[1] Stanford Univ, Sch Med, Div Emergency Med, Stanford, CA 94305 USA
[2] Stanford Univ, Sch Med, Ctr Primary Care & Outcomes Res, Palo Alto, CA 94304 USA
[3] Northwestern Univ, Dept Emergency Med, Feinberg Sch Med, Chicago, IL 60611 USA
[4] Stanford Kaiser Emergency Med Residency Program, Stanford, CA USA
[5] San Mateo Cty Emergency Med Serv Agcy, San Mateo, CA USA
[6] Stanford Univ, Dept Surg, Sch Med, Stanford, CA 94305 USA