Update on Perioperative Acute Kidney Injury

Alexander Zarbock, MD; Jay L. Koyner, MD; Eric A. J. Hoste, MD; John A. Kellum, MD

Disclosures

Anesth Analg. 2018;127(5):1236-1245. 

In This Article

Epidemiology

AKI is a frequently occurring complication during a hospital stay. In the United States, AKI is estimated to occur in 12% of hospital admissions, affecting 2.2 million hospitalized people per year. This comes with a death toll of 220,000 patients per year, an increase of the length of hospital stay by 3 days, and an estimated excess in hospital costs of $12 billion per year.[3] The 30-day mortality rate for patients with AKI is higher than breast cancer, prostate cancer, heart failure, and diabetes combined. AKI is also closely interconnected with chronic kidney disease (CKD): patients with AKI are at greater risk for developing CKD, and vice versa, patients with CKD are at greater risk for developing AKI.[4] Both AKI and CKD are now regarded as part of a syndrome where each is at the opposite end of the spectrum of kidney disease. Given all these elements, kidney disease may now be regarded as a significant global health burden.[5,6]

In patients in the intensive care unit (ICU), major surgery is the second most frequent reported etiology of AKI (SA-AKI).

Definition of AKI

AKI is defined and staged into 3 severity stages by a combination of either an increase of SCr or a period of oliguria (Table 1).[2] Rapid reversal of AKI is defined by a duration of ≤48 hours and acute kidney disease by an episode of AKI lasting between 7 and 90 days.[7] Limitations of this definition include the use of a baseline SCr concentration (Table 2). In elective surgery, this may be assessed by a preoperative blood draw. However, in emergency surgery or trauma, a baseline creatinine value that represents recent kidney function is not always available. Back calculation with the modification of diet in renal disease equation for the assessment of estimated glomerular filtration rate (GFR) can be used to estimate baseline SCr for patients without CKD.[8] This back-calculated estimate of baseline SCr may overestimate or underestimate AKI stage 1, but it is unlikely to misclassify stage 2 or 3.[9] A true decline in kidney function may be underestimated as an increase of SCr may be blunted by decreased production of creatinine in critically ill patients or dilution as a consequence of volume resuscitation.

Epidemiology of SA-AKI

In the worldwide multicenter AKI-EPI study, the incidence of AKI within the first week after ICU admission was 52% in patients who were admitted after scheduled surgery and 56% after emergency surgery. This figure compared to 62% of patients in the medical ICU and an overall incidence of 57%.[10]

Given the heterogeneous and multifactorial etiology of AKI and the wide variation in patient-related risk factors, incidence estimates vary widely. In cardiac surgery, recent meta-analyses showed that AKI had a median rate of 22%, with predominantly low severity AKI stage 1 and use of renal replacement therapy (RRT) in 3% of patients.[11] In major abdominal surgery, the reported incidence varies from 6.7% to 39.3%.[12]

Several large administrative databases show an important increase of the incidence of AKI. This finding may be explained by better administrative coding and a lower threshold for the use of RRT. However, given the changing profile of the hospitalized patient who is getting older, is more frail, and has more comorbidities, this is most likely also reflecting a true increase.[13–16]

Patient Outcomes

SA-AKI is associated with worse patient outcomes, such as increased length of stay in the ICU and hospital and hospital mortality. This association remains even after adjustment for covariates, with a stepwise increase of mortality risk with increasing severity stage of AKI.[10,17,18] This may be explained by the detrimental effects of AKI on other organs predominately mediated by inflammatory changes.[19] AKI is also associated with worse long-term patient outcomes. In a study on patients with AKI treated with RRT, 5-year mortality of 90-day survivors was 30%.[20] Similar to the hospital survival, there is also a stepwise decrease of long-term survival with increasing severity stages of AKI.[21–25]

While acute effects of AKI on patient outcomes can be explained by effects on distant organ function, the effects on long-term outcomes are more difficult to explain. A large proportion of AKI survivors have evidence of CKD, as shown by a decreased estimated GFR or proteinuria.[20] This effect is even more pronounced in patients who already had CKD before the development of AKI. Several large cohort studies have shown that AKI survivors have an increased risk for cardiovascular disease such as myocardial infarction, heart failure, and stroke.[26–28]

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