The impact of obesity on perioperative and postoperative outcomes after elective endovascular abdominal aortic aneurysm repair

Abstract

Background

Obesity is a common and growing health problem in vascular surgery patients, as it is in all patient groups. Evidence regarding body mass index (BMI) on endovascular aneurysm repair (EVAR) outcomes is not clear in the literature. We aimed to determine the impact of obesity on perioperative and midterm outcomes of elective EVAR between obese and non-obese patients.

Methods

Under a retrospective study design, a total of 120 patients (109 males, 11 females, mean age: 74.45 ± 8.59 (53–92 years)) undergoing elective EVAR between June 2012 and May 2020 were reviewed. Patients were stratified into two groups: obese (defined as a body mass index (BMI) ≥ 30 kg/m²) and non-obese (mean BMI < 30 kg/m² (32.25 ± 1.07 kg/m² vs 25.85 ± 2.69 kg/m²)).

Results

Of the 120 patients included in the study, 81 (67.5%) were defined as “nonobese,” while 39 (32.5%) were obese. The mean BMI of the study group was 27.93 ± 3.78 kg/m². In obese patients, the procedure time, fluoroscopy time, and dose area product (DAP) values were longer than those of non-obese patients: 89.74 ± 20.54 vs 79.69 ± 28.77 min (p = 0.035), 33.23 ± 10.14 vs 38.17 ± 8.61 min (p = 0.01) and 133.69 ± 58.17 vs 232.56 ± 51.87 Gy.cm² (p < 0.001). Although there was no difference in sac shrinkage at 12-month follow-up, there was a significant decrease at 6-month follow-up in both groups (p = 0.017). Endoleak occurred in 17.9% (n = 7) of the obese group versus 11.1% (n = 9) of the non-obese group (p = 0.302). Iliac branch occlusion developed in four patients, 3 (3.7%) in the non-obese group and 1 (2.6%) in the obese group (p = 0.608). The all-cause mortality rate was slightly higher in the obese group; however, it did not differ between the groups (p = 0.463).

Conclusion

In addition to the longer procedure times, fluoroscopy times, and DAP values in obese patients, regardless of obesity, significant sac shrinkage in the first 6 months of follow-up was observed in both groups. No difference was documented with regards to mortality or morbidity following EVAR.

Keywords

Abdominal aortic aneurysm obesity endovascular aneurysm repair morbidity

Introduction

Obesity, which is accepted as a body mass index (BMI) > 30 kg/m², has become a growing health problem, especially in the developed countries. According to Center for Disease Control data in 2017, adult obesity in the US reached an all-time high of 38.9%, and it is predicted to reach even higher rates in 2030.¹

The literature suggests that general anesthesia may have more adverse effects on respiratory function in obese patients than non-obese patients and increased cardiovascular risk. Therefore, anesthesia and operation time should be minimized in this patient group.^2,3 Especially in morbidly obese patients (BMI > 40 kg/m²), increased morbidity such as respiratory problems and wound problems have been demonstrated in addition to increased procedure times and length of stay in vascular surgery.^4–6

Conventional abdominal aortic aneurysm (AAA) repair in obese patients poses serious difficulties that prevent access to the surgical field. Endovascular aneurysm repair (EVAR) has become the preferred option, especially for obese patients, due to its advantages, such as less invasiveness, short procedure and anesthesia times, and reduced postoperative morbidity. The results of open aortic repair (OAR) and EVAR have been reported in the most significant studies in the literature. Some studies reported that BMI is an independent risk factor for postoperative morbidity in cardiac, renal, and wound complications, while others found no association, although obesity was associated with reduced mortality.^7–13 This study investigates the influence of obesity in terms of mortality and morbidity for patients undergoing EVAR.

