Aortic Aneu

Anesthetic Technique and Acute Kidney Injury in Endovascular Abdominal

rysm Repair

Minjae Kim, MD,* Joanne E. Brady, SM,*† and Guohua Li, MD, DrPH*†

Objective: Prior studies suggest that general anesthe-

sia (GA) is associated with worse cardiopulmonary

outcomes after endovascular abdominal aortic ane-

urysm repair (EVAR). Patients undergoing EVAR are

at a high risk of developing perioperative acute kidney

injury (AKI), and the relationship between anesthetic

technique and AKI in these patients is not well-

characterized. The authors sought to determine if anes-

thetic technique affected the risk of AKI in patients

undergoing EVAR.

Design: Retrospective, observational cohort study ana-

lyzed using a multivariate logistic regression model to

assess the effects of anesthetic technique on renal

outcome.

Setting: Multiple institutions, mainly in North Am-

erica.

Participants: Patients in the American College of Sur-

geons National Surgical Quality Improvement Program from

2005-2010 undergoing EVAR.

From the *Department of Anesthesiology, Columbia UniversityMedical Center; and †Department of Epidemiology, Columbia Uni-versity Mailman School of Public Health, New York, NY.

Address correspondence to Minjae Kim, MD, Columbia UniversityMedical Center, Department of Anesthesiology, 622 West 168th Street,PH 5, Suite 505C, New York, NY 10032. E-mail: minjae.kim@columbia.edu© 2014 Elsevier Inc. All rights reserved.1053-0770/2601-0001$36.00/0http://dx.doi.org/10.1053/j.jvca.2013.06.001

572 Journal of Cardiotho

Interventions: The authors investigated the association

between anesthetic techniques, comparing GA to alterna-

tive (non-GA) techniques, and AKI.

Measurements and Main Results: AKI was defined as an

increase in the creatinine level of 42 mg/dL and/or dialysis.

Of 13,026 patients, 84.4% underwent GA and 15.6% under-

went non-GA techniques. AKI developed in 2.0% of the GA

group and 1.4% of the non-GA group (unadjusted odds ratio

[OR] 1.43, p ¼ 0.075; adjusted OR [aOR] 1.00, p ¼ 0.99). Risk

factors for AKI include ASA class, ruptured aneurysm,

preoperative renal dysfunction, symptomatic cardiovascular

disease, and perioperative blood transfusion.

Conclusions: Anesthetic technique is not independently

associated with the risk of AKI in patients undergoing EVAR.

& 2014 Elsevier Inc. All rights reserved.

KEY WORDS: acute kidney injury, anesthesia, abdominalaortic aneurysm, endovascular procedures, postoperativecomplications

THE INTRODUCTION of endovascular techniques forabdominal aortic aneurysm (AAA) repair (EVAR)1 has

allowed for minimally invasive methods in the surgical managementof this condition, potentially reducing postoperative complications2

and the risk of perioperative AKI3 compared to patients undergoingopen repair. The minimally invasive nature of EVAR has led to theevaluation of alternative techniques to general anesthesia (GA),including local anesthesia/monitored anesthesia care (MAC) techni-ques,4–6 and there are suggestions that GA may increase cardio-pulmonary morbidity after EVAR compared to alternatives.7 Acutekidney injury (AKI) is also a serious complication of AAA repair,leading to increased morbidity and mortality.8 Despite the reductionin the risk of AKI after EVAR compared to open repair, there is stilla high risk of perioperative AKI after EVAR from renal ischemia-reperfusion injury (IRI) and surgical trauma as well as contrastnephropathy.8 The effects of anesthetic technique on renal morbidityin patients undergoing EVAR are not well studied, and here, theauthors sought to evaluate the effect of anesthetic technique on renaloutcome in patients undergoing this procedure.

