1. Department of Anesthesiology, Perioperative and Pain Medicine, Stanford University School of Medicine, Stanford, California, USA.
2. Anesthesiology Service Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA.
3. Brain and Spinal Injury Center, Department of Neurosurgery, Weill Institute for Neurosciences, University of California San Francisco, San Francisco, California, USA.
4. San Francisco Veterans Affairs Healthcare System, San Francisco, California, USA.