What is altitude sickness?
Altitude sickness covers a range of symptoms that are produced when the body attempts to function at a period of altitude without having enough time to adequately adapt. The adaptation relates to the body’s ability to adjust to the different pressure of oxygen within the environment; as climbers ascend, barometric pressure falls and this causes the partial pressure of oxygen to fall. The end result of a reduction in partial pressure of oxygen is that the body becomes less effective at taking oxygen from the atmosphere, via the lungs, and transporting it to the tissues and organs of the body via red blood cells.
Acclimatization can take a significant period of time. In unacclimatized climbers, reduced oxygen levels can be monitored in the blood at 2500m. Doubling the height to 5000m will cause significantly low blood oxygen levels and lead to a distressing combination of symptoms due to the low oxygen level. Although humans can live habitually at 5000m, for example, the Ethnic Tibetans, there are significant risks of high infant mortality, increased blood pressure within the lungs, and heart failure.
The body is able to adapt to slowly increasing ascension by increasing the number of red blood cells it produces and by altering the chemistry of the blood to encourage blood cells to manage the oxygen that they can transport as optimally as possible. Most humans are unable to tolerate ascent rates of 300m or more per day but training and acclimatization can produce variations in tolerance.
High Altitude Illness
If the body’s capacity to adapt is overcome, i.e. if ascent is too fast, several conditions can develop: acute mountain sickness, high altitude pulmonary oedema, and high altitude cerebral oedema. These conditions are arranged from most common to least common but exist on a spectrum of severity from least severe to most severe. In all cases the most effective treatment is descent.
Acute mountain sickness typically causes the sufferer to experience headache, nausea/vomiting, fatigue/weakness, dizziness, sleeplessness, change in mental state, or swelling of the limbs. Each of these symptoms can exist at varying severity but usually if symptoms are going to develop they are seen at 6-12 hours following ascent and is increasingly more common at increasing altitude. Symptoms are almost always worse at night and develop gradually. For mild symptoms, anti-sickness or analgesic medications are often sufficient to provide relief. Moderate to severe mountain sickness usually requires a combination of oxygen, acetazolamide (Diamox), or dexamethasone. In both scenarios, medication is always considered an adjunctive measure alongside descent.
The specific cause of mountain sickness is unknown but may comprise altered blood flow within the brain and limbs, swelling of the brain, or damage to cells due to the presence of free radicals.