For the authors’ analysis, they obtained data from the 2005-2010 American College of Surgeons National Surgical QualityImprovement Program (ACS NSQIP), a large, multicenterdatabase of surgical outcomes from hospitals throughout NorthAmerica. The ACS NSQIP provides a large, high-quality9

dataset of patient characteristics as well as 30-day morbidityand mortality, providing the opportunity to characterize

anesthetic management in patients undergoing EVAR as wellas to investigate the hypothesis that anesthetic technique isassociated with the development of perioperative AKI inpatients undergoing this procedure.

METHODS

The Columbia University Medical Center Institutional ReviewBoard determined that this study was not subject to review as thedataset did not contain individually identifiable health information. TheACS NSQIP* is a validated, prospectively collected national datasetaimed at improving surgical quality and outcomes.10 The data collectedinclude demographic characteristics, presurgical comorbidities, intra-operative variables, and 30-day postoperative morbidity and mortalitydata. All data are reviewed carefully by each site’s surgical clinicalreviewer, and centers not meeting specific criteria for quality areremoved from the dataset. The systematic sampling process and criteriafor maintaining the high quality of the dataset have been describedpreviously.11 Of note, the ACS NSQIP collects data on major cases,defined as those performed under general, spinal or epidural anesthesia.However, certain procedures, including EVAR, are included regardlessof the anesthetic technique utilized.

The authors obtained the ACS NSQIP participant use data files for theyears 2005-2010. There were 13,286 patients undergoing EVAR as theirprincipal procedure as identified using Current Procedural Terminology(CPT; American Medical Association, Chicago, IL) codes for endovas-cular repair of infrarenal AAA or dissection (CPT codes 34800 [usingaorto-aortic tube prosthesis]; 34802 [using modular bifurcated prosthesis–1 docking limb]; 34803 [using modular bifurcated prosthesis–2 dockinglimbs]; 34804 [using unibody bifurcated prosthesis] and 34805 [usingaorto-uniliac or aorto-unifemoral prosthesis]), as previously described.7

They excluded 241 patients who required preoperative dialysis ormechanical ventilation, as mechanically ventilated patients are likely to

*The American College of Surgeons National Surgical QualityImprovement Program and the hospitals participating in the ACSNSQIP are the source of the data used herein; they have not verifiedand are not responsible for the statistical validity of the data analysis orthe conclusions derived by the authors.

racic and Vascular Anesthesia, Vol 28, No 3 (June), 2014: pp 572–578

ACUTE KIDNEY INJURY IN AORTIC ANEURYSM REPAIR 573

receive GA as their anesthetic without consideration of an alternativetechnique.

The followup period for patients participating in the ACS NSQIP is 30days after their operation. For measuring the outcome of AKI, the authorsare limited to the 2 prespecified endpoints available in the dataset: (1)Progressive renal insufficiency defined as a rise in the creatinine level 42mg/dL above the preoperative value, and/or (2) the need for dialysis in apatient who did not require dialysis prior to the operation. Other measuresof postoperative renal function are not available, including laboratory andurine output data.

Anesthetic technique was identified through the ACS NSQIPdataset for patients undergoing EVAR procedures. Anesthesia typewas identified from the patient's anesthesia record and coded as GA,monitored anesthesia care (MAC), spinal, epidural, regional, local, andnone. The category GA will include all cases identified as using GAeven if there were other techniques involved (eg, combined epiduraland GA). The authors excluded cases coded as “Other” or with missinganesthetic data as they could not clearly determine the nature of theanesthetic management (n ¼ 19). For this study, they were interestedmainly in comparing GA with alternative anesthetic techniques.Therefore, they combined patients receiving an anesthetic techniqueother than GA into a non-GA group.

