1 Central London School of Anaesthesia, London, UK.
2 Department of Anaesthesia, University of California San Francisco, San Francisco, CA, USA.
3 Department of Anaesthesia, Southampton University Hospitals NHS Trust, Southampton, UK.
4 Department of Anaesthesia, Perioperative Medicine and Critical Care, Division of Surgery and Targeted Intervention, University College London, London, UK.
5 Centre for Perioperative Medicine, Division of Surgery and Targeted Intervention, University College London, London, UK. Electronic address: d.wagstaff@ucl.ac.uk.