Material and Method

Under a retrospective study design in line with the ethical standards of the institutional research committee (Protocol number: 2019.09.01.09) and the 1964 Helsinki declaration, from June 2012 to May 2020, records of a total of 120 patients (109 male, 11 female, mean age: 74.45 ± 8.59 (53–92 years)) who underwent elective EVAR were reviewed, and redo cases were excluded. Patients with the lack of preoperative height, weight or BMI data, underweight patients (BMI < 18.5) and ruptured AAA cases were not included in the study. An aneurysm diameter of > 5.5 cm, enlargement of the sac > 1 cm/year, or symptomatic AAA were the indications for repair. Body mass index is calculated as a person’s weight in kilograms divided by height in meters squared. According to the five classifications for BMI used by the National Institute of Health (NIH) and the World Health Organization (WHO), obesity is defined as BMI ≥ 30 kg/m².¹⁴

Six different types of grafts, including Endurant or Endurant II (Medtronic, Minneapolis, MN, USA), Gore Excluder (Gore Medical, Flagstaff, AZ, USA), Anaconda (Vascutek; Inchinnan, Scotland, UK), Endologix AFX (Endologix, Irvine, CA, USA), Ovation (TriVascular; Santa Rosa, CA, USA), and E–vita (JOTEC GmbH; Hechingen, Germany), were used in this period. Two cardiac surgeons did all procedures with 10 years of experience in the angiographic suite (GE Healthcare, INNOVA 540) under general or regional anesthesia. Fluoroscopy times and radiation doses were recorded in all patients. Radiation was measured as a dose area product (DAP) and recorded in grays per centimeters square (Gy.cm²). While the common femoral artery was surgically exposed for access in most cases (93.4%, n = 112), the percutaneous technique was used in a minority of the cases (6.6%, n = 8). A closure device (ProGlide Suture-mediated, Abbot, USA) was used in all patients who underwent percutaneous intervention. Following our standard protocol in the elective EVAR procedure, dual antiplatelet (aspirin and clopidogrel) administration, which started on the day of the procedure, was continued as a single clopidogrel treatment after the first month. The patients who were followed up for at least 2 days postoperatively were discharged as soon as possible, after the second day after the graft integrity was evaluated with anterior-posterior abdominal radiography. The postoperative data were collected at the follow-up visits at 30 days, 6 months, 1 year ,and annually thereafter. While computed tomography angiography (CTA) scan was obtained at the 6 and 12-month follow-ups, routine radiography was performed at all follow-up visits.

All preoperative data and in-hospital and postoperative parameters were compared within two groups (BMI < 30 and BMI ≥ 30 kg/m²). Besides demographic data such as age, gender, and body mass index, anatomical data such as aneurysm diameter and preoperative serum urea, and creatinine and hematocrit levels were recorded. Preoperative comorbidities were coronary artery disease (CAD), chronic obstructive pulmonary disease (COPD), congestive heart failure (CHF), renal failure (defined as serum creatinine ≥ 1.5 mg/dL), peripheral vascular disease (PVD, defined with an anklebrachial index < 0.9 and symptoms of claudication), diabetes mellitus (DM), hypertension (HT), stroke/TIA, and smoking history. Perioperative and in-hospital parameters were as follows: operation time, amount of contrast, blood transfusion, length of stay, postoperative serum levels of urea, creatinine, and hematocrit. Postoperative complications such as myocardial infarction, in-hospital mortality, renal failure (defined as an increase in serum creatinine > 1.5 mg/dL), stroke, limb occlusion, endoleak, wound infection, and deep venous thrombosis were recorded. All-cause mortality, sac shrinkage, endoleak, and reintervention were evaluated in the long-term period.

Statistical Analysis

Normality assumption was investigated with the KolmogorovSmirnov test. Independent samples t was used to analyze numerical variables with normal distribution, while the Mann–Whitney U test was used otherwise. Descriptive statistics were presented as mean ± standard deviation or median, interquartile range, and minimum-maximum values, as appropriate. Categorical data were summarized with frequency and percentages, and Pearson chi-square or Fisher’s exact test was used according to the expected count. Repeated measures analysis of variance was used to compare parameters measured twice between groups. Life tables and KaplanMeier survival analysis analyzed all-cause mortality, and the log-rank test was used to compare groups. Statistical analyses were performed with IBM SPSS v.22, and a p-value of ≤ 0.05 was considered a statistical significance level.

