P Aldam1, N Levy2, G M Hall3. 1. Division of Anaesthesia, Addenbrookes Hospital, Cambridge CB2 0QQ, UK. 2. Department of Anaesthesia, West Suffolk Hospital, Bury St Edmunds IP33 2QZ, UK nicholas.levy@wsh.nhs.uk. 3. Department of Anaesthesia, St George's Hospital Medical School, London SW17 0RE, UK.