A client with COPD is receiving oxygen therapy. Which of the following interventions should the nurse prioritize to ensure the safety of the client?

A. Monitoring oxygen saturation levels: Continuous pulse-ox monitoring directly measures the effectiveness and safety of oxygen therapy and helps detect hypoxemia or hyperoxia promptly; this is the priority safety intervention. B. Assessing vital signs for any changes: Vital signs are important to detect clinical change but are broader and less specific than continuous oxygen saturation monitoring for oxygen-therapy safety. C. Encouraging rest to prevent fatigue: Rest conserves energy and can reduce dyspnea, but it does not directly ensure the safety of oxygen delivery. D. Administering medications to improve airway patency: Bronchodilators or other meds may improve ventilation but administering them is an order-driven intervention and not the immediate priority safety check for ongoing oxygen therapy.