AMS vs HAPE vs HACE Know the Difference

The Altitude Illness Spectrum

Altitude illnesses in Nepal exist on a spectrum from mild inconvenience to life-threatening emergency. Acute Mountain Sickness (AMS) is the starting point, a warning that your body has not yet adapted. High Altitude Pulmonary Oedema (HAPE) and High Altitude Cerebral Oedema (HACE) are serious complications that develop when AMS is ignored. Understanding the distinction is critical for every trekker heading above 3,000 metres.

AMS: The Warning Signal

AMS is defined by the presence of headache plus at least one of the following: fatigue, dizziness, loss of appetite, or nausea. It typically appears within six to twelve hours of arriving at a new altitude. The headache is usually throbbing and worsens when bending over or lying flat.

Treatment is straightforward: stop ascending, rest for 24 hours, and use ibuprofen for headache. Most people improve within a day. The critical rule is never ascend further while symptomatic. Diamox can help accelerate recovery. If symptoms do not improve or worsen over 24 hours, descend 300-500 metres immediately.

HAPE: The Lung Complication

HAPE is the leading cause of altitude-related death. It involves fluid accumulating in the lungs, reducing oxygen exchange. Initial symptoms include reduced exercise tolerance and a dry cough that progressively becomes wet and productive. Breathing becomes laboured even at rest. In severe cases, pink or frothy sputum appears.

HAPE can develop rapidly over hours. The defining sign is breathlessness at rest — not just on exertion. Resting heart rate above 110 bpm at rest, or oxygen saturation falling below 75 percent, are danger thresholds. Treatment requires immediate descent of at least 1,000 metres, supplemental oxygen if available, and nifedipine 30 mg (extended-release) to reduce pulmonary pressure. Gamow Bags provide temporary relief during evacuation.

HACE: The Brain Complication

HACE is oedema of the brain — swelling caused by fluid leakage from blood vessels under low-oxygen conditions. It is less common than HAPE but equally deadly. The hallmark sign is ataxia: the inability to walk a straight line. Test by asking the person to place one foot directly in front of the other heel-to-toe — inability to do so reliably indicates HACE.

Additional symptoms include severe headache unresponsive to ibuprofen, confusion, personality changes, and eventually loss of consciousness. Treatment is immediate descent and dexamethasone 8 mg followed by 4 mg every six hours. A Gamow Bag can stabilise the patient for evacuation.

FAQ

Q: Can HAPE and HACE occur simultaneously?
A: Yes, combined HAPE-HACE is possible and particularly dangerous. Any combination of severe respiratory and neurological symptoms demands emergency descent.

Q: How quickly can HAPE develop?
A: HAPE can progress from mild symptoms to life-threatening within 12-24 hours, particularly if the person continues ascending or exerting heavily. Night-time descent in darkness is justified if HAPE is suspected.

Q: Is a pulse oximeter reliable for detecting HAPE?
A: SpO2 readings are useful indicators. Saturation below 80 percent during rest at altitude warrants serious concern, and below 75 percent is a medical emergency. However, individual baselines vary, so trend monitoring over time is more informative than a single reading.