Fluid Overload Is Associated With Late Poor Outcomes in Neonates Following Cardiac Surgery

Objectives: Acute kidney injury is a severe complication of cardiac surgery associated with increased morbidity and mortality; yet, acute kidney injury classification for neonates remains challenging. We characterized patterns of postoperative fluid overload as a surrogate marker for acute kidney injury and as a risk factor of poor postoperative outcomes in neonates undergoing cardiac surgery. Design: Retrospective cohort study. Setting: Single, congenital heart center destination program. Patients: Four hundred thirty-five neonates undergoing cardiac surgery with cardiopulmonary bypass from January 2006 through December 2010. Interventions: None. Measurements and Main Results: Demographics, diagnosis, and perioperative clinical variables were collected, including daily weights and serum creatinine levels. A composite poor clinical outcome (death, need for renal replacement therapy or extracorporeal life support within 30 postoperative days) was considered the primary outcome measure. Twenty-one neonates (5%) had a composite poor outcome with 7 (2%) requiring renal replacement therapy, 8 (2%) requiring extracorporeal life support, and 14 (3%) dying between 3 and 30 days post surgery. Neonates with a composite poor outcome had significantly higher maximum fluid overload (> 20%) and were slower to diurese. A receiver-operating characteristic curve determined that fluid overload greater than or equal to 16% and serum creatinine greater than or equal to 0.9 on postoperative day 3 were the optimal cutoffs for significant discrimination on the primary outcome (area under the curve = 0.71 and 0.76, respectively). In multivariable analysis, fluid overload greater than or equal to 16% (adjusted odds ratio = 3.7) and serum creatinine adjusted odds ratio 0.9 (adjusted odds ratio = 6.6) on postoperative day 3 remained an independent risk factor for poor outcome. Fluid overload greater than or equal 16% was also significantly associated with cardiac arrest requiring cardiopulmonary resuscitation, prolonged ICU stay, and chest reexploration. Conclusions: This study highlights the importance of monitoring fluid balance in the neonatal cardiac surgical population and suggests that daily fluid overload, a readily available, noninvasive marker of renal function, may be a sensitive and specific predictor of adverse outcomes.