[1] Oxford Univ Hosp NHS Fdn Trust, Dept Anaesthet, Oxford, England
[2] Glasgow Royal Infirm, Dept Anaesthesia, Glasgow, Scotland
[3] Princess Royal Matern Hosp, Glasgow, Scotland
[4] Katholieke Univ Leuven, Dept Cardiovasc Sci, Leuven, Belgium
[5] Univ Hosp Gasthuisberg, Dept Anaesthesiol, Leuven, Belgium
[6] London North West Univ Healthcare NHS Trust, Dept Anaesthesia, London, England