Patient baseline demographic and operative variables were collecteddirectly from the ACS NSQIP dataset. Race/ethnicity was categorized aswhite versus non-white. Age was categorized as less than 60 years ofage, between 60 and 75 years of age, or older than 75 years of age.American Society of Anesthesiologists (ASA) class was categorized into3 groups: ASA 1-2, ASA 3, or ASA 4-5. Body mass index (BMI) wascalculated and categorized into 3 groups: o25, 25 to 30, or 430. Theauthors determined if the aneurysm was ruptured based on the post-operative International Classification of Diseases, Ninth Revision (ICD-9, Centers for Disease Control and Prevention, Hyattsville, MD)diagnosis code (ICD-9 codes 441.1, 441.3, 441.5, 441.6). The estimatedglomerular filtration rate (eGFR, mL/min/1.73m2) was calculated basedon the Modification of Diet in Renal Disease formula incorporatingcreatinine, sex, age, and race12 and categorized into 4 groups:o30, 30 to60, 460, or missing. Missing categories for eGFR (based on creatinine)and hematocrit were included to account for the fact that missingpreoperative laboratory work may itself be a prognostic indicator inpredicting the risk of developing AKI.

Intraoperative and postoperative variables also were collected fromthe dataset. Total operative time was examined as both a continuousand categoric variable. Based on the authors’ analysis of deciles ofoperative time, 3 categories were used: low (deciles 0-2; operative time≤114 min), medium (deciles 3-5; operative time 115-155 min), andhigh (deciles 6-9; operative time ≥156 min).

ACS NSQIP changed its reporting for transfusion variables in 2010.Prior to 2010, the dataset reported separately the number of red bloodcell (RBC) units transfused intraoperatively and whether the patientreceived 44 units of RBCs in the first 72 hours of the postoperativeperiod. Beginning in 2010, transfusion of 1 or more units in theintraoperative period or the first 72 hours of the postoperative period isreported. Patients were identified as having had an intra/postoperativetransfusion if any intraoperative or postoperative transfusion wasreported in the dataset. ACS NSQIP does not identify individualhospitals or characteristics of the hospitals included; as such, residentinvolvement was used as a proxy for teaching hospitals.

The differences in preoperative patient characteristics and comor-bidities between patients receiving GA and non-GA techniques werecompared with the χ2 test. The authors used stepwise multivariatelogistic regression modeling to identify significant covariates to beincluded in the analysis of anesthetic technique on AKI. A significancelevel of 0.12 was required to enter the model and a level of 0.25 wasrequired to remain in the model. In a post-hoc analysis, the authors

explored the possibility that operative time modified the effect ofanesthetic technique on AKI by including an interaction term inthe model.

Odds ratios (ORs) and 95% confidence intervals (CIs) of AKI werecalculated. Statistical analysis was performed using SAS softwareversion 9.2 (SAS Institute, Cary, NC). In all analyses, statisticalsignificance was determined with a p value o0.05.

RESULTS

The authors identified 13,026 patients in the 2005-2010ACS NSQIP undergoing EVAR as their primary procedurewho met the inclusion criteria. Of these, 10,989 (84.4%)received GA while 2,037 (15.6%) received a non-GA technique(Table 1). Among those not undergoing GA, 1,337 (65.6%)patients received a neuraxial technique (spinal/epidural/regional) while 700 (34.4%) received MAC (including localanesthesia and none). Over time, the proportion of EVARprocedures performed under GA steadily increased from 67.1%in 2005 to 86.8% in 2010 (Table 1).

There were differences in the baseline comorbidities anddemographic characteristics between patients undergoing EVARwith GA compared to those receiving non-GA techniques(Table 2). The GA cohort had a greater proportion of patientswho were o60 or between 60 and 75 years of age and whowere ASA 4-5. In addition, there were higher rates of emergencyprocedures, ruptured aneurysms, current smoking, bleedingdisorders, chronic anticoagulation, and significant blood trans-fusions in the 72 hours prior to surgery in the GA group. Thenon-GA cohort had a greater proportion of those 475 years ofage and those who were ASA 1-2 as well as higher rates ofpulmonary comorbidities (dyspnea or chronic obstructive pul-monary disease [COPD]) and resident involvement. Finally,patients with an aorto-aortic tube prosthesis (CPT 34800) hadhigher rates of GA (10.0% v 5.6%) while those with modularbifurcated prosthesis with 1 docking limb (CPT 34802) hadhigher rates of non-GA anesthesia (50.3% v 45.7%).

