1 Bloomsbury Institute of Intensive Care Medicine, Division of Medicine, University College London, Gower St, London, WC1E 6BT, UK.
2 Intensive Care Unit, Department of Acute Medicine, University Hospital Basel, Basel, Switzerland.
3 Bloomsbury Institute of Intensive Care Medicine, Division of Medicine, University College London, Gower St, London, WC1E 6BT, UK. m.singer@ucl.ac.uk.