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

Abstract

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.

Figure 1. Study cohort

Figure 2. Fluid overload and poor composite outcome by post-operative day

(A) Area under the curve for each of the first seven PODs were compared to determine the most predictive time point for poor outcome. (B) The optimal cutoffs of FO on the selected POD for predicting poor outcome from (A) were then determined based on sensitivity and specificity from the ROC curve.

Figure 3. Serum creatinine and poor composite outcome by post-operative day

(A) Area under the curve for each of the first seven PODs were compared to determine the most predictive time point for poor outcome. (B) The optimal cutoffs of S_Cr on the selected POD for predicting poor outcome from (A) were then determined based on sensitivity and specificity from the ROC curve.