Mild Acute Kidney Injury after Noncardiac Surgery Is Associated With Long-term Renal Dysfunction

A Retrospective Cohort Study

Alparslan Turan, M.D.; Barak Cohen, M.D., M.H.A.; Janet Adegboye, B.S.; Natalya Makarova, M.S.; Liu Liu, M.S.; Edward J. Mascha, Ph.D.; Yuwei Qiu, M.D.; Samuel Irefin, M.D.; Brett J. Wakefield, M.D.; Kurt Ruetzler, M.D., Ph.D.; Daniel I. Sessler, M.D.


Anesthesiology. 2020;132(5):1053-1061. 

In This Article

Abstract and Introduction


Background: Perioperative acute kidney injury is common. However, it is unclear whether this merely represents a transient increase in creatinine or has prognostic value. Therefore, the long-term clinical importance of mild postoperative acute kidney injury remains unclear. This study assessed whether adults who do and do not experience mild kidney injury after noncardiac surgery are at similar risk for long-term renal injury.

Methods: This study is a retrospective cohort analysis of adults having noncardiac surgery at the Cleveland Clinic who had preoperative, postoperative, and long-term (1 to 2 yr after surgery) plasma creatinine measurements. The exposure (postoperative kidney injury) and outcome (long-term renal injury) were defined and staged according to the Kidney Disease: Improving Global Outcomes (KDIGO) initiative criteria. The primary analysis was for lack of association between postoperative kidney injury (stage I vs. no injury) and long-term renal injury.

Results: Among 15,621 patients analyzed, 3% had postoperative stage I kidney injury. Long-term renal outcomes were not similar in patients with and without postoperative stage I injury. Specifically, about 26% of patients with stage I postoperative kidney injury still had mild injury 1 to 2 yr later, and 11% had even more severe injury. A full third (37%) of patients with stage I kidney injury therefore had renal injury 1 to 2 yr after surgery. Patients with postoperative stage I injury had an estimated 2.4 times higher odds of having long-term renal dysfunction (KDIGO stage I, II, or III) compared with patients without postoperative kidney injury (odds ratio [95% CI] of 2.4 [2.0 to 3.0]) after adjustment for potential confounding factors.

Conclusions: In adults recovering from noncardiac surgery, even small postoperative increases in plasma creatinine, corresponding to stage I kidney injury, are associated with renal dysfunction 1 to 2 yr after surgery. Even mild postoperative renal injury should therefore be considered a clinically important perioperative outcome.


Both the Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease (RIFLE)[1] and the Kidney Disease: Improving Global Outcomes (KDIGO)[2] stages of acute kidney injury (AKI) are defined in terms of creatinine increase and urine output. Both are well validated in medical patients. For example, AKI reportedly prolongs hospitalization and increases readmissions; it is also associated with increased healthcare costs, sepsis, and mortality.[3–10] However, most of the data regarding outcomes of AKI originate from cohorts of hospitalized medical patients, patients admitted to critical care units, or trauma victims.

By convention—but without other justification—postoperative kidney injury is defined in terms of creatinine alone. One difficulty is that creatinine can increase after surgery because of dehydration or surgical muscle injury, neither of which would necessarily have any prognostic importance. A further difficulty is that nearly all postoperative AKI is stage I, which mostly represents "risk" rather than injury; stage II injury is uncommon, and stage III injury is rare. Nonetheless, the three stages are generally combined into a composite of "acute kidney injury," ignoring the obvious differences in incidence and severity across the three degrees of injury. Examples include studies evaluating the associations between various exposures and postoperative AKI including intraoperative hypotension,[11,12] perioperative anemia,[13] and preoperative use of clonidine or aspirin.[14]

Postoperative acute kidney injury affects 7 to 13% of the 300 million patients undergoing surgery each year.[12,15–18] Risk is similar after cardiac and major abdominal surgery.[15] Postoperative AKI is associated with increased risk of various short- and long-term complications, but whether AKI mediates the risk remains unclear.[19] Similarly, patients with postoperative AKI appear to have increased mortality,[20–25] but this evidence relies on various definitions of AKI, usually considering advanced and severe renal injury.

We therefore evaluated the long-term consequences of mild postoperative AKI, with the expectation that there would be no difference in long-term renal outcomes between those with stage I postoperative AKI and those with no postoperative AKI. The goal of the study was to describe renal status and mortality of surgical patients suffering various degrees of postoperative AKI 1 to 2 yr after surgery. We also tested the primary hypothesis that adults with and without stage I postoperative AKI are at similar risk of long-term renal injury. Secondarily, we tested for similarity on 2-yr mortality in patients with and without postoperative stage I AKI.