[1] Sir Charles Gairdner Hosp, Dept Neurosurg, Perth, WA, Australia
[2] Univ Western Australia, Dept Intens Care Med, Perth, WA 6009, Australia
[3] Univ Western Australia, Sch Populat Hlth, Perth, WA 6009, Australia
[4] Univ Western Australia, Sch Surg, Perth, WA 6009, Australia
[5] Univ Otago, Dunedin Hosp, Dunedin, New Zealand
[6] Univ Otago, Otago Bioeth Ctr, Dunedin, New Zealand