Acute kidney injury (AKI) is a common complication after non-cardiac surgery with adverse short and long term morbidity and mortality. So far there have been no effective therapy for AKI treatment developed, possibly due to the heterogenicity of this syndrome. Therefore, prevention of AKI in high risk patients undergoing non-cardiac surgery, as emphasized by Kidney Disease Improving Global Outcomes (KDIGO), becomes the first priority. However, early prediction of AKI is the first step before taking preventive measures, which really make a great challenge to clinical practitioners because of such a limited time window and complex clinical scenarios. Recently, cumulative evidence have shown that biomarkers and renal ultrasound may play an important role in AKI prediction after non-cardiac surgery. The purpose of this study is to investigate the combination of biomarkers, urine sedimentation and renal resistive index for early prediction of AKI in high risk patients undergoing non-cardiac surgery.

Early prediction of AKI have long been a study hotspot. Various clinical prediction models, biomarkers, urine sedimentation scores and imaging tools are developed and validated in different clinical settings mainly focusing on contrast associated AKI, durg induced AKI and cardiac surgery associated AKI. Due to the heterogenicity of this syndrome, one parameter which fits all patients for prediction of AKI dose not possibly exist. As a result, searching for combination parameters that can well predict AKI after non-cardiac surgery become the first priority for prevention of AKI. Evidence in non-cardiac surgery population have been gradually accumulated in recent years. Biomarkers for G1 cell cycle arrest, e.g. tissue inhibitor of metalloproteinase-2 (TIMP-2) and insulin like growth factor binding protein-7 (IGFBP-7), have demonstrated robust predictive performance in high risk surgical patients. Renal resistive index as calculated by ultrasound have also showed its validity in AKI prediction in patients following orthopedic surgery. Hence, the investigators make an assumption that combination of biomarkers, urine sedimentation and renal resistive index may improve the predictive value of AKI after non-cardiac surgery. The purpose of this study is to investigate the combination of biomarkers, urine sedimentation and renal resistive index for early prediction of AKI in high risk patients undergoing non-cardiac surgery.

Adult patients undergoing non-cardiac surgery and then admitting to surgical intensive care unit (SICU) will be immediately screened for this study. After enrollment, blood and urine samples, in addition to clinical routine tests, will be collected for the tests of biomarkers and urine sedimentation, such as serum creatinine, TIMP-2, IGFBP-7, α-1 microglobulin, microalbumin, transferrin, granular cast and so on. Meanwhile, central venous pressure (CVP) will be measured by primary nurse. If the patients were enrolled at daytime between 8:00-16:00, experienced intensivists will also calculate the renal resistive index (RI) by ultrasound. Urine samples will be collected again for storage after 6 and 12 hours admitting to SICU, at which time urine sedimentation and CVP will be repeatedly measured at the discretion of physician in-charge. AKI is monitored by serum creatinine daily in SICU and on demand in general wards, and by urine output (UO) every 3 hours in SICU. Patients will be followed up for postoperative complications, renal recovery, survival, SICU/in hospital stay and total cost until the first thing that happens: discharge/death, 30d after operation or withdrawing the study. Perioperative data will be recorded by specialized researchers.

Inclusion Criteria:

• Age ≥ 18 years; Undergoing non-cardiac surgery; Admitted to SICU immediately after surgery

Exclusion Criteria:

• Chronic kidney disease stage 5 (CKD-5) or requiring long-term dialysis; Undergoing kidney-related surgery; AKI before admission to SICU; Without Foley catheter placement ;Written informed consent not obtained

High risk patients undergoing non-cardiac surgery