Final answer:
After administering IV morphine, the nurse must prioritize reporting respiratory depression, as it is a life-threatening risk associated with opioid analgesics.
Step-by-step explanation:
The nurse's priority to report after administering IV morphine for pain would be c. Respiratory depression. Morphine, as an opioid analgesic, has a high risk of causing respiratory depression, which can be life-threatening. It is more critical than bradycardia, hypotension, or increased urine output, which although important to monitor, do not generally present the immediacy of risk that respiratory depression does.