Patient and Public Involvement in randomised controlled trials in general and abdominal SURGery: a protocol for the PPISurg systematic review

Abstract

Introduction

Randomised controlled trials (RCTs) are central to generating high-quality evidence in the surgical field but face unique methodological and practical challenges, including recruitment, follow-up, blinding and ensuring patient-centred outcomes. Patient and public involvement (PPI) has emerged as a promising strategy to enhance the relevance, quality and impact of surgical research by actively involving patients throughout the whole research process. Despite growing recognition of its value, the integration and reporting of PPI in surgical RCTs remain inconsistent, and no systematic evaluation has yet addressed its application within general and abdominal surgery.

Methods and analysis

RCTs in general and abdominal surgery published since 2014 will be identified through systematic searches of the databases MEDLINE, Web of Science and CENTRAL. This systematic review and primary (meta-epidemiological) statistical analysis will assess the reporting prevalence, implementation extent and quality of PPI over time. The Guidance for Reporting Involvement of Patients and the Public 2 (GRIPP2)-SF checklist and Cochrane Risk of Bias V.2.0 tool will be used to evaluate PPI reporting and study quality. To enable a comparison between studies reporting PPI and those that do not, propensity score matching will be performed to identify non-PPI studies with similar population and design characteristics. Subsequently, regression analyses will be employed to investigate potential associations between PPI reporting and various trial characteristics, including patient recruitment and retention, outcome selection and methodological quality. The Patient Advisory Board of the Study Centre of the German Society of Surgery is actively engaged in all phases of the systematic review.

Ethics and dissemination

This systematic review does not require ethical approval. Results will be published in an international peer-reviewed scientific journal, as well as distributed in a lay format to the patient community and to the broader public.

PROSPERO registration number

CRD42024524426.

STRENGTHS AND LIMITATIONS OF THIS STUDY.

• This systematic review will comprehensively evaluate the use and reporting of patient and public involvement (PPI) in general and abdominal surgical randomised controlled trials (RCTs), using the Guidance for Reporting Involvement of Patients and the Public 2 (GRIPP2)-SF checklist.

• A meta-epidemiological approach and propensity score matching will allow for the comparison of RCTs incorporating PPI with those without PPI at the trial level.

• Structured participation of the Patient Advisory Board (PAB) in this systematic review in terms of assessment of primary endpoints regarding patient relevance and further interpretation of study results.

• Limitations may include the quality of reporting of PPI in the included RCTs.

Introduction

Randomised controlled trials (RCTs) represent the reference standard of evidence in the surgical field, playing a critical role in advancing clinical practice and informing treatment guidelines. The design and execution of surgical RCTs, however, face unique challenges due to both methodological and psychological complexities.¹ Recruitment issues are a frequent difficulty in general surgical RCTs,²,⁴ alongside significant loss to follow-up, which contributes to attrition bias.⁵ Additional obstacles include the complexity of surgical interventions,⁶ difficulties in blinding, outcome selection⁷ and industry bias.⁸ Furthermore, patient needs and patient-relevant outcomes are often overlooked.

To address these challenges, patient and public involvement (PPI) in clinical research has increasingly been promoted and applied in recent years and thus has become a recognised component of high-quality research as well as a key criterion for obtaining public research funding. PPI involves research conducted with or by patients and the public rather than to, about or for them.⁹ Existing literature highlights several potential benefits of PPI in surgical trials, including optimised identification of research topics, which leads to a higher clinical relevance of research questions,¹⁰,¹³ improved study design,¹⁴,¹⁶ increased participant enrolment¹⁷ and stronger peer endorsement of research. Furthermore, PPI grants patients a voice in research whose outcomes directly affect them and empowers them through active participation in the research process.

Methods for PPI vary, including integrating patients as members of research steering committees^{14 18} or engaging them through questionnaires¹⁹ and interviews.^{20 21} PPI should ideally be implemented during the early stages of research projects in order to ensure sustainable and constant involvement and thus representation of patient interests throughout the entire conduct.¹⁵ In addition to contributing to the planning and execution of trials, patients and the public can also be involved in the analysis, interpretation and dissemination of the results, particularly to ensure that research outcomes are accessible to the broader public. However, there is currently no consensus on which PPI strategies are best suited for specific research phases or types of clinical studies. Additionally, there is no standardised framework for implementing PPI in a structured manner in surgical research.

