude.

Signs + Symptoms

AMS develops usually in the first eight to 24 hours at high altitude. Below 6,000 feet (3000 m), it occurs less often. Symptoms can include:

  • • Persistent headache
  • • Nausea (& possibly vomiting)
  • • Loss of appetite
  • • Lassitude & lethargy
  • • Nosebleeds
  • • Dizziness & lightheadedness
  • • Peripheral edema (swelling of hands, feet)


At this stage, ascent should stop. Rest, have frequent snacks and meals, take NSAIDs (Ibuprofen) and acetaminophen (Tylenol) as needed, and hydrate. Alcohol and sleeping medications (including medications such as Tylenol PM, etc.) are not recommended as they are respiratory suppressants. If the symptoms worsen or do not alleviate, stop your ascent immediately and descend to a lower altitude where the symptoms abate after a day or two of rest.In its most severe form, Acute Mountain Sickness can progress to either pulmonary edema (fluid on the lungs) or cerebral edema (swelling of the brain).

High Altitude Cerebral Edema

AMS and HACE are considered a spectrum of the same altitude illness. The small amount of swelling in the brain that contributes to mild AMS becomes significant swelling and progresses to severe headache, confusion, lethargy, lack of coordination, irritability, vomiting, seizures, coma, and eventually death if untreated (extremely rare). A person with HACE may look like a confused, disoriented drunk person, fumbling with clothing, unable to walk a straight line, and with slurred speech.

HACE usually occurs at altitudes over 9,000 ft (2743 m). Early symptoms of headache and AMS precede the more life threatening symptoms of HACE, and treatment of AMS prevents progression to HACE. In higher elevations in the United States, HACE is typically only seen in conjunction with high altitude pulmonary edema (see below). This is not the case in other areas of the world such as the Himalayas where the altitude is much higher.

Signs + Symptoms

HACE is thought to be a severe form of Acute Mountain Sickness which typically presents between 12 and 24 hours after arrival at altitude. A severe headache, vomiting and lethargy will progress to unsteadiness, confusion, drowsiness and ultimately coma. HACE can kill in only a few hours. A person with HACE will find it difficult to walk heel-to-toe in a straight line – this is a useful test to perform in someone with severe symptoms of acute mountain sickness. HACE should also be suspected if a companion starts to behave irrationally or bizarrely.

  • • Persistent headache
  • • Confusion and ALOR (altered level of responsiveness)
  • • Loss of muscle coordination (ataxia)
  • • Lassitude & lethargy
  • • Loss of consciousness
  • • Dizziness & lightheadedness


Descent is the most effective treatment of HACE and should not be delayed if HACE is suspected. A person with HACE must go down to a lower altitude. Oxygen therapy should be started if available, and Dexamethasone (a prescription, steroid medication) should be given immediately if available. It helps by decreasing vasogenic edema. NSAIDs such as ibuprofen, given in appropriate doses, may be added if the headache is debilitating. If taking Dexamethasone for more than ten days, it requires tapering to prevent complications.

If a person cannot descend due to weather or other conditions, then hyperbaric therapy with a Gamow bag or other hyperbaric bag should be initiated, if available. Supplemental oxygen has been shown to significantly improve the outcome of patients with High Altitude Cerebral Edema.

High Altitude Pulmonary Edema

Of all of the high altitude illnesses, High Altitude Pulmonary Edema (HAPE) is likely the most serious, as a person’s lungs fill with fluid at high elevation (or rarely, moderate elevation). Patients complain of trouble breathing, and they have a cough that starts out dry and becomes wet. They may also cough up blood, as their oxygen levels start to bottom out.

It arises very quickly and has been known to cause death less than 40 hours after a rapid climb to 6000 feet. A warning sign is to observe the person who is the fittest in the group at the start of the climb. If that person’s fitness decreases quickly as he or she climbs higher, then he or she might have contracted it. Another sign is extreme weakness going uphill.

How does HAPE occur?  Simple – there is less oxygen at high altitude, which causes blood vessels in the lungs to constrict or tighten. This leads to fluid leaking into the lungs.

Signs + Symptoms

Symptoms include blue or gray lips or fingernails, a cough with bloody or foamy sputum (saliva), shortness of breath, general weakness, and a gurgling sound in the chest. If these symptoms occur, then immediately descend to a lower elevation as soon as possible in order to take no risks. Pulmonary edema can rapidly progress to coma and death if you keep on climbing. However, if you descend just a few hundreds meters, the symptoms tend to diminish rapidly.

  • • Trouble breathing (dyspnea)
  • • Pink, frothy sputum (saliva)
  • • Decreased exercise ability
  • • Dry cough, changing to a productive cough
  • • Tachycardia (rapid heart rate) at rest
  • • Tachypnea (rapid breathing) at rest
  • • Loss of muscle coordination (ataxia)
  • • Decreasing level of responsiveness (ALOR)
  • • Blue or purple lips (cyanosis)


Immediate evacuation to a lower altitude is the first treatment for HAPE. A descent goal of at least 1,000 ft should help, but may require further descent until symptoms resolve. Additional exercise will worsen HAPE, so care should be taken to assist the patient in limiting exertion during descent.

If supplemental oxygen is available, high flow oxygen at 2 to 4 liters per minute with a goal oxygen saturation of >90% will decrease pulmonary artery pressures and improve the patient’s tachypnea over the course of 24 to 48 hours.

In cases where descent is not possible or may be delayed, the calcium channel blocker nifedipine tends to be the drug of choice. Extended release nifedipine, 30mg given every 12 hours, has been demonstrated to improve clinical symptoms. However, nifedipine provides no added benefit if oxygen and descent are available options. Phosphodiesterase inhibitors similarly act to dilate the pulmonary vasculature and have a role in HAPE prophylaxis but have not been formally evaluated as treatment.

If the patient’s condition is severe in remote situations where descent is not immediately possible, the patient may be placed in a portable hyperbaric bag also known as a Gamow bag, which can simulate descent up to 2700m (9000 ft), though only 500m may be necessary. This device is easy to use and has been successfully employed for HAPE by first responders.


High Altitude Illnesses