The effect of minimum volume standards in hospitals (MIVOS): a systematic review

OBJECTIVES: The relationship between the volume of medical procedures conducted in hospitals and the resulting health outcomes has been described for various surgical and non-surgical medical interventions. As a policy response to this, several countries have implemented minimum volume standards. However, there is currently a lack of systematically compiled evidence assessing their impact. To close this research gap, we conducted a systematic review on the effects of minimum volume standards in hospitals. DESIGN: Systematic review using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach. DATA SOURCES: MEDLINE, PubMed Central and Bookshelf (PubMed), EMBASE (Elsevier), CENTRAL (Cochrane Library), CINHAL (EBSCO), EconLIT (EBSCO), PDQ-Evidence for Informed Health Policymaking, Health Systems Evidence and three trial registries were searched until June 2023. Additionally, manual searches were conducted. ELIGIBILITY CRITERIA FOR SELECTING STUDIES: For inclusion in this review, studies must investigate the effects of minimum volume standards. We accepted all categories of outcomes. Following the Cochrane Effective Practice and Organisation of Care (EPOC) criteria, only a strict set of study designs, namely randomised controlled trials, non-randomised controlled trials, controlled before-after studies and interrupted time series studies, were included. No restrictions were placed on language, publication date or publication status. DATA EXTRACTION AND SYNTHESIS: Two reviewers independently screened titles and abstracts for eligibility, reviewed the full texts and performed data extraction of the included articles. Risk of bias was assessed using the 'Risk Of Bias In Non-Randomised Studies-of Interventions' (ROBINS-I) tool. Certainty of evidence was rated using the GRADE approach. For data synthesis and statistical analyses, we adhered to the EPOC guidance. RESULTS: We included nine studies into our systematic review. Overall, the outcomes reported in the studies are heterogeneous, which did not allow for a meta-analysis, resulting in a narrative analysis of the found evidence. While travel distance increased and length of stay decreased, other reported outcomes such as complications or reoperations were not affected by the introduction of minimum volume standards. Overall, the risk of bias was considered serious for results on outcomes of seven out of the nine included studies and moderate for the remaining two. The certainty of evidence was rated low for complications, reoperations, length of stay and travel distance and very low for mortality (in-hospital; 30 days). CONCLUSION: This systematic review does not provide conclusive evidence on the effects of minimum volume standards in hospitals regarding any outcomes. The certainty of evidence for mortality (in-hospital; 30 days) is very low and low for complications, reoperations and travel distance. The results are based on a relatively small number of studies for most outcomes. There is a need for studies researching the effects of minimum volume standards based on a robust study design. PROSPERO REGISTRATION NUMBER: CRD42022318883.