Among patients undergoing EVAR, AKI developed in 2.0%of the GA group and in 1.4% of the non-GA group (p ¼ 0.075)(Table 3) for an unadjusted OR of 1.43 [0.96, 2.13]. However,after adjusting for patient factors, the OR of AKI associatedwith GA was reduced to 1.00 [0.66, 1.52] (Table 4).

Independent predictors of AKI were ASA class, rupturedaneurysm, histories of angina and rest pain/gangrene, func-tional dependence, and intra/postoperative transfusion(Table 4). Compared to patients with an eGFR 460, thosewith lower eGFR (o30 or 30-60) had significantly higher oddsof developing AKI. Surgical factors played a role as thoseprocedures performed with a modular bifurcated prosthesiswith 2 docking limbs (CPT 34803) had reduced odds ofdeveloping AKI compared to those performed with anaortoaortic tube prosthesis (CPT 34800) (Table 4). In addition,operative time was an important predictor of AKI as, comparedto medium length operative times, low operative times wereassociated with significantly reduced odds of developing AKIwhile high operative times were associated with significantlygreater odds of developing AKI.

In analyzing the data, it appeared as if the effects ofanesthetic technique on AKI rates might vary with operative

Table 1. Anesthetic Technique for Endovascular Abdominal Aortic

Aneurysm Repair Procedures, American College of Surgeons

National Surgical Quality Improvement Program, 2005-2010

GA Non-GA*

2005 243 (67.1%) 119 (32.9%)

2006 809 (77.1%) 240 (22.9%)

2007 1,765 (81.2%) 408 (18.8%)

2008 2,407 (85.2%) 417 (14.8%)

2009 2,800 (87.4%) 404 (12.6%)

2010 2,965 (86.8%) 449 (13.2%)

Total† 10,989 (84.4%) 2,037 (15.6%)

Abbreviations: GA, general anesthesia.

*Non-GA includes spinal, epidural, regional, monitored anesthesia

care, local anesthesia, and none.

†p o 0.0001 Mantel-Haenszel χ2 test.

KIM ET AL574

time. Indeed, stratification analysis demonstrated that inpatients in the low operative time category (n ¼ 3,876), theincidence of AKI was 0.7% for those receiving GA (n ¼ 3,254)and 0.3% for those receiving non-GA techniques (n ¼ 622; p ¼0.30). In patients in the medium operative time category(n ¼ 3,946), the incidence of AKI was 1.0% for the GA group(n ¼ 3,295) and 2.0% for the non-GA group (n ¼ 651; p ¼0.03). In patients in the high operative time category (n ¼5,204), the incidence of AKI was 3.6% for the GA group (n ¼4,440) and 1.7% for the non-GA group (n ¼ 764; p o 0.01).

To allow for the effects of GA to vary with operative time inthe authors’ model, they included an interaction term betweenthese variables, and this term was statistically significantin both simple (p ¼ 0.003) and adjusted models (p ¼ 0.02).In the simple model including anesthetic technique, operativetime and the interaction term, the OR for GA in the lowoperative time category was 2.11 [0.50, 8.98], the OR for GAin the medium operative time category was 0.50 [0.26, 0.95],and the OR for GA in the high operative time category was2.16 [1.22, 3.82]. The ORs in the adjusted model were 1.50[0.35, 6.49], 0.43 [0.22, 0.85] and 1.48 [0.82, 2.69],respectively.

Progressive renal insufficiency developed in 0.8% ofpatients in both the GA and non-GA groups (Table 3), for anunadjusted OR of 1.06 [0.62, 1.80] and an adjusted OR of 0.79[0.46, 1.37]. The interaction between anesthetic technique andoperative time was not significant for this outcome.

Postoperative dialysis was required in 1.3% of the GAgroup and 0.8% in the non-GA group (Table 3), for anunadjusted OR of 1.68 [0.998, 2.82] (p ¼ 0.051) and anadjusted OR of 1.10 [0.64, 1.90]. After incorporating theinteraction between GA and operative time (p ¼ 0.01 forinteraction term), the adjusted ORs for GA were 0.33 [0.15,0.74] in the medium operative time group and 2.03 [0.86, 4.78]in the high operative time group. The OR for the low operativetime group could not be calculated because there were no casesof postoperative dialysis in the non-GA group.

