1 Bloomsbury Institute of Intensive Care Medicine, Division of Medicine, UCL, London WC1E 6BT, UK; Intensive Care Unit, UCL Hospitals NHS Foundation Trust, London, UK; National Institute of Health Research University College London Hospitals Biomedical Research Centre, London, UK. Electronic address: m.singer@ucl.ac.uk.
2 UCL Institute of Healthcare Engineering, London, UK; UCL Mechanical Engineering, London, UK.
3 UCL Mechanical Engineering, London, UK.
4 Bloomsbury Institute of Intensive Care Medicine, Division of Medicine, UCL, London WC1E 6BT, UK; Intensive Care Unit, UCL Hospitals NHS Foundation Trust, London, UK; National Institute of Health Research University College London Hospitals Biomedical Research Centre, London, UK.
5 National Institute of Health Research University College London Hospitals Biomedical Research Centre, London, UK; Office of the Vice Provost (Health), UCL, London, UK.