Longterm Postoperative Analgesia, Intravenous Lidocaine Infusion

patients (n = 20) will receive a loading dose of lidocaine 2 mg ̸ kg slowly IV just before induction of anesthesia, then the lidocaine infusion started at a rate of 3 mg ̸ kg/h, and continued until the end of the operation.

patients (n = 20) will receive an equal volume of 0.9% saline (both the loading and the infusion), the infusion will be initiated at the time of induction of anesthesia and continued until the end of the operation.