C Wai1, K Bhatia2, I Clegg3. 1. Department of Anaesthesia, Central Manchester University Hospitals & St Mary's Hospital, Manchester, UK. 2. Department of Anaesthesia, Central Manchester University Hospitals & St Mary's Hospital, Manchester, UK. Electronic address: kailash.bhatia@cmft.nhs.uk. 3. Department of Anaesthesia, Royal Blackburn Hospital, Blackburn, UK.