The increasing recognition of spinal anesthesia as the method of choice in many operations has seemed to warrant an investigation into its physiologic effect. In this paper we present the results of a series of studies along this line. Since clinical experience has demonstrated that under spinal, as under other, anesthesia the state of the circulation is of primary concern to the surgeon, the first observations have dealt with the cardiac output and blood pressure.
Dogs were used in the experiment. One to two hours before the experiment was begun, morphine (from 10 to 15 mg. per kilogram of weight injected subcutaneously) or barbital (0.3 Gm. per kilogram, intravenously) was given. Arterial pressure was measured by a mercury manometer, the cannula being inserted in the carotid artery. The cardiac output was determined according to the Fick principle, the technic being that employed by Harrison and Leonard.1 The rubber mask