This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2017. Other selected articles can be found online at http://ccforum.com/series/annualupdate2017. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www. springer.com/series/8901. Originally published in the Annual Update in Intensive Care and Emergency Medicine 2017. The number of authors differs in the two versions due to constraints regarding the number of authors in the Annual Update in Intensive Care and Emergency Medicine. In the Annual Update version of the review, the three senior authors appear in the acknowledgement section. In the Critical Care version, these three senior authors appear as full authors of the manuscript. All authors helped draft and revise the manuscript for critical intellectual content.