1 Institute of Academic Anaesthesia, School of Medicine, University of Dundee, Ninewells Hospital, Dundee, UK. Electronic address: g.a.mcleod@dundee.ac.uk.
2 Sunnybrook Research Institute, Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada.
3 Sunnybrook Health Sciences Centre, Toronto, ON, Canada.
4 School of Medicine, University of Dundee, Ninewells Hospital, Dundee, UK.