1. Department of Cardiothoracic Anaesthesia, Freeman Group of Hospitals Trust, High Heaton, Newcastle upon Tyne NE7 7DN, UK,
2. Department of Anaesthesia and Intensive Care, Newcastle General Hospital, Newcastle upon Tyne NE4 6BE, UK,
3. The Women's and Children's Hospital, 72 King William Road, North Adelaide, South Australia 5006