Results

While 109 (90.8%) male patients constituted the majority in the study, only 11 (9.1%) were female. Of the 120 patients included in the study, 81 (67.5%) were “non-obese,” while 39 (32.5%) were “obese.” The mean BMI of the study group was 27.93 ± 3.78 kg/m²: 25.85 ± 2.69 kg/m² in the non-obese group versus 32.25 ± 1.07 kg/m² in the obese group. Baseline characteristics of the two groups are shown in Table 1. No difference was found between the two groups regarding age, gender, HT, CAD, CHF, COPD, preoperative renal failure, preoperative serum urea, serum creatinine, and hematocrit values. We found significant differences in DM, AF, stroke/TIA, and PVD between groups. While DM, AF, and stroke/TIA were more common in the obese group, PVD was more common in the non-obese group.

Table 1.

Baseline characteristics of patients with BMI < 30 or ≥ 30 kg/m².

	All (n = 120)	BMI < 30 kg/m² (n = 81)Non-obese	BMI ≥ 30 kg/m² (n = 39)Obese	p value
Demographics
Age, yr	74.45 ± 8.59	73.91 ± 9.38	75.56 ± 6.64	0.270
Male gender, n (%)	109 (90.8)	74 (91.4)	35 (89.7)	0.774
BMI, kg/m²	27.93±3.78	25.85±2.69	32.25±1.07	< 0.001
Smoking, n (%)	70 (58.33)	50 (61.7)	20 (51.3)	0.277
Hypertension, n (%)	99 (82.5)	67 (82.7)	32 (82.1)	0.928
DM, n (%)	55 (45.83)	32 (39.5)	23 (59.0)	0.045
COPD, n (%)	47 (39.16)	36 (44.4)	11 (28.2)	0.088
PVD, n (%)	26 (21.66)	23 (28.4)	3 (7.7)	0.010
CHF, n (%)	24 (20.0)	13 (16.0)	11 (28.2)	0.119
CAD, n (%)	74 (61.66)	51 (63.0)	23 (59.0)	0.674
Stroke or TIA, n (%)	9 (7.5)	2 (2.5)	7 (17.9)	0.005
Malignancies, n (%)	23 (19.16)	12 (14.8)	11 (28.2)	0.081

BMI, body mass index; DM, diabetes mellitus; COPD, chronic obstructive pulmonary disease; PVD, peripheral vascular disease; CHF, congestive heart failure; CAD, coronary artery disease; TIA, transient ischemic attack; AF, atrial fibrillation.

Continuous data are presented as means ± standard deviation; categorical data are given as counts (percentages).

Aneurysm characteristics and perioperative outcomes are shown in Table 2. Mean aneurysm diameter, operation time, fluoroscopy time, DAP values, and used contrast volume were 6.44 ± 1.1 cm, 82.95 ± 26.71 min, 34.84 ± 9.91, 165.82 ± 72.78, and 95.04 ± 13.24 mL, respectively. While there was no difference between the groups in terms of aneurysm diameter, amount of contrast, blood transfusion and type of anesthesia, procedure, and fluoroscopy times, and DAP values of obese patients were significantly higher. Radiation dose was significantly higher among obese patients compared to non-obese patients (232.56 ± 51.87 vs 133.69 ± 58.17 Gy.cm². p).All devices were successfully placed without the need for open surgery. Majority of the patients in both groups, 55 (67.9%) in the non-obese group and 23 (59%) in the obese group, were operated on with sedation support under epidural anesthesia.

Table 2.

Aneurysm characteristics and perioperative outcomes of patients with BMI < 30 or ≥ 30 kg/m².

	All (n = 120)	BMI < 30 kg/m² (n = 81)Non-obese	BMI ≥ 30 kg/m² (n = 39)Obese	p value
AAA diameter, cm^*	6.44 ± 1.1	6.61 ± 1.15	6.11 ± 0.93	0.019
Anesthesia, n (%)Epidural General	—	65 (80.2%) 10 (12.3%) 6 (7.4%)	26 (66.7%) 10 (25.6%) 3 (7.7%)	0.180
Operation time, minute	82.95 ± 26.71	79.69 ± 28.77 [40–150]	89.74 ± 20.54 [45–130]	0.035
Fluoroscopy time	34.84 ± 9.91	33.23 ± 10.14	38.17 ± 8.61	0.01
DAP, Gy.cm²	165.82 ± 72.78	133.69 ± 58.17	232.56 ± 51.87	0.001
PRBC, units012	—	65 (80.2%) 10 (12.3%) 6 (7.4%)	26 (66.7%) 10 (25.6%) 3 (7.7%)	0.180
Contrast used, mL	95.04 ± 13.24	95.18 ± 13.40 [80–140]	94.74 ± 13.07 [75–135]	0.991

AAA, abdominal aortic aneurysm; BMI, body mass index; DAP, dose area product; PRBC, packed red blood cells. 

