Footnotes

• Twitter @KLechnerMD

• Contributors All authors contributed to this discussion. KL did the literature search, and drafted the manuscript. BS, BL and JS reviewed and edited the manuscript. All authors approved the final version of the manuscript.

• 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 None declared.

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