Clinical effectiveness in the post-anaesthesia care unit: how nursing knowledge contributes to achieving intended patient outcomes This paper reports part of an ongoing study on how nursing knowledge develops in practice and influences patient outcomes. The practice focus is post-anaesthesia nursing, an area which has been under-represented in nursing research. A qualitative approach was used to explore narrative data, collected by in-depth interviews, with 32 experienced post-anaesthesia nurses. Data analysis and interpretation were informed by a phenomenological perspective consistent with a research focus on individual experiences. Interpretation of the narratives gave rise to a description of knowledge development which occurred as nurses gained experience, drew on the available knowledge base, and used knowledge in practice. This led to the identification and description of 'referential' and 'effective' types of knowledge. Referential knowledge comprises the variety of external knowledge sources available to inform practice. When referential knowledge was incorporated into the personal knowledge of the individual nurse in everyday practice, it was transformed into effective knowledge which was used by nurses to achieve desired patient outcomes. The study findings indicate that nurses used effective knowledge as evidence for decision making and interventions in everyday practice. The key finding of the study is that effective nursing knowledge requires practice for its development.