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ERA Model (EVAR)

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The Endovascular Aneurysm Repair Risk Assessment (ERA) Model is a risk assessment model developed to assist with the decision-making process that takes place between a surgeon and a patient considering endovascular repair for an abdominal aortic aneurysm. Surgeons use this model to inform their patients about the likelihood of an adverse outcome following surgery, based on selected preoperative patient variables. This risk assessment model may help surgeons achieve better outcomes through the provision of more personally relevant information to patients.

The ERA Model was developed based on analysis of data obtained from a long-term study of patients who underwent endovascular repair of an abdominal aortic aneurysm in Australia between 1999 and 2001 – the Endovascular Aortic Aneurysm Repair Study (EVAR). Based on eight carefully selected preoperative patient variables - age, gender, ASA, creatinine, aneurysm size, aortic neck angle, infrarenal neck diameter, and infrarenal neck length (last 3 variables optional) the model is able to highlight patients who may be at increased risk of adverse surgical outcomes, including early death (within 30 days of an operation), aneurysm-related death, graft failure and the need for another intervention for their aortic aneurysm, as well as providing a prediction of 3 and 5 year post-operative survival.

Whilst the model was generated with data from Australian patients it has also been validated with data from St George’s Hospital in the UK.

Be advised that:
- The University of Adelaide makes no representations about the accuracy of the content and suitability of the ERA Model, it is provided on an ‘As Is’ basis and cannot accept any liability or responsibility for the accuracy, completeness or currency of the ERA Model.

- The ERA Model is a ‘best fit’ model based on 961 patients who underwent endovascular repair of abdominal aortic aneurysms between November 1999 and May 2001 and whose progress was followed until 2007.

- Caution needs to be exercised when using the ERA Model as it will not necessarily predict what will happen for an individual patient. It simply provides predictions based on what happened to the 961 patients.

- The ERA Model uses generalized linear models (logistic regressions) conducted on the data to predict success measures. Stepwise forward logistic regressions were used to select which of the patient variables were included in each model.

- The ERA Model has also been validated internally, and externally using data from St George’s Hospital in the UK.

- Although care was taken to ensure the accuracy and completeness of the data some inaccuracies and incompleteness may have arisen.

- The Model will be updated as and when improvements are made based on a new cohort of patients and on information obtained for patients undergoing the procedure in different countries.

- Before using or relying on the ERA Model you must make your own assessment of the suitability of the ERA Model and the information or data contained in or generated from the ERA Model.

Work is ongoing at the University of Adelaide to further refine and/or improve the ERA Model based on a new group of patients. Information pertaining to this study, as well as to the ERA Model and the EVAR Study can be found at:

Selected references:
- Barnes M, Boult M, Thompson MM, Holt PJ, Fitridge RA. Personalised Predictions of Endovascular Aneurysm Repair Success Rates: Validating the ERA Model with UK Vascular Institute Data. European Journal of Vascular and Endovascular Surgery. October 2010: 40(4); 436-441.
- Barnes M, Boult M, Maddern G, Fitridge R. A Model to Predict Outcomes for Endovascular Aneurysm Repair Using Preoperative Variables. European Journal of Vascular and Endovascular Surgery. 2008;35(5):571-579.