primary outcome:
Local anaesthetics and regional anaesthesia versus conventional analgesia for preventing persistent postoperative pain in adults and children
Our primary outcome was persistent postoperative pain (PPP) at three or more months after surgery.We defined PPP as new pain, (which did not exist before the operation), but lasting beyond three months after surgery. We defined our primary outcome of interest as a dichotomous contrast, namely the presence versus absence of pain elicited at that clinical encounter. We accepted the dichotomous pain outcomes as reported in the studies, mostly contrasting pain versus no pain, even though definitions varied at times. Use of pain medication is by some assessed as a dichotomous outcome (no pain medication versus pain medication) or as an ordinal outcome (no pain medication versus non‐opioid pain medication versus opioid pain medication) (Lavand'homme 2005). Some primary study authors define the presence or absence of pain in their study as pain exceeding a given threshold on a continuous pain scale, analogous to responder analysis. We accepted the thresholds used by the study authors, though they sometimes employed different scales or instruments. This responder analysis (Andreae 2015c; Dworkin 2009a), also employed during our previous version of this review (Andreae 2015), counts the number of people with an outcome above a defined threshold. Responder analysis informed our approach to missing data imputation (Andreae 2013b), as detailed below (Dealing with missing data). We discussed responder analysis and the heterogeneity of outcome reporting in greater detail in (Overall completeness and applicability of evidence). Studies elicited the presence of pain at different follow‐up intervals beyond our cut‐off of three months and we discuss the two approaches we took (inclusive versus classical analyses) to address this heterogeneity in Data synthesis.We also assessed differences in scores based on validated pain scales, such as the visual analogue scale (VAS); the verbal rating score; or the McGill pain questionnaire (Dworkin 2009b).As a prerequisite for inclusion, studies had to employ an instrument to subjectively measure patient discomfort (Appendix 7). The study authors primarily used a dichotomous outcome, that is presence or absence of (phantom) pain. They also used several continuous pain scales (verbal rating scale (VRS), visual analogue scale (VAS), numeric rating scale (NRS), bodily pain sub‐component of the Short Form Health Survey (SF‐36)). Nine studies did not record pain as a dichotomous outcome but only used continuous pain scales (Blumenthal 2005; Chiu 2008; Gupta 2006; McKeen 2014; O'Neill 2014; Singh 2013; Sprung 2006; Vrooman 2015; Wodlin 2011). One did record pain as a dichotomous outcome but did not report it in the manuscript, and provided the review authors with the data via email (Kurmann 2015). Nine studies (Brown 2004; Burney 2004; Gupta 2006; Karanikolas 2006; Karmakar 2014; Katz 2004; ; McKeen 2014; Sprung 2006; Wodlin 2011), reported continuous complex outcome instruments, like the McGill questionnaire (Dworkin 2009b), or the Short Form Health Survey (SF‐36) (Ware 1992), which are recommended in consensus statements for the assessment of chronic pain (Gewandter 2015; Turk 2006).