Most acute limb ischaemia now occurs on a background of peripheral arterial disease. Even patients presenting primarily with embolic disease may well also have underlying peripheral arterial disease, which is present in up to 30% of people over the age of 70 years. This can be more difficult to diagnose since the classical signs of acute limb ischaemia may be attenuated by the presence of collaterals. In this context, and with an ageing population, the presentation of acute on chronic limb ischaemia is more common. There is also some evidence that the proportion of acute limb ischaemia caused by embolic disease is falling, due to the decreased incidence of rheumatic heart disease and the improvement in the management of atrial fibrillation. Risk factors include hypertension, smoking, and diabetes mellitus interval. A prospective population based study in Oxfordshire running from 2002-2012 determined the incidence and outcome of all acute peripheral arterial events in a population of 92728, finding 510 acute events in 386 patients requiring 803 interventions. Cohort studies from Sweden suggest the incidence is reducing. The incidence of acute limb ischaemia is estimated at approximately population per year, which means a hospital serving a population of 500,000 would expect to see 83 cases per year. The spectrum of acute limb ischaemia therefore ranges from the patient with a few hours history of a painful cold white leg, to the patient with a few days history of short distance claudication or the patient with a sudden increase in ischaemic symptoms on a background of peripheral arterial disease. By convention this usually refers to patients presenting with symptoms for less than 2 weeks. Acute limb ischaemia is defined as any sudden decrease in limb perfusion causing a potential threat to limb viability.
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