[1] Addenbrookes Hosp, Neurosci Crit Care Unit, Cambridge CB2 2QQ, England
[2] Univ Hlth Network, Dept Crit Care Med, Toronto, ON, Canada
[3] Univ Toronto, Interdept Div Crit Care, Toronto, ON M5S 1A1, Canada
[4] Univ Toronto, Dept Med, Toronto, ON M5S 1A1, Canada