An older adult client with emphysema, who continues to smoke cigarettes, returns to the medical unit after a physical therapy session, and is short of breath. The nurse notes that the client is lying supine with the head of the bed elevated to 45 degrees. Oxygen is flowing via nasal cannula at 3L/minute. The client's pulse oximetry is 88%, respiratory rate is 14 breaths/minute, and vital signs are stable. Which intervention should the nurse implement?