Annals of Vascular Surgery
Volume 22, Issue 4 , Pages 513-519, July 2008

Comparative Analysis of Renal Function after Treatment of Infrarenal Abdominal Aortic Aneurysms with a Suprarenal Fixation Device as Opposed to Open Surgery

Vascular Surgery Department, Dr. Peset Hospital, Valencia, Spain

published online 27 May 2008.

Article Outline

We analyzed the repercussions on renal function between suprarenal endograft fixation and open surgery in the treatment of infrarenal abdominal aortic aneurysms (IAAAs) and determined the influential factors. Between 1999 and 2005, 59 IAAAs were treated with elective OS and 56 with SEF. The serum creatinine (Cr) level and its clearance were determined before the procedure, in the intensive care unit (ICU), on discharge, and after 1, 6, 12, and 24 months. A deterioration in renal function was considered to be a >30% increase in Cr or a Cr >2 mg/dL. A univariate statistical analysis and a logistical regression analysis were carried out to determine the predictive factors for repercussions on renal function. There were no statistically significant differences in the rate of renal exacerbation between the groups either on discharge (p = 0.52) or after 1 month (p = 0.483), 6 months (p = 0.451), 12 months (p = 0.457), and 24 months (p = 0.682). The only significant difference was that detected in the ICU (p = 0.033). Diabetes mellitus, time spent in the ICU, postoperative intubation time, intraoperative transfusion, and transfusion in the ICU were factors that influenced the deterioration of renal function in the univariate analysis. The only significant factor in the multivariate analysis was the need for transfusion in the ICU. Exacerbation of renal function occurred in both groups independently of treatment type. In the immediate postoperative period, hemodynamic deterioration is more frequent in the open surgery group. Renal exacerbation tended to disappear in both groups during follow-up.

 

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Introduction 

Since the first description of endovascular repair of an infrarenal abdominal aortic aneurysm (IAAA) in 1991 by Parodi et al.,1 the use of this technique as a treatment option has spread in such a way that it is currently more common than open surgery (OS). Nevertheless, despite the enthusiasm it has generated, approximately one-third of patients continue to be considered unsuitable for endograft. The limitations for endovascular treatment are determined by IAAA anatomy, including inadequate proximal fixation of the graft and the small size of the iliac.2 Although there have been important advances in release devices, as well as in the endograft itself, the excessive angle on the proximal neck and its length are still limiting factors.

Despite the fact that recent clinical trials have suggested that the risks associated with endovascular repair of IAAA are less than those for OS, there is still great concern regarding durability.3, 4 The incidence of endograft migration and/or endoleak is >30% in some cases,5, 6 and these are often responsible for the continued risk of aneurysm rupture that occurs in >1% annually.5, 7 Suprarenal fixation with uncovered stent has been proposed as a method that could improve proximal fixation, allowing the repair of necks with complex morphology or that are short, thereby reducing the risk of later complications (migration, endoleak formation, and rupture of the aneurysm).

Fixing the endograft to the suprarenal aorta requires the insertion of a transrenal stent. It has been implied that the effect of the stent clamps passing through the ostium of the renal arteries is a factor in potential renal function deterioration. At the same time, patients who undergo this type of treatment are already at high risk of developing renal complications given that they are of advanced age and therefore have associated increased risk factors and comorbidity. Also, many of them are diabetics or have a history of previous renal insufficiency (RI), which carries a greater risk. Therefore, deterioration in renal function after endovascular repair of IAAA can reach >20%, and the causes are normally multifactoral, including mechanical causes, the administration of nephrotoxic contrast agents, and renal atheroembolism.8

With regard to OS, RI is the third most common complication after treatment,9 and its presence is a strong predictor of poor life expectancy.10 The only independent predictive factor that has been related to RI after surgical treatment of an IAAA is previous RI.11 Despite precaution in preoperative administration of intravenous contrast, intraoperative administration of diuretic agents, and special care with the placement and timing of the aortic clamp, the incidence of postoperative RI is still significant at about 6%, with a mortality rate of 28%.9, 12 The deterioration in renal function in OS of the IAAA has been attributed to atheroembolism, renal ischemia, intraoperative hypertension in the context of a hemodynamic deterioration, and technical factors related to renal arteries.13, 14

We analyzed the repercussions of suprarenal endograft fixation (SEF) on renal function compared with OS in the treatment of IAAA and determined the influential factors.

