Thirty-day NSQIP database outcomes of open versus endoluminal repair of ruptured abdominal aortic aneurysms
Article Outline
Background
The mortality of ruptured abdominal aortic aneurysm (rAAA) has decreased 3.5% per decade in the last 50 years to a current rate of 40%-50%. Reports have indicated that endovascular repair (EVAR) is feasible for rAAA and may offer potential benefits over open repair. We examined the National Surgical Quality Improvement Program (NSQIP) database to compare 30-day multicenter outcomes for EVAR vs open rAAA repair.
Methods
Patients that underwent rAAA repair in the NSQIP database from 2005 to 2007 were identified through a combination of Current Procedural Terminology (CPT) codes and International Classification of Diseases-Ninth Revision (ICD-9) diagnoses. Preoperative comorbidities, operative duration and transfusion, and 30 day outcomes were evaluated using t tests or Chi-squared tests depending on the variable. A separate multivariable regression was performed for each outcome adjusting for all independently predictive preoperative and intraoperative risk factors.
Results
A total of 427 patients were identified and 76.8% of patients underwent open repair. The open repair groups exhibited lower albumin levels and higher percentage of patients with preoperative hematocrit (Hct) <38% and need for preoperative ventilation. The requirement for preoperative blood transfusion was similar. Patients undergoing open repair had much higher intraoperative transfusion requirements (11.8 ± 8.9 vs 4.2 ± 6.0 red blood cell units, P < .001). After adjustment for preoperative mortality risk factors, the mortality risk was higher for open repair versus EVAR (odds ratio 1.67, 95% confidence interval [CI] 0.91-3.05, P = .096) but did not reach significance. After similar adjustment the composite morbidity odds ratio for open repair versus EVAR was 1.82 (95% CI 1.11-2.99, P = .018) and the pulmonary adverse events odds ratio was 1.99 (95% CI 1.22-3.25, P = .006). Risks for the other outcomes were not significant.
Conclusions
Composite 30-day morbidity risk is lower after EVAR vs open repair of rAAA. Open repair is associated with increased transfusion requirements. Performance of EVAR in rAAA patients with favorable anatomy could potentially result in improved outcome as compared with open repair.
In recent years, the mortality of elective abdominal aortic aneurysm (AAA) repair has been 5% or less, but once rupture occurs, operative mortality is approximately 48%.1 Immediate postoperative death is usually the result of hemorrhagic shock; deaths occurring later are often due to the multisystem organ failure and systemic inflammatory response that develops even after technically successful aneurysmorraphy.2 Case series and reports have demonstrated that endovascular repair (EVAR) is feasible in the setting of ruptured abdominal aortic aneurysm (rAAA),3, 4 and may offer a potential outcome benefit over open repair.5 It is difficult to make true comparisons since most institutional studies are not representative of the population at large. The lower hemodynamic shifts and reduced physiologic challenges associated with endovascular repair may confer a survival benefit in ruptured aneurysm patients.6 We utilized the National Surgical Quality Improvement Program (NSQIP) database to examine the 30-day mortality and morbidity outcomes of endoluminal vs open rAAA repair. Although it is not possible to remove surgeon's selection bias, NSQIP is representative of community as well as academic medical centers and contains preoperative comorbidities, preoperative variables reflecting hemodynamic stability, intraoperative variables, and 30-day morbidity and mortality outcomes.
Methods
Study population
The American College of Surgeons (ACS) NSQIP is a robust reporting system designed to provide reliable, risk-adjusted surgical outcomes data to surgical services and administrators at medical centers throughout the private sector so that surgical quality can be assessed and improved on a national level.7, 8, 9 We analyzed the data from the Participant Use Data File containing vascular surgical cases submitted to the ACS NSQIP in 2005, 2006, and 2007 by 173 hospitals throughout the United States. Veterans Administration NSQIP data was not used for this study.
