Is there a Minimum Caseload that Achieves Acceptable Operative Mortality in Abdominal Aortic Aneurysm Operations?

Benchmarking a Center of Excellence in Vascular Surgery: Using Acute Physiology and Chronic Health Evaluation II to Validate Outcomes in a Tertiary Care Institute

OBJECTIVE

The Society of Vascular Surgery (SVS) has made it a top priority to implement verification of vascular "centers of excellence". Our institutional aortic network was established in 2008 in order to standardize care of patients with suspected acute aortic pathology. The implementation and success of this program has been previously reported. We sought to use our experience as a benchmark for which to develop prognostic modeling to quantify clinical status upon admission and help predict outcomes. Our objective was to validate the Acute Physiology and Chronic Health Evaluation (APACHE) II scoring system using a cohort of aortic emergencies transferred by an organized transfer network.

METHOD

This was a retrospective, single institution review of patients transferred through an institutional aortic network for acute aortic pathology from 2017-2018. Demographics, comorbidities, aortic diagnosis, APACHE II score, as well as 30-day mortality were recorded. Associations with 30-day mortality were evaluated using two-sample t-tests, ANOVA models, Pearson chi-square tests and Fisher exact tests. Receiver operating characteristic (ROC) curves were fit overall and by pathology to predict 30-day mortality by Apache II total score.

RESULTS

There were 395 consecutive transfers were identified. The mean age was 64.7 years. Diagnoses included Type A Dissection (n = 134), Type B (n = 81), Aortic Aneurysm (n = 122), and PAU/IMH (n = 27). Mean APACHE II score on arrival was 12. Overall there were 53 deaths (13.4%) in the cohort. Patients that died had significantly higher Apache II total scores (11.3 vs 16.5, P < .001). The area under the receiver operator characteristic (ROC) curve (AUC) was .66 for the full cohort, indicating a poor clinical prediction test.

CONCLUSION

APACHE II score is a poor predictor of 30-day mortality in a large transfer network accepting all aortic emergencies. The authors believe further refining a prognostic model for diverse population will not only help in predicting outcomes but to objectively quantify illness severity in order to have a basis for comparison among institutions and verification of "centers of excellence".

Configuration of vascular services: a multiple methods research programme

Background

Vascular services is changing rapidly, having emerged as a new specialty with its own training and specialised techniques. This has resulted in the need for reconfiguration of services to provide adequate specialist provision and accessible and equitable services.

Objectives

To identify the effects of service configuration on practice, resource use and outcomes. To model potential changes in configuration. To identify and/or develop electronic data collection tools for collecting patient-reported outcome measures and other clinical information. To evaluate patient preferences for aspects of services other than health-related quality of life.

Design

This was a multiple methods study comprising multiple systematic literature reviews; the development of a new outcome measure for users of vascular services (the electronic Personal Assessment Questionnaire – Vascular) based on the reviews, qualitative studies and psychometric evaluation; a trade-off exercise to measure process utilities; Hospital Episode Statistics analysis; and the development of individual disease models and a metamodel of service configuration.

Setting

Specialist vascular inpatient services in England.

Data sources

Modelling and Hospital Episode Statistics analysis for all vascular inpatients in England from 2006 to 2018. Qualitative studies and electronic Personal Assessment Questionnaire – Vascular evaluation with vascular patients from the Sheffield area. The trade-off studies were based on a societal sample from across England.

Interventions

The data analysis, preference studies and modelling explored the effect of different potential arrangements for service provision on the resource use, workload and outcomes for all interventions in the three main areas of inpatient vascular treatment: peripheral arterial disease, abdominal aortic aneurysm and carotid artery disease. The electronic Personal Assessment Questionnaire – Vascular was evaluated as a potential tool for clinical data collection and outcome monitoring.

Main outcome measures

Systematic reviews assessed quality and psychometric properties of published outcome measures for vascular disease and the relationship between volume and outcome in vascular services. The electronic Personal Assessment Questionnaire – Vascular development considered face and construct validity, test–retest reliability and responsiveness. Models were validated using case studies from previous reconfigurations and comparisons with Hospital Episode Statistics data. Preference studies resulted in estimates of process utilities for aneurysm treatment and for travelling distances to access services.

