What Is the Potential Value of a Randomized Trial of Different Thresholds to Initiate Invasive Ventilation? A Health Economic Analysis gan Christopher J. Yarnell, MD, Kali Barrett, MD, MSc, Anna Heath, PhD, Margaret Herridge, MD, MSc, Robert A. Fowler, MD, MSc, Lillian Sung, MD, PhD, David M. Naimark, MSc, MD, George Tomlinson, PhD