Article ID: CJ-14-0384
Background: Renal insufficiency is the most frequent complication of surgeries that involve suprarenal aortic cross-clamping. Although some studies have assessed the risk of intraoperative renal ischemia by comparing juxtarenal abdominal aortic aneurysms (AAAs) and infrarenal AAAs, a critical limitation is the difference in these patients’ clinical backgrounds and aneurysmal features. The present study evaluated the effect of suprarenal aortic clamping by comparing a juxtarenal AAA group with a subgroup of infrarenal AAAs (ie, short and/or large neck).
Methods and Results: Among patients who underwent open surgery for AAA, the 2 types of AAA were selected and compared: juxtarenal AAA (JR group: n=35) and infrarenal AAA with short (<15 mm) and/or large (>28 mm) aneurysmal neck that only required infrarenal aortic clamping (SL group: n=26). Postoperative renal function was evaluated using the RIFLE classification. There were no significant differences between groups in baseline characteristics, comorbidities, and intraoperative variables. There were no adverse events leading directly to in-hospital mortality in either group. The rate of postoperative renal insufficiency (estimated glomerular filtration rate decrease ≥–25%) was not significantly different between groups.
Conclusions: The outcomes of the 2 groups were similar, indicating that intraoperative renal ischemia with no specific intraoperative protection would not adversely affect postoperative outcomes.
Postoperative outcomes of patients with juxtarenal abdominal aortic aneurysms (AAAs) have been reported as worse than those of patients with infrarenal AAAs, possibly because juxtarenal AAAs require suprarenal aortic cross-clamping and more extended dissection, which may result in organ ischemia or reperfusion injury.1,2 Among the intraoperative procedural factors, temporary renal ischemia has been assumed to have the most influence on poor outcomes; however, this association is still controversial.3–5
To determine the risk of renal ischemia, some studies retrospectively compared the postoperative outcomes of patients with juxtarenal AAA and those with infrarenal AAA.3,6,7 However, a critical limitation of those studies is that the patients have different clinical backgrounds and intraoperative variables such as operation time or intraoperative blood loss. To exclude confounding factors, we selected infrarenal AAA patients in whom the aneurysmal neck was short and/or large. Such selection has been easy since the emergence of endovascular aneurysm repair (EVAR), because the definition and measurement of short and/or large aneurysmal neck, which were previously ambiguous, became clear with each company’s instructions for use (IFU) and with the development of imaging modalities such as computed tomography (CT).
For the evaluation of renal function after AAA surgery, creatinine level has been the gold standard,8,9 but recent studies have used a standardized system of assessment4,10 known as the RIFLE classification (Risk, Injury, Failure, Loss, and Endstage renal disease), which is useful for analyzing acute kidney injuries.11,12 It is based on the degree of estimated glomerular filtration rate (eGFR) and categorizes renal function according to each 25% change in eGFR. We used this unique classification to reveal the chronological change in renal function.
The objective of the study was to evaluate the risk associated with suprarenal aortic clamping by comparing a juxtarenal AAA group with a new conceptual subgroup of infrarenal AAAs (ie, short and/or large neck).
Among patients who underwent open surgery for AAA, the 2 types of AAA were selected: juxtarenal AAA (JR group: n=35) and infrarenal AAA with short and/or large aneurysmal neck that only required infrarenal aortic clamping (SL group: n=26). Juxtarenal AAA was defined as an aneurysm that involved the infrarenal abdominal aortic segment and extended up to and sometimes included the lower margins of the renal artery origin, requiring suprarenal aortic cross-clamping during open repair of the aneurysm.9 Patients in the JR group underwent surgery between January 2001 and July 2013. For precise evaluation of the aneurysmal neck and to identify the patients who would be categorized in the SL group, we used a database that was available after January 2006, when CT images of 1-mm width were routinely available in our institution. All patients provided informed consent, and this study was approved by the institutional ethics committee.
The aneurysmal neck is defined as the infrarenal aorta with a normal (ie, not dilated) diameter. A “short neck” was defined as a neck length <15 mm, and ‘large neck’ was defined as a neck with a diameter >28 mm.
