[Ropivacaine in epidural anesthesia. Dose-response relationship and a comparison with bupivacaine]

Ropivacaine is a new long-acting local anesthetic with a pharmacodynamic profile resembling that of bupivacaine; in addition, ropivacaine has been shown to be less cardiotoxic than bupivacaine in dogs and pigs. To test the dose-response relationship of ropivacaine 0.75% (epinephrine 1:200,000) given epidurally, 47 patients were divided into three groups; the first group received 15 ml (n = 16), the second 20 ml (n = 15), and the third group, 25 ml (n = 16) ropivacaine. Further, to compare bupivacaine 0.75%, bupivacaine 0.5% and ropivacaine 0.75% for epidural anesthesia, 15 ml bupivacaine 0.75% (n = 15) or bupivacaine 0.5% (n = 15) or ropivacaine 0.75% (n = 16) was given epidurally, all with epinephrine added to the solution (1:200,000).

A total of 77 patients with ASA I or II were enrolled in a non-randomized open-label study. All patients were scheduled for varicose vein stripping. Male and female patients aged 18-70 and weighing 50-100 kg were included in the study. Patients were all placed in a sitting position and the epidural space was identified by the "loss of resistance" technique using a midline approach at the L 3/4 interspace; a test dose of 3 ml local anesthetic was then given, followed by injection of the remainder of the local anesthetic at the rate of 10 ml/min 1 min later. Following injection patients were immediately positioned supine. Upward and downward spread of analgesia were determined bilaterally by the pin-prick method, motor blockade was assessed by use of the Bromage scale following each determination of analgesia. Heart rate and blood pressure were obtained immediately before blockade and every 5 min until 3 h after the injection. RESULTS. The different volumes of ropivacaine 0.75% (15, 20, and 25 ml) brought about adequate analgesia in the sacral and lumbar regions in all patients. In the thoracic region T 6, T 5 and T 4 were reached. The time of onset of analgesia (segment L-1 in all three groups) was 6.4 +/- 2.9 min, 7.7 +/- 2.3 min, and 5.6 +/- 2.9 min for the 15-, 20- and 25-ml groups, respectively. The highest thoracic dermatome was reached after 20 +/- 6 min, 26 +/- 11 min, and 18 +/- 5 min. The duration of sensory anesthesia at the T 10 dermatomal level was 250 +/- 68, 249 +/- 77, and 278 +/- 51 min. Two-segment regression time was 160 +/- 67 min for bupivacaine 0.75%, 140 +/- 60 min for bupivacaine 0.5%, and 124 +/- 29 min for ropivacaine 0.75%. The total duration of sensory block was 303 +/- 58, 290 +/- 70, and 343 +/- 55 min for 15-, 20- and 25-ml groups, respectively. The degree of motor block achieved was 1.6, 1.8, and 2.0 (Bromage), respectively. Sensory anesthesia was considered adequate for surgery in all patients, and no signs of systemic toxicity were observed in any of the patients. The comparison of bupivacaine 0.75%, bupivacaine 0.5% and ropivacaine 0.75% revealed the same latency period of analgesia for bupivacaine 0.75% and ropivacaine 0.75%. This was shorter than for bupivacaine 0.5% (bupivacaine 0.75%: 6.4 +/- 2.1, bupivacaine 0.5%: 7.8 +/- 4...