DISCUSSION

This study of a large, national surgical outcomes dataset from2005-2010 demonstrated that the use of GA for patients undergoing

the EVAR procedure has been increasing over time. Patientsreceiving GA appeared to be a sicker group as evidenced by agreater proportion of patients with high ASA class, higher rates ofsmoking, prior myocardial infarctions, bleeding disorders, andpreoperative transfusion requirements as well as a greater likelihoodof undergoing an emergency procedure with a ruptured aneurysm.Those receiving non-GA techniques were older and had higherrates of pulmonary comorbidities (dyspnea and COPD). Overall,GA was associated with a higher (although not statisticallysignificant) rate of perioperative AKI compared to non-GAtechniques (crude OR ¼ 1.43, p ¼ 0.076). However, this increasedrisk can be explained by patient comorbidities and operative factorsbecause after adjustment, there was no association between GA andAKI (adjusted OR¼ 1.00, p¼ 0.99). Thus, GA does not appear tobe associated with the risk of developing AKI after EVAR.

Several risk factors for the development of AKI in EVARpatients were identified. Not surprisingly, preoperative renalfunction was a significant predictor of AKI as well as ASAclass, ruptured aneurysm, functional dependence, and bloodtransfusions. Interestingly, symptomatic cardiovascular dis-eases (angina and rest pain/gangrene) were significant predic-tors of AKI, but prior revascularizations (coronary andperipheral) were not. The authors cannot determine here ifthe risk of AKI would decrease if these patients delayed theirprocedure for revascularization therapy, and this is a potentialarea for further study. However, it is possible that theypresented for urgent/emergent procedures that necessitatedimmediate surgical intervention of the aneurysm. Increasingoperative time was also a significant predictor of AKI. It ispossible that the length of the procedure itself affects AKI ratesdirectly, but it more likely serves as a useful proxy for factorsthat increase AKI risk, such as increased surgical complexity.

Though the utilization of GA increased over time, there wasno significant change in the rate of AKI over time (not shown).In addition, certain risk factors for AKI identified in generalsurgical patients,13 including ascites, congestive heart failure,hypertension, male sex, diabetes, and age, were not significantpredictors in the authors’ model. While preoperative anemia isa risk factor for AKI in patients undergoing cardiac surgery,14 itis not significant in their analysis. It is possible that there areunique factors associated with anemia and cardiopulmonarybypass that are not present in those undergoing EVAR.

It might be surmised that non-GA techniques would offerclear, significant benefits over GA. Indeed, GA was associatedwith higher rates of AKI compared to regional anesthesia inpatients undergoing total joint arthroplasty.15 On the otherhand, local anesthesia has not been shown to reduce post-operative stroke or death after carotid endarterectomy com-pared to GA,16 and there are no clinically important differencesbetween regional anesthesia and GA after hip fracture sur-gery.17 Anesthetic technique also may affect other aspects ofcare, such as postoperative cognitive function, pain control,quality of life, and costs associated with healthcare.18

Although an early review found no differences in cardiopul-monary morbidity and mortality between GA or local anesthesiaafter EVAR,19 several reports suggest that alternatives to GA arepreferable for EVAR,20–22 including a recent study demonstratingthat GA was associated with an increased risk of cardiaccomplications compared to locoregional anesthesia.23 The impact

Table 2. Characteristics of Patients Undergoing Endovascular Abdominal Aortic Aneurysm Repair by Anesthetic Technique, American College of

Surgeons National Surgical Quality Improvement Program, 2005-2010

GA Non-GA

n ¼ 10,989 n ¼ 2,037 P*

Age o60 627 (5.7) 86 (4.2) o0.001†

60-75 5,349 (48.7) 932 (45.8)

475 5,013 (45.6) 1,019 (50.0)

Female Yes 1,968 (17.9) 358 (17.6) 0.718

No 9,021 (82.1) 1,679 (82.4)

