Aim. To explore how protocol‐based care affects clinical decision‐making.

Background. In the context of evidence‐based practice, protocol‐based care is a mechanism for facilitating the standardisation of care and streamlining decision‐making through rationalising the information with which to make judgements and ultimately decisions. However, whether protocol‐based care does, in the reality of practice, standardise decision‐making is unknown. This paper reports on a study that explored the impact of protocol‐based care on nurses’ decision‐making.

Design. Theoretically informed by realistic evaluation and the promoting action on research implementation in health services framework, a case study design using ethnographic methods was used. Two sites were purposively sampled; a diabetic and endocrine unit and a cardiac medical unit.

Methods. Within each site, data collection included observation, postobservation semi‐structured interviews with staff and patients, field notes, feedback sessions and document review. Data were inductively and thematically analysed.

Results. Decisions made by nurses in both sites were varied according to many different and interacting factors. While several standardised care approaches were available for use, in reality, a variety of information sources informed decision‐making. The primary approach to knowledge exchange and acquisition was person‐to‐person; decision‐making was a social activity. Rarely were standardised care approaches obviously referred to; nurses described following a mental flowchart, not necessarily linked to a particular guideline or protocol. When standardised care approaches were used, it was reported that they were used flexibly and particularised.

Conclusions. While the logic of protocol‐based care is algorithmic, in the reality of clinical practice, other sources of information supported nurses’ decision‐making process. This has significant implications for the political goal of standardisation.

Relevance to clinical practice. The successful implementation and judicious use of tools such as protocols and guidelines will likely be dependant on approaches that facilitate the development of nurses’ decision‐making processes in parallel to paying attention to the influence of context.