The use of Clinical Practice Guidelines (CPGs) is known to enable better care outcomes by promoting a consistent way of treating patients. This paper describes a user-centered design approach involving nurses, to develop a prototype expert system for modelling CPGs for Pressure Ulcer management. The system was developed using Visirule, a software tool that uses a graphical approach to modeling knowledge. The system was evaluated by 5 staff nurses and compared nurses' time and accuracy to assess a wound using CPGs accessed via the Intranet of an NHS Trust and the expert system. A post task qualitative evaluation revealed that nurses found the system useable with a systematic design, that it increased access to CPGs by reducing time and effort required by other usual methods of access, that it provided opportunities for learning due to its interactive nature, and that its recommendations were more actionable that those provided by usual static CPG documents.