Acute Kidney Injury in children undergoing open heart surgery: a single center prospective observational study

Background: Acute kidney injury (AKI) is a common complication after cardiovascular surgery (CS-AKI), and it is strongly associated with increased patient morbidity and mortality. Pediatric patients may present different pathophysiology and risk factors than adults. Defining and addressing perioperative risk factors is crucial to reduce the incidence of CS-AKI and related complications, and consequently improve quality of life and patient’s survival. Purpose: The primary aim of this study was to assess the incidence of CS-AKI in the immediate post-operative period in children undergone to open heart surgery, and to study the role of possible risk factors (e.g. age, body surface area, type of surgery, hemodynamic parameters, fluid balance, nephrotoxic medication). Secondary aim was to study the impact of CS-AKI on outcomes as length-of-stay (ICU/Hospital-LOS), ventilator free days (VFD) and mortality. Methods: Secondary analysis of a prospective observational single-center study over a period of 30 months (May 2021 - November 2023) involving pediatric patients who underwent open-heart surgery at the Pediatric Cardiac Surgery Unit of the University Hospital of Padua, Italy. Collected data included demographic information, past medical history, hospitalization details, intraoperative and postoperative data (hemodynamic parameters, fluid balance, urinary output, renal function tests, furosemide dose, nephrotoxic medications) within the first 72 hours post-op. Primary outcome was post-operative CS-AKI incidence. Secondary outcomes were ICU-LOS and Hospital-LOS, duration of mechanical ventilation (VFD) and mortality. VFD were calculated at 28 days from surgery. Categorical variables were represented using percentages, while continuous variables were described using either mean with standard deviation or median with interquartile range. Univariate logistic regression was used to assess the impact of significant risk factors on CS-AKI. Results were considered statistically significant for a p-value < 0.05. Results: CS-AKI occurred in 41.6% of patients, 22.7% classified as Stage 1, 11.0% as Stage 2 and 7.8% as Stage 3 according to the KDIGO classification. Among the risk factors analyzed, noteworthy results were observed for both intraoperative and hemodynamic variables. Intraoperatively, significant factors included surgery time, CPB time, and ACC time, with CPB time > 120 minutes showing the strongest association OR 2.48 [95% CI: 1.28; 4.79]. Postoperatively, hemodynamic factors such as SBP, MAP, CVP, and OPP were also significant. Specifically, an increased risk associated with CS-AKI was observed for SBP < 5th percentile (OR 2.75 [95% CI: 1.36; 5.53]), MAP < 50th percentile (OR 3.05 [95% CI: 1.54; 6.06]), CVP > 7 mmHg (OR 3.31 [95% CI: 1.33; 8.20]), and OPP both < 5th and 50th percentile (OR 3.42 [95% CI: 1.62; 7.21] and OR 4.56 [95% CI: 1.48; 14.04] respectively). CS-AKI was associated with extended stays in both the intensive care unit and the hospital. Conclusion: The role of prolonged cardiopulmonary bypass (CPB) time in the development of CS-AKI has been confirmed. Hypotension and hypoperfusion are identified as critical contributors to CS-AKI, highlighting the necessity for meticulous, age-specific monitoring and targeting of mean arterial pressure (MAP) and organ perfusion pressure (OPP) to effectively manage and mitigate the risk of CS-AKI.