Types of studies

We will include randomised trials (RCTs) and controlled clinical trials (CCTs) comparing hybrid repair to open surgical repair (OSR) for thoracic aortic arch aneurysms (TAAs).

Types of participants

We will include participants with TAAs in Zones 0 to 4, diagnosed using conventional methods such as computed tomography (CT) or Magnetic Resonance Imaging (MRI), or both. There will be no limitations on participants' gender, age, ethnicity or treatment setting (e.g. elective versus emergency). We will consider aneurysms of all morphologies (e.g. fusiform, saccular and any size). We will exclude patients that require concomitant aortic valve replacement, dissective TAAs, traumatic TAAs or infective TAAs. We will exclude cases treated with purely or total endovascular technique.

Types of interventions

We will include the following comparisons:

• Type I hybrid technique versus OSR;

• Type II hybrid technique versus OSR; and

• Type III hybrid technique versus OSR.

Types of outcome measures

Primary and secondary outcomes are guided by the International Aortic Arch Surgery Study Group (IAASSG) (Yan 2014).

Electronic searches

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

• the Cochrane Vascular Specialised Register; and

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

See Appendix 2 for details of the search strategy which will 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 through handsearching relevant journals. The full list of the databases, journals and conference proceedings which have been searched, as well as 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In addition, the CIS will search the following trial registries for details of ongoing and unpublished studies: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); and

• 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 (AE and EPK) will independently screen all titles and abstracts identified from the searches to identify those which might meet the inclusion criteria. We will retrieve the full text of studies identified as potentially relevant by at least one author. The same review authors will independently screen full‐text articles for inclusion or exclusion. Any disagreement 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).

Data extraction and management

Two review authors (AE and EPK) will independently extract data from the eligible studies using an adapted 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 (AE) will enter extracted data into Review Manager Software 5.3 (RevMan 2014). A second review author (NH), will check for accuracy and consistency against the data extraction sheets.

Assessment of risk of bias in included studies

Two review authors (AE and EPK) will independently assess each study for risk of bias according to the following criteria, as recommended by the Cochrane Handbook (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); and

• 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).

Measures of treatment effect

Unit of analysis issues

We will consider the unit of analysis to 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 examining the Chi² test for heterogeneity. We will assess heterogeneity of the overall results for the main outcomes by use of Chi², I² and Tau² statistics, according to the Cochrane Handbook (Higgins 2011).

We will regard statistical heterogeneity as substantial if an 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.

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 (Higgins 2011).

Data synthesis

We will carry out statistical analysis using the Review Manager 5.3 (RevMan 2014). We will use fixed‐effect meta‐analysis for synthesizing 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 average treatment effect is clinically meaningful. 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.

Subgroup analysis and investigation of heterogeneity

Subgroup analyses will be limited to primary outcomes. Planned subgroup analyses include:

• classification based on proximal treatment zone and the extent of the disease (number of zones into which the aneurysm extends);

• connective tissue disease versus degenerative disease;

• associated aortic valve repair;

• elective versus emergency;

• gender (males versus females); and

• stay in intensive care unit versus no stay in intensive care unit.

Sensitivity analysis

We will repeat the analyses including high‐quality trials only. For the purpose of this review, we will classify trials judged as ‘low risk of bias’ for sequence generation and allocation concealment as high‐quality trials. We will also repeat the analyses including RCTs only.