Continuous data are presented as means ± standard deviation; categorical data are given as counts (percentages).

Describes the maximal diameter of AAA.

The mean hospital length of stay was 4.05 ± 1.67 days for all of the patients. Our standard protocol for selective EVAR procedures includes 1 day of preoperative assessment, 1 day of postoperative intensive care unit (ICU) follow-up, and 1 day of clinical follow-up. There was no significant difference between the two groups regarding postoperative in-hospital outcomes and follow-up results, except for the 6-month shrinkage of the sac. Table 3 Aneurysm diameter change amount over time differs in groups (p = 0.017). According to the pairwise comparisons for the interaction effect, there was a significant difference between groups in terms of the change between pre-op and 6 months (p = 0.002), while there was no significant difference between pre-op and 12 months (p = 0.073), and six months and 12 months (p = 0.331) (see Figure 1). In four patients, three in the non-obese group and one in the obese group, who received postoperative routine dual antiplatelet therapy, iliac branch occlusion developed during their hospitalization. Limb occlusion was observed in the completion imaging during the procedure in three patients and on the first postoperative day in the other patient. While the common iliac artery was stented after thrombectomy in two patients with a stenotic iliac lesion and anatomical angulation at the baseline, femoro-femoral bypass was performed in the other two patients who could not undergo thrombectomy or thrombolysis. Re-intervention was performed for femoral artery repair due to bleeding during follow-up in one patient who used a closure device. All wound complications seen after EVAR were superficial, except for one deep incisional surgical site infection in the obese group requiring re-hospitalization. The wound was primarily sutured in this patient after 10 days of vacuum-assisted wound closure (VAC) treatment. Non-fatal myocardial infarction was observed on the postoperative 14th day in one patient in the non-obese group and postoperative first month in one patient in the obese group.

Table 3.

In-hospital and long-term outcomes of patients during follow-up.

	All (n = 120)	BMI < 30 kg/m² (n = 81)Non-obese	BMI ≥ 30 kg/m² (n = 39)Obese	p value
Length of stay, day	4.05 ± 1.67	3.98 ± 1.63 [3–10]	4.17 ± 1.77 [3–9]	0.803
AAA diameter, cm* Sac shrinkage 6 m Sac shrinkage 12 m	6.44 ± 1.1	6.61 ± 1.15 6.26 ± 1.09^# 6.18 ± 1.07	6.11 ± 0.93 5.95 ± 0.95^# 5.83 ± 1.02	0.017 ^&
Baseline serum urea (mg/dL) Postoperative serum urea (mg/dL)	—	46.04 ± 30.12 47.94 ± 29.39	41.95 ± 21.11 52.54 ± 29.53	0.001 ^&
Baseline serum creatinine (mg/dL) Postoperative serum creatinine (mg/dL)	—	1.08 ± 0.41 1.21 ± 0.54	1.07 ± 0.45 1.30 ± 0.73	0.081^&
Baseline HCT Postoperative HCT	—	36.94 ± 5.22 33.62 ± 4.95	38.03 ± 6.71 34.72 ± 6.61	0.978^&
Limb occlusion, n (%)	—	3 (3.7)	1 (2.6)	0.608
Re-intervention, n (%)	—	4 (4.9)	1 (2.6)	0.668
Endoleak, n (%)	—	9 (11.1)	7 (17.9)	0.302
Wound infection, n (%)	—	2 (2.5)	4 (10.3)	0.087
Hematoma, n (%)	—	3 (3.7)	3 (7.7)	0.389
AAA rupture	—	0	0	—
MI, n (%)	—	1 (1.2)	1 (2.6)	0.546
DVT, n (%)	—	1 (1.2)	0	0.675
Mortality, n (%)	—	16 (19.8)	10 (25.6)	0.463

BMI, body mass index; AAA, abdominal aortic aneurysm; MI, myocardial infarction; DVT, deep vein thrombosis. 

