• clinical nurse specialists;
  • community nurses;
  • complex nursing interventions;
  • evaluation research;
  • intensive care;
  • mechanical ventilation;
  • methodology;
  • weaning protocols

Aim.  This paper outlines the difficulties in defining and evaluating a complex intervention and a number of currently available models for assisting this process are discussed.

Background.  Interventions aimed at producing change in the delivery and organization of healthcare services require rigorous evaluation to demonstrate their effectiveness. Evaluation poses difficulties, however, because these interventions are usually very complex.

Methods.  A framework developed by the United Kingdom Medical Research Council to evaluate complex interventions is described. The use of this framework in designing and evaluating a nurse-led intervention in intensive care for weaning patients from mechanical ventilation is discussed. Semi-structured interviews, a questionnaire survey and observational work were undertaken to define the components of the intervention, which was subsequently evaluated in an exploratory trial using a quasi-experimental design.

Conclusion.  The framework was a useful tool and can be easily applied in developing and evaluating complex nursing interventions. Three key challenges emerge from this experience: (i) relevant research evidence should be used systematically in developing the components of the intervention, (ii) the definition and measurement of complex intervention outcomes needs to be improved and (iii) appropriate research designs must be used when evaluating complex interventions.