[1] Univ Auckland, Dept Anesthesiol, Auckland 1, New Zealand
[2] Univ Auckland, Ctr Med & Hlth Sci Educ, Auckland 1, New Zealand
[3] Harvard Univ, Sch Med, Boston Childrens Hosp, Dept Anesthesia, Boston, MA 02115 USA
[4] Stanford Sch Med, Dept Perioperat & Pain Med, Stanford, CA USA