Assessment of acute kidney injury using estimated glomerular filtration rate and blood urea nitrogen in pediatric patients undergoing cardiac surgery: Experience from single institution in Afghanistan

Background: Acute kidney injury (AKI) is a significant complication in pediatric cardiac surgery, especially among congenital heart disease (CHD) patients. Its incidence is rising globally due to increased cardiac procedures. Children with cardiac surgery-associated AKI (CSA-AKI) face worse postoperative outcomes, including prolonged mechanical ventilation, higher morbidity, mortality, and healthcare costs. Mechanisms of AKI are multifactorial, involving prolonged cardiopulmonary bypass (CPB), hypoperfusion, and inflammatory responses such as systemic inflammatory response syndrome (SIRS) and compensatory anti-inflammatory response syndrome (CARS). Hemolysis during CPB releases free hemoglobin, causing endothelial dysfunction, while reactive oxygen species (ROS) exacerbate kidney injury. Objectives: This study aimed to assess the incidence of AKI in pediatric patients undergoing cardiac surgery, utilizing estimated glomerular filtration rate (eGFR) and blood urea nitrogen (BUN) levels while considering factors like age, gender, surgery type, complexity, and CPB duration to enhance understanding of postoperative renal outcomes. Methods: A retrospective cross-sectional study was conducted at the French Medical Institute for Mother and Children (FMIC) in Kabul, analyzing data from 383 pediatric patients (ages 0-18) who underwent open-heart surgery between January 1, 2022, and September 30, 2024. Patients with pre-existing renal dysfunction or incomplete data were excluded. AKI was defined and staged using the Kidney Disease: Improving Global Outcomes (KDIGO) criteria. Logistic regression analyses identified AKI predictors, reporting odds ratios (OR), and p-values. Results: Among 383 pediatric patients (median age 5 years; 57 % male), renal function declined significantly post-surgery, with median GFR decreasing from 123.9 to 89.9 mL/min/1.73 m(2) (30% reduction; p < 0.001). AKI occurred in 33 % (n = 128), classified as Stage 1 (13 %), Stage 2 (16 %), and Stage 3 (4 %) per KDIGO criteria. Significant predictors of AKI included higher preoperative creatinine (aOR = 32.97, p = 0.02), elevated postoperative BUN (aOR = 1.11, p = 0.010), longer bypass duration (aOR = 1.02 per minute, p = 0.014), higher baseline GFR (aOR = 1.012, p = 0.009), and younger age (aOR = 0.26, p = 0.03). Higher postoperative GFR was protective (aOR = 0.97, p < 0.001). The model demonstrated moderate explanatory power (Nagelkerke R-2 = 0.44) and showed good discrimination (AUC = 0.81; 95 % CI: 0.76-0.86; p < 0.001). Conclusion: AKI occurred in 33 % of pediatric cardiac surgery patients, with key risk factors including younger age, higher preoperative creatinine, elevated postoperative BUN, longer bypass time, and higher baseline GFR. Postoperative GFR was protective. These findings highlight the importance of early identification and targeted perioperative management to reduce AKI risk and improve outcomes in this vulnerable population.