Defining oliguria during cardiopulmonary bypass and its relationship with cardiac surgery-associated acute kidney injury.

<bold>Background: </bold>While urine flow rate ≤0.5 ml kg-1 h-1 is believed to define oliguria during cardiopulmonary bypass (CPB), it is unclear whether this definition identifies risk for acute kidney injury (AKI) . The purpose of this retrospective study was to evaluate if urine flow rate during CPB is associated with AKI.<bold>Methods: </bold>Urine flow rate was calculated in 503 patients during CPB. AKI in the first 48 h after surgery was defined by the Kidney Disease: Improving Global Outcomes classification. Adjusted risk factors associated with AKI and urine flow rate were assessed.<bold>Results: </bold>Patients with AKI [n=149 (29.5%)] had lower urine flow rate than those without AKI (P<0.001). The relationship between urine flow and AKI risk was non-linear, with an inflection point at 1.5 ml kg-1 h-1 Among patients with urine flow <1.5 ml kg-1 h-1, every 0.5 ml kg-1 h-1 higher urine flow reduced the adjusted risk of AKI by 26% (95% CI 13-37; P<0.001). Urine flow rate during CPB was independently associated with the risk for AKI. Age up to 80 years and preoperative diuretic use were inversely associated with urine flow rate; mean arterial pressure on CPB (when <87 mmHg) and CPB flow were positively associated with urine flow rate.<bold>Conclusions: </bold>Urine flow rate during CPB <1.5 ml kg-1 h-1 identifies patients at risk for cardiac surgery-associated AKI. Careful monitoring of urine flow rate and optimizing mean arterial pressure and CPB flow might be a means to ensure renal perfusion during CPB.<bold>Clinical Trial Registration: </bold>ClinicalTrials.gov NCT00769691 and NCT00981474. [ABSTRACT FROM AUTHOR]