[1] Johns Hopkins Univ, Sch Med, Dept Emergency Med, Baltimore, MD 21218 USA
[2] Brown Univ, Warren Alpert Med Sch, Dept Emergency Med, Providence, RI 02912 USA
[3] Baylor Coll Med, Dept Med, Sect Emergency Med, Houston, TX 77030 USA
[4] Univ Calif San Francisco, Dept Emergency Med, San Francisco, CA 94143 USA
[5] Univ Massachusetts, Med Sch, Dept Emergency Med, Worcester, MA 01605 USA
[6] Stanford Sch Med, Dept Emergency Med, Stanford, CA USA
[7] Univ Connecticut, Dept Emergency Med, Sch Med, San Francisco, CA USA
[8] Univ Penn, Perelman Sch Med, Dept Emergency Med, Philadelphia, PA 19104 USA