[1] St Vincents Med Ctr, Dept Anesthesiol, Bridgeport, CT 06606 USA
[2] Univ Minnesota, Med Sch, Dept Anesthesiol, Minneapolis, MN USA
[3] Childrens Minnesota Hosp, Dept Anesthesiol, Minneapolis, MN USA
[4] Yale Univ, Sch Med, Dept Obstet Gynecol & Reprod Sci, New Haven, CT USA