Aim: To explore the relationship between the practice environment and nurse outcomes in two Intensive Care Unit (ICU) models. Background: Internationally the demand for intensive care is increasing. A large capacity multi-specialty integrated critical care service, the "hot-floor", is emerging as the preferred organisational model. Benefits include resource consolidation and improved utilisation, operational synergies, operational flexibility and demand management. A large clinical workforce with commensurate frontline management, education and support positions are required. The association between these factors, within the ICU hot-floor work environment, and nurse outcomes is not known. Methods: Registered nurses (RNs) working in two ICUs, one a hot-floor model and one traditional ICU, completed a structured questionnaire. Nurse perceptions of work-life and organisational factors, and dimensions of burnout were examined using the Practice Environment Scale-Nursing Work Index (PES-NWI) and Maslach's Burnout Inventory (MBI). Results: Units matched on service level characteristics, training accreditation, patient casemix, operational and clinical care processes. Nurses in had similar demographic characteristics, professional attributes and experience. Workforce structures were also similar though the hot-floor had relatively less dedicated resources for frontline nurse management and clinical education positions. Hot-floor nurses worked more paid overtime and were redeployed less frequently to external wards. Nurse manager leadership and support was less effective, and nurses expressed lower personal accomplishment. Conclusions: Improved demand management achieved through greater operational flexibility is a key driver for the hot-floor model. Planning for enhanced organisational effectiveness requires corresponding improvements in the work environment to optimise nurse retention to ensure organisational sustainability.