Impact of minimum hematocrit during cardiopulmonary bypass on mortality in patients undergoing coronary artery surgery

Background: The hematocrit on cardiopulmonary bypass (CPB) frequently falls to a low level during many cardiac surgical procedures. This study was designed to explore the impact on mortality of minimum hematocrit level achieved during the CPB after coronary artery surgery. Methods and Results: Two thousand seven hundred thirty-eight sequential isolated coronary artery surgery patients during a 42-month period at a tertiary academic centre were included in this study. Thirty-one standardized preoperative risk factors used in a multiple logistic regression revealed eight statistically significant independent predictors for postoperative mortality. Minimum hematocrit level during CPB was then added to the regression model and was found to be an independent risk factor for mortality. The entire patient population was divided into dichotomous groups using different minimum hematocrit levels on CPB for the determination of cutoff points by multiple logistic regression. After adjusting for other risk factors, the minimum hematocrit level of 14% was found to be a statistically significant cutoff point. Patients with minimum hematocrit levels ≤14% were found to have an increased probability of risk-adjusted mortality (odds ratio, 2,70; P=.002). A subgroup analysis revealed that high-risk patients with minimum hematocrit levels ≤17% were found to have a significantly increased probability of postoperative mortality (odds ratio, 2.20; P=.017). Conclusions: Minimum hematocrit level during CPB is an independent risk factor for mortality after coronary artery surgery. There is a significantly increased risk of mortality for hematocrit levels ≤14%. For high-risk patients, there is a significantly increased risk of mortality for hematocrit levels ≤17%.