6 Clinical conditions found at high altitudeДЄltitude illness is a collection of different conditions that occur at high altitude: high-altitude headaches (HAH), AMS, HACE, HAPE and other less common conditions such as retinal haemorrhage, high-altitude syncope, cerebral venous thrombosis and cortical blindness. The likely causes for this are hypoxia-induced blood flow and pressure increases, and capillary leakage mediated by chemicals such as bradykinin, nitric oxide, arachidonic acid and vascular endothelial growth factor. Although the exact pathogenesis remains unclear, increased capillary leakage causing cerebral oedema in acute mountain sickness (AMS) and high-altitude cerebral oedema (HACE), 8 and similar pulmonary changes in HAPE, 9 have been consistently described.

Individual and genetic variances exist in this acclimatisation response, 7 and inadequate responses lead to the pathological changes of altitude illness. increased erythropoietin secretion, increased haemoglobin production within three days and diuresis, causing increased haematocrit.cerebral vasodilation caused by hypoxia, which can lead to cerebral oedema.vasoconstriction of the pulmonary vasculature, which in the extreme situation is responsible for high-altitude pulmonary oedema (HAPE).increased sympathetic tone causing increased heart rate, blood pressure and cardiac output.The body responds (acclimatisation) to low oxygen within minutes of the traveller arriving at a place of high altitude and this process continues for weeks. Decreasing oxygen availability due to altitude 5 5 The decreased oxygen in inspired air in places at high altitude, hypobaric hypoxia, is the central causative factor for the development of altitude illness. As altitude increases, barometric pressure decreases and, consequently, the amount of oxygen in each breath decreases (Figure 1). High altitude is used in this article to mean altitudes higher than 2500 m at which a traveller sleeps significant altitude illness is unlikely below this height. The management of altitude illness is not covered, as treatment is usually provided by expedition doctors or clinics at high altitude. 4 The aims of this paper are to understand the conditions that constitute altitude illness, provide guidelines to evaluate the risks of altitude illness, and offer evidence-based advice to prevent travellers from developing altitude illness. General practitioners (GPs) are still the most frequented source of information for travellers, and are well positioned to help empower travellers to care for themselves overseas. Although not always recognised by travellers, cities such as Cusco (3400 m), La Paz (3700В m) and Lhasa (3600 m) are at altitudes where altitude illness is likely to develop. 3 Trekkers are generally well prepared and usually have good support from the companies they trek with however, recent deaths on Mount Everest remind us of the dangers of altitude illness.ДЄdventurous travellers are not the only ones at risk high-altitude cities are becoming popular tourist destinations for travellers of all ages and with varying severity of chronic illness. 2 Each year, more than 20,000 people attempt to climb Mount Kilimanjaro (5895 m) in Tanzania. 1 Since the first scaling of Mount Everest in 1953, the number of trekkers annually in the surrounding Sagarmatha National Park has increased from about 1400 in 1972вЂ“73 to more than 20,000 in 2004. In 2013, more than 100 million people visited altitudes that could lead to altitude illness.

Increasing numbers of people are travelling to places at high altitude.

Altitude sickness prevention