1 Anaesthesia and Critical Care, Division of Clinical Neuroscience, School of Medicine, University of Nottingham, Nottingham, UK; Nottingham University Hospitals NHS Trust, Nottingham, UK. Electronic address: david.hewson@nottingham.ac.uk.
2 Anaesthesia and Critical Care, Division of Clinical Neuroscience, School of Medicine, University of Nottingham, Nottingham, UK; Nottingham University Hospitals NHS Trust, Nottingham, UK.
3 The Ottawa Hospital, Ottawa, ON, Canada; University of Ottawa, Ottawa, ON, Canada.