Comparison of analgesia induced by continuous epidural infusion of plain 1% lidocaine and 1% lidocaine prepared by dilution of 2% lidocaine with the same volume of saline

Study Objective: To compare the extent of sensory block induced by continuous epidural infusion of plain 1% lidocaine and 2% lidocaine diluted with saline to 1% lidocaine. Design: Prospective, randomized, blinded study. Setting: University hospital. Patients: 40 ASA physical status I inpatients scheduled for lower extremity orthopedic surgery. Interventions: After surgery with lumbar epidural anesthesia with 0.75% ropivacaine, patients were randomized to two postoperative epidural infusion groups to receive plain 1% lidocaine (plain group) or 2% lidocaine diluted with the same volume of normal saline (dilution group). Continuous epidural infusion was started at a rate of 6 mL/h. Measurements and Main Results: Regression of sensory block was significantly prolonged in the plain group, resulting in a significant difference in the spread of sensory block between the two agents from 4 to 6 h postoperatively. There also was a significant difference from the two groups in the level of motor block (modified Bromage scale) between 3 and 5 h postoperatively. Conclusions: Two percent lidocaine diluted with the same volume of saline is a less potent than the plain 1% lidocaine. The effect of saline as a diluent on epidurally administrated local anesthetics may be of clinical importance.