Optimal methods for the use of ‘pain’ as an outcome in systematic reviews of post-operative pain management: a Network Innovation Fund project

In 2019, Cochrane launched the CRG Networks Innovation Fund to support projects that lead to harmonization of processes of review production and/or editorial procedures and improvements in content or quality across the CRG Networks and the Cochrane Library. Our project aims to provide guidance on the optimal management of pain as an endpoint in systematic reviews including trials of interventions used in a post-operative environment.

Our Objectives are:

  1. to establish a common position on how to conceptualise the measurement of pain as a private mental event subjectively reported by either the patient or an observer;
  2. to establish an optimal approach to the use of pain states including change in pain state or a satisfactory state with low or no pain; and
  3. to provide a framework for dealing with acute post-operative pain for non-pain experts undertaking systematic reviews (in particular Cochrane Reviews) where pain following an operation is an outcome. 

This project will be led by Cochrane PaPaS, and will involve an invited workshop of experts in the field of post-operative pain for some of the tasks.

We will focus on:

  1. sources of heterogeneity in methods and reporting;
  2. the use of primary and secondary endpoints, including surrogate and indirect measures;
  3. drafting a template and decision-making flowchart; and
  4. testing that template and flowchart with different reviews across the MOSS Network. The final result will be a published article in an open access journal and shared across the Networks.

The process of synthesizing evidence from clinical trials (and other well conducted studies) for the treatment and management of pain involves making numerous decisions about the place of pain and analgesia in both the trials and the reviews. Pain as an outcome is a deceptively simple endpoint. To the lay-person it may seem simple; one wants to reduce pain. There are, however, multiple reasons why the decisions one makes about pain as an outcome are far from simple. Multiple sources of variance in the treatment of pain as an outcome translate into inconsistency and confusion.

Evidence synthesis requires a series of related protocolised decisions about the appropriate endpoints for use in systematic review with a consideration of:

  1. optimal methods for combining different measurement technologies;
  2. the use of state versus continuous change measures of outcome [1]; and
  3. appropriate and relevant cut-offs for change of status (e.g., moving from moderate pain intensity to a state of no-worse than mild pain or clinically important effects [2; 3]. 

We will outline how best to present results in summary formats such as GRADE, PLSs, and abstracts, which is critical to consistent and high quality Cochrane Reviews.

Within Cochrane there is a tremendous wealth of experience in these matters, and we look forward to working with the community to complete this project.


  1. Moore RA, Moore OA, Derry S, Peloso PM, Gammaitoni AR, Wang H. Responder analysis for pain relief and numbers needed to treat in a meta-analysis of etoricoxib osteoarthritis trials: bridging a gap between clinical trials and clinical practice. Ann Rheum Dis 2010;69(2):374-379
  2. Collins SL, Moore RA, McQuay HJ. The visual analogue pain intensity scale: what is moderate pain in millimetres? Pain 1997;72(1-2):95-97
  3. Moore RA, Straube S, Aldington D. Pain measures and cut-offs - 'no worse than mild pain' as a simple, universal outcome. Anaesthesia 2013;68(4):400-412