BACKGROUND:Abnormal respiratory rates are one of the first indicators of clinical deterioration in emergency department(ED) patients. Despite the importance of respiratory rate observations, this vital sign is often inaccurately recorded on ED observation charts, compromising patient safety. Concurrently, there is a paucity of research reporting why this phenomenon occurs. OBJECTIVE:To develop a substantive theory explaining ED registered nurses' reasoning when they miss or misreport respiratory rate observations. DESIGN:This research project employed a classic grounded theory analysis of qualitative data. PARTICIPANTS:Seventy-nine registered nurses currently working in EDs within Australia. Data collected included detailed responses from individual interviews and open-ended responses from an online questionnaire. METHODS:Classic grounded theory (CGT) research methods were utilised, therefore coding was central to the abstraction of data and its reintegration as theory. Constant comparison synonymous with CGT methods were employed to code data. This approach facilitated the identification of the main concern of the participants and aided in the generation of theory explaining how the participants processed this issue. RESULTS:The main concern identified is that ED registered nurses do not believe that collecting an accurate respiratory rate for ALL patients at EVERY round of observations is a requirement, and yet organizational requirements often dictate that a value for the respiratory rate be included each time vital signs are collected. The theory 'Rationalising Transgression', explains how participants continually resolve this problem. The study found that despite feeling professionally conflicted, nurses often erroneously record respiratory rate observations, and then rationalise this behaviour by employing strategies that adjust the significance of the organisational requirement. These strategies include; Compensating, when nurses believe they are compensating for errant behaviour by enhancing the patient's outcome; Minimalizing, when nurses believe that the patient's outcome would be no different if they recorded an accurate respiratory rate or not and; Trivialising, a strategy that sanctions negligent behaviour and occurs when nurses 'cut corners' to get the job done. Nurses' use these strategies to titrate the level ofemotional discomfort associated with erroneous behaviour, thereby rationalising transgression CONCLUSION: This research reveals that despite continuing education regarding gold standard guidelines for respiratory rate collection, suboptimal practice continues. Ideally, to combat this transgression, a culture shift must occur regarding nurses' understanding of acceptable practice methods. Nurses must receive education in a way that permeates their understanding of the relationship between the regular collection of accurate respiratory rate observations and optimal patient outcomes.