Plasma Concentrations and Analgesic Effects of Ropivacaine 3.75 mg/mL During Long-Term Extrapleural Analgesia After Thoracotomy

Fourteen patients received long-term extrapleural analgesia with ropivacaine for postoperative pain relief after posterolateral thoracotomy. We determined plasma concentrations of ropivacaine as well as pain scores and opioid consumption to assess the analgesic effect. In this prospective study, an extrapleural catheter was placed with its tip near the third rib before chest closure. The extrapleural block started with 10 mL of 7.5 mg/mL of ropivacaine followed 30 minutes later by an infusion of 3.75 mg/mL of ropivacaine at a fixed rate of 0.1 mL/kg/h for 71.5 hours. Mean total and free ropivacaine concentrations increased until day 1, reached similar values on day 2, and subsequently decreased. In 13 patients, free drug levels did not exceed 0.14 mg/L. Coincidence of above-average total ropivacaine concentrations up to 4.8 mg/L and low plasma binding resulted in free drug concentrations up to 0.31 mg/L in 1 patient. An impaired ropivacaine plasma binding was observed in 2 patients after major surgical blood loss, in 3 patients in a state of a moderate postoperative acidosis, and in 1 patient after intravenous administration of clindamycin. All free ropivacaine concentrations measured were below the toxic threshold, and we observed no clinical signs of ropivacaine-related toxicity. The magnitude of pain scores and the opioid consumption pointed out a sufficient postoperative analgesia. A dose of 0.375 mg/kg/h of ropivacaine can safely be administered for long-term extrapleural analgesia after thoracotomy.