Incidence of AKI after Cardiac Surgery

Background: Cardiac surgery is a life-saving intervention, however, the development of cardiac surgery–associated acute kidney injury (CS-AKI) is associated with longer hospital stay, higher hospitalization costs and increased postoperative mortality. Here, the incidence of CS-AKI is described in patients undergoing cardiac surgery over a 1-year period examining the major risk factors in this patient population. Methods: Local databases were used to collect data. 429 patients underwent cardiac surgery between the 1st January 2023 and 1st January 2024. For all patients, demographic data was collected including age, gender, past medical history and type of cardiac surgery. Serum creatinine was recorded on day 0, 1, 3, 5 and on discharge. Patients with end stage kidney disease requiring dialysis were excluded (n = 4). AKI was defined by AKIN criteria. Results: Majority of patients had normal renal function pre-operatively (n = 380/425), of these 32% (n = 138) developed CS-AKI. Over 80% of these patients developed an acute kidney injury (AKI) on the first postoperative day. Out of these, 23 were female, 115 were male and 77 people were aged above 65 years. Around 81% (n=112) developed stage 1, 8% (n=11) stage 2 and 11% (n=15) stage 3 AKI. A total of 56 patients were active smokers of these only 25% (n = 14) developed CS-AKI. Breakdown of risk factors for the 138 patients with CS-AKI were as follows; hypertension (n=99), dyslipidaemia (n=75), heart disease (n=61), diabetes mellitus (n=41), obesity (n=14), smoking (n=14), structural abnormality (n=8), one patient had previously required RRT for a contrast-induced AKI. A large proportion of patients with stage 3 AKI (n=11) had undergone a cardiac bypass. The average duration of renal replacement therapy (RRT) for those requiring it (n=13) with stage 3 AKI was 17.4 days, of these 5 patients recovered renal function to be dialysis independent. While 6 other patients requiring RRT died from complications of surgery. The mean serum on discharge was 117.7 umol/L (range = 54 – 493 umol/L). Conclusion: A post-operative AKI can have short- and long-term complications. Even if the renal function initially recovers patients are still at risk of developing pre-mature chronic kidney disease. Studies are required to develop a system for AKI risk prediction in the setting cardiac surgery.