ASSOCIATION OF MEAN ARTERIAL PRESSURE, MINIMUM HEMATOCRIT AND MAXIMUM GLUCOSE WITH MORTALITY IN CARDIAC SURGERY

Abstract

Introduction: With an aging population in the United States, the number and complexity of coronary artery bypass grafting procedures (CABG) is increasing. Risk stratification schemes have been developed to predict outcome which are predominately based upon unalterable preoperative patient characteristics. [1] The impact of alterable intraoperative physiologic variables upon outcome is less well defined. The use of an intraoperative data acquisition system permits automatic recording of many physiologic variable measured during cardiac surgery. The purpose of this study was to determine if minimum intraoperative hematocrit (MINHCT), maximum glucose concentration (MAXGLC) or mean arterial pressure (MAP) influence in-hospital mortality after CABG. Methods: Outcome data for 2830 patients undergoing CABG surgery at the Duke Heart Center were merged with data from the intraoperative database for analysis. Preoperative risk factors described by Hannan, et al. [1] were used to calculate a predictive probability of death. Because preoperative hypertension (HTN) may influence the intraoperative MAP but is not included as part of the Hannan score, HTN was included as an independent predictor variable for analysis. A query of the intraoperative database yielded values for HCT, GLC and MAP for each patient. MAPALT50, defined as the integrated area below a MAP of 50mmHg at each minute during cardiopulmonary bypass (CPB), provided an index of low MAP. MAPAGE50, defined as the area greater than or equal to a MAP of 50mmHg at each minute during CPB, provided an index of high MAP. Univariate logistic regression was performed on each of the predictor variables to determine association with mortality. Variables found significant (p<0.05) by univariate analysis were tested in a multiple variable model controlling for Hannan score and CPB using backwards stepwise logistic regression. Results: Among the 2830 patients studied, mortality rate was 1.8%. Hannan score was significantly associated with mortality (p=0.0001, c-index=0.696). No significant association was present between mortality and HCT, GLC or MAPALT50 by univariate analysis. HCT and Hannan score covaried (p=0.0001, r=-0.15). MAPAGE50 was significantly associated with mortality by univariate analysis and after controlling for Hannan score but became completely insignificant (p=0.9679) when controlling for CPB time. HTN was an independent predictor of mortality after controlling for Hannan score and CPB duration. Discussion: As expected, Hannan score accurately predicted mortality. HTN proved to be an independent predictor of in-hospital mortality in our patient population. In spite of earlier research which suggests that high MAP during CPB improves outcome, [2] or that lower hematocrit increases mortality, [3] this study finds no evidence to support the hypothesis that MAP less than 50mmHg or lower hematocrit on CPB increases in-hospital mortality.