1. Radcliffe Department of Medicine, University of Oxford, Oxford, UK
2. Nuffield Department of Anaesthetics, Oxford University Hospitals NHS Foundation Trust, Oxford, UK
3. Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK
4. Department of Anaesthesia and Intensive Care, Royal Papworth Hospital, Cambridge, UK