Pharmacokinetics of bupivacaine after bilateral ultrasound-guided transversus abdominis plane block following cesarean delivery under spinal anesthesia

BackgroundTransversus abdominis plane block is an effective method of post-cesarean analgesia. There are no data available about plasma bupivacaine levels after this block in adults. This study aimed to assess bupivacaine pharmacokinetic parameters after ultrasound-guided transversus abdominis plane blocks following cesarean delivery under spinal anesthesia.MethodsA prospective observational study in parturients undergoing elective cesarean delivery under hyperbaric bupivacaine spinal anesthesia was conducted. After surgery, patients received bilateral transversus abdominis plane block (50 mg bupivacaine each side). Venous blood samples were collected immediately before performing the block and at 10, 20, 30, 45, 60, 90, 120, 180, 240, 720 and 1440 minutes. High performance liquid chromatography was used to measure total plasma bupivacaine concentrations. Mean bupivacaine area under the curve (AUC) was calculated from 0 to 24 hours.ResultsData were collected from 17 parturients. Mean age and body mass index were 31 ± 6 y and 30 ± 4 kg/m² respectively. Mean plasma bupivacaine concentration before the block was 171 ng/mL. Mean peak concentration was 802.36 ng/mL (range 231.8 to 3504.5 ng/mL). Mean time to peak concentration was 30 min and mean area-under-the-curve (0–24 h) was 4505.4 h.ng/mL. Mean elimination half-life was 8.75 h. Three subjects had concentrations above the quoted toxic threshold and mild symptoms suggestive of neurotoxicity were reported by two subjects, but no treatment was required.ConclusionSingle-dose bilateral transversus abdominis plane block using 100 mg of bupivacaine, after spinal anesthesia for cesarean delivery, can result in toxic plasma bupivacaine concentrations.