Definitions

AKI was defined according to the Kidney Disease Improving Global Outcomes (KDIGO) clinical practice guideline³. Due to the lack and accuracy of urine output, we employed SCr to define AKI as an increase by 0.3 mg/dL within 48 h or a 50% increase from baseline within 7 days. The definition of AKI was based on the dynamic criteria described by Nanfang Hospital⁶. The SCr data collected during hospitalization were sorted in increasing order by sequential test time. For any time point t, a baseline average SCr was dynamically defined as the average value of SCr within 7 days before the point t, then each available SCr value within 7 days after point t was compared with this baseline average Scr. The date of AKI diagnosis was defined as the earliest day on which the SCr change met the KDIGO criteria. The baseline value for further analysis in patients with AKI was defined as the value at the time of AKI diagnosis. AKI stages were determined by the peak SCr level after AKI detection, with a rise of less than 100% indicating stage 1, a rise of 100% or more indicating stage 2, and a rise of 200% or more over baseline indicating stage 3.

The primary and secondary outcomes were in-hospital death and the need for dialysis, respectively. In this study, dialysis included temporary or maintenance hemodialysis and peritoneal dialysis, and continuous renal replacement therapy (CRRT).

Diagnosis codes for admission and discharge were used to identify comorbidities. The Charlson comorbidity score was used to calculate the burden of comorbidity³⁰. The Chinese surgical operation grading system was used to classify the procedure from grade 1 to grade 4 based on its difficulty, complexity, and risk. In this study, major surgery was defined as grade 4 surgery, as well as grade 3 invasively surgical operation in major body cavities (heart, intracranial, chest, abdomen, or pelvic).