Serum creatinine and estimated creatinine clearance do not predict perioperatively measured creatinine clearance in neonates undergoing congenital heart surgery.

Objective: To describe changes in creatinine clearance (CrCl) in a small group of neonates who underwent surgery for repair of transposition of the great arteries or palliation of hypoplastic left heart syndrome. To determine whether serum creatinine, urine output, or the Schwartz formula accurately predict measured CrCl in these patients.

Design: Prospective, randomized controlled trial with subsequent extraction of information regarding renal function from the database.

Setting: A 14-bed pediatric intensive care unit in a children's hospital.

Patients: A total of 14 neonates (hypoplastic left heart syndrome, 6; transposition of the great arteries, 8).

Measurements: Demographic information, urine output, serum creatinine, and 24-hr CrCl preoperatively and postoperatively on days 1 and 2.

Main Results: Weight, age, and body surface area were 3.3 +/- 0.6 kg, 8.2 +/- 6.9 days, and 0.2 +/- 0.02 m2, respectively. Urine output increased from 1.8 +/- 0.5 mL x kg(-1) x hr(-1) preoperatively to 2.4 +/- 0.8 mL x kg(-1) x hr(-1) on postoperative day 1 (p = .02) and 2.8 +/- 1.1 mL x kg(-1) x hr(-1) on postoperative day 2 (p = .007). Serum creatinine changed from 0.64 +/- 0.15 mg/dL preoperatively to 0.72 +/- 0.40 mg/dL on postoperative day 1 (p = .4, not significant) to 0.78 +/- 0.41 mg/dL on postoperative day 2 (p = .17, not significant). Measured CrCl changed from 22.8 +/- 9.4 mL x min(-1) x 1.73 m(-2) preoperatively to 25.1 +/- 31 mL x min(-1) x 1.73 m(-2) on postoperative day 1 (p = .77, not significant) and 24.9 +/- 19.9 on postoperative day 2 (p = .69, not significant). No difference in measured CrCl was noted based on hypoplastic left heart syndrome vs. transposition of the great arteries. Median overestimation of CrCl by the Schwartz equation was 58% preoperatively, 78% on postoperative day 1, and 53% on postoperative day 2. Clinically significant correlations were not noted between measured CrCl and serum creatinine or urine production preoperatively, on postoperative day 1, or on postoperative day 2. Bland-Altman plot demonstrated that the Schwartz equation was a biased and imprecise estimate of CrCl at all three time points.

Conclusions: Perioperative CrCl is unpredictable in neonates with transposition of the great arteries and hypoplastic left heart syndrome. Serum creatinine, urine output, and the Schwartz formula do not accurately predict CrCl. Reliance on estimates of CrCl could result in toxic concentrations of drugs eliminated by the kidneys.