A 52-year-old male with severe hepatic cirrhosis (Child-Pugh C) is scheduled for emergency upper GI endoscopy under general anesthesia for variceal bleeding. Induction is performed with etomidate and fentanyl. After intubation, vecuronium 0.1 mg/kg IV is administered for muscle relaxation. Thirty minutes into the procedure, the patient remains profoundly paralyzed despite adequate time for drug metabolism. Train-of-four monitoring shows 0/4 responses. What is the most appropriate next step?