Footnotes

• Twitter @Olivierdefre

• Contributors IVH: concept and design of the study, research of the available literature, data collection, analysis and interpretation of data, writing up of the first draft of the paper, revising article, review and approval of the final draft. ODF: concept and design of the study, research of the available literature, data collection, analysis and interpretation of data, writing up of the first draft of the paper, revising article, review and approval of the final draft. FP: data collection, analysis and interpretation of data, drafting article, review and approval of the final draft. JC: data collection, analysis and interpretation of data, drafting article, review and approval of the final draft. AML: concept and design of the study, analysis and interpretation of data, writing up of the first draft of the paper, revising article, review and approval of the final draft. CV: concept and design of the study, analysis and interpretation of data, revising article, review and approval of the final draft. SVB: concept and design of the study, analysis and interpretation of data, revising article, research of the available literature, review and approval of the final draft. SVP: concept and design of the study, analysis and interpretation of data, revising article, review and approval of the final draft. DM: concept and design of the study, statistical analysis and interpretation of data, revising article, review and approval of the final draft. AH: concept and design of the study, analysis and interpretation of data, writing up of the first draft of the paper, revising article, review and approval of the final draft. All authors agreed to be accountable for all aspects of the work thereby ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests AH has consulted, advised and/or performed industry-sponsored research for Philipps, GE, Sonosite, Konica Minolta, Codman & Shrutleff (Johnson and Johnson), Cadence, Insitu Biologics, Heron Therapeutics, Pacira, Baxter and BBraun Medical. AH receives royalty income from BBraun Medical. He owns and directs NYSORA, the New York School of Regional Anesthesia. The other authors declare no conflicts of interest.

• Provenance and peer review Not commissioned; externally peer reviewed.