Two authors will independently evaluate studies for eligibility. Screening for eligibility of studies will be performed on titles and abstracts, followed by full-text screening for citations considered potentially eligible by either screener. All citations identified in the screening process as potentially eligible will undergo full text evaluation to determine eligibility by two independent reviewers. Any disagreements between the two reviewers will be resolved through discussion and consensus, and a third reviewer will be consulted if required. Following full-text review, data from eligible studies will be recorded using standardised extraction forms using the Covidence web source (www.COVIDENCE.org). The standardised forms will capture information about types of postsurgical pain, details of postsurgical pain management, pain intensity, cardiovascular risk factors, measures of HRV and participant characteristics. As an optional secondary outcome for the review, postoperative cardiovascular outcomes will be recorded if it is included in eligible studies.
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