High Altitude
As altitude increases, the amount of oxygen available to be breathed decreases leading to low oxygen levels (hypoxia). The body will attempt to acclimatize to this lack of oxygen but may not be able to adequately compensate and Acute Mountain Sickness (AMS), High Altitude Cerebral Oedema (HACE) and High Altitude Pulmonary Oedema (HAPE) may develop. These conditions may be fatal.
At Altitudes of 1500-2500m exercise performance can be reduced but altitude sickness is rare. At 2500m hypoxia occurs even at rest and symptoms of altitude sickness can be present. At levels over 4000m acclimatization is always required to prevent illness. At extreme altitude (>5500m) illness can occur despite acclimatization and sustained inhabitation is impossible.
Acclimatization includes several physiological changes to the lungs, heart and blood including increased breathing rate, increased heart rate and blood pressure and an increase in the number of red blood cells which carry oxygen. Excessive urination, periodic breathing (pauses in breathing during sleep) and insomnia are other changes that people commonly experience. Individuals acclimatize at different rates.
Altitude Sickness can affect anyone. It is not related to levels of physical fitness or gender and can occur in people who have been to high altitudes without problems previously. Those who have had altitude sickness before are at increased risk. Altitude sickness can be exacerbated by rate of ascent, the altitude reached, strenuous exercise, ill health, dehydration, hypothermia, inadequate caloric intake, fatigue, alcohol and certain drugs.
Several other difficulties are associated with high altitude and mountaineering including avalanche, falls, hypothermia/cold injury and sun exposure to name a few.
High Altitude Illness
Acute Mountain Sickness (AMS)
AMS reflects a lack of acclimatization. It is not a reflection of lack of fitness or ‘a failure’ and its presence should not be ignored as the consequences can be serious. People most at risk include those with prior episodes of AMS, fast ascent, higher altitudes and those who are overweight.
Symptoms include headaches, loss of appetite, nausea, fatigue, dizziness and insomnia. It feels like a bad hangover. People who have a persistent headache (despite fluid and paracetamol) and one of the other symptoms at altitude should assume they have AMS. A headache does not have to be present to have AMS but is usually present.
The treatment of AMS includes rest, fluids, and analgesics (eg. paracetamol, codeine, anti-inflammatories). Stopping ascent may be all that is necessary however descent (500-1000m) will speed recovery.
Acetazolamide is a diuretic medication that is used to treat AMS. The effect of this medication is to speed up acclimatization. It does not protect against worsening AMS with continued ascent. Acetazolamide is a sulpha-based drug, those with sulpha allergies should not take it. Side effects include taste alteration and numbness and tingling in the hands and feet.
Dexamethasone is a steroid that decreases the swelling of the brain. It does not improve acclimatization. Side effects include euphoria, sleep difficulty and raised blood sugar levels. It should be used in combination with acetazolamide and/or descent.
Ibuprofen has been shown to be effective in the treatment of AMS symptoms.
Oxygen at night will improve the symptoms of AMS but delays acclimatization.
A hyperbaric bag can he used when descent is not possible, although this treatment is usually reserved for the more serious conditions of HAPE and HACE.
AMS can progress to HAPE or HACE (see below).
High Altitude Pulmonary Oedema (HAPE)
HAPE is the most common cause of high altitude fatality. Younger people and men may be more susceptible. HAPE is due to fluid in the lungs caused by an increase in pressure in the vessels that carry blood to the lungs. It is reversible so early recognition and treatment is vital.
It manifests as shortness of breath, chest tightness, pink frothy sputum, cough, cyanosis (blueness of lips/fingers) and fatigue. Symptoms of AMS may or not be present prior. It usually occurs within 2 - 4 days of ascent. HAPE can be confused with other lung conditions such as high altitude cough, pneumonia and asthma.
The most effective treatment is rapid descent. Oxygen should be administered. Exertion and cold stress should be minimized. Medications should only be used as an adjunct to descent and oxygen. Nifedipine has been shown to be effective. More controversial therapies include frusemide and morphine.
High Altitude Cerebral Oedema (HACE)
HACE is due to brain swelling. Symptoms include confusion, loss of coordination, severe headache, drowsiness and loss of consciousness. Symptoms of AMS are almost always present first. Progression to HACE can occur in as little as 12 hours, but usually takes 1 - 3 days. Loss of co-ordination (ataxia) leads to patients being unable to ‘walk a straight line’. This condition can be rapidly fatal. The best treatment is rapid descent. Oxygen should be given if available. A hyperbaric bag should be used if rapid descent is not possible. The most effective medication for the treatment of HACE is dexamethasone.
Prevention
Gradual ascent – leave time to gradually ascend according to your own body’s ability to acclimatize. Two or three nights should be spent at 2500-3000m before further ascent. Above 3000m sleeping elevation should not be >600m higher than the night before; with a second night at the same elevation every 300-900m. “Climb high, sleep low” is useful to remember.
Avoid alcohol and sedative drugs. Eat a high carbohydrate diet.
Acetazolamide has been proven to be effective in the prevention of AMS and HACE. Spironolactone was shown to have similar efficacy to acetazolamide in one study. Dexamethasone may be used for prophylaxis in certain circumstances, such as forced rapid ascent or those who have had AMS in the past. Ginko biloba is often recommended, although no clinical data supports its efficacy.
Nifedipine is effective in the prevetion of HAPE, although it can cause low blood pressure, headache and ankle swelling. It should be restricted to HAPE-suscetpible climbers only. Salmeterol has been shown to reduce the risk of HAPE by more than 50%. There is also anectdotal evidence for the use of acetazolamide in the prevention of HAPE.
