Plasma concentration of ropivacaine after intercostal blocks for video-assisted thoracic surgery

Background. Absorption of local anaesthetics following intercostal blocks is rapid. Therefore, plasma concentrations of ropivacaine during intercostal blocks with ropivacaine 2, 5, 7.5 and 10 mg ml(-1) (ropivacaine 5 ml injected into each of four intercostal spaces) in patients undergoing video-assisted thoracic surgery were determined. Methods. After informed consent and ethics committee approval, 64 patients were randomly allocated to four groups for intercostal nerve block (ropivacaine 2, 5, 7.5 or 10 mg ml(-1) at the end of surgery). Central (mixed) venous and arterial plasma samples were collected before the start of intercostal application, and 2, 5, 10, 15, 20, 30, 45, 60 and 90 min afterwards. Plasma concentrations of ropivacaine were measured by high performance liquid chromatography. Results. Maximum venous plasma concentrations occurred after the mean times of 10.7 (range, 5-15), 10.8 (5-20), 11.3 (5-20) and 12.2 (5-45) min, respectively for each group. The groups had mean concentrations of 1.3 (sd, 0.6; range, 0.3-2.3), 2.1 (1.0; 0.5-4.5), 2.4 (1.0; 1.2-5.1) and 2.5 (0.9; 1.7-5.6) mug ml(-1), respectively. Maximum arterial plasma concentration following 1.0% ropivacaine occurred after 16 (5-45) min with a mean of 2.3 (0.6; 1.5-3.6) mug ml(-1). No signs of central nervous system or cardiac toxicity were observed. Conclusions. After intercostal blocks the absorption of ropivacaine is rapid compared with other techniques for regional anaesthesia and results in relatively high venous and arterial plasma concentrations, especially if a dose of 100 mg or more is used.