Abstract
The effects of isoflurane on the determinants of blood flow during Coronary Artery Bypass Graft (CABG) surgery are not completely understood. This study characterized the influence of isoflurane on the diastolic Pressure-Flow (P-F) relationship and Critical Occlusion Pressure (COP) during CABG surgery. Twenty patients undergoing CABG surgery were studied. Patients were assigned to an isoflurane or control group. Hemodynamic and flow measurements during CABG surgery were performed twice (15 minutes after the discontinuation of extracorporeal circulation (T15) and again 15 minutes later (T30)). The zero flow pressure intercept (a measure of COP) was extrapolated from a linear regression analysis of the instantaneous diastolic P-F relationship. In the isoflurane group, the application of isoflurane significantly increased the slope of the diastolic P-F relationship by 215% indicating a mean reduction of Coronary Vascular Resistance (CVR) by 46%. Simultaneously, the Mean Diastolic Aortic Pressure (MDAP) decreased by 19% mainly due to a decrease in the systemic vascular resistance index by 21%. The COP, cardiac index, heart rate, Left Ventricular End-Diastolic Pressure (LVEDP) and Coronary Sinus Pressure (CSP) did not change significantly. In the control group, the parameters remained unchanged. In both groups, COP significantly exceeded the CSP and LVEDP at both time points. We conclude that short-term application of isoflurane at a sedative concentration markedly increases the slope of the instantaneous diastolic P-F relationship during CABG surgery implying a distinct decrease with CVR in patients undergoing CABG surgery.
Highlights
In a theoretical approach to the Pressure-Flow (P-F) relationship in arterioles, these calculations are a simplification of the actual variable tissue characteristics in the vascular bed of an organ (Hoffman & Spaan, 1990)
Mean Arterial Pressure (MAP), Cardiac Index (CI), HR and Systemic Vascular Resistance Index (SVRI) did not change during the entire study period
This study investigated the influence of short-term isoflurane administration on the instantaneous diastolic P-F relationship for the calculation of Coronary Vascular Resistance (CVR) and Critical Occlusion Pressure (COP) in patients undergoing elective Coronary Artery Bypass Graft (CABG) surgery
Summary
In a theoretical approach to the Pressure-Flow (P-F) relationship in arterioles, these calculations are a simplification of the actual variable tissue characteristics in the vascular bed of an organ (Hoffman & Spaan, 1990). Results from other investigators demonstrated that the risk of perioperative myocardial ischemia was not increased during isoflurane anesthesia compared with other volatile anesthetics or total intravenous anesthetic regimens (Leung et al, 1991; Pulley et al, 1991). Regarding volatile anesthetics, maximal increases in global coronary blood flow were obtained during isoflurane anesthesia (Crystal et al, 2000). According to the fact that volatile anesthetics (Landoni et al, 2013) and in particular isoflurane are beneficial for myocardial ischemia and has been shown to improve survival in cardiac surgery (Bignami et al, 2013; Chiari et al, 2005; Ge et al, 2010; Lang et al, 2013), this study aimed at investigating the impact of isoflurane on the diastolic P-F relationship and COP during CABG surgery
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