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.