Acute kidney injury (AKI) is a common complication among patients requiring cardiopulmonary bypass (CPB) during paediatric cardiac surgery. Plasma-free haemoglobin (PFH) produced by haemolysis during CPB contributes to AKI. This study aimed to determine the association between PFH and postoperative AKI during paediatric cardiac surgery requiring CPB.

This prospective, single-centre, observational study included children aged <5 yr who underwent cardiac surgery requiring CPB. PFH was measured pre-CPB, every 30 min during CPB, after modified ultrafiltration, on ICU admission, and once a day at 1–3 days after surgery. The study outcome included the relationship between peak PFH concentrations and the development of postoperative AKI up to 3 days after surgery. Additionally, multivariable analysis was performed to determine the risk factors for AKI.

Of 179 patients, 74 (41%) developed postoperative AKI. Patients who developed AKI had significantly higher peak PFH concentrations (80 mg dl⁻¹ [inter-quartile range, 50–132.5] vs 60 mg dl⁻¹ [40–100]; P=0.006). Multivariable analysis did not identify peak PFH concentrations as an independent risk factor for postoperative AKI (odds ratio [OR] 1.00; 95% confidence interval [CI]: 0.99–1.00; P=0.268). Factors associated with postoperative AKI were age in months (OR 0.96; 95% CI: 0.94–0.99; P=0.007) and CPB duration (OR 1.02; 95% CI: 1.01–1.02; P<0.001).

There was an association between postoperative AKI and CPB time rather than PFH. Perioperative peak PFH concentrations were significantly higher in patients with postoperative AKI after paediatric cardiac surgery requiring CPB.