Factors that mediate change in creatinine and acute kidney injury after the Norwood operation: Insights from high-fidelity haemodynamic monitoring data

Background: Acute kidney injury is a common postoperative complication of paediatric cardiac surgery associated with increased morbidity and mortality. The purpose of this study is to characterise associations between haemodynamic parameters, clinical parameters, and medical interventions, on acute kidney injury. Methods: Nine patients with univentricular physiology undergoing the Norwood procedure from a single-centre tertiary care paediatric cardiac ICU were included (September 2022 to March 2023). Patients were monitored with the T3 software. Data were analysed using a Fisher exact test, Mann-Whitney-U test, LASSO-based machine learning techniques, and receiver operator curve analyses. Results: Over 27,000 datapoints were included. Acute kidney injury occurred in 2 patients (22%) during this period. Net fluid balance and renal oxygen extraction were independently associated with acute kidney injury, while commonly used metrics of pressure (systolic, diastolic, or mean arterial blood pressure) were not. The resulting acute kidney injury risk score was (4.1 × fluid balance) + (1.9 × renal oxygen extraction). The risk score was significantly higher in acute kidney injury with a score of 32.9 compared to 7.9 (p < 0.01). Optimal cut-offs for fluid balance (7 mL/hr) and renal oxygen extraction (29%) were identified. Higher serum creatinine:baseline creatinine ratio was associated with a higher mean airway pressure, higher renal oxygen extraction, higher mean arterial blood pressure, higher vasoactive inotropic score, and fluid balance. Conclusion: Among patients with univentricular physiology undergoing the Norwood procedure, renal oxygen extraction and a higher net fluid balance are independently associated with increased risk of acute kidney injury. Renal perfusion pressure is not significantly associated with acute kidney injury.