A 68-year-old woman with a 15-year history of type 2 diabetes mellitus and hypertension is admitted for elective abdominal aortic aneurysm repair. Postoperatively, she is prescribed intravenous patient-controlled analgesia (PCA) with morphine. On postoperative day 2, she develops acute confusion, miosis, and respiratory depression (RR 10/min, SpO₂ 88% on room air). Her serum creatinine is 2.8 mg/dL (baseline 1.2 mg/dL). Which of the following is the MOST appropriate immediate management?