[1] Univ Tennessee, Dept Anesthesiol, Med Ctr, Memphis, TN USA
[2] Univ Vermont, Larner Coll Med, Dept Anesthesiol, Burlington, VT USA
[3] Univ Vermont, Dept Orthoped & Rehabil Courtesy, Larner Coll Med, Burlington, VT USA
[4] Univ Vermont, Larner Coll Med, Dept Surg Courtesy, Burlington, VT USA
[5] Brigham & Womens Hosp, Dept Anesthesiol Perioperat & Pain Med, 75 Francis St, Boston, MA 02115 USA
[6] Brigham & Womens Hosp, Ctr Perioperat Res, 75 Francis St, Boston, MA 02115 USA