1 Division of Pain Medicine, Stanford University School of Medicine, Department of Anesthesiology, Perioperative, and Pain Medicine, Neurosciences, and (by courtesy) Neurology, 1070 Arastradero Road, Suite 200, MC 5596, Palo Alto, CA 94304-1345, USA. Electronic address: smackey@stanford.edu.
2 Department of Anesthesiology, Perioperative and Pain Medicine, Stanford University School of Medicine, 300 Pasteur Drive, Room H3589, Stanford, CA 94305-5640, USA. Electronic address: rgp@stanford.edu.