Data collection
The ACS NSQIP collects data on 135 variables, including preoperative risk factors, intraoperative variables, and 30-day postoperative morbidity and mortality outcomes for patients undergoing surgical procedures in both the inpatient and outpatient setting. Data are prospectively collected in a standardized fashion according to strict clinical definitions by dedicated surgical nurse reviewers. Patients are followed throughout their hospital course and after discharge from the hospital up to 30 days postoperatively. Nurse reviewers collect data from computerized and paper patient medical records, doctor's office records, and telephone interviews with patients. The accuracy and reproducibility of the data have been previously demonstrated.10 Patients in the database that underwent repair of ruptured abdominal aortic aneurysm in the ACS NSQIP database from 2005 to 2007 were identified by a postoperative International Classification of Diseases-Ninth Revision (ICD-9) diagnosis code of 441.3, “abdominal aneurysm – ruptured” and by primary procedure Current Procedural Terminology (CPT) codes. Repairs were classified as either EVAR (CPT code 34800-34805) or open (CPT code 35082 or 35103). To be included in the database, patients had to survive long enough to undergo an operation.
Analyses
Outcomes analyzed included 30-day mortality and morbidity. Morbidities analyzed were pulmonary adverse events (ventilation greater than 48 hours, unplanned intubation, and/or postoperative pneumonia), sepsis or septic shock, renal insufficiency or failure, surgical site infection (superficial, deep, or organ/space), cardiac arrest or infarction, and nervous system adverse events (coma greater than 48 hours, peripheral nerve injury with neurologic deficit, and/or stroke with neurologic deficit), and composite morbidity (one or more of previously listed morbidities plus wound dehiscence, urinary tract infection, graft/prosthesis failure, bleeding requiring postoperative transfusion, deep vein thrombosis, and/or pulmonary embolism; all uniformly defined by the ACS NSQIP protocol).
Preoperative risks, operative variables and outcome rates were compared by repair type using t tests or Chi-squared tests, depending on the variable. A separate multivariable regression was performed for each outcome adjusting for all independently predictive preoperative and intraoperative risk factors. All of the over 55 ACS NSQIP risk factors were considered for inclusion and entered via forward stepwise regression (P for entry <.05, exit >.10). Repair type (open versus EVAR) was then forced into the final model.
Results
The ACS NSQIP dataset from 173 hospitals contained 427 patients undergoing ruptured AAA repair in the years 2005 to 2007. The mean age was 73.3 ± 9.6 years and 330 (77%) were male. There was no difference in history of tobacco use, chronic obstructive pulmonary disease (COPD), and coronary artery disease (CAD). More than three-quarters (328; 76.8%) underwent open repair (Table I). As indicators of preoperative hemodynamic status, we report American Society of Anesthesiologists (ASA) status, percentage of patients with hematocrit <38%, percentage of patients requiring >4 units of preoperative blood transfusion, preoperative renal failure, impaired sensorium, coma, and preoperative ventilation within 48 hours of surgery. As shown in Table I, there was higher percentage of patients requiring preoperative ventilation and hematocrit <38% in the open repair group; also, preoperative albumin was lower in these patients. The difference in the requirement of preoperative blood transfusion was not significant. Operative duration was similar (EVAR 195 ± 113 minutes vs open 203 ± 90 minutes, P = .449) but open repair resulted in much higher requirement for intraoperative blood transfusion (EVAR 4.2 ± 6.0 units vs open 11.8 ± 8.9 units, P < .001).