Continuous data are presented as means ± standard deviation; categorical data are given as counts (percentages).

^&p-value of interaction effect for group x period.

^#pairwise comparisons for interaction effect; p = 0.002 for pre-op and 6 months, p = 0.073 for pre-op and 12 months, p = 0.331 for 6 months and 12 months.

Although there were no significant differences between the groups, postoperative urea and creatinine values were increased in both groups. Serum urea change amount over time differs in groups (p = 0.001). In addition, a much faster increase was observed in the postoperative urea values in the obese group compared to the non-obese group (see Figure 2(a)). Creatinine change amount over time was not statistically significant between the groups (p = 0.081). In addition, the main effect of the groups was also not significant (p = 0.656), while the creatinine change over time was statistically significant (p < 0.001) regardless of the groups. Creatinine was changed similarly in both groups and increased significantly in both groups (see Figure 2(b)). Hematocrit change amount over time was not statistically significant between the groups (p = 0.978). In addition, the main effect of the groups was also not significant (p = 0.310), while the hematocrit change over time was statistically significant (p < 0.001) regardless of the groups. Hematocrit was changed similarly in both groups and decreased significantly in both groups (Figure 2(c)).

Endoleak except for type 1 whether documented in completion angiogram or developed during follow-up seen in 16 (13.3%) patients, of which 9 (11.1%) were in the non-obese group and 7 (17.9%) were in the obese group. Although similar between groups, there was a trend toward a slightly higher incidence of endoleak among obese patients.

The all-cause mortality rate was slightly higher in the obese group; however, it did not differ between the groups (p = 0.463). Also, survival for all-cause mortality following EVAR in 48 months using KaplanMeier life-table analysis was also similar between the two groups (p = 0.763; log-rank test) Figure 3.

Discussion

Increased obesity among adults, especially in developed countries, has been a serious public health problem, and public health programs focus on this challenge. Obesity has directly led to aortic aneurysms due to obesity-induced aortic wall inflammation and adipokine release, leading to aortic wall weakening and subsequent aneurysm formation. Interesting publications are showing that the prevalence of AAA increases in obese individuals.^1,15–17

There are similar results in the literature regarding the effects of obesity on AAA endovascular repair. Respiratory problems are more common after general anesthesia since increased body mass index will cause a decrease in oxygen delivery and an increase in carbon dioxide.^2,3 Therefore, short operation times and regional anesthesia may be advantageous in endovascular repair of AAA, especially in obese patients. Although there was no difference between the groups in this study, most patients in both groups were operated on under regional anesthesia. Although the procedure time was shorter in both groups than open surgery, it was significantly longer in obese patients, consistent with the literature.^5,11,18 We thought that in addition to anatomical problems in obese patients, femoral cut-down incision and surgical closure might lead to longer procedure times. However, it should be kept in mind that obese patients may have more X-ray absorption due to increased subcutaneous and visceral fat tissue.

We could not demonstrate any significant difference in all-cause mortality or during 48-month follow-up between the groups. Also, some other researchers have shown similar mortality rates between obese and non-obese patients, in line with our study.^10–13,18 However, Giles et al. reported mortality rates three times higher than overall EVAR mortality in the underweight population and two times higher in morbidly obese patients.⁸ Interestingly, Miller et al. found better all-cause mortality in overweight and obese EVAR patients. They showed significantly improved survival rates for overweight patients up to 10 years after EVAR.¹⁹ Similarly, Davenport et al. reported lower mortality rates after vascular surgery in patients with mild obesity.⁴

Galfos et al. reported a 2.5-fold increase in wound infections in obese patients than non-obese patients in their study conducted on all vascular surgical procedures.²⁰ In EVAR procedures, instead of the traditional inguinal incision for the exposure of the femoral arteries, percutaneous methods have been used more frequently in parallel with the development of devices in recent years. In a study, the rate of wound infection for the percutaneous technique compared with femoral cut down was 0.2% vs > 2%.²¹ However, femoral cut-down still to be used in more than half of all EVAR cases due to the reasons such as unsuitable anatomy, groin scarring, surgeon preference or calcification. In our series, the groin incision with femoral cut down was used in most patients, especially on the side where the main body of the graft will be implanted. In our study, the overall infection rate was 5%, and all were superficial. Although it was higher in the obese group than in the non-obese group, no significant difference was found between the two groups (10.3% vs 2.5%); however, several other studies reported higher rates of wound infections in obese versus non-obese patients in both EVAR and open procedures.^5,7,8 Similar to our results, Park et al. found no significant difference in wound infection between obese and non-obese patients.¹³ Despite the consensus in the literature about the increase in wound infections in obese patients, the lack of statistical difference in our study may be due to the small sample size, although the rate was higher in obese patients.

