Types of studies

We will include randomised controlled trials (RCTs) and controlled clinical trials (CCTs) assessing endovascular techniques and OSR techniques in the treatment of TAAAs.

Types of participants

We will include people with a primary TAAA of any type (Crawford Classifications Type I to V; see Description of the condition). Aneurysm formation post aortic dissection will not be included.

Types of interventions

We will include all studies comparing endovascular repair versus OSR. For both endovascular and OSR, there are a number of devices used and all device types will be included.

Types of outcome measures

The selection of primary and secondary outcomes was guided by the SVS reporting standards for thoracic endovascular aortic repair (TEVAR) (Fillinger 2010). The timepoints we expect to report will be primarily guided by the included studies, but will likely be 30 days, 12 months and 5 years unless otherwise stated.

Electronic searches

The Cochrane Vascular Information Specialist (CIS) will search the following databases for relevant trials:

• Cochrane Vascular Specialised Register;

• Cochrane Central Register of Controlled Trials (CENTRAL) via the Cochrane Register of Studies Online.

See Appendix 1 for details of the search strategy to be used to search CENTRAL.

The Cochrane Vascular Specialised Register is maintained by the CIS and is constructed from weekly electronic searches of MEDLINE Ovid, Embase Ovid, CINAHL, AMED and handsearching relevant journals. The full list of the databases, journals and conference proceedings that have been searched, and the search strategies used, are described in the Specialised Register section of the Cochrane Vascular module in the Cochrane Library (www.cochranelibrary.com).

In addition, the CIS will search the following trial registries for details of ongoing and unpublished studies:

• ClinicalTrials.gov (www.clinicaltrials.gov);

• World Health Organization International Clinical Trials Registry Platform (www.who.int/trialsearch).

Searching other resources

We will review citations of included papers identified from the search strategy described above.

Selection of studies

Two review authors (JC and EPK) will independently screen all titles and abstracts identified from searches to identify those that might meet the inclusion criteria. We will retrieve the full text of studies identified as potentially relevant by at least one review author. The same review authors will independently screen full text articles for inclusion or exclusion. Any disagreements will be resolved by discussion or, if necessary, we will consult a third review author (NH). All studies excluded at the full text stage will be listed as excluded studies and reasons for their exclusion will be presented in the 'Characteristics of excluded studies' table. We will report the screening and selection process in an adapted PRISMA flowchart (Liberati 2009).

Multiple reports of one study will be collated so that the study, and not the report, is the unit of analysis.

Data extraction and management

Two review authors (JC and EPK) will independently extract data from the eligible studies using an adapted and piloted data extraction form provided by the Cochrane Vascular Group. Any disagreements will be resolved by discussion or if necessary, we will consult with a third review author (NH). One review author (JC) will enter extracted data into Review Manager 5 (RevMan 2014), and a second review author (NH) will check them for accuracy and consistency against the data extraction sheets.

We will aim to describe the studies according to the following:

• trial design;

• diagnosis of TAAA;

• demographic characteristics of participants;

• type of intervention (open and endovascular repair);

• frequency of primary and secondary outcomes;

• treatment centre.

Assessment of risk of bias in included studies

Two review authors (JC and EPK) will independently assess each study for risk of bias according to the following criteria, as recommended by the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011):

• random sequence generation (selection bias);

• allocation concealment (selection bias);

• blinding of participants and personnel (performance bias)*;

• blinding of outcome assessment (detection bias)*;

• incomplete outcome data (attrition bias);

• selective reporting (reporting bias);

• other sources of bias.

We will judge all included studies as having low, high or unclear risk of bias on the basis of these criteria. We will resolve disagreements by discussion or, if necessary, we will consult with a third review author (NH).

*Due to the nature of the type of intervention, blinding of participants and personnel (i.e. participants, clinicians and outcome assessors) will not be possible, therefore, these domains will be deemed high risk of bias.

Measures of treatment effect

Unit of analysis issues

The unit of analysis will be each individual participant.

Dealing with missing data

We will record missing and unclear data for each included study. If possible, we will perform all analyses using an intention‐to‐treat approach, that is, we will analyse all participants and their outcomes within the groups to which they were allocated, regardless of whether they received the intervention. If necessary, we will contact study authors to request missing data.

Assessment of heterogeneity

We will assess the degree of heterogeneity by visual inspection of forest plots and by using the Chi² test for heterogeneity. We will assess heterogeneity of the overall results for the main outcomes using the Chi², I² and Tau² statistics, according to the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011).

We will regard statistical heterogeneity as substantial if the I² is greater than 50% and either the T² is greater than zero, or there is a low P value (less than 0.10) in the Chi² test for heterogeneity.

If we identify substantial clinical, methodological or statistical heterogeneity across included trials, we will not report pooled results from the meta‐analysis but will instead use a narrative approach to data synthesis. If we identify substantial heterogeneity, we will explore possible reasons by grouping trials that have similar populations.

Assessment of reporting biases

We will investigate publication bias using funnel plots, if there are 10 or more studies included in the review as recommended by the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011).

Data synthesis

We will carry out statistical analysis using Review Manager 5 (RevMan 2014). We will use fixed‐effect meta‐analysis for synthesising data where it is reasonable to assume that trials are estimating the same underlying treatment effect. If there is clinical heterogeneity sufficient to expect that the underlying treatment effects differ between trials, or if substantial statistical heterogeneity is detected, we will use random‐effects meta‐analysis to produce an overall summary where the mean treatment effect is clinically meaningful.

Subgroup analysis and investigation of heterogeneity

Planned subgroup analyses will include:

• Type I OSR versus endovascular treatment;

• Type II OSR versus endovascular treatment;

• Type III OSR versus endovascular treatment;

• Type IV OSR versus endovascular treatment;

• Type V OSR versus endovascular treatment;

• connective tissue disorder versus non‐connective tissue disorder;

• physician modified devices (chimney/parallel graft repairs) versus off the patient specific devices (branched/fenestrated repair);

• intercentre efficacy.

Sensitivity analysis

We will repeat the analyses including high quality trials only. For this review, trials judged, as 'low risk of bias' for sequence generation and allocation concealment will be classified as high quality trials. We will also repeat the analyses including RCTs only.