[1] Case Western Reserve Univ, Cleveland Clin, Dept Gen Anesthesia & Pain Management, Outcomes Res,Lerner Coll Med, Cleveland, OH 44106 USA
[2] St Thomas Hosp, Guys & St Thomas NHS Fdn Trust, London, England
[3] St Thomas Hosp, Dept Anaesthesia, London, England
[4] Stanford Univ, Sch Med, Dept Anesthesiol Perioperat & Pain Med, Palo Alto, CA 94304 USA
[5] VA Palo Alto Hlth Care Syst, Palo Alto, CA USA