[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Conditions](https://durgical.com/en/conditions/) › High-altitude illness (AMS, HACE, HAPE)

[Conditions](https://durgical.com/en/conditions/) · [Emergency medicine and toxicology](https://durgical.com/en/conditions/)

# High-altitude illness (AMS, HACE, HAPE)

Illness caused by going up too fast to high altitude, where there is less oxygen. It ranges from headache to life-threatening fluid in the brain or lungs.

Updated 2026-11-01

## Structures involved

Tap one to see what it is and open it in 3D.

- [Pulmonary arteries](https://durgical.com/en/anatomy/right-pulmonary-artery/)
- [White matter](https://durgical.com/en/anatomy/white-matter-of-telencephalon/)
- [Segmental lung vessels](https://durgical.com/en/anatomy/pulmonary-trunk-chest/)
- [Lateral ventricles](https://durgical.com/en/anatomy/lateral-ventricle/)
- [Cerebellum](https://durgical.com/en/anatomy/anterior-quadrangular-lobule/)
- [Retina](https://durgical.com/en/anatomy/retina/)
- [Optic disc](https://durgical.com/en/anatomy/optic-disc/)

## Why it happens

- [Edema and effusions: the four mechanisms](https://durgical.com/en/general-pathology/edema-and-effusions-the-four-mechanisms/)
- [High altitude and acclimatization](https://durgical.com/en/physiology/high-altitude-and-acclimatization/)
- [The pulmonary circulation and hypoxic vasoconstriction](https://durgical.com/en/physiology/the-pulmonary-circulation-and-hypoxic-vasoconstriction/)
- [Cerebral blood flow, brain metabolism and intracranial pressure](https://durgical.com/en/physiology/cerebral-blood-flow-brain-metabolism-and-intracranial-pressure/)
- [Physiology of pulmonary edema](https://durgical.com/en/physiology/physiology-of-pulmonary-edema/)

## What it is

A group of illnesses caused by low oxygen pressure (hypobaric hypoxia) after a fast ascent, usually above about 2,500 m: acute mountain sickness (AMS), high-altitude cerebral oedema (HACE) and high-altitude pulmonary oedema (HAPE). HACE and HAPE can be fatal.

## Who gets it

Relevant across the Andes: Bogotá sits at about 2,600 m, and many Colombian travellers visit high cities and mountains such as the páramos, the snow-capped peaks, Cusco or La Paz. AMS is common in fast ascents; HACE and HAPE are rarer and mostly above 3,000 to 4,000 m. Lifelong highland residents can develop a separate condition, chronic mountain sickness (Monge disease).

## Causes

- Fast ascent to high altitude without acclimatisation
- Low barometric pressure that lowers inspired oxygen (hypobaric hypoxia)
- Individual susceptibility, shown by previous episodes
- Re-ascent after time at low altitude (re-entry HAPE in highland residents)

## Risk factors

- Rapid ascent or flying directly to high altitude
- Sleeping at a much higher altitude than the night before
- Previous AMS, HACE or HAPE
- Strenuous exertion soon after arrival
- Alcohol or sedatives; heart or lung disease, sickle cell disease or pulmonary hypertension

## Pathophysiology

Low oxygen pressure causes hypoxaemia. In the brain, vasodilation and increased capillary permeability lead to swelling; HACE is vasogenic oedema, typically of the [white matter](https://durgical.com/en/anatomy/white-matter-of-telencephalon/). In the lung, hypoxic vasoconstriction is uneven, so pulmonary artery pressure rises and over-perfused capillaries leak, giving non-cardiogenic oedema (HAPE). Acclimatisation (more ventilation, renal bicarbonate loss, later more red cells) takes days.

## Classification

- Acute mountain sickness (AMS): headache with nausea, fatigue, dizziness or poor sleep
- High-altitude cerebral oedema (HACE): AMS plus ataxia or altered mental status
- High-altitude pulmonary oedema (HAPE): breathlessness, cough, reduced exercise tolerance
- Chronic mountain sickness (Monge disease): excessive polycythaemia in long-term highland residents

## Symptoms and signs

- Headache within hours of arrival, with nausea or vomiting and loss of appetite
- Fatigue, dizziness and poor sleep
- HACE: unsteady gait (ataxia), confusion, drowsiness, progressing to coma
- HAPE: breathlessness out of proportion to effort, dry cough, then breathlessness at rest and frothy or bloody sputum
- Fast pulse, crackles and cyanosis in HAPE

## Red flags

- Ataxia (failing the heel-to-toe walk) or any change in alertness
- Breathlessness at rest or bloody sputum
- Very low oxygen saturation for the altitude
- Symptoms worsening despite rest or after further ascent

## Diagnosis

**Clinical**
Clinical diagnosis in the setting of a recent ascent; AMS severity can be scored with the Lake Louise score. Heel-to-toe walking tests for ataxia; [chest](https://durgical.com/en/anatomy/region/chest/) examination for crackles.

