1. Department of Medicine, University of British Columbia, Vancouver, British Columbia, Canada
2. Division of Neurosurgery, Department of Surgery, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada
3. Division of Neuroanesthesia, Department of Anesthesiology, Pharmacology and Therapeutics, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada
4. Division of Otolaryngology, Department of Surgery, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada