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Background
Anemia and cardiovascular disease Approximately seven million people in the United Kingdom, and 30% of patients admitted to the ICU have co‐existing cardiovascular disease (CVD) [1–3] and this proportion may rise as the average age of both the general population and patients admitted to the ICU increase. Patients with CVD will have impaired compensatory mechanisms to enable maximum oxygen delivery to the tissues in the event of anemia (Fig. 1). Anemia causes an increase in cardiac output, which stresses the heart to increase heart rate and stroke volume. In acute illness, global oxygen demand is increased, further stressing the heart. This is exacerbated by the frequent presence of tachycardia and hypotension, which reduce blood flow to the coronary arteries, and by catecholamines that increase myocardial work. Significant left ventricular coronary flow occurs only during diastole and the subendocardial region is particularly at risk of ischemia because of the high pressure in the left ventricle [4]. At rest, the myocardium extracts approximately 75% of the oxygen delivered by coronary blood flow [5], and there is therefore little reserve when myocardial oxygen consumption is increased in critical illness. Atheroma‐related flow limitation further compromises myocardial oxygen delivery.