1. Department of Anaesthesia and Perioperative Medicine, Royal Brisbane and Women's Hospital, School of Medicine, University of Queensland, Narcosia Anaesthesia Group, Brisbane, Queensland
2. Department of Anaesthesia and Perioperative Medicine, Royal Brisbane and Women's Hospital, School of Medicine, University of Queensland, Brisbane, Queensland
3. Statistics Unit, QIMR Berghofer Medical Research Institute, Brisbane, Queensland
4. Department of Anaesthesia, St Vincent's Hospital, Melbourne Medical School, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Melbourne, Victoria