Implementation of the quality management system improves postoperative pain treatment: a prospective pre-/post-interventional questionnaire study. - Usichenko, T. I.; Röttenbacher, I.; Kohlmann, T.; Jülich, A.; Lange, J.; Mustea, A.; Engel, G.; Wendt, M. (BJA: The British Journal of Anaesthesia, 2013)