Background: Acute kidney injury (AKI) is one of the more serious complications following cardiac surgery, consistently linked to prolonged mechanical ventilation and higher in-hospital mortality. This study examined whether preoperative anaemia and impaired renal function are associated with AKI and death in a high-risk cardiac-surgery cohort requiring extended postoperative ICU monitoring and how these associations behave after adjustment for procedure type and intraoperative variables. Methods: In this single-centre retrospective cohort study, we screened 950 patients admitted to a cardiothoracic ICU between January 2018 and January 2024. After standard exclusion criteria and an audit of operative records, 553 cardiac-surgery patients formed the principal analysis cohort. AKI was defined by KDIGO criteria using serial postoperative serum-creatinine measurements during the first 7 days. Multivariable logistic regression for AKI and in-hospital mortality was built sequentially: Model A (baseline only); Model B (+procedure type); and Model C (+intraoperative variables: aortic cross-clamp time, intraoperative RBC units, and intraoperative inotrope use). Calibration was assessed by the Hosmer–Lemeshow test. Total cardiopulmonary bypass duration was not separately captured in the institutional database and is disclosed as a limitation. Results: AKI occurred in 174 of 553 patients (31.5%), and in-hospital mortality was 16.6% (92/553). Patients with AKI were older (median 77 vs. 68 years, p < 0.001), with lower preoperative haemoglobin (11.4 vs. 12.3 g/dL, p < 0.001) and lower eGFR (38.1 vs. 63.7 mL/min/1.73 m2, p < 0.001). The aortic cross-clamp time was shorter in AKI patients (56 vs. 70 min, p = 0.043), a counterintuitive finding likely reflecting residual confounding by case-mix and procedure selection rather than a protective operative effect. In the fully adjusted multivariable model, the haemoglobin–AKI association attenuated and was no longer independently significant (OR 0.89 per 1 g/dL, 95% CI 0.73–1.08, p = 0.24), while intraoperative RBC transfusion emerged as an independent predictor (OR 1.12 per unit, p = 0.046). For mortality, AKI remained an independent predictor after full adjustment for procedure type and intraoperative variables (OR 7.14, 95% CI 1.45–35.13, p = 0.016), with cross-clamp time (OR 1.30 per 10 min, p = 0.010) and intraoperative RBC units (OR 1.48 per unit, p < 0.001) also independently associated. Both fully adjusted models showed acceptable calibration (Hosmer–Lemeshow p = 0.48 for AKI, p = 0.56 for mortality). Conclusions: In cardiac-surgery patients with a prolonged ICU stay, AKI is independently associated with in-hospital mortality even after adjustment for operative variables. The univariable association between preoperative haemoglobin and AKI is attenuated after adjustment for procedure type and intraoperative transfusion exposure, suggesting confounding or mediation by operative and case-mix factors rather than an independent direct association. The contribution of this analysis is aetiological/analytical rather than predictive (modest discrimination, AUROC 0.67 for AKI), and findings should be interpreted within the selected high-risk ICU ≥ 72 h population.
Balkan et al. (Wed,) studied this question.