[1] Univ Toronto, Dept Anesthesiol & Pain Med, Toronto, ON, Canada
[2] Sunnybrook Hlth Sci Ctr, Dept Anesthesia, 2075 Bayview Ave,Room M3-200, Toronto, ON M4N 3M5, Canada
[3] Sunnybrook Hlth Sci Ctr, Dept Crit Care Med, Toronto, ON, Canada
[4] Stanford Univ, Sch Med, Dept Anesthesiol Perioperat & Pain Med, Palo Alto, CA USA
[5] Univ Virginia, Anesthesiol, Charlottesville, VA USA
[6] Univ Virginia, Neurol Surg, Charlottesville, VA USA
[7] McMaster Univ, Dept Anesthesia, Hamilton, ON, Canada