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Methods 

Between 1999 and 2005, 160 IAAAs were treated in our center, of which 59 were treated with elective OS and 101 endovascularly, 59 of the latter (58.4%) with Zenith® (Cook, Bloomington, IN) SEF. Demographic data of the patients were collected retrospectively in both groups and are shown in Table I. One hundred percent of the patients were male. In the SEF group, three patients had terminal RI with periodic hemodialysis and were therefore excluded from the study.

Table I. Demographic data for SEF and OS groups
SEF group (n = 56)OS group (n = 59)p
Age (years)72 (range 51-83)66 (range 56-81)0.385
Smoking21.4% (n = 12)34% (n = 20)0.279
Diabetes mellitus7.1% (n = 4)11.8% (n = 7)0.349
Arterial hypertension73.2% (n = 41)72.8% (n = 43)0.600
Dyslipidemia32.1% (n = 18)25.4% (n = 15)0.269
Hyperuricemia10.7% (n = 6)8.4% (n = 5)0.519
Ischemic heart disease35.7% (n = 20)28.8% (n = 17)0.468
Coronary surgery/stent8.9% (n = 5)10.2% (n = 6)0.537
Other heart diseases21.4% (n = 12)8.4% (n = 5)0.044
Previous CVA12.5% (n = 7)6.7% (n = 4)0.235
COPD26.7% (n = 15)18.6% (n = 11)0.206
GDU10.7% (n = 6)13.5% (n = 8)0.429
Previous RI12.5% (n = 7)6.7% (n = 4)0.235
Single kidney7.1% (n = 4)5.1% (n = 3)0.471
ASA IV76.7% (n = 43)37.2% (n = 22)0.001

CVA, cerebrovascular accident; COPD, chronic obstructive pulmonary disease; GDU, gastroduodenal ulcer.

The suprarenal component of the Zenith endograft is made up of 0.018-inch stainless steel wires; the uncovered part is 26 mm long and is made up of 10 or 12 supports (10 supports for diameters <28 mm 12 supports for diameters ≥28 mm). Each support ends distally in a 5 cm- or 0.093 inch-long hook. The suprarenal component is fixed to the polyester graft with a monofilament stitch.

Treatment techniques for IAAA through SEF or OS have already been described in other studies.15, 16 The study of renal function in both groups included establishing the concentration of serum creatinine (Cr) prior to treatment, in the intensive care unit (ICU), on discharge, and after 1-, 6-, 12-, and 24-month follow-up. A study of the permeability of the renal arteries as well as the detection of renal hemorrhage was carried out through computed tomography (CT) on discharge and after 1, 6, 12, and 24 months.

To adjust the Cr figures to the age and weight of the patients, Cr clearing (CrC) was calculated using the Cockgraft-Gault formula: (140 − age) x weight/Cr x 72.17, 18, 19, 20 Exacerbation of renal function was defined in our study as an increase >30% of Cr prior to treatment or a value of Cr >2 mg/dL. Permeability of the renal arteries was defined as continuity of contrast flow in the CT between the aorta and the main renal artery. Data were also collected on secondary treatment carried out during the follow-up related to renal problems as well as the need for hemodialysis in any of the patients.

Regarding statistical analysis, dispersion measurements were expressed as the mean ± standard deviation, and those variables with extreme values that could compromise the mean (amount of bleeding and postoperative intubation time) were expressed as the median. Contingency tables with the χ2 test and the difference of proportions test compared category and nominal variables of two independent samples, respectively; and the Mann-Whitney U-test was used to analyze nonparametric variables. Analysis of variance was applied to compare the means or medians. For factors predictive of the effects on renal function, a univariate analysis was conducted using the χ2 test and the Fisher test for category variables and the Mann-Whitney U-test for continuous variables. Later, a multivariate analysis was carried out using logistic regression, after cataloguing the variables that were significant in the univariate study, in order to determine those variables with more specific weight as risk factors for renal function deterioration. All results were analyzed using SPSS statistical software (SPSS, Inc., Chicago, IL).

