Plasma ropivacaine concentrations after ultrasound-guided transversus abdominis plane block for open retropubic prostatectomy

Abstract

Ropivacaine-induced vasoconstriction may affect the early absorption speed of ropivacaine; however, the effects of dose on pharmacokinetics following transversus abdominis plane (TAP) block have not been studied. In this study, we have examined plasma ropivacaine concentrations following TAP block with various ropivacaine concentrations (0.25, 0.5, and 0.75 %). With the approval of our University ethics committee and informed consent, 39 adult patients undergoing open retropubic prostatectomy were enrolled. Patients were randomly assigned to three groups (n = 13 each) receiving TAP block with 20 ml (10 ml each side) of different concentrations of ropivacaine. To determine plasma concentrations, blood samples were drawn before and 15, 30, 45, 60, 90, 120, and 180 min after completion of bilateral TAP blocks. Plasma ropivacaine concentrations were analyzed by gas chromatography with mass spectrometry. We found that the peak plasma concentrations (C(max)) increased dose dependently (0.41 ± 0.14, 0.89 ± 0.55, and 1.56 ± 0.50 µg/ml), but the times to C(max) (23.0 ± 15.8, 23.1 ± 14.5, and 20.8 ± 11.5 min) were not different between 0.25, 0.5, and 0.75 % ropivacaine doses, respectively. Terminal elimination half-life (t(1/2)), total body clearance (CL), and distribution volume (V(d)) were also not different among the three groups. Ropivacaine concentration did not alter pharmacokinetic profile following TAP blocks.