Firsthand Perspective

Having dealt with both HACE and HAPE at over 6,000m, I can tell you from hard-earned experience that you don’t want to risk getting either.  Both will end your trip, and likely that of your teammates too.

Stabilising and evacuating a HACE casualty takes huge effort and puts others at risk.  The best way to avoid becoming a casualty yourself is simple: listen to your body.

If you develop symptoms of AMS, speak up early and act.  Ignoring them is how AMS turns into HACE or HAPE, and how your expedition ends early.

Trusted Sources

This article draws on experience gained in the mountains and on guidance from:

• UIAA Medical Commission – Field Management of AMS, HAPE, HACE (Volume 2)
• UIAA MedCom – Drugs at Altitude
• Wilderness Medical Society Practice Guidelines (2024 update)
• Centers for Disease Control – High-Altitude Travel & Illness
• Peter H. Hackett & Robert C. Roach – “High-Altitude Illness”, NEJM 2001
• Luks & Swenson (2011–2022) – key papers on high-altitude physiology
• Peter Bärtsch, Erik Swenson, Maggiorini et al. – HAPE pathophysiology

These research-backed insights form the foundation for understanding high altitude sickness, HACE and HAPE, and how they develop on real expeditions.

What Is HACE?

High Altitude Cerebral Oedema (HACE) is a life-threatening swelling of the brain caused by the low-oxygen environment at high altitude.

Research by Hackett & Roach, and Luks & Swenson shows that rapid ascent can disrupt the blood–brain barrier, allowing fluid to leak into brain tissue.  HACE often develops from untreated AMS.

Typical symptoms include a severe headache, loss of coordination (ataxia, the UIAA calls this the key diagnostic sign), confusion or irritability, behaviour changes, difficulty speaking or thinking clearly, and, in advanced stages, collapse or unconsciousness.

Ataxia is strange to see.  It looks as if someone has suddenly lost their balance or coordination, they might stumble, veer sideways, or struggle to walk in a straight line.  It can be subtle at first and easy to miss unless you’re watching closely as they move around.

➡️ If ataxia and confusion are present at altitude, treat as HACE until proven otherwise.

What Is HAPE?

High Altitude Pulmonary Oedema (HAPE) is the accumulation of fluid in the lungs caused by low-oxygen stress rather than infection.

Studies by Bartsch and Swenson show that uneven pulmonary vasoconstriction raises pressure in lung capillaries, forcing fluid into air spaces.  HAPE can occur even in the absence of AMS.

Someone suffering from HAPE may show breathlessness at rest (the key danger sign), reduced exercise tolerance, a persistent cough, rattling or crackles in the chest, and cyanosis (blue lips or nails).

In my experience, one of the earliest warning signs of HAPE is a persistent cough.  It often starts mild and becomes progressively harsher, sometimes producing frothy or blood-stained phlegm as the condition worsens.

➡️ Any breathlessness at rest at altitude should be treated as HAPE until proven otherwise.

Evidence-Based Treatment

For either HACE or HAPE, there is only one course of action: Descent, Descent, and more Descent.

In all cases of high altitude sickness, HACE and HAPE, all major authorities agree that immediate descent is mandatory and that descent remains the single most effective and reliable treatment..

“Medications may help stabilise the patient, but they do not replace descent.” — Wilderness Medical Society

Aim to descend 500 to 1,000 m — and keep going until symptoms improve.

Supplemental oxygen can relieve symptoms and buy time, but it is not a cure.

Medications

• For HACE: Dexamethasone reduces brain inflammation and pressure.
• For HAPE: Nifedipine lowers pulmonary artery pressure and improves oxygenation.

These medications only buy time; they are no substitute for immediate descent.

💡 There’s an old mountaineers’ saying: “Dex means Down.”

In recent years, it has become increasingly common for trekkers to buy dexamethasone over the counter and take it without understanding the consequences.  Dexamethasone can mask symptoms and must never be used to justify further ascent.

The WMS calls prophylactic or casual Dex use “dangerous, inappropriate, and contrary to accepted altitude-illness protocols.”

Portable Hyperbaric Chambers

Research by Gamow and Schoene has shown that portable hyperbaric chambers can simulate 1,500 to 2,000 m of descent and can be lifesaving when evacuation is delayed.

They work, but they’re heavy, labour-intensive, and only useful if readily available.  Having used one myself at over 6,000m to stabilise a HACE casualty, my advice is simple: don’t get HACE in the first place.

Preventing HACE and HAPE

Preventing high altitude sickness, HACE and HAPE starts long before you feel unwell, through smart planning, gradual ascent, and awareness.

The best prevention is a sensible ascent profile.

The UIAA and WMS recommend:

• No more than 300 to 500m of sleeping altitude gain per day above 3,000m.
• A rest or acclimatisation day every 3–4 days.

These limits are built into all Monkey Mountaineering itineraries, and we believe this is a key reason for our excellent safety and success rates.

Coupled with a steady ascent profile is the principle that you should never climb higher if you have symptoms of AMS.

This is the single most effective way to prevent both HACE and HAPE.

Other steps you can take include:

• Stay Hydrated and Well-Fuelled.  Dehydration and fatigue increase the risk of AMS.  WMS guidelines directly link good nutrition and hydration with improved acclimatisation. For practical tips on what, when and how much to drink, see our blog on hydration for trekking at altitude.
• Avoid Alcohol and Sedatives.  They suppress breathing and disrupt sleep, two major risk factors for altitude illness (see our related post: Alcohol at Altitude – Three Reasons to Wait.).
• Sleep Low When Possible.  The “climb high, sleep low” principle is proven to reduce AMS incidence.  Never sleep more than 500 m higher than the previous night.  For example, many Mera Peak trekkers bypass Base Camp and climb from Khote to High Camp (~900 m gain) and pay for it the next day.  One extra night at Base Camp makes all the difference.
• Travel with Experienced, Trained Leaders.  Guides familiar with UIAA and WMS protocols recognise warning signs early and act decisively.

Why You Rarely See These Illnesses on Well-Run Expeditions

Operators who design itineraries around sound altitude science see extremely low rates of HACE and HAPE.

At Monkey Mountaineering we:

• Keep ascent profiles conservative.
• Build rest days into every itinerary.
• Monitor morning and evening wellness.
• Carry the right medical kit and oxygen.
• Encourage honest communication, there’s no stigma in speaking up.
• Maintain a “health first” culture where safety outranks summit pressure.

That’s why our success and safety record remains consistently strong.

Final Thoughts

HACE and HAPE are serious.  But with the right preparation and awareness, high altitude sickness, HACE and HAPE are almost entirely preventable and can be avoided, leaving you free to enjoy the rewards of the mountains safely.

The research is clear:

Ascend slowly.  Recognise problems early.  Descend decisively.

And remember… Dex means Down.  Always.

🧭 Further Reading

• The Essentials of Altitude Sickness
• Avoiding Altitude Sickness – 5 Top Tips
• UIAA MedCom Guidance
• Wilderness Medical Society Guidelines