Effect of hypotension due to spinal anesthesia on coronary blood flow and myocardial metabolism in man.

The induction of spinal anesthesia resulted in hypotension and decreased coronary blood flow and myocardial oxygen consumption. At the same time the myocardial extraction coefficient of oxygen was not increased, indicating myocardial oxygenation to be adequate for the lower work load. This does not imply that local ischemia might not occur in the presence of coronary artery sclerosis. The coronary arteriovenous differences of glucose, lactate and pyruvate were not changed during the period of hypotension. H IGH spinal anesthesia was used many years ago. It has been revived recently for its hypotensive effects.' However, some have expressed concern about the effect of the hypotension on the circulation to vital organs. Previous studies in this laboratory have dealt with the general hemodynamic effects2 and with the cerebral3 and hepatic4 metabolism and blood flow. The present study employs the method of coronary sinus cathe-terization, devised by Goodale and associates5 to determine the effects of arterial hypoten-sion, due to spinal anesthesia on the coronary blood flow and oxygen and carbohydrate metabolism of the human heart. METHODS Twelve patients were selected at random from the medical wards. Their ages and diagnoses are listed in table 1. The general technics, including the method of premedication and catheterization of the right side of the heart, were carried out as previously described.2 The coronary sinus was catheterized and the coronary blood flow, myocardial oxygen, glucose, lactate and pyruvate consumption were determined by methods described previously.' 7 The coronary vascular resistance was calculated by dividing the mean arterial blood pressure (millimeters of mercury) by the coronary blood flow (milliliters per 100 Gm. of myocardium per second). The myocardial extraction coefficient for oxygen was determined as the quotient of the coronary arteriovenous difference for oxygen divided by the arterial level (i.e., A X 100). This term expresses the per cent of oxygen that was extracted by the myocardium from a unit of blood and has been characterized in detail in a previous report.' These determinations were carried out in six of the above patients, followed by the induction of spinal anesthesia. In four of these patients the level of anesthesia was high, as indicated by a loss of tactile sensitivity to or above T-4, and by an increase in the rate of finger blood flow and pulse volume. In two patients the anesthesia level was low. In all patients, however, there was a significant fall in arterial blood pressure. …