1 Oxford Trauma & Emergency Care (OxTEC), Nuffield Department of Orthopaedics, Rheumatology, and Musculoskeletal Sciences, University of Oxford, Oxford, UK david.metcalfe@ndorms.ox.ac.uk.
2 Emergency Medicine Research in Oxford (EMROx), Oxford University Hospitals NHS Foundation Trust, Oxford, UK.
3 Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.
4 Department of Anaesthesia, Aneurin Bevan Health Board, Newport, UK.