Results

Systematic reviews provided evidence of an association between increasing volume of activity and improved outcomes for peripheral arterial disease, abdominal aortic aneurysm and carotid artery disease. Reviews of existing patient-reported outcome measures did not identify suitable condition-specific tools for incorporation in the electronic Personal Assessment Questionnaire – Vascular. Reviews of qualitative evidence, primary qualitative studies and a Delphi exercise identified the issues to be incorporated into the electronic Personal Assessment Questionnaire – Vascular, resulting in a questionnaire with one generic and three disease-specific domains. After initial item reduction, the final version has 55 items in eight scales and has acceptable psychometric properties. The preference studies showed strong preference for endovascular abdominal aortic aneurysm treatment (willingness to trade up to 0.135 quality-adjusted life-years) and for local services (up to 0.631 quality-adjusted life-years). A simulation model with a web-based interface was developed, incorporating disease-specific models for abdominal aortic aneurysm, peripheral arterial disease and carotid artery disease. This predicts the effects of specified reconfigurations on workload, resource use, outcomes and cost-effectiveness. Initial exploration suggested that further reconfiguration of services in England to accomplish high-volume centres would result in improved outcomes, within the bounds of cost-effectiveness usually considered acceptable in the NHS.

Limitations

The major source of evidence to populate the models was Hospital Episode Statistics data, which have limitations owing to the complexity of the data, deficiencies in the coding systems and variations in coding practice. The studies were not able to address all of the potential barriers to change where vascular services are not compliant with current NHS recommendations.

Conclusions

There is evidence of potential for improvement in the clinical effectiveness and cost-effectiveness of vascular services through further centralisation of sites where major vascular procedures are undertaken. Preferences for local services are strong, and this may be addressed through more integrated services, with a range of services being provided more locally. The use of a web-based tool for the collection of clinical data and patient-reported outcome measures is feasible and can provide outcome data for clinical use and service evaluation.

Future work

Further evaluation of the economic models in real-world situations where local vascular service reconfiguration is under consideration and of the barriers to change where vascular services do not meet NHS recommendations for service configuration is needed. Further work on the electronic Personal Assessment Questionnaire – Vascular is required to assess its acceptability and usefulness in clinical practice and to develop appropriate report formats for clinical use and service evaluation. Further studies to assess the implications of including non-health-related preferences for care processes, and location of services, in calculations of cost-effectiveness are required.

Study registration

This study is registered as PROSPERO CRD42016042570, CRD42016042573, CRD42016042574, CRD42016042576, CRD42016042575, CRD42014014850, CRD42015023877 and CRD42015024820.

Funding

This project was funded by the National Institute for Health Research (NIHR) Programme Grants for Applied Research programme and will be published in full in Programme Grants for Applied Research; Vol. 9, No. 5. See the NIHR Journals Library website for further project information.

Association between operation volume and postoperative mortality in the elective open repair of infrarenal abdominal aortic aneurysms: systematic review

Background

An inverse association between the case volume per hospital and surgeon and perioperative mortality has been shown for many surgical interventions. There are numerous studies on this issue for the open treatment of infrarenal aortic aneurysms.

Aim

To present the available data on the association between the case volume per hospital and surgeon and perioperative mortality in the elective open repair of infrarenal aortic aneurysms in a systematic review.

Materials and methods

Using the PubMed, Cochrane Library, Web of Science Core Collection, CINAHL, Current Contents Medicine (CCMed), and ClinicalTrials.gov databases, a systematic search was performed using defined keywords. From the search results, all original papers were included that compared the elective open repair of an infrarenal aortic aneurysm in a “high volume” center with a “low volume” center or by a “high volume” surgeon with a “low volume” surgeon, as defined in the respective study.

Results

After deduplication, the literature search yielded 1021 hits of which 60 publications met the inclusion criteria. Of these, 37/43 studies showed a lower mortality in “high volume” compared to “low volume” centers and 14/17 comparisons showed a lower mortality for “high volume” compared to “low volume” surgeons. The effect measures, usually odds ratios, ranged from 0.37 to 0.99 for volume per hospital and 0.31 to 0.92 for volume per surgeon. Regarding the threshold values for the definition of “high volume” and “low volume,” a clear heterogeneity was shown between the individual studies.

Discussion

The available data on the association between the case volume per hospital and surgeon and perioperative mortality in the elective open repair of infrarenal aortic aneurysms show that interventions performed in “high volume” centers or by “high volume” surgeons are associated with lower mortality. To ensure the best possible outcome in terms of low perioperative mortality in the open repair of infrarenal aortic aneurysms, the aim should be centralization with high case volume per hospital and surgeon.

