A nurse is assisting with the care of a client in the emergency department and reports severe radiating chest pain and shortness of breath. The client appears restless, frightened, and slightly cyanotic. The provider prescribes oxygen by nasal cannula at 4 L/min stat, cardiac enzyme levels, IV fluids, and a 12-lead ECG. Which of the following actions should the nurse take first?

A. Initiate oxygen therapy: Oxygen is indicated if the client is hypoxic (SpO₂ <90%) or in respiratory distress. However, routine oxygen for all chest pain is not first priority; oxygen should be given based on assessment. B. Attach the leads for a 12-lead ECG: A 12-lead ECG should be obtained immediately (goal within 10 minutes) for chest pain to identify STEMI and guide urgent treatment — this is the time-critical diagnostic step. C. Obtain a blood sample: Cardiac enzymes are important but take time to result and are not the first immediate diagnostic action; ECG comes first. D. Insert the IV catheter: IV access is important for meds/fluids but after the immediate diagnostic ECG in this scenario.