White Yes 9,177 (83.5) 1,669 (81.9) 0.080

No 1,812 (16.5) 368 (18.1)

ASA class 1-2 680 (6.2) 214 (10.5) o0.0001†

3 7,895 (71.9) 1,418 (69.6)

4-5 2,408 (21.9) 405 (19.9)

Emergency Yes 697 (6.3) 77 (3.8) o0.0001†

No 10,292 (93.7) 1,960 (96.2)

Ruptured aneurysm Yes 563 (5.1) 70 (3.4) 0.001†

No 10,426 (94.9) 1,967 (96.6)

Functionally dependent Yes 549 (5.0) 90 (4.4) 0.266

No 10,436 (95.0) 1,947 (95.6)

Body mass index o25 2,896 (27.0) 546 (27.7) 0.131

25-30 4,142 (38.7) 787 (40.0)

430 3,435 (32.1) 586 (29.8)

Estimated glomerular filtration rate (mL/min/1.73m2) o30 365 (3.3) 54 (2.7) 0.001†

30-60 3,900 (35.5) 750 (36.8)

460 6,376 (58.0) 1,137 (55.8)

Missing 348 (3.2) 96 (4.7)

Current smoker Yes 3,335 (30.4) 543 (26.7) 0.001†

No 7,654 (69.7) 1,494 (73.3)

Dyspnea Yes 2,539 (23.1) 536 (26.3) 0.002†

No 8,450 (76.9) 1,501 (73.7)

Chronic obstructive pulmonary disease Yes 2,044 (18.6) 454 (22.3) 0.0001†

No 8,945 (81.4) 1,583 (77.7)

Current pneumonia Yes 18 (0.2) 7 (0.3) 0.089

No 10,971 (99.8) 2,030 (99.7)

Diabetic Yes 1,658 (15.1) 282 (13.8) 0.148

No 9,331 (84.9) 1,755 (86.2)

Angina Yes 208 (1.9) 41 (2.0) 0.717

No 10,781 (98.1) 1,996 (98.0)

Hypertension Yes 8,715 (79.3) 1,594 (78.3) 0.282

No 2,274 (20.7) 443 (21.8)

Coronary revascularization (PCI or CABG) Yes 4,192 (38.2) 765 (37.6) 0.613

No 6,797 (61.9) 1,272 (62.4)

Congestive heart failure Yes 145 (1.3) 35 (1.7) 0.157

No 10,844 (98.7) 2,002 (98.3)

Myocardial infarction Yes 135 (1.2) 14 (0.7) 0.035†

No 10,854 (98.8) 2,023 (99.3)

PVD requiring intervention Yes 634 (5.8) 116 (5.7) 0.894

No 10,355 (94.2) 1,921 (94.3)

Rest pain/gangrene Yes 123 (1.1) 15 (0.7) 0.121

No 10,866 (98.9) 2,022 (99.3)

Stroke (with or without neuro deficit) Yes 1,627 (14.8) 298 (14.6) 0.837

No 9,362 (85.2) 1,739 (85.4)

Hematocrit (%) 430 10,203 (92.9) 1,856 (91.1) o0.0001†

≤30 448 (4.1) 68 (3.3)

Missing 338 (3.1) 113 (5.6)

Bleeding disorders Yes 1,309 (11.9) 142 (7.0) o0.0001†

No 9,680 (88.1) 1,895 (93.0)

Transfusions 44 Units 72 hours prior to surgery Yes 43 (0.4) 2 (0.1) 0.038†

No 10,946 (99.6) 2,035 (99.9)

Preop SIRS/sepsis/septic shock Yes 252 (2.3) 40 (2.0) 0.345

No 10,602 (97.7) 1,979 (98.0)

ACUTE KIDNEY INJURY IN AORTIC ANEURYSM REPAIR 575

Table 2 (continued )

GA Non-GA

n ¼ 10,989 n ¼ 2,037 P*

Resident involvement Yes 7,113 (64.8) 1,405 (69.2) o0.001†

No 3,867 (35.2) 625 (30.8)

