Kilimanjaro)ĪMS and HACE are the neurological forms of altitude illness and are likely to represent two points on a spectrum of the same disease with HACE being the more severe form. All individuals ascending > 500 m/day (in sleeping elevation) above 3,000m without extra days for acclimatisation.All individuals ascending to > 3,500m in one day.All individuals with a history of HACE or HAPE.Individuals with a history of AMS ascending to > 2,800m in one day.All individuals ascending > 500 m/day (in sleeping elevation) at altitudes above 3,000m but with an extra day for acclimatisation every 1,000m.The altitudes correspond to sleeping altitude and they assume ascent will start from elevations 2,800m in one day These risk groups refer to unacclimatised individuals. The Wilderness Medicine Society has combined knowledge of individual and trip-related risk factors to categorise the risk of AMS. Previous performance at altitude is probably the best predictor. Despite knowledge of these risk factors, accurately determining an individual’s susceptibility to altitude illness is not possible. Physical fitness does not appear to protect against altitude illness. Risk factors relating to the individual include: previous history of altitude illness, normal residence below 900m, exertion on arrival to altitude and certain pre-existing cardiovascular conditions. the ascent of Mount Kilimanjaro in less than 7 days) are of concern. Ideally expeditions or treks should comply with Wilderness Medicine Society suggested maximum ascent rates (see preventing altitude illness). These are important to consider when planning a trip to altitude. Risk factors relating to the trip include: the rate of ascent, absolute change in altitude and sleeping altitude. The risk of developing altitude illness is determined by both factors relating to the trip and those of the individual. Both are extremely rare below 2,800m and seem to occur at an incidence of around 1-2 percent at altitudes between 4-5,000m. HACE and HAPE are much less common than AMS. Approximately 9-25 percent of unacclimatised individuals ascending to 2,000-3,000m develop AMS compared to 35-50 percent of those ascending to 3,500-4,500m. Studies of altitude illness report marked variation in prevalence, mainly as a result of the different ways these studies were performed. If ascent is too swift, then acclimatisation may not occur rapidly enough and altitude illness may ensue. This adjustment process is known as acclimatisation. If an individual ascends gradually to high altitude the human body is usually able to adjust to these reduced oxygen levels. This results in a reduced number of oxygen molecules taken in with each breath and ultimately to reduced oxygen delivery to the body’s tissues. With increasing altitude, the percentage of inspired oxygen remains constant at 21 percent however, the air pressure (barometric pressure) decreases. Altitude illnesses include acute mountain sickness (AMS), high altitude cerebral oedema (HACE) and high altitude pulmonary oedema (HAPE). Altitude illness usually occurs at altitudes over 2,500m, however it is recognised that susceptible individuals can experience illness below this altitude.Īltitude illness is the term used to describe a number of conditions that may occur shortly after individuals ascend rapidly to high altitude. High altitude is defined as an elevation above 1,500m and can be subdivided into the following categories: high altitude 1,500m–3,500m, very high altitude 3,500-5,500m and extreme altitude > 5,500m. In recent years travel to high altitude has become increasingly popular and accessible.
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