Outcomes of aortic aneurysm surgery in England: a nationwide cohort study using hospital admissions data from 2002 to 2015

Background

The United Kingdom aortic aneurysms (AA) services have undergone reconfiguration to improve outcomes. The National Health Service collects data on all hospital admissions in England. The complex administrative datasets generated have the potential to be used to monitor activity and outcomes, however, there are challenges in using these data as they are primarily collected for administrative purposes. The aim of this study was to develop standardised algorithms with the support of a clinical consensus group to identify all AA activity, classify the AA management into clinically meaningful case mix groups and define outcome measures that could be used to compare outcomes among AA service providers.

Methods

In-patient data about aortic aneurysm (AA) admissions from the 2002/03 to 2014/15 were acquired. A stepwise approach, with input from a clinical consensus group, was used to identify relevant cases. The data is primarily coded into episodes, these were amalgamated to identify admissions; admissions were linked to understand patient pathways and index admissions. Cases were then divided into case-mix groups based upon examination of individually sampled and aggregate data. Consistent measures of outcome were developed, including length of stay, complications within the index admission, post-operative mortality and re-admission.

Results

Several issues were identified in the dataset including potential conflict in identifying emergency and elective cases and potential confusion if an inappropriate admission definition is used. Ninety six thousand seven hundred thirty-five patients were identified using the algorithms developed in this study to extract AA cases from Hospital episode statistics. From 2002 to 2015, 83,968 patients (87% of all cases identified) underwent repair for AA and 12,767 patients (13% of all cases identified) died in hospital without any AA repair. Six thousand three hundred twenty-nine patients (7.5%) had repair for complex AA and 77,639 (92.5%) had repair for infra-renal AA.

Conclusion

The proposed methods define homogeneous clinical groups and outcomes by combining administrative codes in the data. These methodologically robust methods can help examine outcomes associated with previous and current service provisions and aid future reconfiguration of aortic aneurysm surgery services.

Comparative analysis of the outcomes of elective abdominal aortic aneurysm repair in England and Sweden

Background

There is substantial international variation in mortality after abdominal aortic aneurysm (AAA) repair; many non‐operative factors influence risk‐adjusted outcomes. This study compared 90‐day and 5‐year mortality for patients undergoing elective AAA repair in England and Sweden.

Methods

Patients were identified from English Hospital Episode Statistics and the Swedish Vascular Registry between 2003 and 2012. Ninety‐day mortality and 5‐year survival were compared after adjustment for age and sex. Separate within‐country analyses were performed to examine the impact of co‐morbidity, hospital teaching status and hospital annual caseload.

Results

The study included 36 249 patients who had AAA treatment in England, with a median age of 74 (i.q.r. 69–79) years, of whom 87·2 per cent were men. There were 7806 patients treated for AAA in Sweden, with a median of age 73 (68–78) years, of whom 82·9 per cent were men. Ninety‐day mortality rates were poorer in England than in Sweden (5·0 versus 3·9 per cent respectively; P < 0·001), but were not significantly different after 2007. Five‐year survival was poorer in England (70·5 versus 72·8 per cent; P < 0·001). Use of EVAR was initially lower in England, but surpassed that in Sweden after 2010. In both countries, poor outcome was associated with increased age. In England, institutions with higher operative annual volume had lower mortality rates.

Conclusion

Mortality for elective AAA repair was initially poorer in England than Sweden, but improved over time alongside greater uptake of EVAR, and now there is no difference. Centres performing a greater proportion of EVAR procedures achieved better results in England.

Improving in England

[Patient volume and quality in surgery for abdominal aortic aneurysm]

BACKGROUND Patient volume is assumed to affect quality, whereby complex procedures are best performed by those who perform them frequently. We have conducted a systematic review of the research on the association between patient volume and quality of vascular surgery. In this article we describe the outcomes for abdominal aortic aneurysm surgery.MATERIAL AND METHOD We undertook systematic searches in relevant databases. We searched for systematic reviews, and randomised and observational studies. The search was concluded in December 2015. We have summarised the results descriptively and assessed the overall quality of the evidence.RESULTS Forty-six observational studies fulfilled our inclusion criteria. We found a possible association for both hospital and surgeon volume. Higher patient volume may possibly be associated with lower 30-day mortality and lower hospital mortality for both open and endovascular surgery. Although the association appears to apply to both elective and acute hospitalisations, there is greater uncertainty with regard to the most ill patients. For hospital volume there may also be fewer complications for open and endovascular surgery, as well as for all surgery assessed as a whole. We considered the evidence base to be medium to very low quality.INTERPRETATION We found a possible correlation between patient volume and quality indicators such as mortality and complications. It may be advantageous to allocate planned procedures to institutions and surgeons with high volume, while this is less certain with regard to acute hospitalisations.

