[1] Royal Surrey Cty Hosp NHS Fdn Trust, Dept Anaesthesia & Intens Care, Guildford GU2 7XX, Surrey, England
[2] Royal United Hosp Bath NHS Trust, Dept Anaesthesia & Intens Care, Bath, Avon, England
[3] South Devon Healthcare NHS Fdn Trust, Torbay Hosp, Dept Anaesthesia & Perioperat Med, Torquay, Torbay, England
[4] Royal Devon & Exeter NHS Fdn Trust, Dept Anaesthesia & Intens Care, Exeter, Devon, England
[5] Univ Bradford, Sch Hlth Studies, Bradford BD7 1DP, W Yorkshire, England