Efficacy And Pharmacokinetics Of Transversus Abdominis Plane Block With Different Concentrations Of Ropivacaine After Cesarean Section Under General Anesthesia

Objective: To observe efficacy, safety and pharmacokinetics of transversus abdominis plane block with different concentrations of ropivacaine after cesarean section under general anesthesia.Method: Ninety women were chosen to receive ultrasound-guided bilateral transversus abdominis plane block(TAP block) after cesarean section under general anesthesia. According to the concentration used in TAP blocks, the patents are randomized to three groups. Group A,B and C received respectively 0.45%,0.35% and 0.25% ropivacaine 20 ml each side in bilateral transversus abdominis plane. Visual analogue scale(VAS) and Bruggrmann comfort scale(BCS) were recorded at 1h, 2h, 4h, 8h, 12 h and 24 h after cesarean section. Arterial blood samples were collected at 2min, 10 min, 15 min, 20 min, 25 min, 30 min, 40 min, 120 min, 240 min, 480 min, 960 min after TAP blocks. Blood samples were analyzed for plasma ropivacaine concentrations by liquid phase chromatography and mass spectrometry(LC-MS/MS). The pharmacokinetic parameters were calculated using the computer program DAS 2.0.Results: Three groups' curves of plasma concentration of ropivacaine against time fit into a two-compartment mode. The peak concentration(Cmax) and Area under the blood concentration curve(AUC) of Group A after TAP blocks are significantly higher than Group B and C; Cmax or AUC of Group B and C have no significant difference. Three patients in Group A developed slight local anesthetic poisoning symptom, and Cmax of the three patients is lower than the plasma concentrations of local anesthetics poisoning threshold. All the three patients showed suspected local anesthetic systemic toxicity.The time needed to reach the peak plasma concentration of ropivacaine(Tmax), has no significant difference among three groups. Visual analogue scale(VAS) at 8h and later observation time points after cesarean section in Group C, was significantly higher than Group A and B; Bruggrmann comfort scale(BCS) at 8h and later observation time point after cesarean section in Group C was significantly lower than Group A and B. VAS or BCS of Group B and C at all time points have no significant difference.Conclusion: Curves of plasma concentration of ropivacaine against time, when different concentrations of ropivacaine are used in bilateral transversus abdominis plane block(TAP block), fit into a two-compartment pharmacokinetic model. Cmax or AUC of high concentration(0.45%) of ropivacaine is higher than that of medium(0.35%) and low concentration(0.25%) of ropivacaine. The anesthetic efficacy of low(0.25%) concentration of ropivacaine for TAP blocks at 8h and later observation time point after cesarean section is worse than that of medium(0.35%) and high(0.45%) concentration of ropivacaine. 0.35% ropivacaine 40 ml bilateral TAP blocks for caesarean section under general anesthesia can provide good anesthetic efficacy and comfortableness, and is safer.