1 Department of Anaesthesia, Wythenshawe Hospital, Manchester University NHS Foundation Trust, Manchester, UK; Lancaster Medical School, Lancaster University, Lancaster, UK. Electronic address: cliff.shelton@nhs.net.
2 Department of Anaesthesia, Raigmore Hospital, NHS Highland, Inverness, UK.
3 Department of General Surgery, Imperial College Healthcare NHS Trust, London, UK; Division of Surgery, Department of Surgery and Cancer, Imperial College London, London, UK.