Current procedural terminology Group

Using aortoaortic tube prosthesis (34800) 1,099 (10.0) 113 (5.6) o0.0001†

Using modular bifurcated prosthesis [1 docking limb] (34802) 5,021 (45.7) 1,024 (50.3)

Using modular bifurcated prosthesis [2 docking limbs] (34803) 3,556 (32.4) 642 (31.5)

Using unibody bifurcated prosthesis (34804) 787 (7.2) 137 (6.7)

Using aortouniliac or aorto-unifemoral prosthesis (34805) 526 (4.8) 121 (5.9)

NOTE. Categoric variables expressed as number (%).

Abbreviations: ASA, American Society of Anesthesiologists; CABG, coronary artery bypass graft; GA, General Anesthesia; PCI, percutaneous

coronary intervention; PVD, peripheral vascular disease; SIRS, systemic inflammatory response syndrome.

*Differences among categoric variables analyzed with χ2 test.

†p o 0.05.

Table 3. Renal Outcomes by Anesthetic Technique, American College

of Surgeons National Surgical Quality Improvement

Program, 2005-2010

GA Non-GA Total

10,989 2,037 13,026 P*

Acute Kidney Injury 215 (2.0) 28 (1.4) 243 (1.9) 0.075

Renal Insufficiency 91 (0.8) 16 (0.8) 107 (0.8) 0.845

Dialysis 144 (1.3) 16 (0.8) 160 (1.2) 0.048†

NOTE. Categoric variables expressed as number (%).

Abbreviations: GA, General Anesthesia

*Differences analyzed with χ2 test.

†p o 0.05.

KIM ET AL576

of anesthetic technique on renal outcomes in EVAR patients hasnot been defined clearly. In addition, there are limitations to non-GA techniques in lengthier procedures as patients may not toleratelocal/MAC or neuraxial techniques for extended periods of time.Indeed, of the 67 cases with operative times 4500 min, only 1was performed with a non-GA technique. However, a sensitivityanalysis demonstrated that these extremes of operative time didnot affect the main result (not shown).

A unique aspect of GA involves the use of volatile anesthetics(VAs) and they have been shown to reduce the risk of AKI inanimal24 and in vitro25 models. The clinical data focus on cardiacsurgery where sevoflurane preconditioning reduced levels of therenal biomarker cystatin c26 but did not affect creatinine levels,27

postoperative oliguria, or dialysis rates.28 In other organ systems,VAs have been shown to be protective in the heart29,30 andliver.31,32 However, some recent studies also demonstrated a lackof VA-mediated protection, including a lack of cardioprotection innoncardiac surgery33 and renal protection in cardiac surgery.28

Here, the authors are unable to determine the proportion ofpatients receiving VAs for the maintenance of GA, and this is anissue that will require further study.

As the anesthetic decision was not randomized in theretrospective cohort study, the authors are concerned aboutpossible selection bias that could influence the outcome. Inorder to account for this potential confounding, they conductedseparate analyses (not shown) using propensity score meth-ods34 to determine the likelihood of receiving GA, and thefindings were consistent with their main analysis. However,even the use of propensity score methods cannot account forvariables influencing the anesthetic decision that are notcaptured in the dataset, such as factors related to surgeons,anesthesiologists, and institutions as well as vascular anatomy,and this remains a potential source of bias.

Despite the lack of an overall association between GA andAKI in the authors’ study, an interesting post-hoc analysisdemonstrated that the effect of anesthetic technique on the riskof AKI varied by the length of the procedure as indicated byoperative time. Using a model allowing for the effect of GA onAKI to vary with operative time, the authors found a significantassociation between GA and reduced AKI rates in those with amoderate length of procedure (115-155 min), indicating that

there may be a subset of patients in whom anesthetic techniqueaffects the risk of AKI. Further study is necessary to exploreand validate these findings.

