[1] Harvard Univ, Sch Med, Childrens Hosp, Dept Anesthesia, Boston, MA 02115 USA
[2] Harvard Univ, Sch Med, Childrens Hosp, Dept Pediat, Boston, MA 02115 USA
[3] McMaster Univ, Dept Clin Epidemiol & Biostat, Hamilton, ON, Canada
[4] McMaster Univ, Dept Med, Div Clin Care, Hamilton, ON, Canada
[5] Univ Calif San Francisco, Dept Pediat Crit Care, San Francisco, CA 94143 USA
[6] Hop Henri Mondor, Serv Reanimat Med, F-94010 Creteil, France