Postoperative Acute Kidney Injury Is Associated With Progression of Chronic Kidney Disease Independent of Severity

BACKGROUND: Both postoperative acute kidney injury (AKI) and preoperative chronic kidney disease (CKD) are associated with significantly worse outcomes following surgery. The relationship of both of these conditions with each other and with CKD progression after surgery remains poorly studied. Our objective was to assess if there was an interaction between preoperative kidney function estimated by preoperative estimated glomerular filtration rate (eGFR)/CKD stage, postoperative AKI, and eGFR/CKD progression within 1 year of surgery. Our hypothesis was that AKI severity would be associated with a faster time to eGFR/CKD stage progression within 1 year of surgery in a graded-fashion, which would be exacerbated by preoperative kidney dysfunction. METHODS: This was a retrospective cohort study at Landspitali University Hospital in Iceland, which serves about 75% of the population. Participants included adults receiving their first major anesthetic between 2005 and 2018. Patients with CKD stage 5, undergoing major urologic procedures, or having missing creatinine values for follow-up of eGFR stage were excluded from analysis. The primary exposure was postoperative AKI stage within 7 days after surgery classified by the kidney disease improving global outcome (KDIGO) criteria. The primary outcome was time to progression of CKD by at least 1 eGFR/CKD stage within 1-year following surgery. Multivariable Cox proportional hazards models were used to estimate hazard of eGFR/CKD stage progression, including an interaction between AKI and preoperative CKD on eGFR/CKD stage progression. RESULTS: A total of 5548 patients were studied. In the multivariable model adjusting for baseline eGFR/CKD stage, when compared to patients without AKI, postoperative AKI stage 1 (hazard ratio [HR], 5.91; 95% confidence interval [CI], 4.34-8.05), stage 2 (HR, 3.86; 95% CI, 1.82-8.16), and stage 3 (HR, 3.61; 95% CI, 1.49-8.74) were all independently associated with faster time to eGFR/CKD stage progression within 1 year following surgery, though increasing AKI severity did not confer additional risk. The only significant interaction between the degree of AKI and the preexisting renal function was for stage 1 AKI, where the odds of 1-year eGFR/CKD stage progression actually decreased in patients with preoperative CKD categories 3a, 3b, and 4. CONCLUSIONS: KDIGO-AKI was independently associated with eGFR/CKD stage progression within the year following surgery after adjustment for baseline eGFR/CKD stage and without an interaction between worse preoperative kidney function and higher stage AKI. Our observations suggest that further studies are warranted to test whether CKD progression could be prevented by the adoption of perioperative kidney protective practices.