[1] Sligo Reg Hosp, Dept Anaesthesia & Intens Care Med, Sligo, Ireland
[2] Galway Univ Hosp, Dept Anaesthesia & Intens Care Med, Galway, Ireland
[3] St James Hosp, Dept Anaesthesia & Intens Care Med, Dublin 8, Ireland
[4] Royal United Hosp, Dept Anaesthesia & Intens Care Med, Bath BA1 3NG, Avon, England
[5] Oxford Univ Hosp, Nuffield Dept Anaesthet, Oxford, England