While a few scientific journals now require PPI to be explicitly reported in protocol and result articles, the systematic adoption of PPI in surgical research remains limited. The first systematic review by Jones et al on this topic revealed a scarcity of reports on PPI, and when reported, showed suboptimal quality and transparency.⁹ Since then, several RCTs incorporating PPI have been published across various surgical fields, including general surgery.^{18 22 23} Moreover, the GRIPP (Guidance for Reporting Involvement of Patients and the Public) reporting tool, the first international evidence-based guideline for reporting PPI has been updated to establish an international consensus on key reporting items to further improve the quality, transparency and consistency of the PPI evidence base.²⁴ Despite these advancements, the implementation and integration of PPI in surgical RCTs remain unclear, including the potential benefits of PPI in improving various outcomes. Furthermore, differences between surgical specialties and heterogeneous patient populations with specific needs can lead to distinct methodological challenges in recruitment, follow-up and outcome selection, which may particularly benefit from PPI integration. To date, no systematic evaluation of PPI in general and abdominal surgical research, which studies both some of the most frequently performed operations (eg, appendectomy, cholecystectomy) as well as highly complex oncologic multiorgan procedures (eg, pancreaticoduodenectomy), has been conducted, and evidence for recommendations for a more structured implementation of PPI in the future is missing.

Objective

The aim of this systematic review is to assess the prevalence, extent and reporting quality of PPI in RCTs in the field of general and abdominal surgery. Moreover, RCTs incorporating PPI will be compared with those without to evaluate their impact on patient recruitment, selection of primary and secondary endpoints and overall methodological quality to ultimately provide practical evidence-based recommendations for PPI application in surgical research.

Methods

Study design

The Patient and Public Involvement in randomised controlled trials in general and abdominal SURGery (PPISurg) project is a systematic review and primary (meta-epidemiological) statistical analysis, which has been registered in the PROSPERO database (registration number: CRD42024524426) in March 2024. This study protocol has been written according to the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols 2015 guidelines (online supplemental table 1).²⁵ The systematic literature search commenced after PROSPERO registration and screening were completed by October 2025. Data extraction of included studies and analyses will be conducted from November 2025 to January 2026.

Eligibility criteria

Types of studies

Eligible studies for this systematic review are all RCTs involving patients undergoing any type of general or abdominal surgery, which encompasses procedures involving the oesophagus, stomach, small intestine, large intestine, liver, pancreas, gallbladder, appendix, bile ducts and thyroid gland, as well as proctological interventions, transplant surgery and hernia repairs. To capture the current state and implementation of PPI in surgical trials over the last decade, RCTs published since 2014 will be included, as PPI in clinical research has become increasingly widespread and established since then. RCTs with reported PPI in general and abdominal surgery, regardless of the type of surgical intervention, will be included. A trial will be considered to have ‘reported PPI’ if any aspect of patient or public involvement is described in the abstract, full text, acknowledgements or supplementary materials. This includes mention of all levels of PPI,²⁶ for example, patient or public contributors, advisory boards, consultations, coauthorships or collaborations in any research phase.

As comparators, RCTs that do not report any PPI, regardless of the type of surgical interventions in general or abdominal surgery, will be included based on predefined matching criteria. RCTs focusing on interventions in other surgical specialties, including cardiothoracic, endoscopic, dental, dermatological, gynaecological, neurosurgical, orthopaedic, otolaryngological, paediatric, plastic, urological or vascular surgery, will be excluded to ensure a realistic and feasible scope, avoid variability in PPI practices across specialties and provide findings directly applicable to the field of general and abdominal surgery.

Data sources and search strategy

A systematic literature search and hand-search will be conducted in all relevant electronic bibliographic databases for surgical literature: MEDLINE (via PubMed), Web of Science and CENTRAL. Additionally, databases of funded projects from organisations requiring PPI (eg, National Institute for Health and Care Research, German Federal Ministry of Research, Technology and Space (BMFTR)) will be manually reviewed for relevant RCTs with reported PPI. Reference lists from relevant articles and systematic reviews will also be hand-searched for additional studies. The complete preliminary search strategy is included in online supplemental table 2.

Eligible articles identified through database searches will be further complemented by searching the Science Citation Index (via Web of Science) for studies citing the included trials. All search results will undergo an eligibility assessment.