Demographic data, including age, sex, aneurysmal diameter, and comorbidities, were obtained from the medical records. Ischemic heart disease was defined as a history of myocardial infarction, or previous coronary intervention. Cerebrovascular disease was defined as a history of hemorrhage or infarction accompanied by neurogenic symptoms.
All procedures were performed via a transperitoneal approach. All patients received intravenous heparin before aortic cross-clamping. After a vascular tape was looped around the aorta and renal arteries, we clamped the suprarenal aorta first, then clamped the renal arteries using bulldog arterial clamps. For intraoperative renal protection, we did not use cold renal perfusion in all cases, but rather systemic drugs, such as mannitol, in some cases. If a patient had postoperative oliguria, furosemide was used under the conditions of sufficient volume loading. After proximal anastomosis, we removed the clamps and confirmed pulsation of the renal arteries. If pulsation seemed to be weak, we checked the flow using ultrasonography. Fortunately, we did not encounter any cases requiring immediate re-intervention.
Data on eGFR were obtained at the following time points: 1 day, 3 days, 7 days, and more than 7 days after the operation (within 3 months). The maximum absolute eGFR value was obtained to evaluate the chronological change in renal function. Postoperative renal function was evaluated by reference to the RIFLE classification, which was developed by the Acute Dialysis Quality Initiative and originally used to classify acute renal dysfunction.11 Renal function was also categorized according to every 25% change in eGFR. Renal dysfunction was defined as a decrease in eGFR >25%, and renal improvement was defined as an increase in eGFR >25%. Although the RIFLE classification is basically used in the acute phase (within 7 days of the operation), we also used our modified renal function classification in the chronic phase (after 7 days until 3 months, postoperatively).
Statistical AnalysisIntragroup differences were compared by t-test for continuous variables and chi-square test for categorical variables. Values are reported as mean±standard deviation. Multiple logistic regression analysis was also performed to compare the groups. Kaplan-Meier survival analyses with log-rank and Cox proportional hazard model were used to evaluate the overall survival rate. All tests were 2-sided with statistical significance set at P<0.05.
Baseline patient characteristics, including age, sex, maximal anteroposterior aneurysmal diameter, and preoperative eGFR, are shown in the Table. Patients in the SL group were approximately 3 years older than those in the JR group; however, this difference was not statistically significant (P=0.10). Comorbidities, including hypertension, ischemic heart disease, cerebrovascular disease, diabetes mellitus, dyslipidemia, respiratory failure, smoking (ex- and current), family history of AAA (first-degree relatives), and hostile abdomen, and use of aspirin, β-blockers, and statins are also shown in the Table. There were no significant differences in these variables between the 2 groups.
| Variable | JR group (n=35) | SL group (n=26) | P value |
|---|---|---|---|
| Age (years) | 72.0±7.8 | 75.2±6.9 | 0.10 |
| Male sex (%) | 29 (82) | 21 (80) | 0.83 |
| Aneurysmal diameter (anteroposterior, mm) | 55.1±14.3 | 57.5±7.9 | 0.43 |
| eGFR (ml·min–1·1.73 m–2) | 57.1±21.1 | 54.3±19.7 | 0.60 |
| Comorbidities (%) | |||
| Hypertension | 27 (77) | 19 (73) | 0.71 |
| Ischemic heart disease | 19 (54) | 12 (46) | 0.52 |
| Cerebrovascular disease | 7 (20) | 4 (15) | 0.64 |
| Diabetes mellitus | 9 (25) | 4 (15) | 0.32 |
| Dyslipidemia | 15 (42) | 15 (57) | 0.25 |
| Respiratory failure | 14 (40) | 7 (26) | 0.28 |
| Smoking (ex- or current) | 31 (88) | 22 (84) | 0.65 |
| Family history of AAA | 3 (8) | 2 (7) | 0.90 |
| Hostile abdomen | 7 (20) | 5 (19) | 0.94 |
| Medications (%) | |||
| Aspirin | 12 (34) | 11 (42) | 0.52 |
| β-blocker | 6 (17) | 7 (26) | 0.35 |
| Statin | 17 (48) | 15 (57) | 0.48 |
| Intraoperative variables | |||
| Operation time (min) | 249±60 | 242±54 | 0.63 |
| Intraoperative blood loss (ml) | 1,156±768 | 1,236±496 | 0.64 |
| In-hospital duration after the operation (days) | 17.5±12.7 | 15.8±5.7 | 0.59 |
| Duration of clamping renal arteries (min) | 31.9±9.5 | ||
AAA, abdominal aortic aneurysm; eGFR, estimated glomerular filtration rate; JR, juxtarenal; SL, infrarenal AAA with short (<15 mm) and/or large (>28 mm) aneurysmal neck that only required infrarenal aortic clamping.
