Abstract: The objective of this paper is to outline a study firstly, assessing ICU nurses' ability in articulating respiratory physiology to provide rationale for their clinical decision-making and secondly, the barriers that limit the articulation of this knowledge. Using an evaluation methodology, multiple methods were employed to collect data from 27 ICU nurses who had completed an ICU education programme and were working in one of two tertiary ICUs in New Zealand. Quantitative analysis showed that nurses articulated a low to medium level of knowledge of respiratory physiology. Thematic analysis identified the barriers limiting this use of respiratory physiology as being inadequate coverage of concepts in some ICU programmes; limited discussion of concepts in clinical practice; lack of clinical support; lack of individual professional responsibility; nurses' high reliance on intuitive knowledge; lack of collaborative practice; availability of medical expertise; and the limitations of clinical guidelines and protocols. These issues need to be addressed if nurses' articulation of respiratory physiology to provide rationale for their clinical decision-making is to be improved.