What have we learned from network meta-analysis applied to critical care? A narrative review.

INTRODUCTION: It is widely accepted in modern medicine that medical decisions must be supported by scientific evidence. Identifying the best intervention when several options are available constitute a great challenge for every clinician. Traditional meta-analysis (TMA) allows summarizing evidence from studies that compare the same two interventions for one event (head to head studies or direct comparisons). Network meta-analysis (NMA) is a relatively new procedure that allows to compare multiple interventions for one event, even when non head to head studies have been conducted (indirect evidence). Other advantages of MNA include increasing the accuracy of the results and ranking all the interventions according to their effectiveness. These features are of paramount importance as (a) they summarize information from events (e.g. diseases or outcomes) that has more than 2 possible interventions (e.g. treatments or procedures), (b) they strengthen the level of guideline recommendations and (c) they identify new hypotheses based on indirect comparison.

EVIDENCE ACQUISITION: Manuscripts published in Pubmed.

EVIDENCE SYNTHESIS: This narrative review was written mainly for clinicians non trainees in statistics with the aim to describe what NMAs are. First, we provide a description of the usefulness, interpretation, assumptions and main plots related to NMAs. Second, we analyzed some examples of NMAs related to critical care medicine. As this is a narrative review, all manuscripts have been selected, according to our best knowledge, with the aim to illustrate different features, options or applications of MNA in critical care. Third, we include a pragmatic approach about how results from NMAs can improve the clinical practice as well an R script with a database to conduct an MNAs and reproduce figures and tables that have been shown here.

CONCLUSIONS: NMA is an established, robust, objective and reproducible statistic technique that has been applied to several critical care areas. Clinical practice guidelines have started to include MNA evidence to support their recommendations. In future years, it seems highly probable that this technique will increase it applicability in almost all areas of critical care medicine.