[1] Royal Infirm Edinburgh NHS Trust, Dept Anaesthesia, Edinburgh, Midlothian, Scotland
[2] Univ Edinburgh, Dept Psychol, Edinburgh EH8 9YL, Midlothian, Scotland
[3] Western Gen Hosp, Dept Anaesthesia, Edinburgh EH4 2XU, Midlothian, Scotland
[4] Univ Washington, Dept Anesthesiol, Seattle, WA 98195 USA
[5] Univ Washington, Dept Neurointens Care, Seattle, WA 98195 USA