A 52-year-old man receives 250 mg of 0.5% lidocaine for interscalene brachial plexus block. Thirty minutes later, in the recovery room, he reports dizziness, mild confusion, and tremors. His heart rate is 105 bpm, blood pressure 148/92 mmHg, and oxygen saturation 96% on room air. He is alert and responsive. What is the most appropriate immediate management?