High Altitude Sickness - AMS, HACO, HAPO


Mountain sickness is very common in the Himalayas whether we trek or drive in. Any altitude above 8,000 feet can develop signs and symptoms in the body which should be immediately noticed and not taken lightly. For a better understanding we have shared our understanding of these terminologies with our experience in trekking and travelling in the mountains.


For any trek it is sensible to enquire the altitude of the campsites in order to plan the route best suited to better acclimatization. If not acclimatized well, the body starts giving signs and symptoms that signify mountain sickness – acute version. Symptoms are what people feel and is only felt or experienced by the person for instance – headache, stomach aches, lack of sleep, indigestion, acidity, fatigue are all symptoms. Signs are generally visible such as vomiting, diarrhoea, panting for air, short of breath, dizziness. Any sign and symptom hitting together in a combination can be termed as AMS (Acute mountain sickness). AMS being the initial phase can be cured with proper care followed by a descent. Avoiding AMS and still continuing to gain altitude is the worst thing that can be done. AMS if not diagnosed could escalate to the next level – HAPO or HACO or even both.

HACO (High Altitude Cerebral Oedema)

Before we discuss about what High Altitude Cerebral Oedema is let’s understand what high altitude could do to the brain? While gaining altitude, insufficient amount of oxygen can severely damage the cells and neurons in the brain. Due to lack of oxygen flow, the brain cells could leak fluids into the cranial cavity resulting in swelling of the brain. This is extremely dangerous as if not administered with steroids can lead to serious permanent nerve damage and also death. Just like the body sends signs and symptoms in AMS, it also gives signs and symptoms in HACO. Headache, inability to walk in a straight line, mood swings – as in suddenly starting to laugh and then suddenly crying, not being able to remember name place time day or night, loss of consciousness, confusion in basic day to day tasks, drowsiness are all severe signs of HACO. Another severe hit in HACO is getting a stroke – inability to speak/ form sentences, losing control over a limb, temporary paralysed left/ right side. The only way to recover from this phase is to descend immediately with right amount of steroids – Dexamethazone (Dex) in combination with Acetazolamide (Diamox), followed with supplementary oxygen. It is important to sit upright and keep warm. If not descended immediately, permanent damage to the brain or even death is certain.

HAPO (High altitude Pulmonary Oedema)

Before we discuss about what High Altitude Pulmonary Oedema is let’s understand what high altitude could do to the lungs? As the air gets thinner lack of oxygen caused by the lower air pressure, leads to heavy and deep breathing. This could cause liquid to accumulate in the lungs. Once fluids start to accumulate in the lungs the body starts to send signs and symptoms. Uneasiness in breathing even while resting, regular coughing, froth and also blood in the spit, cyanosis (turning blue/ purple) of fingernails, lips, tongue are major signs.

If not immediately descended with supplemental oxygen and administered with the right drugs, HAPO can also escalate to death. Once recovered fully, HAPO can relapse on being exposed to similar altitude, so one needs to be extra careful in this condition. Nifidipine is one drug that can be used along with an immediate descend up till 400 metres/ tree- line (at least) to see recovery.

The point of the above information is to be aware of the basic signs and symptoms our bodies give. The sooner we identify and take care, the better we recover and safer we trek.