[1] Yeovil Dist Hosp, Dept Surg, Yeovil, England
[2] Yeovil Dist Hosp, Dept Anaesthet, Yeovil, England
[3] Univ Bristol, Dept Social Med, Bristol BS8 1TH, Avon, England
[4] Univ Bristol, Dept Clin Sci, Bristol BS8 1TH, Avon, England
[5] Taunton & Somerset Hosp, Dept Res & Dev, Taunton, Somerset, England
[6] Thames Valley Univ, Ctr Res & Implementat Clin Practice, London, England
[7] Bristol Royal Infirm & Gen Hosp, Dept Resp Med, Bristol BS2 8HW, Avon, England