The intraoperative period is regularly associated with factors and events that can adversely affect the myocardial oxygen demand–supply relation-ship. Activation of the sympathetic system plays a major role. Hypertension and enhanced contractil-ity increase myocardial oxygen demand, whereas tachycardia increases demand and reduces supply. Although myocardial ischemia is commonly associ-ated with tachycardia, it can occur in the absence of any apparent hemodynamic derangement.
The overwhelming priority in managing patients with ischemic heart disease is maintaining a favorable myocardial supply–demand rela-tionship. Autonomic-mediated increases in heart rate and blood pressure should be controlled by deep anesthesia or adrenergic blockade. Excessive reductions in coronary perfusion pressure or arte-rial oxygen content are to be avoided. Although exact limits are not defined or predictable, diastolic arterial pressure should generally be maintained at 50 mm Hg or above. Higher diastolic pressures may be preferable in patients with high-grade coro-nary occlusions. Excessive increases—such as those caused by fluid overload—in left ventricular end-diastolic pressure should be avoided because they increase ventricular wall tension (afterload) and can reduce subendocardial perfusion . Transfusion carries its own risks and consequently there is no set transfusion trigger in patients with CAD; however, anemia can lead to tachycardia, worsening the balance between myocardial oxygen supply and demand.