Pattern of hemodynamic alterations during coronary artery operations.

Twenty-four patients were studied to determine the relative importance of cardiac and peripheral factors in the hemodynamic changes associated with coronary artery operations. None had preoperative evidence of ventricular impairment. Anesthetic management was standardized for all. Sequential hemodynamic measurements revealed the following: (1) Five minutes following induction of anesthesia, all hemodynamic indices were stable except for an increase in heart rate (p less than 0.001). Sternotomy and pericardiectomy were followed by a drop in cardiac index (p less than 0.01) and systolic blood pressure (p less than 0.01). (2) Late during bypass, there was a significant, parallel reduction in both hematocrit and systemic vascular resistance (SVR) (p less than 0.001 and 0.01, respectively). (3) Five minutes after termination of bypass, cardiac output was markedly elevated (p less than 0.001) in association with a decrease in SVR (p less than 0.001), marked hemodilution (p less than 0.001), and tachycardia (p less than 0.001). (4) Following sternal closure, and despite the fact that the hematocrit was still reduced (p less than 0.001), there developed a trend of increased mean arterial pressure (MAP) and SVR with a reduction in cardiac index. These changes were further accentuated 1 hour postoperatively. The SVR was 33% higher than in the previous stage (p less than 0.01), whereas the high cardiac index recorded with initiation of bypass declined significantly to preoperative values. Throughout the studies, there was a strong correlation between alterations in hematocrit and changes in cardiac index and SVR. Blood pressure variations showed no correlation with changes in cardiac output but were significantly related to alterations of peripheral resistance. Sequential determinations of plasma renin activity and catecholamine levels showed no significant alterations in either. The alterations reported describe not only group averages but also the behavior of every patient investigated. The results suggest that in patients with normal or only mild left ventricular impairment, the major factor influencing arterial pressure variations during coronary artery operations and in the postoperative period was the change in peripheral resistance rather than alterations in cardiac output. In the treatment of hypotension under these conditions, one should take into account variations in peripheral vascular resistance and not depend solely on assumed changes in myocardial performance.