1. Department of Anaesthesia, The Ulster Hospital, UNDAH Trust, Dundonald, Belfast BT16 0RH, UK,
2. Northern Ireland Regional Maxillo Facial Unit, The Ulster Hospital, UNDAH Trust, Dundonald, Belfast BT16 0RH, UK,
3. Department of Anaesthesia, Craigavon Area Hospital, Craigavon, Co. Armagh BT63 5QQ,UK