[1] Johns Hopkins Univ, Sch Med, Dept Anesthesiol & Crit Care Med, Baltimore, MD 21205 USA
[2] Johns Hopkins Univ, Sch Med, Dept Hlth Policy & Management, Baltimore, MD 21205 USA
[3] Johns Hopkins Univ, Sch Med, Dept Pulm & Crit Care Med, Baltimore, MD 21205 USA
[4] Johns Hopkins Univ, Sch Med, Dept Anesthesiol & Crit Care, Baltimore, MD 21205 USA
[5] Johns Hopkins Univ, Bloomberg Sch Publ Hlth, Hlth Syst Program, Dept Int Hlth, Baltimore, MD 21205 USA
[6] Univ Michigan, Sch Med, Dept Surg, Ann Arbor, MI 48109 USA
[7] Dartmouth Hitchcock Med Ctr, Dept Surg, Lebanon, NH 03766 USA