Summary:
Introduction: The paravertebral block is a technique being used increasingly for intra- and post-operative anaglesia over the last few years, tending to replace the epidural anesthesia, mainly because it provides minimum motor blockade. It seems to have a safer and equally effective profile compared to other analgesic techniques, although there are differing views and this is not universally accepted in the international bibliography. Many are still in favor of epidural administration because of its known effectiveness and long use.
Ropivacaine is a local anesthetic which has almost entirely replaced bupivacaine, due to the increasing cardiotoxicity of the latter. The aim of the present study was to investigate ropivacaine pharmacokinetics after thoracic paravertebral block; an administration technique not fully studied.
Methods: A prospective clinical – laboratory study was carried out between the Laboratory of Biopharmaceutics – Pharmacokinetics, National Kapodistrian University of Athens and the B’ University Anesthesiology Clinic of the “Attikon” Hospital. Patients who took part in the study underwent thoracic surgery and received analgesia with paravertebral block at the beginning of surgery with a bolus dose of 125 mg of ropivacaine followed by continuous infusion 4 ml/h at the end of surgery for the first three postoperative days. Blood samples (arterial and venous) were collected during the surgery and during the continuous infusion and were assayed using High Performance Liquid Chromatography. The pharmacokinetic parameters were assessed with the use of WinNonlin, while SPSS 25 statistical software was used for statistical analysis.
Results: Postoperatively, patients had mild pain in rest and moderate pain during movement. Test results were normal before and after surgery, indicating that the health status of the patients was good throughout ropivacaine administration. The pharmacokinetic parameters were not normally distributed and therefore median values (range) are cited for each parameter. The pharmacokinetic analysis was performed separately for arterial and venous blood. After bolus administration the peak plasma concentration was Cmax 1.16 ug/ml (0.7-2.04), time to reach peak concentration was tmax 15 min (15-90) and AUC 162.11 ug/ml*min (341.25) in arterial blood, and Cmax 0.91 ug/ml (1.81), tmax 60 min (177.5) and AUC 90.97 ug/ml*min (87.38-428.62) for venous blood. Following bolus and continuous infusion arterial blood parameters were Cmax 2.71 ug/ml (2.06-3.16), tmax 5955 min (3007-5995) and AUC 12829 ug/ml*min (10078.05-15551), while venous blood parameters were Cmax 2.73ug/ml (2.5-3.47), tmax 5955 min (3015-5995) and AUC 13968.84 ug/ml*min (9508.55-17081.61).
Peak concentrations in both arterial and venous blood were found to exceed the defined concentration limits for the occurrence of neurotoxicity without any patients experiencing any adverse effects.
Conclusions: This study describes paravertebral ropivacaine administration in 10 patients undergoing thoracic surgery, and will be continued in order to get a more robust sample size for the pharmacokinetic analysis of ropivacaine after paravertebral block. So far, it appears that adequate pain control is achieved during postoperative pain management.
Keywords:
Ropivacaine, Pharmacokinetics, Paravertebral Block, Thoracic Surgery
