1 Department of Neurological Surgery, University of California, San Francisco, San Francisco, California, USA.
2 Department of Neurological Surgery, University of California, San Francisco, San Francisco, California, USA. Electronic address: nitin.agarwal@ucsf.edu.
3 Department of Anesthesiology, University of California, San Francisco, San Francisco, California, USA.
4 Department of Neurosurgery, University of Miami, Miami, Florida, USA.