A 52-year-old man undergoes elective open cholecystectomy under general anesthesia. Intraoperatively, he receives 0.1 mg/kg morphine. In the post-anesthesia care unit (PACU), he is started on patient-controlled analgesia (PCA) with morphine: demand dose 2 mg, lockout interval 10 minutes, 4-hour limit 30 mg. At 2 hours post-op, he reports inadequate pain relief (VAS 7/10) and requests frequent doses. His respiratory rate is 14/min, SpO₂ 96% on room air, and he is alert and oriented. What is the most appropriate next step in PCA management?