Intraoperative variables are shown in the Table. Operation time, intraoperative blood loss and hospitalization after the operation were similar in both groups. In 16 cases, bilateral clamping of the renal arteries was required, and in the other 19 cases, cross-clamping between renal arteries was performed. Duration of renal arterial clamping in the JR group was 31.9±9.5 min.
There was no in-hospital mortality. The difference in overall survival rate between the 2 groups was not statistically significant (P=0.86) (Figure 1). In-hospital postoperative systemic complications in the JR group were as follows: venous rebleeding, 1; occlusion of the ipsilateral renal artery, 1; pneumonia, 1; ileus, 1; brain infarction, 1. The complications in the SL group were as follows: acute arterial thrombosis of lower limb, 1; pneumonia, 2; ileus, 1; increment of chronic heart failure, 1. None of these complications was related directly to patients’ deaths.
Overall survival rates show no statistically significant difference between the 2 groups of abdominal aortic aneurysm (AAA) patients (JR, juxtarenal; SL, infrarenal AAA with short (<15 mm) and/or large (>28 mm) aneurysmal neck that only required infrarenal aortic clamping).
The change in eGFR in both groups is shown in Figure 2. Time points were set as pre-operation, then postoperative day (POD) 1, 3, 7, and after POD 7.
Change in estimated glomerular filtration rate at several time points (preoperative (pre-ope), postoperative day (POD) 1, 3, 7, and after POD 7) in 2 groups of abdominal aortic aneurysm (AAA) patients (JR, juxtarenal; SL, infrarenal AAA with short (<15 mm) and/or large (>28 mm) aneurysmal neck that only required infrarenal aortic clamping).
The distributions of the maximum absolute value of eGFR change in both groups are shown in Figures 3 and 4. In the JR group, renal function improved (the value changed more than 25%) in 9 patients and deteriorated in 10 patients in the acute phase; however, in the chronic phase, it improved and deteriorated in 3 and 5 patients, respectively (Figure 3). Similarly, in the SL group, renal function improved in 7 patients and deteriorated in 4 patients in the acute phase; however, in the chronic phase, it improved and deteriorated in 1 patient each (Figure 4). The number of patients whose renal function deteriorated was not significantly different between the 2 groups, in either the acute (P=0.22) or chronic (P=0.17) phase. The renal function of most of the patients in both groups normalized in the long term. Hemodialysis was temporarily required by 1 patient in the JR group, whose renal function had originally deteriorated (eGFR: ml·min–1·1.73 m–2). Another patient in the JR group whose renal function improved initially finally required hemodialysis 4 years after the operation.
Change in postoperative renal function in the juxtarenal abdominal aortic aneurysm (JR) group of patients categorized according to the RIFLE classification. eGFR, estimated glomerular filtration rate.
Change in postoperative renal function in the SL group of AAA patients. AAA, abdominal aortic aneurysm; eGFR, estimated glomerular filtration rate; SL, infrarenal AAA with short (<15 mm) and/or large (>28 mm) aneurysmal neck that only required infrarenal aortic clamping.
Renal insufficiency is reported to be the most frequent complication after juxtarenal or pararenal AAA repair;2,13 however, it is difficult to evaluate the effect of renal ischemia independently by simply comparing juxtarenal and infrarenal AAAs. Based on our experience, we considered that temporary renal ischemia during the operation itself does not adversely affect postoperative outcomes, given that the procedure is performed uneventfully. Therefore, in order to evaluate the independent risk of renal ischemia, we selected a subgroup of infrarenal AAA patients and matched them against a juxtarenal AAA group.
