Plasma levels of ropivacaine and bupivacaine during postoperative patient controlled thoracic epidural analgesia

Abstract

The postoperative continuous epidural application of local anesthetics can cause side effects like motor blockade and systemic intoxication. The study was performed to evaluate the plasma levels of two local anesthetics and their analgesic and side effects in continuous postoperative epidural analgesia. In a prospective, randomized and double-blind study we have compared side effects of ropivacaine 0.375% (group R) vs. bupivacaine 0.125% in combination with sufentanil 0.5 microg ml(-1) (group B/S) via thoracic epidural catheters for a duration of 96 hours after major abdominal surgery in 30 gynaecological tumor patients. Analgesic effects, side effects and plasma levels of the respective local anesthetic were measured 24, 48, 72 and 96 h after start of epidural infusion. No differences were seen in demographics, perioperative data and analgesic effects. The following cumulative doses of local anesthetics were applied (Group R vs. B/S (median/minimum-maximum ml)): 24 h: 151/121-225 vs. 141/83-171; 48 h: 311/237-424 vs. 299/184-497; 72 h: 454/366-566 vs. 440/256-598; 96 h: 572/399-859 vs. 568/284-711. Plasma levels of local anesthetics remained far below the toxic threshold of 0.6 micro g/ml (Group R vs. B/S (median/minimum-maximum micro g/ml): 24 h: 0.05/0.03-0.24 vs. 0.0/0.0-0.02; 48 h: 0.06/0.02-0.15 vs. 0.006/0.0-0.02; 72 h: 0.05/0.0-0.11 vs. 0.0/0.0-0.02; 96 h: 0.02/0.01-0.32 vs. 0.0/0.0-0.01). The incidence and intensity of motor block (Bromage scale) and other side effects did also not differ between groups. The present study shows that thoracic epidural infusion with bupivacaine 0.125% and with a higher concentration of ropivacaine 0.375% during 96 h provides plasma levels of unbound local anesthetic far below the toxic threshold.