Novel biological risk factors for 7‐day postoperative kidney injury in elective major non‐cardiac surgery: a retrospective observational study

Summary Introduction Few UK studies have explored the epidemiology of postoperative acute kidney injury after diverse types of elective major non‐cardiac surgery. Fewer still have compared postoperative acute kidney injury risk factors with conditions such as peri‐operative myocardial injury that might have similar pathophysiology. This study aimed to characterise postoperative acute kidney injury and its clinical consequences in elective major non‐cardiac surgery, and to assess risk factors for postoperative acute kidney injury including those related to peri‐operative myocardial injury. Methods All elective major non‐cardiac surgical episodes, occurring between 2015 and 2020, were identified retrospectively. Patients without measured peri‐operative renal parameters were not studied. Our primary outcome was 7‐day postoperative acute kidney injury rate, defined using Kidney Disease Improving Global Outcomes criteria. Multivariable logistic regression modelling was used to assess risk factors for postoperative acute kidney injury. Results Postoperative acute kidney injury occurred in 1334/13,790 (9.7%) episodes, with 663 (49.7%) occurring on day 1. Postoperative acute kidney injury was associated with increased peri‐operative complications (OR 1.8, 95%CI 1.6–2.1, p < 0.001), unanticipated critical care admissions (OR 2.4, 95%CI 1.6–3.5, p < 0.001) and in‐hospital mortality (OR 8.0, 95%CI 5.1–12.5, p < 0.001). Independent risk factors for postoperative acute kidney injury include: raised creatinine; hypertension; anaemia; platelet: lymphocyte ratio; heart rate; male sex: renin‐angiotensin‐aldosterone system blockade; and intra‐abdominal surgery. Discussion Postoperative acute kidney injury is common and is associated with adverse outcomes. Prevalence peaks initially within the first 48 h, with a secondary rise seen from day 5 onwards, suggesting a different aetiology. It is determined by a combination of patient and surgical risk factors, with the former relating to physiological, rather than chronological, renal age. In common with peri‐operative myocardial injury, postoperative acute kidney injury is independently associated with factors affecting autonomic tone and myeloid skewing.