1 Department of Anaesthesia and Intensive Care Medicine, Warrington & Halton Hospitals NHS Foundation Trust, Lovely Lane, Warrington, Cheshire WA5 1QG, UK.
2 Department of Anaesthesia, Royal United Hospitals Bath Foundation Trust, Combe Park, Bath BA1 3NG, UK.
3 Department of Anaesthesia and Intensive Care Medicine, University Hospital South Manchester, Southmoor Road, Wythenshawe, Manchester M23 9LT, UK [email protected].