[1] Univ Glasgow, Western Infirm, Dept Surg, Glasgow G11 6NT, Lanark, Scotland
[2] Univ Glasgow, Robertson Ctr Biostat, Glasgow, Lanark, Scotland
[3] Univ Glasgow, Western Infirm, Dept Anaesthet, Glasgow G11 6NT, Lanark, Scotland
[4] Gartnavel Royal Hosp, Dept Gen Surg, Glasgow, Lanark, Scotland