Use of Hospital Episode Statistics to investigate abdominal aortic aneurysm surgery

BACKGROUND

A coding framework was evaluated to study patients undergoing open surgical replacement of an abdominal aortic aneurysm (AAA) in the English Hospital Episode Statistics (HES) database. The objective was to create groups of patients who are homogeneous with respect to diagnosis, prognosis and treatment.

METHODS

The frequency and consistency of potentially relevant diagnosis (International Classification of Diseases, 10th revision) and procedure (Office of Population Censuses and Surveys Classification, 4th revision) codes were assessed in patients admitted to English National Health Service hospitals between April 2003 and March 2008. Administrative codes were compared with diagnosis and procedure codes to check that patients who had undergone emergency surgery for a ruptured AAA were admitted as an emergency.

RESULTS

Of 20 290 patients undergoing AAA replacement, 19 250 (94·9 per cent) had a consistent diagnosis (unruptured or ruptured AAA); 79·3 per cent of patients with an emergency replacement were coded as having a ruptured AAA and 95·7 per cent of those with a non-emergency replacement as having an unruptured AAA. Of patients who had undergone emergency replacement of a ruptured AAA, 93·3 per cent were coded as having been admitted as an emergency.

CONCLUSION

Coding consistency was high. The proposed framework could define homogeneous groups by combining diagnosis, procedure and administrative codes. It also allows an assessment of potential miscoding at national and hospital level.

Centralization harnessing volume-outcome relationships in vascular surgery and aortic aneurysm care should not focus solely on threshold operative caseload

There has been great interest in the setting of threshold operative volumes for safety to guide centralisation of vascular surgical services by healthcare commissioners. This editorial examines the evidence for designing services around a numeric safety threshold in the relationship between volume and outcome in vascular surgery. Thresholds should be aimed at the best outcomes and equity of care. Equity means access to the most up-to-date technology and all the relevant support services for elective and emergency cases. The relationship of volume and outcome with quality is complex, and demands a shift in focus to infrastructural and procedural improvements that drive high-quality services rather than the concentration of planning exclusively around an operative volume threshold.

Volume versus Outcome When Treating Abdominal Aortic Aneurysm Electively — Is There Evidence to Centralise?

Aim:

To identify evidence for the minimum annual case load of open repairs of abdominal aortic aneurysms compatible with an acceptable perioperative mortality rate.

Method:

A PubMed search resulted in 137 references, sixteen articles with original data on volume and mortality not older than ten years were identified and selected for review

Result:

Three studies found no volume-mortality relationship when controlled for age, sex and medical risk. Six studies verified volume thresholds of 20 procedures per year or more. In seven studies hospital volumes of 7–17 elective abdominal aortic aneurysm (AAA) repairs per year were sufficient to reach a mortality rate of a national average or similar to that of higher volume centres. No studies were published on the minimum annual case-load of EndoVascular Aneurysm Repair (EVA R), or of a combination of EVAR and open repair.

Conclusion:

Recent studies in North America and in Europe indicate that 10–15 procedures annually can be sufficient to safely perform open AAA repairs. Centres regularly performing less should consider referral. Continuous monitoring and audit of risk-adjusted perioperative mortality rates should be practiced in all centres.

Demonstrating safety through in-hospital mortality analysis following elective abdominal aortic aneurysm repair in England

Background

The aims were to assess the evidence that individual hospitals had mortality rates in excess of the national average after abdominal aortic aneurysm (AAA) repair and to develop an effective method for monitoring mortality using local data.

Methods

Hospital Episode Statistics identified patients undergoing elective infrarenal AAA repair. A technique was developed that compared individual hospital mortality rates with the mortality rate in the remainder of England. The strength of evidence that the death rate was less than elsewhere, and less than twice elsewhere, was quantified using a test of statistical significance. A moving average chart technique was devised using local data for mortality monitoring and comparison to the national average.

Results

For 30 hospitals, the mortality rate was significantly greater than elsewhere, and in three hospitals it was demonstrably greater than twice that in the remainder of England. The moving average chart appeared to provide a useful technique for local mortality monitoring.

Conclusion

Different mortality rates exist for AAA repair within England. Mortality can be monitored locally and compared with the national average.

The Relationship Between Volume and Outcome Following Elective Open Repair of Abdominal Aortic Aneurysms (AAA) in 131 German Hospitals

OBJECTIVES

Several studies indicate that high-volume hospitals have better results in open repair of unruptured abdominal aortic aneurysms (AAA). Up to now no studies had addressed this question in German hospitals.

DESIGN

Post-hoc-analysis from a prospective physician-led registry.

