1 Barts and The London School of Medicine and Dentistry, Queen Mary University London, Garrod Building, Turner Street, Whitechapel, London, E1 2AD, UK. c.turner@smd11.qmul.ac.uk.
2 Barts and The London School of Medicine and Dentistry, Queen Mary University London, Garrod Building, Turner Street, Whitechapel, London, E1 2AD, UK.
3 London's Air Ambulance, Barts Health Trust, London, UK.
4 The Norwegian Air Ambulance Foundation, Drøbak, Norway.
5 Department of Health Studies, University of Stavanger, Stavanger, Norway.