Relationship between intra-operative urine output and postoperative acute kidney injury in paediatric cardiac surgery: A retrospective observational study.

Background: Intra-operative urine output (UO) has been shown to predict postoperative acute kidney injury (AKI) in adults; however, its significance in children undergoing cardiac surgery remains unknown.

Objective: To explore the association between intra-operative UO and postoperative AKI in children with congenital heart disease.

Design: A retrospective observational study.

Setting: A tertiary hospital.

Patients: Children aged >28 days and <6 years who underwent cardiac surgery at Fuwai Hospital from 1 April 2022 to 30 August 2022.

Main outcome measures: AKI was identified by the highest serum creatinine value within postoperative 7 days using Kidney Disease Improving Global Outcomes (KDIGO) criteria.

Results: In total, 1184 children were included. The incidence of AKI was 23.1% (273/1184), of which 17.7% (209/1184) were stage 1, 4.2% (50/1184) were stage 2, and others were stage 3 (1.2%, 14/1184). Intra-operative UO was calculated by dividing the total intra-operative urine volume by the duration of surgery and the actual body weight measured before surgery. There was no significant difference in median [IQR] intra-operative UO between the AKI and non-AKI groups (2.6 [1.4 to 5.4] and 2.7 [1.4 to 4.9], respectively, P  = 0.791), and multivariate logistic regression analyses showed that intra-operative UO was not associated with postoperative AKI [adjusted odds ratio (OR) 0.971; 95% confidence interval (CI), 0.930 to 1.014; P  = 0.182]. Regarding the clinical importance of severe forms of AKI, we further explored the association between intra-operative UO and postoperative moderate-to-severe AKI (adjusted OR 0.914; 95% CI, 0.838 to 0.998; P  = 0.046).

Conclusions: Intra-operative UO was not associated with postoperative AKI during paediatric cardiac surgery. However, we found a significant association between UO and postoperative moderate-to-severe AKI. This suggests that reductions in intra-operative urine output below a specific threshold may be associated with postoperative renal dysfunction.

Trial registration: Clinicaltrials.gov identifier: NCT05489263.