In the present study, those receiving a technique other thanGA were combined into 1 group, as the authors mainly wereinterested in evaluating the effects of GA on AKI. Whenseparating the non-GA group into a neuraxial anesthesia groupand an MAC group, they again found no significant associa-tions between anesthetic technique and AKI, although therewas a lack of statistical power to detect a difference among the3 groups. Although the authors recognize that there aredifferences between neuraxial and MAC anesthesia, based ontheir analysis, they felt that combining them into one non-GAgroup was appropriate for the purposes of this study.

In addition to limitations regarding retrospective analyses oflarge medical datasets,35 there are some additional importantlimitations to the ACS NSQIP relevant to this study. The datasetdefines progressive renal insufficiency as an increase in thepostoperative creatinine level of 42 mg/dL although creatininechanges as small as 0.3 mg/dL may constitute clinicallysignificant AKI.36,37 As such, there is likely an underreportingof the total rate of AKI by accounting only for severe creatininechanges following surgery. Many important variables affectingthe risk of AKI are not collected, such as intraoperativehemodynamics,38 nephrotoxic radiocontrast dye, and fenestratedgrafts.39 In addition, conversions from one technique to another(eg, MAC to GA) are not captured. Despite these limitations, the

Table 4. Logistic Regression of Acute Kidney Injury by Anesthetic Technique, American College of Surgeons National Surgical Quality

Improvement Program, 2005-2010

Adjusted Model*

OR 95% CI

General anesthesia 1.00 [0.66, 1.52]

ASA class (ref ¼ ASA 3)ASA 1-2 0.74 [0.30, 1.84]

ASA 4-5 1.50† [1.10, 2.04]

Ruptured aneurysm 2.04† [1.39, 3.00]

eGFR (mL/min/1.73m2) (ref ¼ 460)o30 13.1† [8.46, 20.2]

30-60 2.91† [2.10, 4.04]

Missing 1.86 [0.57, 6.09]

Angina 2.36† [1.21, 4.63]

Rest pain/gangrene 2.84† [1.36, 5.93]

Functionally dependent 1.97† [1.35, 2.87]

Chronic obstructive pulmonary disease 1.33 [0.97, 1.82]

Hematocrit (%) (ref ¼ ≤30)430 1.50 [0.97, 2.33]

Missing 0.80 [0.21, 3.03]

Resident involvement 0.72† [0.53, 0.96]

Intra/postoperative transfusion 5.41† [3.97, 7.39]

Operative time (ref ¼ Medium [115-154 min])Low [≤114 min] 0.59† [0.35, 0.99]

High [≥155 min] 1.88† [1.32, 2.69]

CPT (Ref ¼ Using aorto-aortic tube prosthesis [34800])Using modular bifurcated prosthesis [1 docking limb] (34802) 0.68 [0.45, 1.03]

Using modular bifurcated prosthesis [2 docking limbs] (34803) 0.57* [0.37, 0.89]

Using unibody bifurcated prosthesis (34804) 0.69 [0.37, 1.31]

Using aorto-uniliac or aorto-unifemoral prosthesis (34805) 0.86 [0.49, 1.49]

c-statistic 0.876

Hosmer-Lemeshow p-value 0.681

Abbreviations: ASA, American Society of Anesthesiologists; CI, confidence interval; CPT, Current Procedural Terminology; eGFR, estimated

glomerular filtration rate; OR, odds ratio.

*Multivariable model excludes 26 records with missing values in 1 or more covariates in the model.

†p o 0.05.

ACUTE KIDNEY INJURY IN AORTIC ANEURYSM REPAIR 577

dataset still provides valuable insight of the effects of anesthetictechnique on perioperative AKI.

The authors have demonstrated using a large-scale nationaldataset that, in patients undergoing EVAR, GA is notassociated with the risk of AKI compared to alternativeanesthetic techniques and that the utilization of GA for thisprocedure has been increasing over time. Understanding theclinical implications of anesthetic decisions on perioperative

outcomes is critical as anesthesiologists continue to care for theincreasing number of patients presenting for endovascularmanagement of their AAAs.

ACKNOWLEDGMENT

The authors would like to thank Charles W. Emala, MD forvaluable assistance with manuscript preparation.

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