A Hollingsworth1, G Danjoux2, S J Howell3. 1. Department of Vascular Surgery, James Cook University Hospital, Middlesbrough, UK. 2. Department of Anaesthesia, James Cook University Hospital, Middlesbrough, UK Health and Social Care Institute, Teesside University, Middlesbrough, UK. 3. Leeds Institute of Biomedical and Clinical Sciences, University of Leeds, UK Department of Anaesthesia, Leeds General Infirmary, Leeds, UK s.howell@leeds.ac.uk.