Data collection

Retrieved studies will be uploaded to the Covidence systematic review software (Veritas Health Innovation, Melbourne, Australia, available at www.covidence.org and, after removing duplicates, will be independently screened by two reviewers for study titles and abstracts. In the second stage of the screening process, full-text reports of the remaining studies will be assessed. Reviewer disagreements will be resolved through consensus or consultation with a third reviewer. The study selection process will be conducted according to the flowchart shown in figure 1.

Figure 1. Preferred Reporting Items for Systematic Reviews and Meta Analyses flowchart of the literature search and selection process. RCT, randomised controlled trial.

Data from eligible trials will be extracted using a standardised electronic data form within the Covidence software. For RCTs with insufficient PPI reporting in the result publication, corresponding study protocols will be searched for PPI and study authors will be contacted to obtain additional information.

Outcome parameters

The primary objective of this systematic review is to investigate how often PPI is reported in trials focusing on general and abdominal surgery and to determine whether the proportion of RCTs performing and adequately reporting PPI has increased over time. Additionally, the following outcomes will be analysed to assess both the extent of PPI implementation and its potential benefits:

1. The scope of PPI and stages of trial planning and implementation where PPI is applied will be examined, including the following aspects: priority setting, commissioning, trial design, conduct and management of trial, analysis of data, publication and dissemination of data, including publication in lay language.

2. The type and extent of PPI will be investigated as follows:

   1. PPI types according to ‘Briefing notes for researchers—public involvement’²⁶ : consultation (=asking members of the public for their views and using these to inform your decision-making) versus collaboration (=an ongoing partnership between researchers and the members of the public for shared decision-making in the research process) versus co-production (=researchers and the public work together, sharing power and responsibility from the start to the end of the project, patients as coauthors and joint grant holders).

   2. Involvement of patient representatives in trial conduct and management as members of the trial committees (eg, steering group, data and safety monitoring board).

   3. Total number of patient representatives involved.

3. Quality, transparency and consistency of the reported PPI will be assessed by application of the GRIPP2-SF reporting checklist,²⁴ which is the first international evidence-based, consensus-informed guidance for reporting PPI in research. The short version of the checklist is supposed to be applied in trials with any topic where PPI is a secondary or tertiary focus and is therefore applicable in this systematic review scope. The checklist contains the sections aim, methods, results, discussion and reflections.

4. Costs for PPI conduct will be evaluated.

The following endpoints will be compared between trials with and without PPI:

• 5 1Feasibility of recruitment as defined by whether the planned sample size for patient recruitment could be achieved (yes/no) and whether patient recruitment was completed in the planned time period (yes/no) according to the protocol publication.
• 5 2Retention in clinical trials in terms of dropout rate as defined by a dropout rate that does not exceed the originally planned dropout rate by 5% (yes/no).
• 5 3The type of chosen primary and secondary outcomes will be assessed:

  1. Patient-reported outcomes used as primary endpoints (yes/no).

  2. Patient-relevant endpoint used as primary endpoint as judged by the Patient Advisory Board (PAB) of the Study Centre of the German Society of Surgery (SDGC) (yes/no). To this end, primary endpoints of all RCTs with PPI, as well as those of corresponding propensity score-matched RCTs, will be judged individually through a consensus process taking into account several patient-relevant factors. Each trial will be independently reviewed by at least two PAB members; discrepancies will be discussed in consensus meetings.

  3. Frequencies of surrogate primary endpoints.

  4. Number of patient-reported outcomes (including primary and secondary endpoints).

• 5 4Significant result of the primary endpoint favouring the interventional group (yes/no).
• 5 5Methodological quality of RCTs according to the Cochrane Collaboration Risk of Bias V.2.0 tool, including evaluation of randomisation procedures and allocation to provide an overall risk of bias judgement at the study level.²⁷

Data synthesis

To address the research question of the impact of PPI in surgical RCTs, a meta-epidemiological analysis will be conducted, as the outcome is observed at the trial level rather than the patient level. Accordingly, trials will be categorised into those with and without reported PPI. All variables will be analysed descriptively, and appropriate summary statistics will be provided. For categorical variables, absolute and relative frequencies will be reported, while continuous variables will be described using either mean±SD or median with IQR, as appropriate. Outcomes 1–4, which are only assessed in studies reporting PPI, will be presented both as frequencies and cumulative frequencies over time. The influence of time on the frequency of RCTs reporting PPI will be evaluated using a univariate regression model.

