A 68-year-old woman with diabetes and hypertension undergoes epidural anesthesia for hip arthroplasty. The anesthesiologist injects 18 mL of 2% lidocaine with 1:200,000 epinephrine at L2–L3. After 20 minutes, the patient develops tinnitus, perioral numbness, and tremor. Blood pressure is 165/98 mmHg, heart rate 128/min, and the patient is anxious. What is the most appropriate immediate management?