The prevalence of endoleak, which is the most common complication after EVAR, defined as the presence of blood between the graft and the aneurysm wall, is 10–20%, and type 2 is the most common.²² Risk factors associated with endoleak include age, smoking, arterial hypertension, aneurysm anatomy, obesity, as well as patent inferior mesenteric artery (IMA) or lumbar arteries. In our study, although there was no difference between the groups, the endoleak rate was higher in obese patients. Similarly, Frego et al. found a higher incidence of endoleak in patients with a BMI > 25 kg/m².²³ In addition to the sac enlargement, especially in type 1 endoleak, a persistent type 2 endoleak can also lead to a new type I or III endoleak. Conversely, aneurysm sac shrinkage is considered a sign of EVAR’s long-term success. Some investigators have achieved significant sac shrinkage 6 months before EVAR by embolization of branch vessels.²⁴ On the other hand, Timur et al. noted that a significant proportion of patients who underwent embolization for endoleak treatment continued to expand in the medium- and long-term.²⁵ In our study, a significant decrease in the sac was observed in both groups, especially in the non-obese group, at a 6-month follow-up. In addition, there was no difference between the groups in terms of sac shrinkage in the 12-month follow-up. We have seen that the shrinkage of the sac seen in the early period after graft placement does not continue in the long-term. In EVAR, many factors such as graft type, mural thrombus, obesity, and aortic anatomy may be responsible for aneurysm sac regression and other prognostics such as endoleak or stent wall apposition.

Contrast-related acute kidney injury is one of the complications that increase postoperative mortality and morbidity after EVAR. We, therefore, evaluated the incidence of acute kidney injury (AKI) after elective EVAR, as well as related factors affecting AKI occurrence, investigating the volume of contrast, serum urea, and creatinine levels as a predictive factor. Although there was an increase in postoperative urea and creatinine levels in both groups, there was no significant difference between the groups, but it was more common in obese patients. Furthermore, obese patients in our study were more likely to have well-known risk factors for kidney injury after EVAR, such as DM, HT, and CHF. While the reported incidence rates of AKI for elective EVAR vary widely, from 2.9% to 18.8%, comparative studies have consistently found higher rates for open surgery.²⁶ Another interesting observation in this study was iliac limb thrombosis, which is common in non-obese patients. Especially in one patient, the main body could be deployed after balloon dilatations due to stenotic iliac lesions. Although two patients had stenotic iliac lesions, the number of cases is insufficient to allow a reliable interpretation of this issue.

We found that obese patients had longer fluoroscopy times with longer procedure times. Obese patients are exposed to increased radiation during EVAR because it induces increased X-ray techniques to obtain appropriate images due to increased tissue thickness in obese patients.^19–27 Our study found increased DAP values in obese patients compared to the non-obese group, consistent with the literature.

This study looked at many different variables, resulting in a comprehensive overview of the differences and similarities between obese and non-obese patients undergoing EVAR. However, limitations of this study were its retrospective design and relatively small study sample. Additionally, one of the main limitations of this study is the lack of long-term results, although the mean follow-up was approximately 48 months. Future studies with a large sample size examining the effect of obesity on EVAR outcomes will provide more detailed information on this subject.

Conclusion

We have found that obesity was associated with longer procedure time, fluoroscopy time, and higher DAP values during EVAR. In addition, regardless of obesity, significant sac shrinkage in the first 6 months of follow-up and increased postoperative urea and creatinine values were observed in both groups. We showed that obesity had no significant effect on all-cause mortality and morbidity following EVAR.

Footnotes

Declaration of conflicting interests

The authors declared no conflicts of interest concerning the authorship and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Ayhan Sahin

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