The effect of continuous lumbar epidural infusion of ropivacaine (0.1%, 0.2%, and 0.3%) and 0.25% bupivacaine on sensory and motor block in volunteers - A double-blind study

Background and Objectives. In animal studies, ropivacaine has shown more pronounced sensory block than motor block, which makes it an interesting drug for postoperative pain relief. The aim of this study was to investigate the dose response of sensory and motor block during continuous epidural infusion of 0.1, 0.2, or 0.3% ropivacaine in volunteers in a double-blind manner. Bupivacaine 0.25% and isotonic saline were used as reference and control, respectively. Methods. Each treatment group consisted of eight healthy men. After a bolus dose of 10 mL at the L2-L3 interspace, the solution in question was infused at 10 mL/h for 21 hours. Sensory block was evaluated by the pinprick, light touch, and Thermotest methods. Motor block was measured by the Bromage scale, by average rectified electromyography in abdominal muscles, and by mechanical measurement of isometric muscle force in the lower extremities. Mobilization of the subjects was attempted throughout the investigation. Results. The number of blocked dermatomes (evaluated by pinprick) with 0.1% ropivacaine was significantly smaller than with the other test solutions (P =.002-.0008). Motor block was minimal with 0.1% ropivacaine, so that all subjects could be mobilized; it was moderate with 0.2 and 0.3% ropivacaine and most intense with 0.25% bupivacaine. The regression phase was significantly shorter with all three concentrations of ropivacaine than with bupivacaine (P < .01). Conclusions. Ropivacaine 0.1% produced limited analgesia and minimal motor block, so that ambulation was possible throughout the investigation. With 0.2 and 0.3% ropivacaine, analgesia was more extensive, and motor block was considered moderate. Ropivacaine 0.2% should be evaluated for future postoperative pain treatment.