Background and Aims Erector Spinae Plane Block (ESPB) can be applied at all vertebral levels and low thoracic applications are reported in abdominal surgeries. To our knowledge there exists no study of the pharmacokinetics of different local anesthetics in low thoracic ESPB. Here, we aimed to measure and determine the time-concentration relation of the plasma bupivacaine levels at different time points after low thoracic ESPB.

Methods The observational pharmacokinetic study was performed between March 2021 and March 2022 after IRB approval. ASA class I-II patients aged between 18–65 y undergoing laparoscopic Nissen fundoplication were enrolled into the study. Patients who had paraspinal surgery or a history of previous abdominal surgery were excluded. At the end of the surgery, under general anesthesia, 20 mL of 0.25% bupivacaine was used consecutively to perform bilateral USG-guided ESPB at T9 level, using the out-of-plane technique. Blood samples were taken prior to ESPB and at 5th, 10th, 20th, 30th, 45th, 60th, 90th, 120th, 240th and 720th minutes after ESPB. Plasma bupivacaine concentration was measured using enzyme-linked immunosorbent assay (ELISA).

Results 12 male and 5 female patients with mean age of 39.35±14.93 y were included. Peak mean plasma bupivacaine concentration was observed at 30m (0.022±0.010 μg/ml). The highest concentration was 0.041μg/ml at 60m, in one case. There was no difference in any of the measurements between men and women (p>0.05).

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Abstract B6 Figure 1

Plasma bupivacaine concentration and time profile demonstrated with Box-plot. X axis: Time points after ESPB block, Y axis: Concentration of plasma Bupivacaine (mcg/mL)

Conclusions Twenty mL of 0.25% bupivacaine for ESPB at the lower thoracic level offers safe pharmacokinetics.