1 Warwick Clinical Trials Unit, University of Warwick, Coventry CV4 7AL, UK.
2 Surrey Peri-operative Anaesthesia Critical Care Collaborative Research Group, Faculty of Health and Medical Sciences, University of Surrey, Guildford GU27XH, UK.
3 South Central Ambulance Service NHS Foundation Trust, Otterbourne SO21 2RU, UK; University Hospital Southampton, Southampton SO16 6YD, UK.
4 Warwick Clinical Trials Unit, University of Warwick, Coventry CV4 7AL, UK; Heart of England NHS Foundation Trust, Birmingham B9 5SS, UK. Electronic address: [email protected].