Propensity score matching (PSM)

To facilitate a meaningful comparison of outcomes 5–9 between trials with and without reported PPI, a PSM will be performed to match RCTs without PPI to those with PPI. The PSM will be conducted using the nearest neighbour method, with a planned 3:1 matching ratio to enhance the statistical power of subsequent analyses. Given that approximately 20 studies reporting PPI are expected, a ratio of 3:1 is considered a good trade-off between statistical power and the practical feasibility of extracting the necessary data for analysis. Since we anticipate a large number of non-PPI studies, we expect to identify a sufficient number of studies to be matched with the PPI studies. Predefined study-level matching criteria—(1) number of participants, (2) single-centre or multicentre trial, (3) surgical field, (4) continent of trial implementation, (5) year of publication and (6) malignant or benign surgical indication—will be used to estimate the propensity scores. Following matching, the null hypothesis (H₀) will be tested that PPI is not associated with the specified trial characteristics (which are the above-defined outcomes 5–9) against the alternative hypothesis (H₁) that it is associated. Depending on the outcome scale, either linear or logistic regression models will be applied, incorporating matching weights to account for the allocation ratio. Both PPI and propensity scores will be included as covariates, and, if feasible, the matching covariates will replace the propensity score in the models. Cluster-robust SE will be calculated for the regression coefficients and reported alongside their 95% CIs.

Publication bias will be assessed using separate funnel plots for PPI and non-PPI studies. Sensitivity analyses will be conducted based on study quality, including only studies with a low risk of bias. Statistical significance will be defined as two-sided p values below 0.05, though p values used in descriptive statistics will be interpreted descriptively. All analyses will be performed using R (V.4.5.1 or later), along with the tidyverse and MatchIt extensions.²⁸ The Grading of Recommendations, Assessment, Development and Evaluations framework²⁹ will be used to assess the certainty of the cumulative evidence for each assessed outcome.

Patient and public involvement (PPI)

The framework of this systematic review, including its research questions and endpoints, was jointly developed in collaboration with the PAB of the SDGC to guarantee high quality and relevance from a patient’s perspective. The PAB, founded in 2021, has around 20 members who have had one or more mostly oncological abdominal operations in the past. The patient representatives in the PAB are highly experienced partners in terms of patient involvement, based on their previous involvement and methodological education in clinical research and were found to be a suitable patient target population to involve in this study and contribute their experiences and priorities. Members of the PAB are involved in every stage, from the study design (advising function for study design and inclusion criteria) and analysis of the data to the dissemination of the results in lay-term language at patient conferences and in self-help group newsletters, websites and magazines. Additionally, all included trials will be assessed by the PAB to evaluate the primary endpoint’s relevance from a patient’s perspective. The PAB will further participate in formulating recommendations arising from this study to guide future PPI strategies in surgical trials. Reporting of PPI in this study in the final manuscript will be done according to the GRIPP2-SF checklist.²⁴

Discussion

For the advancement of evidence-based surgery, meticulous design and execution of RCTs are pivotal, as is the effective translation of their findings into clinical practice. Including the perspectives of patients and the public can greatly improve the relevance and clinical implications of research outcomes and their implementation in patient care. It has further been shown that PPI improves recruitment in clinical trials.¹⁷ When patients are systematically involved from defining the research question, at the outset of the trial design and, consequently, in the development of recruitment strategies, this collaboration directly impacts the conduction phase of a study. While a few studies have explored the involvement of patients and the public in surgical trials,^{9 15 17} most were conducted at a time when the concept of PPI was relatively new, and recommendations for its implementation were still lacking, leaving its current impact largely unclear.

Critics argue that PPI is sometimes pursued for superficial reasons, such as meeting funding requirements, rather than being meaningfully integrated into research. Further concerns about tokenism and doubts about the feasibility and benefits of PPI might hinder its widespread acceptance.

Thus, stronger evidence is needed regarding the prevalence, extent, quality of reporting and potential benefits of PPI in RCTs in surgery. A comprehensive understanding of current PPI practices is essential not only to assess how PPI is currently conducted and reported but also to enable the development of targeted guidance that establishes it as a cornerstone of clinical research. This systematic review of the available evidence on PPI in surgical trials could promote its broader implementation and provide clearer recommendations on how to effectively implement PPI to maximise its potential benefits.

Ethics and dissemination

No approval by an independent ethical committee is needed for this systematic review, as no primary patient data will be collected. Results will be published in a peer-reviewed scientific journal. Further dissemination of the results will be made in lay-term language, for example, on patient conferences and in self-help group newsletters through the PAB.