[The equipotency of ropivacaine, bupivacaine and etidocaine].

Abstract

Ropivacaine, congenerate to bupivacaine and mepivacaine has been widely studied in laboratory animals, but there have been few investigations of its efficacy in human epidural anesthesia and peripheral nerve blocks. The aim of this study was to compare the three long-acting local anesthetics (bupivacaine 0.75%, ropivacaine 1% and etidocaine 1%) and to try, with reference to previous studies, to make some statement about the equipotency of ropivacaine relative to bupivacaine and etidocaine. METHODS. In a double blind randomized study, epidural anesthesia was carried out with 20 ml bupivacaine 0.75% (n = 24) and ropivacaine 1% (n = 21). Following this study epidural anesthesia was carried out with 20 ml etidocaine 1% (n = 20) in an open study. Patients with ASA I or II were enrolled in the study. All patients were scheduled for varicose vein stripping. Male and female patients aged 18-70 years and weighing 50-100 kg were included in the study. Patients were all placed in a sitting position, after which the epidural space was identified by the "loss of resistance" technique and a midline approach, at the L-3/4 interspace. Injections of 3 ml of the local anesthetic were given, followed by the remainder of the local anesthetic at 10 ml/min 1 min later. Following injection patients were immediately positioned supine. Analgesia was determined by the pin-prick method and motor blockade was assessed according to the Bromage scale. Heart rate and blood pressure were monitored until 3 h after injection. RESULTS. The latency of analgesia for the first blocked segment (T 12 for bupivacaine and ropivacaine and L-1 for etidocaine) was 6.0 min for bupivacaine 0.75, 5.5 min for ropivacaine 1%, and 5.2 min for etidocaine 1%, and the highest thoracic dermatome (T 5 for bupivacaine, T 4 for ropivacaine and T 7 for etidocaine) was reached after 24 +/- 10, 26 +/- 9, and 30 +/- 18 min for bupivacaine, ropivacaine, and etidocaine, respectively. The duration of sensory anesthesia at the T 10 dermatomal level was 257 +/- 102, 278 +/- 67, and 191 +/- 86 min for bupivacaine, ropivacaine, and etidocaine, respectively. The two-segment regression time was 199 +/- 80 min for bupivacaine, 201 +/- 52 min for ropivacaine, and 174 +/- 81 min for etidocaine. The total duration of sensory block was 340 +/- 103 min for bupivacaine, 428 +/- 65 min for ropivacaine and 223 +/- 62 min for etidocaine, respectively. In the ropivacaine and bupivacaine groups sensory anesthesia was considered adequate for surgery in all cases but one in each group; in the etidocaine group, however 60% of the patients showed inadequate analgesia and all these patients (12/20) required additional analgesics. Bupivacaine achieved an average of motor block 2.1, ropivacaine 2.3, and etidocaine 2.4. CONCLUSION. The results of this study indicate that ropivacaine is an effective local anesthetic agent. Its potency is about equal to that of bupivacaine and much higher than that of etidocaine...