National prospective cohort study of the burden of acute small bowel obstruction oleh M. J. Lee, A. E. Sayers, T. M. Drake, P. J. Marriott, I. D. Anderson, S. P. Bach, M. Bradburn, D. Hind, A. Verjee, N. S. Fearnhead, on behalf of NASBO steering group and NASBO collaborators