Patrick B Murphy1, Amanda J Piper2, Nicholas Hart3. 1. Lane-Fox Respiratory Service, Guy's and St Thomas' NHS Trust, St Thomas' Hospital, London SE1 7EH, UK; Respiratory Failure Service, Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney, NSW, Australia. Electronic address: patrick.murphy@gstt.nhs.uk. 2. NIHR Biomedical Research Centre, Guy's and St Thomas' NHS Foundation Trust and King's College London, London, UK. 3. Lane-Fox Respiratory Service, Guy's and St Thomas' NHS Trust, St Thomas' Hospital, London SE1 7EH, UK; Respiratory Failure Service, Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney, NSW, Australia.