[1] Univ Toronto, Interdept Div Crit Care Med, Toronto, ON, Canada
[2] Univ Toronto, Dept Anesthesiol & Pain Med, Toronto, ON, Canada
[3] St Michaels Hosp, Dept Anesthesia, Toronto, ON, Canada
[4] Boston Univ, Chobanian & Avedisian Sch Med, Dept Med, Ctr Pulm, Boston, MA USA
[5] Med Coll Wisconsin Lib, Milwaukee, WI USA
[6] Univ Oxford, Clin Trial Serv Unit, Oxford, England
[7] Univ Oxford, Epidemiol Studies Unit, Nuffield Dept Populat Hlth, Oxford, England
[8] Weill Cornell Med, Dept Anesthesiol, New York, NY USA
[9] Univ Massachusetts, Sch Med, Div Hlth Syst Sci, Boston, MA USA