Association Between Cardiopulmonary Bypass Time and Early Postoperative Acute Kidney Injury in Adults.

Introduction Cardiopulmonary bypass (CPB) has improved the safety and precision of complex cardiac surgery, but its inflammatory, embolic, and hemodynamic effects may contribute to postoperative acute kidney injury (AKI). This study explored whether longer CPB duration was associated with early postoperative AKI and related renal and clinical recovery outcomes in adult cardiac surgical patients. Methodology This prospective observational comparative study was conducted at the Department of Cardiac Surgery of the National Institute of Cardiovascular Diseases (NICVD) in Dhaka, Bangladesh, from July 1, 2022, to June 30, 2024. It included 100 adult cardiac patients aged 18-65 years who underwent cardiac surgery under CPB, selected by convenience sampling after ethical approval. Patients were divided into two equal groups after surgery according to recorded CPB duration: Group A included 50 patients with CPB time ≤120 minutes, while Group B included 50 patients with CPB time >120 minutes. Patients with pre-existing chronic kidney disease, kidney transplant history, emergency surgery, ejection fraction below 30%, previous cardiac surgery, or surgery without CPB were excluded. Results The two study groups were broadly comparable at baseline, with similar mean age (37.8±13.73 vs. 38.46±13.30 years; p=0.8), age distribution (p=0.93), gender distribution (male 58% vs. 52%; p=0.69), comorbidities, body mass index (BMI) profile, and underlying cardiac disease pattern. Smoking, hypertension, diabetes mellitus, and dyslipidemia were distributed without significant difference, while most patients in both groups had normal BMI, and isolated valvular heart disease was the commonest diagnosis. The intended difference between the groups was clearly established by CPB duration, with a mean CPB time of 93.00±11.42 minutes in Group A and 137.10±12.08 minutes in Group B (p<0.001). After surgery, patients with longer CPB time showed lower urine output at 24, 48, and 72 hours, with all differences reaching statistical significance (p<0.001). Although baseline serum creatinine was statistically insignificant (0.83±0.11 vs. 0.86±0.13 mg/dL; p=0.108), postoperative serum creatinine became significantly higher in Group B at 24, 48, and 72 hours (p<0.001). Postoperative AKI occurred in seven patients (14%) in Group A but in 23 patients (46%) in Group B, showing more than a threefold higher occurrence among patients with CPB time >120 minutes (p<0.001). Renal replacement therapy was required only in Group B in four patients (8%), and in-hospital mortality also occurred only in Group B in three patients (6%), though these differences were not statistically significant. Patients in the longer CPB group required longer mechanical ventilation (8.90±3.84 vs. 6.98±2.69 hours; p<0.001), longer ICU stay (10.15±4.68 vs. 4.87±1.58 days; p<0.001), and longer postoperative hospital stay (14.36±5.55 vs. 10.11±3.05 days; p<0.001). Conclusion Prolonged CPB time was significantly associated with greater early postoperative renal stress, higher AKI occurrence, and slower recovery, though the findings require cautious interpretation due to the single-center design, convenience sampling, short follow-up, and unadjusted perioperative factors.