Performing the Systematic Review

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The process for performing a systematic review is based on the protocol of the Cochrane Collaboration. The PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) guidelines are used to perform the literature search and assess the quality and level of evidence of all included studies.
The most critical aspect of the literature search is to ensure that the appropriate “search terms” are clearly defined. The search terms are as broad as possible, to maximize the scope of the search and reduce the risk of missing relevant publications. Search terms include words or phrases related to pain and possible interventions, as well as procedure-specific terms []. For example, pain-related terms will include: pain OR analgesi* OR anaesthe* OR anesthe* OR vas OR "visual analog*" OR vrs OR mcgill OR epidural OR neuraxial OR intrathecal OR spinal OR caudal OR interpleural OR “peripheral nerve” OR “peripheral block” OR intercostal OR “nerve block” OR NSAID OR COX-2 OR paracetamol OR acetaminophen OR gabapentin OR pregabalin OR clonidine OR opioid OR ketamine OR corticosteroid). These terms are applied in various combinations, together with the use of the “related articles” function to maximize the search. Several electronic databases (e.g., Ovid Medline, Medline InProcess, other non-indexed citations, and Medline EPub ahead of print, Embase, and Cochrane controlled trials register published by the Cochrane Library) are utilized to identify studies published within a pre-defined time period, as determined by the PWG; secondary literature searches may also be performed and relevant systematic reviews identified in the Cochrane library.
Randomised controlled clinical trials and systematic reviews of analgesic, anaesthetic and surgical interventions, addressing pain management in the surgical procedure being reviewed are included. The RCT should report pain scores using linear pain scale, e.g. visual analogue scale (VAS) or verbal or numerical rating scale (VRS or NRS). While there is evidence that studies published in English are more likely to report beneficial effects for a particular treatment or intervention than studies published in other languages, only English language studies are included.
The selection process is performed in a step-wise process according to the PRISMA checklist. Two reviewers select the studies independently by screening the titles and/or abstracts according to a priori defined inclusion criteria (see above). The results between the two reviewers are matched. Any disagreements are resolved by consensus within the subgroup. At any stage, in the case of insoluble discrepancies, a third reviewer is involved in the discussion. Abstracts (if only titles were screened) and/or full-text of the papers included from the first step are reviewed and irrelevant papers excluded. Any disagreements are resolved by consensus. The number of excluded studies in this step and the reasons for exclusion are documented . In addition, reference lists of all relevant studies from the electronic search will be manually searched to identify additional eligible studies.
All included studies will be assessed for quality of reporting of methodology and results using the Cochrane Collaboration’s tool. Numerical scores (total 1–5) for study quality: assigned using the method proposed by Jadad 1996, to indicate whether a study reports appropriate randomisation, double-blinding and statements of possible withdrawals. Empirical research confirms that low-quality trials are associated with an increased estimate of treatment benefit compared to high-quality trials. Allocation concealment assessment: indicates whether there was adequate prevention of foreknowledge of treatment assignment by those involved in recruitment (A adequate, B unclear, C inadequate, D not used). Empirical research has shown that trials with inadequate or unclear allocation concealment report significantly greater estimates of treatment effect than those trials in which concealment was adequate. Allocation concealment was found to be more important for preventing bias than other aspects of study quality, such as generation of the allocation sequence and double-blinding. Statistical analyses and patient follow-up assessment: indicates whether statistical analyses were reported, and whether patient follow-up was greater or less than 80%. Additional study quality assessment: including an assessment of how closely the study report meets the requirements of the CONSORT statement.
The information from the included studies is extracted and tabulated, with similar interventions grouped together for ease of analyses. The information recorded includes, but is not be limited to, interventions evaluated, characteristics of study design, treatment in the control group (e.g., placebo or active comparator), patient numbers in each group, population (age, gender, opioid tolerance and psychiatric ailments), details about surgical procedure, duration of follow-up, pain scores at rest/on movement, supplementary analgesic use, time to first request for rescue analgesia, opioid-related adverse events such as postoperative nausea and vomiting, whether any other additional outcomes were assessed, Jadad score, patient follow-up >80% and appropriate statistics reported, allocation concealment, and whether  CONSORT requirements are met. In addition, a column will include the conclusions of the study in detail.
Qualitative results will be reported for all specified outcomes, and details of the assigned levels of evidence will be recorded.
Quantitative analyses will be performed if the studies are determined as suitable, according to the Prospect criteria. Data should be are homogenous and reported in an appropriate way. In addition, for the studies to be grouped together they should have uniformity in the analgesic technique(s) utilized. Studies that do not report mean and standard deviation data (for continuous variables) or proportion of patients affected (for dichotomous variables), are not included in the meta-analyses.
The information used to determine recommendation of an analgesic technique includes analyses of the systematic review. The studies that have been selected based on the Cochrane approach then undergo critical evaluation for relevance of the design with respect to the validity of the analgesic/analgesic technique in current perioperative care practice. For example, if the study design does not include an analgesic technique that would be considered as “basic” for the surgical procedure, it would not be considered optimal. Also, the subgroup will determine if the analgesic intervention would further improve postoperative pain relief and/or outcome when added to the “basic” analgesic regimen. For example, adding intravenous lidocaine infusion or TAP blocks to patients undergoing laparoscopic cholecystectomy may not be beneficial over the “basic” analgesic regimen of paracetamol + NSAIDs or COX-2 specific inhibitors + port site infiltration). Furthermore, analyses of the balance between the invasiveness of the analgesic technique and the consequences of postoperative pain as well as a balance between the analgesic efficacy and adverse event profile of the intervention is used to develop recommendations to ensure that patient safety is maintained. In addition, patient characteristics (e.g., opioid tolerance and psychiatric ailments) may be included.