[1] Univ Coll Hosp, London NW1 6BU, England
[2] Joint UCL UCLH Comprehens Biomed Res Ctr, Surg Outcomes Res Ctr, London WC1E 6BT, England
[3] Cent London Sch Anaesthesia, Ctr Anaesthesia, London NW1 2BU, England
[4] Diana Princess Wales Hosp, Dept Surg, Grimsby DN33 2BA, Lincs, England
[5] Doncaster Royal Infirm, Dept Vasc Surg, Doncaster DN2 5LT, England
[6] No Gen Hosp, Dept Surg, Sheffield S5 7AU, S Yorkshire, England