Background
Acute kidney injury (AKI) is a common occurrence in hospitalized patients and it has a detrimental effect on patient outcome. Indeed, AKI is associated with increased costs, length of hospital stay and in-hospital mortality [
1‐
3]. Postoperative AKI has been associated with higher risk of developing chronic kidney disease (CKD) [
4,
5] and increased early [
6‐
17] and long-term mortality [
10‐
22], comparable to the consequences of AKI facing critically ill patients. Postoperative AKI is hence of particular interest, serving as a measurable indicator of perioperative harm and an important potential target for intervention [
23].
The clinical characteristics and the impact of AKI in cardiac surgery have been extensively studied [
24,
25], and most of the published data regarding AKI in the noncardiac surgery population are limited to high-risk aortic procedures [
26‐
31]. Abdominal surgery is frequently associated with AKI. Recently, a number of studies have addressed AKI following major abdominal surgery [
11,
19,
32,
33], especially since it shows a pathophysiology that is distinct from that of cardiac and vascular surgery. Therefore, it is unsuitable to assume that the risk factors for AKI after abdominal surgery are the same as those after cardiac and vascular surgery. The purpose of this review is therefore to perform a critical and contemporary review of the incidence, risk factors, pathogenesis and outcome of AKI in patients undergoing major nonvascular abdominal surgery.
Outcomes
Various studies have verified the deleterious impact of AKI on the early outcomes of patients, namely longer lengths of hospital stay, increased healthcare costs, increased mortality and an increased likelihood of discharge to an extended care facility [
46,
93‐
97]. Granting that AKI patients may have more comorbidities than non-AKI patients, these do not appear to account for all of the increased early mortality associated with AKI [
3,
46,
97,
98]. Other factors should perhaps be regarded since even increases in SCr considered as minor lead to worse outcomes [
88,
97,
98]. Accordingly, AKI has been progressively more thought of as part of a systemic disease with underlying mechanisms that cause multiorgan dysfunction including the kidney, which could help explain the decreased survival observed in AKI patients [
87,
99].
An observational study by Grams et al. demonstrated an association between postoperative AKI after major surgery and longer lengths of stay (15.8 vs 8.6 days) and higher rates of 30-day hospital readmission (21 vs 13%) [
48].
The association between a higher incidence of other postoperative complications, increased length of stay, higher healthcare costs and increased hospital readmissions and postoperative AKI related to major abdominal surgery has also been widely described. Lee et al. performed a retrospective analysis of 595 esophageal cancer surgery patients and established that the extent of hospital stay was significantly longer in patients with AKI [
62]. In a retrospective review of 339 colectomies by Causey et al., AKI development was associated with a 5-day increase in hospital length of stay and nearly doubled the rate of other infectious complications (56 vs 30%) [
61]. Tomozawa et al. reported that AKI after liver resection surgery was correlated with prolonged length of stay, and increased rates of artificial ventilation, need for reintubation, and requirement for renal replacement therapy [
65]. In a retrospective study by Kim et al. gastric surgery patients with AKI had significantly longer hospital stay and higher prevalence of intensive care unit (ICU) admission after the operation (mean 18.7 vs 12.0 days,
P < 0.001; 9.1 vs 1.2%,
P < 0.001, respectively) [
67].
The influence of postoperative AKI on higher in-hospital and 30-day mortality has also been demonstrated after major abdominal surgery. Kim et al. conducted a retrospective study of 4718 gastric surgery patients and reported that the in-hospital and 3-month mortality for patients with AKI were significantly higher than those for patients without AKI (3.5 vs 0.2%,
P < 0.001; 3.8 vs 0.3%,
P < 0.001, respectively), and moreover that the rate of in-hospital and 3-month mortality increased with the advancement in the stage of AKI, in a stepwise manner [
67]. In a retrospective analysis of 642 liver resection patients by Tomozawa et al., AKI was associated with increased mortality (14.1 vs 2.3%,
P < 0.0001) [
65]. In a study by Teixeira, et al., 450 major abdominal surgery patients were retrospectively studied and postoperative AKI was independently associated with increased in-hospital mortality (20.8 vs 2.3%,
P < .0001; unadjusted OR 11.2, 95% CI 4.8–26.2,
P < .0001; adjusted OR 3.7, 95% CI 1.2–11.7,
P = 0.024), furthermore there was a direct relationship between more severe AKI and increased in-hospital mortality [
8]. O’Connor has also recently reported a 12.6-fold relative mortality risk in patients with postoperative AKI after major abdominal surgery [
23].
Additionally, it is known that the detrimental effects of AKI persist after hospitalization, with greater risk of developing CKD and increased long-term mortality in AKI patients [
20,
100,
101]. Progression to CKD results from an inadequate resolution of the acute insult following AKI, with persistent inflammation, increased transformation of pericytes into myofibroblasts in response to tubular injury, and consequent build-up of extracellular matrix and vascular rarefaction, leading to permanent scarring in renal structure and changes in renal function [
102]. The risk of development or progression of CKD occurs in proportion to the severity of AKI [
103]. The increased risk of proteinuria and hypertension and GFR decline described after AKI are known risk factors for cardiovascular disease, and may contribute to the decrement in survival observed among AKI survivors [
104‐
107].
The long-term effect of AKI in postoperative patients has also been described. In a retrospective cohort study of 10,518 patients with AKI discharged after a major surgery, Bihorac et al. [
20] reported that even small changes in creatinine level during hospitalization were associated with an independent long-term risk of death. Also, Grams et al. [
48] performed an observational study of 3.6 million veterans submitted to major surgery and described an association between postoperative AKI and 1-year end-stage renal disease (0.94 vs 0.05%), and mortality (19 vs 8%), with more severe stage of AKI relating to poorer outcomes.
In a retrospective cohort of 390 major abdominal surgery patients, Gameiro et al. [
108] demonstrated that AKI was independently associated with worse renal outcomes, comprising renal function decline and/or long-term need for dialysis (47.2 vs 22.0%,
P < 0.0001), as well as with mortality after hospital discharge (47.2 vs 20.5%,
P < 0.0001).
Conclusion
AKI is a frequent occurrence following major abdominal surgery and is independently associated with both in-hospital and long-term mortality, as well as with a higher risk of progressing to CKD. Preventive strategies such as hemodynamics stabilization, fluid balance control, evasion of nephrotoxins, improved preoperative patient management (body weight reduction, hypertension, diabetes, cardiovascular and pulmonary disease control) and prevention/treatment of any postoperative complications encountered could potentially reduce postoperative AKI and thereby improve patient outcomes.