Dose-response studies of Ropivacaine in blood flow of upper extremity after supraclavicular block: a double-blind randomized controlled study

BACKGROUND The sympathetic block of upper limb leading to increased blood flow has important clinical implication in microvascular surgery. However, little is known regarding the relationship between concentration of local anesthetic and blood flow of upper limb. The aim of this dose-response study was to determine the ED50 and ED95 of ropivacaine in blood flow after supraclavicular block (SB). METHODS Patients undergoing upper limb surgery and supraclavicular block were randomly assigned to receive 30ml ropivacaine in concentrations of 0.125%(A Group), 0.2%(B Group), 0.25%(C Group), 0.375%(D Group), 0.5%(E Group), or 0.75%(F Group) (n=13 per group). All patients received supraclavicular block (SB). Time average maximum velocity (TAMAX), cross-sectional area (CSA) of brachial artery and skin temperatures (Ts) were measured repeatedly at the same marked points, they were taken at baseline (before block, t0) and at 30min after SB (t1). Blood flow(BF) = TAMAX× CSA×60 sec.. Relative blood flow (ΔBF) = BFt1/ BFt0. Success of SB was assessed simultaneously. Supplementary anesthesia and other adverse events (AE) were recorded. RESULTS Significant increase in TAMAX, CSA, BF and Ts were seen in all concentration groups at t1 comparing with t0 (P<0.001). There was an upward trend of TAMAX, CSA, BF with the increasing concentration of ropivacaine except Ts. There was no significant different of Ts at t1 among different concentration group. The dose-response formula of ropivacaine on ΔBF was Y=1+3.188/(1+10^((-2.451-X) × 1.730)) and ED50/ED95 (95%CI) were 0.35/1.94%(0.25-0.45/0.83-4.52), and R2 (coefficient of determination) =0.85. ED50/ED95 (95%CI) values of sensory block were 0.18/0.33% (0.15-0.21/0.27-0.51), R2=0.904. CONCLUSIONS The dose-response curve between SB ropivacaine and the changes of BF was determined. The ED50/ED95 of ropivacaine of ΔBF are 0.35/1.94% (0.25-0.45/0.83-4.52). TAMAX, CSA and BF consistently increased with ropivacaine concentration. The maximal sympathetic block needs higher concentration than that complete sensation block needs which may benefit for microvascular surgery. TRIAL REGISTRATION Clinicaltrials.gov NCT02139982 . Retrospectively registered (Date of registration: May, 2014).