Altitude sickness

Altitude sickness, also known as acute mountain sickness, AMS, altitude illness, or soroche, is a pathological condition that is caused by acute exposure to low air pressure (usually outdoors at high altitudes). It commonly occurs above 2,400 metres (approximately 8,000 feet). Acute mountain sickness can progress to high altitude pulmonary edema (HAPE) or high altitude cerebral edema (HACE).

Altitude sickness is caused by reduced partial pressure of oxygen. The percentage of oxygen in air remains essentially constant with altitude at 21 percent, but the air pressure drops with altitude.

Generally, different people have different susceptibilities to altitude sickness. For some otherwise healthy people Acute mountain sickness (AMS) can begin to appear at around 2000 meters (6,500 feet) above sea level. AMS is the most frequent type of altitude sickness encountered. Symptoms often manifest themselves 6 to 10 hours after ascent and generally subside in 1 to 2 days, but they occasionally develop into the more serious conditions. Symptoms are described as headache with fatigue, stomach sickness, dizziness, and sleep disturbance as additional possible symptoms. Exertion aggravates the symptoms.

High altitude pulmonary edema (HAPE) and cerebral edema (HACE) are the most ominous of these symptoms, while acute mountain sickness, retinal haemorrhages, and peripheral edema are the less severe forms of the disease. The rate of ascent, the altitude attained, the amount of physical activity at high altitude, as well as individual susceptibility, are contributing factors to the incidence and severity of high-altitude illness.

Altitude sickness usually occurs following a rapid ascent and can usually be prevented by ascending slowly. In most of these cases, the symptoms are only temporary and usually abate with time as altitude acclimatisation occurs. However, in more extreme cases symptoms can be fatal.

Signs and symptoms
Headache is a primary symptom used to diagnose altitude sickness, although headache is also a symptom of dehydration. A headache occurring at an altitude above 2,400 meters (8000 feet), combined with any one or more of the following symptoms, could be an indication of altitude sickness.

  • Lack of appetite, nausea, or vomiting
  • Fatigue or weakness
  • Dizziness or light-headedness
  • Insomnia
  • Pins and needles
  • Shortness of breath upon exertion
  • Persistent rapid pulse
  • Drowsiness
  • General malaise
  • Peripheral edema (swelling of hands, feet, and face).

Symptoms of life-threatening conditions resulting from extreme altitude sickness include:

  • pulmonary edema (fluid in the lungs):
    • persistent dry cough
    • fever
    • shortness of breath even when resting
  • cerebral edema (swelling of the brain):
    • headache that does not respond to analgesics
    • unsteady walking
    • increasing vomiting
    • gradual loss of consciousness.

Prevention by Altitude acclimatization
Altitude acclimatization is the process of adjusting to decreasing oxygen levels at higher elevations, in order to avoid altitude sickness. Once above approximately 3,000 metres (10,000 feet), most climbers and high altitude trekkers follow the "golden rule" - climb high, sleep low. For high altitude climbers, a typical acclimatization regime might be to stay a few days at a base camp, climb up to a higher camp (slowly), then return to base camp. A subsequent climb to the higher camp would then include an overnight stay. This process is then repeated a few times, each time extending the time spent at higher altitudes to let the body "get used" to the oxygen level there, a process that involves the production of additional red blod cells. Once the climber has acclimatised to a given altitude, the process is repeated with camps placed at progressively higher elevations. The general rule of thumb is to not ascend more than 300 metres (1,000 feet) per day to sleep. This process cannot safely be rushed, and this explains why climbers need to spend days (or even weeks at times) acclimatising before attempting to climb a high peak.

The only real cure once symptoms appear is for the sufferer to move to a lower altitude as quickly as possible. For serious cases of AMS, a Gamow bag can be used to reduce the effective altitude by as much as 1,500 meters (5,000 feet). A Gamow bag is a portable plastic pressure bag inflated with a foot pump.

Acetazolamide may treat mild cases of altitude sickness.

Patients can sometimes control mild altitude sickness by consciously taking ten to twelve large, rapid breaths every five minutes. If overdone, this can remove too much carbon dioxide and cause tingling in the extremities of the body.

Other treatments include injectable steroids to reduce pulmonary edema, and inflatable pressure vessels to relieve and evacuate severe mountain-sick persons.