[1] Univ London St Georges Hosp, Sch Med, Dept Anaesthesia & Intens Care Med, London SW17 0RE, England
[2] Univ Liverpool, Dept Clin Psychol, Liverpool L69 3BX, Merseyside, England
[3] Charing Cross Hosp, Hammersmith Hosp NHS Trust, Directorate Surg & Anaesthesia, Pain Serv, London, England
[4] BUPA Hosp, Clin Serv Dept, Cardiff, S Glam, Wales