BACKGROUND: Postoperative pain is one of the major obstacles in the prevention of complications during patient recovery. Pain and its management have gained great interest among researchers, clinicians and policy-makers. PURPOSES: To explore the relationship between two variables in pain assessment (length of time after surgery and ventilator status) and medication decisions made by critical care nurses, and to identify nurses' concerns about opioid use. METHODS: A convenience sample of 71 critical care nurses participated in the survey. RESULTS: Certain patient conditions such as length of time after surgery and ventilator status affected nurses' assessment and management of pain. Nurses' knowledge about pain assessment and management may affect patient care and outcomes.