Rapid response systems (RRSs) have been developed and implemented with the aim of improving recognition of and response to deteriorating patients. However, there is little evidence to support the effectiveness of such systems. A recurring theme within the clinical literature is that these systems are not activated or used effectively by nursing staff and the reasons for this are not fully understood. The practices of nurses who used an RRS are explored in this thesis. Ward patients also appear to be more vulnerable to deterioration in the hosptial after-hours; in response to this, a number of patient safety initatives have been developed. One of these initiatives is an after-hours nurse-led RRS, a service run by Advanced Practice Nurses (APNs). To date, there has been limited exploration of the impact of this patient safety intiative on patient outcomes. Whether the introduction the APN after-hours service improved patient outcomes is also explored in this thesis. To develop in-depth knowledge and understanding of this contemporary and complex area of clinical practice, a single exploratory case study with two separate units of analysis was used. The context of the case was a large teaching hospital in Queensland; the case was the deteriorating ward patient. The first unit of analysis was nurse’s practices of using an RRS. The second unit of analysis was patient outcomes. In the first unit of analysis, 15 registered nurses who had cared for a deteriorating ward patient were interviewed about their practices of using an RRS and the resulting transcripts were thematically analysed. Four themes relating to participants experiences and perceptions of RRSs emerged from the data. These themes were: (1) sensing clinical deterioration; (2) resisting and hesitating; (3) pushing the button; and (4) reflecting on the Medical Emergency Team (MET).