[1] Oregon Hlth & Sci Univ, Dept Emergency Med, Portland, OR 97239 USA
[2] Johns Hopkins Univ, Dept Emergency Med, Baltimore, MD USA
[3] Western Carolina Univ, Emergency Med Care Program, Cullowhee, NC 28723 USA
[4] Univ Texas Hlth Sci Ctr Houston, Dept Emergency Med, Houston, TX USA