[1] Univ Texas SW Med Ctr Dallas, Dallas, TX 75390 USA
[2] Univ Toronto, Toronto Western Hosp, Toronto, ON M5T 2S8, Canada
[3] Harvard Univ, Beth Israel Deaconess Med Ctr, Sch Med, Dept Anesthesia Pain & Crit Care, Boston, MA 02215 USA
[4] Northwestern Univ, Feinberg Sch Med, Dept Anesthesiol, Chicago, IL 60611 USA
[5] Duke Univ, Med Ctr, Dept Anesthesiol, Durham, NC 27710 USA
[6] Univ Kentucky, Lexington, KY USA
[7] Dartmouth Hitchcock Med Ctr, Ctr Perioperat Serv Outpatient Surg, Lebanon, NH 03766 USA
[8] Suny Downstate Med Ctr, Dept Anesthesiol, Ambulatory Surg Unit, Brooklyn, NY 11203 USA