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Results 

The two groups were compared in advance; there were no significant statistical differences in age, risk factors, or prevalence of comorbidities except for the prevalence of other, nonischemic heart diseases (p = 0.044) and the anesthetic risk value (greater prevalence of American Society of Anesthesiologists [ASA] IV in the SEF group with p = 0.001) (Table I). The mean follow-up was 20 ± 15.7 months for the SEF group and 36.2 ± 17.7 months for the OS group. There were 13 follow-up losses (11.3%), all of which were from the SEF group and 10 of which were patients from other health-care areas who preferred to carry out follow-up tests in their own hospitals, as well as those we were not able to contact by telephone; the other three patients refused the CT tests and analysis. Mean time in surgery was 190 ± 51 min in the SEF group and 204 ± 59 min in the OS group, and there were no significant statistical differences between the groups (p = 0.193). The mean contrast dose used in the SEF group was 222 ± 82 mL. There was no association between the amount of contrast used and the degree of renal function exacerbation in the SEF group. The mean aortic clamp time was 61.3 ± 21.2 min in the OS group. The suprarenal clamp was only necessary in two cases (3.3%). Suprarenal aortic clamping did not influence the degree of renal function exacerbation. The median volume of bleeding was 250 mL for the SEF group and 1,000 mL for the OS group, which is a statistically significant difference (p = 0.01). Intraoperative blood transfusion was necessary in 28.5% of cases in the SEF group (n = 16), while in the OS group it was needed in 81.3% of cases (n = 48) (p < 0.001). The mean packed red blood cells transfused in surgery in the SEF group was 0.7 and that in the OS group, 2.8 (p < 0.001). The median postoperative intubation time was 0 hr in the SEF group (most of the patients who underwent general anesthetic were extubated in the operating theater), while in the OS group it was 5 hr (p = 0.097). The mean stay in the ICU was 1.2 ± 0.7 days in the SEF group and 3.4 ± 2.8 days in the OS group (p = 0.018). A blood transfusion in the ICU was necessary in 23.2% of cases in the SEF group (n = 13), while in the OS group it was necessary in 23.7% of cases (n = 14) (p = 0.562). The mean packed red blood cells transfused in surgery in the SEF group was 0.7 and that in the OS group, 0.8 (p = 0.665). The mean stay in hospital was 6.9 ± 3.2 days in the SEF group and 10.5 ± 8 days in the OS group (p = 0.024). Postoperative morbidity was 1.7% in the SEF group (n = 1) and 1.6% in the OS group (n = 1) (p = 0.634).

Table II shows the mean values for Cr and CrC. Comparing Cr and CrC in the ICU and after 1, 6, 12, and 24 months with respect to the preoperative Cr and CrC in each group, there were no significant statistical differences, except in the Cr and CrC figures in the ICU of the OS group (p < 0.05). Despite the fact that there were no differences in the SEF group, we observed an increasing tendency in Cr and a decreasing tendency in CrC in the follow-up, as shown in Figure 1.

Table II. Cr and CrC values in follow-up
SEF groupOS groupp between groups
CrpCrCpCrCpCrCppCr*pCrC*
Preop1.32 ± 0.46 62.8 ± 21.5 1.10 ± 0.37 77.3 ± 24.8 0.0080.002
ICU1.27 ± 0.43>0.0564.6 ± 21.1>0.051.26 ± 0.60<0.0572.7 ± 27.4<0.050.9280.092
Discharge1.32 ± 0.45>0.0562.3 ± 20.6>0.051.14 ± 0.42>0.0575.2 ± 24.4>0.050.0440.004
1 month1.30 ± 0.45>0.0562.5 ± 19.6>0.051.14 ± 0.41>0.0574.6 ± 22.5>0.050.0650.004
6 months1.32 ± 0.46>0.0562 ± 19>0.051.13 ± 0.38>0.0574.4 ± 21.8>0.050.0300.003
12 months1.35 ± 0.56>0.0560.9 ± 20>0.051.15 ± 0.40>0.0573.6 ± 21.9>0.050.0320.003
24 months1.37 ± 0.53>0.0560.8 ± 19.8>0.051.18 ± 0.45>0.0573.7 ± 23.5>0.050.0960.013

p, comparison with preoperative values; pCr*, comparison of Cr between groups; pCrC*, comparison of CrC between groups.

