A 38-year-old woman is on postoperative day 2 following open cholecystectomy. She is using IV-PCA with morphine (demand dose 1.5 mg, lockout 12 minutes). Over the past 4 hours, she has pressed the button 3 times and reports good pain control (pain score 2/10). However, the nursing staff notes that she is drowsy, her respiratory rate has dropped to 12/min, and her oxygen saturation is 94% on room air. What is the most appropriate immediate intervention?