Table I. Demographics and select comorbidities in patients undergoing EVAR versus open repair of ruptured abdominal aortic aneurysms
| Preoperative risk factor | EVAR N = 99 | Open repair N = 328 | P |
|---|---|---|---|
| Age (mean years ± SD) | 72.1 ±10.5 | 73.6±9.3 | .167 |
| Male (%) | 79.8 | 76.5 | .497 |
| Smoking (%) | 39.4 | 30.8 | .111 |
| COPD (%) | 19.2 | 13.4 | .156 |
| Preop Albumin (mean g/dL ± SD) (EVAR n = 57, 58%; Open n = 186, 57%) | 3.56±0.78 | 3.30±0.73 | .017* |
| ASA Physical Status Class | .169 | ||
| ASA IV (%) | 56.6 | 50.8 | |
| ASA V (%) | 26.3 | 37.3 | |
| Hematocrit < 38% (%) | 44.4 | 59.5 | .008* |
| Preop transfusion >4 u PRBC's (%) | 2.0 | 6.1 | .108 |
| Preop. renal failure (%) | 1.0 | 1.8 | .575 |
| Preop ventilation w/in 48 hr of surgery (%) | 9.1 | 19.2 | .018* |
| Impaired sensorium (%) | 7.1 | 12.5 | .134 |
| Preop coma (%) | 4.0 | 6.1 | .436 |
| Immediate preop functional status | .059 | ||
| Partially dependent (%) | 14.1 | 15.5 | |
| Fully dependent (%) | 23.2 | 34.8 | |
| Hx of angina, MI or CHF (%) | 9.1 | 5.8 | .246 |
| Prior cardiac operation or PCI (%) | 27.3 | 21.3 | .218 |
Unadjusted mortality, composite morbidity, pulmonary adverse events, and sepsis/septic shock were significantly higher after open repair than EVAR (Chi-squared P < .05, Table II). The other outcome rates were all higher in open repair patients, but not significantly so. Cardiac arrest or infarct was twice as frequent after open repair (8.2% versus 4.0%) but this was not statistically significant in this sample of 427 patients. Independent ACS NSQIP preoperative risk factors for mortality in rAAA patients from forward stepwise regression were ASA Class, preoperative ventilation, age, severe COPD, do not resuscitate (DNR) status, functional status, and white blood cell count ≤ 4500/mm3 (Appendix, Table III). After adjustment for these variables, the risk of mortality was higher for open repair versus EVAR (odds ratio 1.67, 95% CI 0.91-3.05, P = .096) but did not reach significance. After similar adjustment, the composite morbidity odds ratio for open repair versus EVAR was 1.82 (95% CI 1.11-2.99, P = .018, model in appendix Table IV) and the pulmonary adverse events odds ratio was 1.99 (95% CI 1.22-3.25, P = .006, model not shown). Risks for the other outcomes were not significant (P > .05).
Table II. Unadjusted and risk-adjusted outcomes by type of repair in patients with ruptured abdominal aortic aneurysms
| 30-day outcome | EVAR (n = 99) | Open repair (n = 328) | Chi-squared P | Risk adjusted5 OR open repair vs EVAR (95% CI) | Wald P |
|---|---|---|---|---|---|
| Mortality (%) | 22.2 | 37.2 | .003* | 1.67(0.91-3.05) | .096 |
| Composite morbidity1 (%) | 45.5 | 62.5 | .003* | 1.82(1.11-2.99) | .018* |
| Pulmonary adverse events2 (%) | 34.3 | 50.0 | .006* | 1.99(1.22-3.25) | .006* |
| Sepsis/septic shock (%) | 19.2 | 29.9 | .037* | 1.60(0.88-2.89) | .118 |
| Renal insufficiency/ failure (%) | 18.2 | 20.4 | .624 | 1.26(0.69-2.30) | .456 |
| Surgical site infection3 (%) | 5.1 | 8.5 | .255 | 2.01(0.71-5.72) | .190 |
| Cardiac arrest or infarction (%) | 4.0 | 8.2 | .159 | 2.56(0.73-9.0) | .144 |
| Nervous system adverse events4 (%) | 2.0 | 5.2 | .181 | 2.40(0.53-10.86) | .257 |
1Composite morbidity included patients experiencing one or more of 21 adverse events uniformly defined by the National Surgical Quality Improvement Program (NSQIP) protocol. |
2Pulmonary adverse events included postoperative pneumonia, unplanned reintubation and/or ventilation longer than 48 hours. |
3Surgical site infections included superficial deep or organ/space surgical site infections. |
4Nervous system adverse events included peripheral nerve injury with neurologic deficit, stroke with neurologic deficit, and/or coma greater than 48 hours. |
5For each of the outcome logistic regressions, all of the over 55 NSQIP risk factors were considered for inclusion and entered into the model via forward stepwise regression. (P for entry <.05, exit >.10). Repair type (open versus EVAR) was then forced into the final model. The mortality and composite morbidity models are shown in the appendix. |
Discussion
Elective endoluminal AAA repair has gained broad acceptance, but it is not yet known to what extent rAAAs are suitable for that approach. Mortality rates after EVAR for rAAA vary from 11% to 45% in the literature.11, 12 When EVAR is performed selectively in patients who have favorable neck morphology and are not hemodynamically unstable, mortality as low as 8% has been observed.13 Using an intention to treat by endovascular repair policy, Arya at al14 reported a mortality rate of 59% after open rAAA repair vs 39% after EVAR, similar findings were reported by Dalainas et al.12 Cardiovascular instability has served as a selection bias towards open repair and thus it is possible that EVAR has been performed on patients with a greater chance of survival.15 Nevertheless, EVAR has been shown to have less of an adverse impact on patient physiology including the cardiac, respiratory, and renal systems as well as reduced inflammatory response.16, 17 Furthermore, the potential for venous injuries from dissection of the aortic neck is significant in the presence of a retroperitoneal hematoma or free rupture;18 this is circumvented with an endoluminal approach. The physiologic trauma and the hemodynamic shifts of EVAR are less than that of an open repair but there is no high level evidence in favor of either approach.19