Analyzing the deterioration of renal function (increase >30% in Cr or Cr >2 mg/dL) which happened in the ICU in two patients in the SEF group (3.6%) and in nine patients of the OS group (15.3%), there was a significant statistical difference between the groups (p = 0.033). There were no statistically significant differences in the rate of renal exacerbation between the groups either on discharge (SEF 5.4% [n = 3], OS 6.9% [n = 4]; p = 0.52) or after 1 month (SEF 5.4% [n = 3], OS 3.4% [n = 2]; p = 0.483), 6 months (SEF 3.9% [n = 2], OS 1.7% [n = 1]; p = 0.451), 12 months (SEF 3.9% [n = 2], OS 1.8% [n = 1]; p = 0.457), and 24 months (SEF 2.7% [n = 1], OS 2.1% [n = 1]; p = 0.682) (Table III). In those patients with renal function exacerbation, hemodialysis was not required. No cases of renal artery stenosis or occlusion were found in the follow-up, nor were there any signs of renal hemorrhage in the CT or the need for a second intervention in relation to renal problems.

Table III. Renal exacerbation rate in the two groups
Renal exacerbation rate
ICUDischarge1 month6 months12 months24 months
OS group15.3% (n = 9/59)6.9% (n = 4/58)3.4% (n = 2/58)1.7% (n = 1/58)1.8% (n = 1/56)2.1% (n = 1/47)
SEF group3.6% (n = 2/56)5.4% (n = 3/56)5.4% (n = 3/56)3.9% (n = 2/51)3.9% (n = 2/51)2.7% (n = 1/36)
p0.0330.520.4830.4510.4570.682

Preoperative RI has been related to a greater risk of deterioration in renal function following treatment.11 To investigate this association in our sample, we analyzed the subgroup of patients with previous RI (Cr >2 mg/dL). No patients in the SEF group developed renal function exacerbation, while in the OS group this deterioration occurred in one patient (25%). This difference was not statistically significant (p = 0.364).

To study those factors predictive of renal function exacerbation in the ICU in the OS group, a univariate analysis was carried out with the variable categories prior RI, smoking, diabetes mellitus (DM), previous ischemic heart disease, other heart diseases, single-kidney patients, anesthetic risk, intraoperative associated surgery, intraoperative autologous blood transfusion, need for intraoperative transfusion, and need for postoperative transfusion and with the continuous variables age, length of operation, volume of bleeding, postoperative intubation time, packed red blood cells transfused in surgery and the ICU, and length of stay in the ICU. The presence of DM (p = 0.01), mean stay in the ICU (p = 0.01), mean postoperative intubation time (p = 0.01), need for intraoperative transfusion (p = 0.021), and need for transfusion in the ICU (p = 0.011) were factors that influenced the deterioration in renal function in the univariate analysis. Later, a multivariate analysis was carried out through logistic regression with those variables that were significant in the univariate study, to determine which variables carried more weight in relation to the risk of developing renal function exacerbation; and a positive association with need for transfusion in the ICU was obtained (odds ratio [OR] = 4.24, 95% confidence interval [CI] 1.09-16.36).

