M D Stoneham1, J Quinlan2. 1. Nuffield Division of Anaesthetics, Oxford University Hospitals Trust, Oxford OX3 9DU, UK Nuffield Department of Anaesthetics, John Radcliffe Hospital, Level 1 John Radcliffe Hospital, Oxford, Oxon OX3 9DU, UK mark.stoneham@nda.ox.ac.uk. 2. Nuffield Division of Anaesthetics, Oxford University Hospitals Trust, Oxford OX3 9DU, UK Nuffield Department of Anaesthetics, John Radcliffe Hospital, Level 1 John Radcliffe Hospital, Oxford, Oxon OX3 9DU, UK.