Morphine sulfate via intravenous patient-controlled analgesia (PCA) pump is prescribed for a client with severe chronic back pain. Thirty minutes after initiating the PCA pump, the practical nurse (PN) notes that the client has become lethargic. Which action should the PN take?

A. Reinforce PCA pump teaching: Teaching about PCA use is important, but it is not the immediate priority when a client shows signs of lethargy. Education can be addressed later, once the client’s condition has been stabilized and safety is ensured. B. Check the IV insertion site for swelling: Inspecting the IV site for infiltration or phlebitis is a routine step, but it does not address the potential systemic effect of morphine causing central nervous system depression. C. Determine the client's pain scale rating: Assessing pain level is typically part of routine evaluation for clients on PCA, but when lethargy develops, the focus must shift to assessing possible opioid toxicity rather than pain relief effectiveness. D. Measure the client's vital signs: Obtaining vital signs is the most immediate and appropriate action. Respiratory depression, hypotension, or bradycardia may indicate opioid overdose or excessive sedation. Prompt assessment allows the PN to recognize early signs of morphine toxicity and intervene quickly to prevent respiratory compromise.