Local and regional anesthetic techniques for the patient with ischemic heart disease
Care of the patient with ischemic heart disease still revolves around balancing oxygen supply and demand. Oxygen supply is dependent on the coronary blood flow and the oxygen content of the coronary arterial blood, and the distribution of that coronary blood flow. Coronary blood flow in turn is governed by the diastolic arterial blood pressure and coronary vascular resistance. The oxygen demand of the heart is related to the rate at which the heart beats, the tension that heart muscle develops in its wall, and the contractile performance of the heart. In the clinical evaluation of myocardial oxygen supply and demand, we really have little more than an estimation of the oxygen-carrying capacity of blood and the diastolic arterial blood pressure. Fortunately, it has been demonstrated that myocardial oxygen demand is quite accurately correlated with the product of heart rate and systolic blood pressure. Perhaps it is more correct to consider these two determinants separately.
In patients with ischemic heart disease, the oxygen supply is much more dependent on the perfusion pressure of the coronary arteries inasmuch as there are fixed obstructions to flow, and coronary vascular resistance cannot be varied appreciably in these areas. In addition, there is evidence that flow through stenotic areas is better preserved with lower viscosity blood. To keep oxygen supply at reasonable levels in the patient with ischemic heart disease, diastolic arterial pressure should be kept within 10 torr of angina-free level and the hemoglobin level should be ± 12 g/dl.
Since oxygen demand . . .