Rationale

Paediatric Critical Care (PCC) has 30 units across the United Kingdom, comprising a total of approximately 400 beds [1]. The occupancy rate of PCC beds runs critically high (above 85% occupancy) most of the year and studies have shown an increasing demand for PCC beds with concern that demand may soon outstrip resources [1]. One reason for increasing demand is the greater number of a heterogeneous group of children with complex critical illness (CCI) who often have prolonged lengths of stay (PLOS). The definition for a PLOS PCC admission varies from >14 to >28 days. Over the last two decades, PLOS PCC admissions have increased significantly and now account for between 42-51% of PCC patient days [2]. PLOS PCC patients have a high resource utilisation and a median overall hospital length of stay of 98 days [3]. PCC has a decreasing overall trend in mortality, but PLOS patients have significantly higher mortality than the general PCC population [3].

Existing classification systems of CCI patients are variable and do not allow for accurate documentation of the incidence of PCC admission and subsequent mortality or morbidity [4].

Objectives

This systematic review aims to primarily examine the current nomenclature and associated criteria of children with complex critical illness. Additionally, the systematic review will investigate secondary outcome measures of priority in this undefined patient population.

Study design

This systematic review protocol was developed using systematic review published methodology [2,10–14]. It is reported according to the Preferred Reporting Items for Systematic Review and Meta-analyses (PRISMA-P) [10], this is detailed in the Checklist in S1 Checklist. The study was registered in the International Prospective Register of Systematic Reviews (PROSPERO; registration number is: CRD42024529649) after confirming no similar systematic reviews were already registered. An accurate audit trail has been kept allowing for reproducibility [13]. This study is exempt from ethics approval as this work is carried out on published documents.

Eligibility criteria

The following criteria will be considered for this review

Information sources

This review is reviewing experimental studies, randomised controlled trials, non-randomised controlled trials, before and after studies, and interrupted time-series studies. In addition, analytical observational studies including prospective and retrospective cohort studies, case-control studies, and analytical cross-sectional studies are being considered for inclusion. This review will consider descriptive observational study designs and descriptive cross-sectional studies for inclusion. Qualitative studies are also being considered that focus on qualitative data including, but not limited to, designs such as grounded theory, ethnography, qualitative description, and action research. Children with CCI are a heterogeneous group with a wide range of clinical management needs within PCC. To gain a deeper understanding of the topic and present a balanced perspective, “Tier 1” grey literature will be reviewed. This includes book chapters, government reports, think tank publications, and policy documents according to Adams et al. [15,16].

Search strategy

The search strategy includes all languages, using translation online tools [17] and language capabilities of author team (English, Spanish and Portuguese) and full-text papers. The search strategy aimed to locate both published and unpublished studies. An initial limited search of Ovid MEDLINE was done to identify articles on the topic. The text words contained in the titles and abstracts of relevant articles, and the index terms used to describe the articles were used to develop a full search strategy for The Cochrane Library, the Cumulative Index to Nursing and Allied Health Literature (CINAHL), MEDLINE, EMBASE, Trip database (see Search strategy in S1 Appendix).

The search strategy, including all identified keywords and index terms, will be adapted for each included database and/or information source. The reference list of all included sources of evidence will be screened for additional studies.

Ongoing consultation with a health librarian will aid the specificity and comprehensiveness of the search. The MEDLINE search strategy is within the PROSPERO registration appendix to allow another reviewer the ability to replicate and/or evaluate the search. The impact of novel treatments on enhancing survival has grown more prevalent over the past ten years, as evidenced by a four-fold increase in long-stay patients in PCC, which is associated with a higher mortality rate [18]. Data management and selection process

Following the search, all identified citations will be collated and uploaded into Covidence, and duplicates removed. Titles and abstracts will be screened by three independent reviewers for assessment against the inclusion criteria. All sampling decisions will be transparent and justified with a PRISMA search flow diagram [2].

The full text of selected citations will be assessed in detail against the inclusion criteria by two or more independent reviewers. Reasons for the exclusion of sources of evidence at full-text review that do not meet the inclusion criteria will be recorded and reported in the systematic review. The search results and study inclusion process will be reported in full in the final systematic review and presented in a Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) flow diagram [19].

Data collection process

Data will be extracted from papers included in the review by three independent reviewers using the systematic review software tool Covidence. The data extracted will include specific details about the participants, concept, context, study methods, and key findings relevant to this systematic review.

Data will also be clustered geographically into related subgroups to identify themes whilst maintaining a detailed audit trail. A narrative summary will accompany the tabulated results and will describe how the results relate to the systematic review objectives.

A draft extraction form is provided in S1 Table. The draft data extraction tool will be modified as required during each data extraction process. Modifications will be detailed in the systematic review. Any disagreements that arise between the reviewers will be resolved through discussion, or with an additional reviewer/s. If appropriate, authors of papers will be contacted to request missing or additional data, where required. Critical appraisal of individual sources of evidence will be done.

Quality assessment

The quality and validity of the studies selected will be assessed using the critical appraisal skills program checklists (CASP) to mitigate bias [20–23]. Eight studies (four quantitative and four qualitative studies) will be randomly picked to test and further refine the quality assessment tool by all reviewers. Consistencies and inconsistencies between reviewers will be noted, alongside this, the scoring system will be modified according to problems encountered.

Qualitative studies will be evaluated utilising the GRADE-CERQual approach [24]. The evidence will be presented in a summary of qualitative findings table, incorporating CERQual assessment of confidence in the evidence scores for each summary of review finding.

Quantitative data will be geographically clustered into related subgroups to identify themes while maintaining a detailed audit trail. A narrative summary will accompany the tabulated results and will describe how the results relate to the review objectives and questions.

Patient and public involvement

This protocol was developed with public and patient involvement. They were involved from the first principal onwards. The research questions have been developed as a result of the author teams’ engagement with children with complex critical illness and their families in PCC. A parent of a child with CCI has commented on the methods and was integral to the protocol finalisation. A parent advisory group is being formed for the consensus work following the review.