What is critical ischaemia and how common is it?
As arterial disease progresses to involves more of the arterial tree of the leg, the blood flow to the lower leg and foot becomes less and less. A point will be reached at which the blood flow is not enough to keep the tissues nourished adequately. The tissues then cause pain. The toes are commonly involved as they are furthest away from the source of blood supply (the heart).
Patients with intermittent claudication notice that their walking distance becomes shorter and shorter.
The next stage is pain in the toes in bed ('night pain') which is relieved by getting out of bed and walking around or by dangling the leg out of bed. At night the blood is further diverted away from the foot because the rest of the body is warm and the foot is elevated. By dangling the foot out of bed, gravity helps blood flow and the foot is cooled down.
The next stage is pain in the toes all the time ('rest pain'). The pain is usually so severe that very strong pain killers are needed (usually morphine).
Further progression leads to ulcers and gangrene. The picture below shows a typical foot ulcer due to critical ischaemia:
Diabetic patients may not present with this stepwise progression of symptoms in that they may present with foot ulcers without preceding intermittent claudication.
The risk factors for arterial disease have been outlined in the sections on atherosclerosis and intermittent claudication (what is intermittent claudication and how common is it?).
The Vascular Surgical Society of Great Britain and Ireland estimated in 1995 that the incidence of critical ischaemia is 400 new cases per million of the population per year.