[1] Univ Coll London Hosp NHS Fdn Trust, Natl Hosp Neurol & Neurosurg, Dept Neuroanaesthesia & Neurocrit Care, Queen Sq, London, England
[2] UCL, Queen Sq Inst Neurol, Dept Brain Repair & Rehabil, London, England
[3] Univ British Columbia, Dept Anesthesiol Pharmacol & Therapeut, Vancouver, BC, Canada
[4] St Pauls Hosp, Dept Anesthesia, Providence Hlth Care, Vancouver, BC, Canada
[5] St Pauls Hosp, Ctr Hlth Evaluat & Outcome Sci, Vancouver, BC, Canada