[1] Univ Pittsburgh, Childrens Hosp Pittsburgh, Sch Med, Dept Anesthesiol & Crit Care Med, Pittsburgh, PA USA
[2] Univ Pittsburgh, Childrens Hosp Pittsburgh, Sch Med, Dept Pediat, Pittsburgh, PA USA
[3] George Washington Univ, Med Ctr, Dept Anesthesiol, Childrens Natl Med Ctr, Washington, DC 20037 USA
[4] George Washington Univ, Med Ctr, Dept Pediat, Childrens Natl Med Ctr, Washington, DC 20037 USA
[5] Univ Washington, Sch Med, Childrens Hosp & Reg Med Ctr, Dept Anesthesia & Pediat, Seattle, WA USA
[6] Univ Penn, Sch Med, Childrens Hosp Philadelphia, Dept Anesthesiol, Philadelphia, PA 19104 USA
[7] Primary Childrens Med Ctr, Dept Anesthesiol, Salt Lake City, UT 84103 USA
[8] Glaxo Wellcome Inc, Anesthesia Clin Dev, Res Triangle Pk, NC 27709 USA
[9] Glaxo Wellcome Inc, Dept Clin Stat, Res Triangle Pk, NC 27709 USA