[1] Univ N Carolina, Div Pulm & Crit Care Med, Dept Med, Chapel Hill, NC 27599 USA
[2] Univ N Carolina, Dept Biostat, Chapel Hill, NC 27599 USA
[3] Univ N Carolina, Dept Surg, Div Trauma & Crit Care, Chapel Hill, NC 27599 USA
[4] Univ Chicago, Dept Med, Sect Pulm & Crit Care, Chicago, IL 60637 USA
[5] Univ N Carolina, Div Pharmacotherapy & Expt Therapeut, Sch Pharm, Chapel Hill, NC 27599 USA
[6] UNC Hosp, Chapel Hill, NC USA
[7] Univ Virginia, Dept Med, Div Pulm & Crit Care, Charlottesville, VA 22903 USA
[8] Stanford Univ, Med Ctr, Div Pulm & Crit Care, Stanford, CA 94305 USA
[9] Univ S Carolina, Dept Med, Div Pulm & Crit Care Med, Columbia, SC 29208 USA