MATERIAL AND METHODS

Since 1999, the German Society for Vascular Surgery has conducted a prospective registry for open and endovascular repair of AAAs. This study includes 131 hospitals who conducted n=10163 elective open repairs for unruptured AAA between 1999 to 2004. All perioperative variables including annual volume as a continuous variable were analysed in a step-wise logistic regression model. In order to define a threshold annual volume an additional logistic regression analysis was performed by use of annual volume groups (0-9, 10-19, 20-29, 30-39, 40-49, 50 or more). The relationship between annual volume and further outcome parameters (length of procedure, blood transfusion, length of stay) were also analyzed.

RESULTS

The overall mortality rate was 3.2%. The stepwise logistic regression model identified the following predictors of an increased perioperative mortality: age (OR 1.084, 95% CI 1.066-1.102), AAA diameter (OR 1.008, 95% CI 1.001-1.016), length of procedure (OR 1.008, 95% CI 1.006-1.009), ASA-Score (OR 2.636, 95% CI 2.129-3.264), suprarenal clamping (OR 1.447, 95% CI 1.008-2,078), blood transfusion (OR 1.786, 95% CI 1.268-2.514). Annual volume was moderately predictive (OR 1.003, 95% CI 1-1.006) but failed to reach statistical significance (p=0.07). The analysis of volume groups identified a significantly higher risk for hospitals with an annual volume of 1-9 AAA-repairs by comparison to hospitals with an annual volume of 50 or more AAA-repairs (OR 1.903, 95% CI 1.124-3.222). Operations at low volume hospitals were also longer (p<0.001), with an extended postoperative stay (p<0.001) and a higher transfusion rate (p<0.001).

CONCLUSIONS

Patient's age, ASA classification, AAA diameter, length of procedure, suprarenal clamping and blood transfusion are predictive variables for an increased perioperative mortality in elective open AAA repair. Mortality is also increased by a low annual volume. Further studies are needed to examine whether these data are applicable to all German hospitals.

Epidemiological study of the relationship between volume and outcome after abdominal aortic aneurysm surgery in the UK from 2000 to 2005

Background

The aim was to assess the relationship between hospital volume and outcome after abdominal aortic aneurysm (AAA) surgery in the UK.

Methods

Hospital Episode Statistics (2000–2005) were classified as elective, urgent or ruptured AAA repair. Analysis was by modelling of mortality rate, complication rate and length of hospital stay with regard to the annual operative volume, after risk adjustment.

Results

There were 112 545 diagnoses, or repairs, of AAAs, of which 26 822 were infrarenal aneurysms. The mean mortality rate was 7·4, 23·6 and 41·8 per cent for elective, urgent and ruptured AAA repair respectively. Elective AAA repair undertaken at high-volume hospitals showed volume-related improvements in mortality (P &lt; 0·001). Patients were discharged from hospital earlier (P &lt; 0·001). The critical volume threshold was 32 elective AAA repairs per year. For urgent repair, patients at high-volume hospitals had a reduced mortality rate (P = 0·017) with an increased length of stay (P = 0·041). There was no relationship between volume and outcome for ruptured AAA repairs.

Conclusion

Increased annual volumes were associated with significant reductions in mortality for elective and urgent AAA repair, but not for repair of ruptured AAAs.

Relation between hospital volume and outcome of elective surgery for abdominal aortic aneurysm: a systematic review

OBJECTIVES

Our aim was to analyse the relation between hospital volume and peri-operative mortality in abdominal aortic aneurysm surgery.

DESIGN

Systematic review.

METHOD

The Medline, Embase and Cochrane databases were searched to identify all population based studies reporting on the volume outcome relationship published between 1966 and 2006. Two independent observers performed methodological quality assessment and data extraction. Outcome was 30-day or in-hospital mortality in relation to hospital volume.

RESULTS

Twenty-four articles were included. Overall peri-operative mortality ranged from 2.3 to 9.9%. The cut-off values for a high- or low-volume hospital appeared to range from 8 to 50 operations annually. The peri-operative mortality in low volume hospitals (LVH) ranged from 3.0 to 13.8% (median 6.2%) and from 1.8 to 7.4% in high volume hospitals (HVH) (median 4.3%). In 14 studies a significantly lower mortality was found in HVH as opposed to LVH; in 10 articles no such difference between HVH and LVH could be proved.

CONCLUSION

We found some evidence for a relation between the volume of AAA surgery and peri-operative mortality. There seems to be a nonsignificant trend in favour of high volume hospitals. However we could not derive an unequivocal volume threshold for safely performing AAA surgery.