Introduction: Postoperative acute kidney injury (AKI) confers poor outcomes after cardiac surgery. Conventional ultrafiltration (CUF) is performed on cardiopulmonary bypass (CPB) to raise hematocrit, avoid intraoperative blood transfusion, and provide renal protection. These protective effects remain unclear with high CUF volumes, which may cause hypovolemia and renal hypoperfusion.
Hypothesis: Higher CUF volumes will be associated with increased AKI and poor outcomes.
Methods: Retrospective analysis of 1,791 consecutive patients undergoing cardiac surgery (CABG, CABG/Valve, Valve only) was performed between June 2013 and December 2015. Institutional CPB protocol with CUF was used during all cases. Uni- and multivariable logistic regression analyses determined predictors for AKI. CUF volume analyses were performed, defined by two extreme quartiles or by Youden index derived from ROC analysis, and compared for their effect on AKI rate. Mortality data was acquired from the Social Security Administration’s Death Master File through 1 year after index surgery.
Results: CUF volume independently predicted AKI (p<0.0001)(Fig 1A). Critical CUF volume associated with AKI, defined by 3rd quartile, was > 2,900 ml (OR=1.72, 95% CI 1.25, 2.38) and defined by Youden index, was > 2,239 ml, (OR=1.52, 95% CI 1.22, 1.89). While associated with increased intraoperative blood transfusion volume (p=0.002), CUF volume in AKI patients (N=903) predicted increased ICU (p<0.001) and hospital LOS (p<0.001). AKI incidence was associated with increased 30-day mortality (HR=2.78, 95% CI 1.06 - 7.27; p=0.037) but no significant difference in survival was seen when AKI group was stratified by CUF volume (Fig 1B), based on a small number of events (N=25). AKI did not yield significant HR for death between 30 days - 1 year.
Conclusions: CUF volume removal during CPB predicted blood transfusion requirements, postoperative AKI, and ICU/Hospital LOS, while AKI predicted 30-day mortality.