1 From Harvard Medical School (D.H., R.J.Y., M.P.S.), the Department of Anesthesia, Critical Care, and Pain Medicine, Massachusetts General Hospital (D.H.), the Department of Anesthesiology, Perioperative, and Pain Medicine, Brigham and Women's Hospital (R.J.Y.), and the Anesthesiology, Critical Care, and Pain Medicine Service, VA Boston Healthcare System (M.P.S.), Boston, and the VA Bedford Healthcare System, Bedford (M.P.S.) - all in Massachusetts; and the Departments of Anesthesiology and Critical Care Medicine, Neurology, Physical Medicine and Rehabilitation, and Psychiatry and Behavioral Sciences, Johns Hopkins Medical Institutions, Baltimore, and the Departments of Physical Medicine and Rehabilitation and Anesthesiology, Walter Reed National Military Medical Center, Bethesda - both in Maryland (S.P.C.).