Dr. David A. Petrie, MD, FRCP is a Professor and the head of the Dalhousie Department of Emergency Medicine and the chief of the Central Zone, NSHA. After medical school at Dalhousie and an internship in Ottawa he worked for two years in small towns in Ontario and Nova Scotia. Since his specialty training in emergency medicine at the University of Western Ontario (1992-1996), he has been a faculty physician and trauma team leader at the Halifax infirmary. Petrie has been medical director of the Halifax regional ground EMS system, and medical director of the LifeFlight Critical Care transport program. His academic interests are prehospital and trauma systems research, the impact of critical thinking on clinical decision making, and the implications of complex adaptive systems modelling to health care system reform.