Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive).[3][4] Ischemia is generally caused by problems with blood vessels, with resultant damage to or dysfunction of tissue i.e. hypoxia and microvascular dysfunction.[5][6] It also implies local hypoxia in a part of a body resulting from constriction (such as vasoconstriction, thrombosis, or embolism).
Ischemia causes not only insufficiency of oxygen, but also reduced availability of nutrients and inadequate removal of metabolic wastes. Ischemia can be partial (poor perfusion) or total blockage. The inadequate delivery of oxygenated blood to the organs must be resolved either by treating the cause of the inadequate delivery or reducing the oxygen demand of the system that needs it. For example, patients with myocardial ischemia have a decreased blood flow to the heart and are prescribed with medications that reduce chronotrophy and ionotrophy to meet the new level of blood delivery supplied by the stenosed vasculature so that it is adequate.
The signs and symptoms of ischemia vary, as they can occur anywhere in the body and depend on the degree to which blood flow is interrupted.[4] For example, clinical manifestations of acute limb ischemia (which can be summarized as the "six P's") include pain, pallor, pulseless, paresthesia, paralysis, and poikilothermia.[7]
Without immediate intervention, ischemia may progress quickly to tissue necrosis and gangrene within a few hours. Paralysis is a very late sign of acute arterial ischemia and signals the death of nerves supplying the extremity. Foot drop may occur as a result of nerve damage. Because nerves are extremely sensitive to hypoxia, limb paralysis or ischemic neuropathy may persist after revascularization and may be permanent.[8]
Cardiac ischemia may be asymptomatic or may cause chest pain, known as angina pectoris. It occurs when the heart muscle, or myocardium, receives insufficient blood flow.[9] This most frequently results from atherosclerosis, which is the long-term accumulation of cholesterol-rich plaques in the coronary arteries. In most Western countries, Ischemic heart disease is the most common cause of death in both men and women, and a major cause of hospital admissions.[10][11]
Both large and small intestines can be affected by ischemia. The blockage of blood flow to the large intestine (colon) is called ischemic colitis.[12] Ischemia of the small bowel is called mesenteric ischemia.[13]