**Tests**
Pulse oximetry (low saturation, worse than expected in HAPE). Glucose and other tests to exclude other causes of confusion.

**Imaging**
Chest X-ray in HAPE shows patchy, often asymmetric infiltrates with a normal-sized heart; echocardiography shows high pulmonary artery pressure. MRI in HACE can show white-matter oedema, especially in the [corpus callosum](https://durgical.com/en/anatomy/corpus-callosum/).

## Differential diagnosis

- Dehydration, exhaustion or hypoglycaemia
- Migraine or other headache disorders
- Carbon monoxide poisoning from stoves in closed shelters
- Pneumonia, pulmonary embolism or cardiogenic pulmonary oedema
- Stroke, intoxication or hypothermia

## Goal of treatment

Stop ascending, improve oxygenation and descend early in severe illness; prevent illness with gradual ascent.

## Treatment

**Acute**
Descent is the definitive treatment for HACE and HAPE and for AMS that does not improve; even a few hundred metres help. No further ascent while symptoms persist.

**Acute**
Supplemental oxygen, or a portable hyperbaric bag when descent is impossible.

**Medical**
AMS: rest, simple analgesics and antiemetics; carbonic anhydrase inhibitors (acetazolamide) speed acclimatisation and are used mainly for prevention. HACE: corticosteroids (dexamethasone). HAPE: calcium-channel blockers (nifedipine) or phosphodiesterase-5 inhibitors lower pulmonary artery pressure.

**Follow-up**
Repeated checks of mental status, gait, breathing and oxygen saturation; hospital care for severe cases.

**Lifestyle**
Gradual ascent with rest days, avoiding alcohol and sedatives, and avoiding hard exertion in the first days.

## Complications

- Coma and death from HACE
- Respiratory failure and death from HAPE
- Retinal haemorrhages at high altitude
- Recurrence on later ascents in susceptible people

## Prognosis

AMS usually resolves within one to two days without further ascent. HACE and HAPE recover well with early descent and oxygen but can kill within hours if missed, especially in remote places. People who have had HAPE have a high chance of recurrence.

## Prevention

- Slow, staged ascent and rest days; above about 3,000 m, limiting the rise in sleeping altitude each day
- Climbing high during the day and sleeping lower
- Preventive medication in people at high risk or with past episodes, as advised by a clinician

## Test yourself

Think of the answer, then tap the question to see it.

## What is the main symptom of acute mountain sickness?

Headache after a recent ascent, usually with nausea, fatigue, dizziness or poor sleep.

## Which signs mark progression from AMS to HACE?

Ataxia and altered mental status (confusion, drowsiness, coma).

## What is the mechanism of HAPE?

Uneven hypoxic pulmonary vasoconstriction raises pulmonary artery pressure, and over-perfused capillaries leak, causing non-cardiogenic pulmonary oedema.

## What is the definitive treatment of HACE and HAPE?

Descent, together with oxygen; steroids are added for HACE and pulmonary vasodilators for HAPE.

## Which drug class is used mainly to prevent acute mountain sickness?

Carbonic anhydrase inhibitors (acetazolamide), which speed acclimatisation.

[Add to my cards (5)](https://durgical.app/estudiar/?add=/en/conditions/high-altitude-illness/)

## Related conditions

- [Pulmonary hypertension and cor pulmonale](https://durgical.com/en/conditions/pulmonary-hypertension-and-cor-pulmonale/)
- [Chronic obstructive pulmonary disease (COPD)](https://durgical.com/en/conditions/chronic-obstructive-pulmonary-disease/)
- [Sickle cell disease](https://durgical.com/en/conditions/sickle-cell-disease/)
- [Heart failure](https://durgical.com/en/conditions/heart-failure/)
- [Carbon monoxide poisoning](https://durgical.com/en/conditions/carbon-monoxide-poisoning/)
- [Ischaemic stroke](https://durgical.com/en/conditions/ischaemic-stroke/)
- [Migraine](https://durgical.com/en/conditions/migraine/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [High-Altitude Travel and Altitude Illness](https://www.cdc.gov/yellow-book/hcp/environmental-hazards-risks/high-altitude-travel-and-altitude-illness.html) (CDC Yellow Book, Centers for Disease Control and Prevention, 2026); [Acute mountain sickness](https://medlineplus.gov/ency/article/000133.htm) (MedlinePlus, US National Library of Medicine, 2026).

[← All conditions](https://durgical.com/en/conditions/)

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/conditions/high-altitude-illness/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/high-altitude-illness/