A study based on 43,033 Medicare beneficiaries showed a survival benefit of EVAR vs open repair; this was correlated with increasing annual surgeon and hospital volume in both open and endoluminal aneurysm repair and rAAA experience.20 This benefit was not confirmed by recent comparative studies in the community and university settings.21, 22, 23 Often, limiting factors for performance of EVAR are lack of trained personnel as well as equipment and grafts. Mehta et al5 stressed the importance of establishing a multidisciplinary protocol ensuring availability of staff with experience in endoluminal procedures in the operating room and adequate equipment. Using this standardized protocol, they achieved a mortality rate of 18% with emergent endovascular repair of hemodynamically stable and unstable patients. Hemodynamic instability does not necessarily preclude EVAR as permissive hypotension may reduce hemorrhage,24 and intraaortic balloon occlusion can be used for endoluminal control of aortic rupture.25, 26
In the present study, mortality after open repair was significantly higher; this difference did not persist after adjustment for independent preoperative mortality risk factors. The adjusted mortality risk ratio of 1.67 favored EVAR. Pulmonary adverse event rate and composite morbidity was higher after open repair; Greco et al27 have also found a lower rate of postoperative complications after EVAR. Similarly, the requirement for intraoperative blood transfusions was significantly higher for open repair; this has been reported by other investigators as well.28, 29 Reduced need for blood transfusion may be associated with better outcome since several groups have demonstrated that patients receiving allogeneic transfusions have had higher mortality rates, higher risk of ICU admission, longer hospital and ICU stays, higher postoperative infection rates, higher risk of developing ARDS, longer time to ambulation, higher incidence of atrial fibrillation, and higher risk of ischemic outcomes compared with nontransfused cohorts.30, 31, 32, 33, 34, 35 There was a higher percentage of patients with preoperative hematocrit <38% among patients undergoing open repair but the need for preoperative transfusion was not significantly different.
Serum albumin has been shown to be a significant predictor of postoperative morbidity and mortality;36, 37 patients undergoing open repair in our study had significantly lower pre-procedure albumin levels indicating worse physiologic status as compared with the patients that underwent EVAR. This, in addition to the higher percentage of patients with hematocrit <38%, may be at least partially responsible for the better outcomes observed in the EVAR group, since the patient population with relatively reduced reserves underwent an open procedure with major physiologic impact.
Our study represents a retrospective review, and surgeon preference determined treatment method thus introducing selection bias. In addition, preoperative hemodynamic parameters and morphologic characteristics of the aneurysms to determine anatomic suitability of an endoluminal approach are not available in the NSQIP database. We used several markers that reflect preoperative hemodynamic status to address this limitation. Furthermore, perqutaneous balloon occlusion of the suprarenal aorta renders EVAR feasible even in the presence of hemodynamic instability. Timaran et al38 reported that with the use of endografts with body diameter up to 36 mm, more than 63% of aneurysms are suitable for EVAR regardless of patient age, fitness, or aneurysm size. In the Amsterdam Acute Aneurysm Trial,39 the anatomy of the aorta and iliac arteries was considered appropriate for endovascular repair in 45.8% of the patients. Similarly, Slater et al40 found that 49% of the patients treated for rAAA in a tertiary academic center would have been anatomic candidates for EVAR, and a feasibility rate of 59% has been reported by Hassen-Khodia et al.4 Lesperance et al41 analyzed the Nationwide Inpatient Sample and reported increase in use of EVAR for rAAA from 6% in 2001 to 11% in 2004; a significant mortality benefit was seen with EVAR at teaching hospitals, whereas in non-teaching facilities, EVAR carried a higher risk of in-hospital death. Therefore, there appears to be increasing use of EVAR for rAAA since the beginning of the decade, but during the last two years of our study the utilization of this method has reached a plateau as it was applied to approximately one-quarter of the patients.
