[1] Univ Vermont, Dept Med, FAHC, Burlington, VT 05401 USA
[2] Univ Penn, Sch Med, Dept Anesthesiol, Philadelphia, PA 19104 USA
[3] Univ Penn, Sch Med, Dept Crit Care, Philadelphia, PA 19104 USA
[4] Barnes Jewish Hosp, St Louis, MO 63110 USA
[5] Univ N Carolina, Sch Med, Dept Emergency Med, Chapel Hill, NC USA
[6] Virginia Commonwealth Univ, Dept Med, Richmond, VA 23298 USA