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Discussion 

Renal function exacerbation following IAAA treatment, whether through open surgery or an endovascular method, is a frequent complication; some studies show it to be the third most common complication in both treatment alternatives,9, 21 and it is also a factor in poor survival prognoses.10 The cause of this deterioration is usually multifactorial; in OS the most common factors are renal atheroembolism, renal ischemia after aortic clamping, hemodynamic deterioration, and iatrogenic lesions in renal arteries (such as dissection or occlusion). With endovascular treatment, radiological contrast, which is potentially nephrotoxic, should be included. Also, in the case of SEF, suprarenal fixation increases renal morbidity,22 although some studies have shown the safety of this type of endograft.23, 24, 25, 26, 27

Despite there being no clear definition regarding what constitutes an exacerbation of renal function, most studies that have looked at this aspect measure the Cr value as it is a parameter that is easy to obtain, increasing the sensitivity through definition of the aforementioned deterioration as a 30% increase of the base figure or an increase of >2 mg/dL.28, 29, 30 Also, CrC was calculated using the Cockgraft-Gault formula, obtaining a parameter that better evaluates renal function since it adjusts Cr to the weight and age of each patient.

When analyzing the mean of the Cr and CrC figures in our preoperative series and comparing them in the two groups, there were statistically significant differences: The SEF group had significantly higher figures, which can be attributed to the fact that this group is of a more advanced age and has an associated comorbidity rate, and they had also undergone preoperative studies which used nephrotoxic contrast (such as CT and arteriography) in a short space of time. Nevertheless, if we compare the Cr and CrC figures for each group in the ICU, on discharge, and after 1, 6, 12, and 24 months compared to the preoperative values, we can see that there were no statistically significant differences except for the OS group in the ICU (p < 0.05). Nevertheless, in the SEF group there was a progressive increase in the mean values for Cr in the follow-up and a decrease in CrC values, probably due to the fact that these patients had follow-up treatment using CT with contrast during the first 2 years with a mean of five or six studies in 2 years, which could contribute to this slight progressive deterioration in renal function, a fact that other studies corroborate (Fig. 1).30, 31 Therefore, it has been proposed that the frequency of these tests be reduced, especially during the first year, or that they be substituted with noninvasive diagnostic techniques such as the echo-Doppler test. Another hypothesis that has been suggested to explain this progressive increase in Cr figures is continued damage to the renal arteries caused by the suprarenal fixation stent.30 Nevertheless, the long-term effect of arterial flow through the transrenal stent is unknown, although it has been investigated on an experimental level, which showed an increase in turbulence in the area of the stent but no decrease in flow.32

Our study identified a strong association between the need for transfusion in the ICU and deterioration in renal function in the ICU of those patients who underwent OS. This need for transfusion in the ICU is indicative of the hemodynamic deterioration suffered by these patients during surgery, mainly due to surgical bleeding, with the need for transfusion both in the operating room and later in the ICU and an inotropic support. In fact, in the OS group greater intraoperative bleeding (median 1,000 mL) was observed. Therefore, renal function in these patients must be intensively observed and the appropriate treatment adopted to avoid severe renal failure. Early detection of signs of hypoperfusion is important, including hypertension and levels of lactate in blood (useful above all in patients who do not have initial hypertension but already have tissue hypoxia). Patients should be monitored closely both during and after surgery in order to maintain a mean blood pressure of ≥65 mm Hg, a central venous pressure between 8 and 12, and a urine deficit of 0.5-1 mL/kg/hr. To achieve this, adequate fluid replacement and/or inotropic support, if necessary, must be carried out to maintain adequate gas exchange (mixed venous saturation ≥70%) and transfusion of compact red blood cells to maintain adequate hemoglobin levels in the blood.

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Conclusions 

Exacerbation of renal function occurred in both groups independently of treatment type. In the immediate postoperative period, this deterioration was most frequent in the OS group, probably related to the hemodynamic deterioration. In follow-up, this deterioration tended to disappear in both groups, although the Cr figures showed a constant increase in the SEF group, probably due to the repeated diagnostic tests that use contrast and the effect of the suprarenal fixation stent. Multicenter randomized prospective studies would be needed to confirm this hypothesis.

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PII: S0890-5096(08)00096-4

doi:10.1016/j.avsg.2008.02.013

Annals of Vascular Surgery
Volume 22, Issue 4 , Pages 513-519, July 2008

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