Subgrouping infrarenal AAAs by short and/or large neck is a new approach to avoiding the bias of different clinical background and aneurysmal features in a comparison of juxtarenal and infrarenal AAAs. The operative strategy used for AAAs has changed drastically since the emergence of EVAR. Preoperative evaluation of CT images, including size planning of the stent graft, is critically important for procedural success of EVAR. “Hostile neck”, a term that has been used ambiguously, is defined by several parameters that have concrete values provided by the IFU: short neck (<15 mm), severe angulation (>60°), large diameter (>28 mm), massive atheroma, and severe calcification. We categorized “short” and “large” neck factors, which would cause the operative procedure to be difficult, as a subgroup, arbitrarily and empirically. Fortunately, the 2 groups were well matched and suitable for comparison.
Interestingly, many studies have reported that all-cause mortality in patients with juxtarenal or pararenal AAAs is not higher than that of patients with infrarenal AAA;3,5,6 however, a few reported higher mortality and morbidity.7 A retrospective study by Chong et al, comparing suprarenal and infrarenal clamping, showed results that were similar to ours; however, their study had a selection bias, as mentioned before, and revealed acceptable low mortality but significant postoperative renal insufficiency.3 Other reports also showed low mortality and technical factors as strong predictors of postoperative renal insufficiency: prolonged operative time, renal ischemic time, clamp position, and left renal vein division.4,14 Contrary to those results, we found that by matching the control group, suprarenal aortic cross-clamping had only a slight adverse effect on postoperative renal function.
For renal protection, we did not routinely use any special medications, such as n-acetylcysteine, or cold renal perfusion, because there is no definite evidence. In addition, we assumed that cold perfusion may prolong operation time and increase the risk of arterial dissection or thrombosis. Various strategies of renal protection have been attempted, but their effects are controversial.7,15 Most institutions use some of the abovementioned renal protection methods depending on the circumstances, but not routinely.4,6,13 Based on our results, we will continue our renal protection strategy, including no use of renal perfusion.
An interesting finding was the temporary improvement in postoperative renal function that occurred in approximately 25% of the patients. We assume that this unique phenomenon was related to increased renal arterial flow. Postoperative hydration should directly affect renal function. Another hypothesis is the effect of aortic volume change after aneurysm repair. We previously simulated the change in renal flow after aneurysm repair with an electronic circuit model.16 After the diameter of the infrarenal aorta aneurysm changed from 5 cm to 2 cm, renal flow theoretically increases approximately 10% (the formula and details of the model are not shown).
Study LimitationsFirst of all, this was a retrospective study. Secondly, it included a relatively small number of patients, which may be insufficient for evaluating postoperative complications in detail. Thirdly, for a few patients in the JR group, suprarenal aortic clamping was required because of severe calcification and massive neck atheroma rather than because of extension of the aneurysm to the renal artery. It might be inappropriate to use the term “juxtarenal” for these patients.17 Finally, the RIFLE classification is generally used for evaluating renal insufficiency in the acute phase, so the utilization of the classification in the chronic phase may be inappropriate. The follow-up period of 3 months we set for evaluating operation-related renal insufficiency was defined arbitrarily. A greater number of patients and more details such as physiological data acquired from ultrasound echogram scans of renal arterial flow are necessary in further studies.
In conclusion, subgrouping short and/or large neck infrarenal AAAs, as we did in the current study, is a new concept, particularly in this endovascular era, and the clinical characteristics and aneurysmal features are comparable enough to those of juxtarenal AAA to evaluate the independent effect of intraoperative renal ischemia. We compared mortality, perioperative complications, and renal insufficiency between these 2 groups, and the outcomes were similar. Our results suggest that suprarenal aortic clamping with no specific intraoperative renal protection does not adversely affect postoperative outcomes.
All authors declare no conflicts of interest.