In conclusion, our data indicate that EVAR confers a morbidity benefit for rAAA as well as a trend towards improved mortality. The literature suggests that 45% or more of rAAA patients should be anatomic candidates for EVAR; this implies underutilization of this method in the NSQIP population. Performance of EVAR in rAAA patients with favorable anatomy could potentially result in lower morbidity and decreased transfusion requirements as compared with open repair. Further studies are necessary to determine if more widespread use of EVAR bestows a survival benefit to these critically ill patients.
The American College of Surgeons National Surgical Quality Improvement Program and the hospitals participating in the ACS NSQIP are the source of the data used herein; they have not verified and are not responsible for the statistical validity of the data analysis or the conclusions derived by the authors.
Author contributions
Tables (online only)
Table III (online only). Mortality logistic regression model in patients undergoing repair for ruptured abdominal aortic aneurysm (N = 426)
Mortality logistic regression model in ruptured AAA repair patients Model Chi-squared P < .001, H-L statistic 8.4 P = .391, c-index = 0.82 | ||||
|---|---|---|---|---|
| Odds ratio | Sig. | 95% CI for OR | ||
| Lower | Upper | |||
| Open Repair vs EVAR | 1.668 | .096 | .913 | 3.046 |
| ASA Physical Status Class vs 1-3 | .000 | |||
| ASA 4 | 3.018 | .051 | .996 | 9.149 |
| ASA 5 | 10.068 | .000 | 3.263 | 31.065 |
| Preoperative ventilation | 2.446 | .015 | 1.190 | 5.028 |
| Age (per year from mean) | 1.040 | .004 | 1.013 | 1.067 |
| History of COPD | 2.478 | .006 | 1.298 | 4.732 |
| DNR Status | 9.463 | .048 | 1.020 | 87.824 |
| Functional status vs independent | .038 | |||
| Partially dependent | .556 | .143 | .253 | 1.221 |
| Fully dependent | 1.667 | .092 | .920 | 3.019 |
| WBC ≤ 4500 | 5.880 | .061 | .924 | 37.414 |
Table IV (online only). Morbidity logistic regression model in patients undergoing repair for ruptured abdominal aortic aneurysm (N = 426)
Morbidity logistic regression model in ruptured AAA repair patients Model Chi-squared P < .001, H-L statistic 15.1 P = .057, c-index = 0.72 | ||||
|---|---|---|---|---|
| Odds ratio | Sig. | 95% CI for OR | ||
| Lower | Upper | |||
| Open repair vs EVAR | 1.821 | .018 | 1.110 | 2.985 |
| Age (per year from mean) | 1.035 | .003 | 1.012 | 1.059 |
| Steroid treatment for chronic condition | .284 | .025 | .094 | .856 |
| Sodium < 135 | .442 | .007 | .244 | .800 |
| Hematocrit < 38% | 1.938 | .004 | 1.233 | 3.046 |
| Preop coma | .398 | .073 | .146 | 1.089 |
| Preop renal failure | >10⁎ | .999 | .000 | . |
| Functional status vs independent | .004 | |||
| Partially dependent | 1.757 | .071 | .953 | 3.238 |
| Fully dependent | 2.594 | .002 | 1.419 | 4.740 |
| Preop ventilation | .366 | .009 | .173 | .776 |
| Hematocrit > 45% | 3.019 | .019 | 1.201 | 7.585 |
⁎All seven patients with preoperative renal failure experienced morbidity making precise estimation of the odds ratio impossible in this dataset. It is clearly a high risk factor. |
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Competition of interest: none.
The editors and reviewers of this article have no relevant financial relationships to disclose per the JVS policy that requires reviewers to decline review of any manuscript for which they may have a competition of interest.
PII: S0741-5214(09)01817-5
doi:10.1016/j.jvs.2009.08.086
Published by Elsevier Inc.
