The MEC₉₀ of Ropivacaine for Ultrasound-Guided Pectoral Nerve Block Type II for Modified Radical Mastectomy: A...

This study aimed to determine the 90% minimum effective concentration (MEC₉₀) of a fixed volume of 30 mL ropivacaine for ultrasound-guided pectoral nerve block type II (PECS IIblock) in patients undergoing modified radical mastectomy (MRM), using a biased-coin design up-and-down sequential method (BCD-UDM).

Patients were enrolled sequentially according to the BCD-UDM protocol. All patients received 30 mL of ropivacaine for ultrasound-guided PECS II block. The initial ropivacaine concentration was 0.2%, and the concentration administered to each subsequent patient was determined by the PECS II block response of the preceding patient. After a negative response, the concentration was increased by 0.02%. After a positive response, the next concentration was determined by biased-coin randomization: with an 11% probability of decreasing by 0.02% and an 89% probability of remaining unchanged. A positive response was defined as a sensory block score of grade 1 or higher within the T2-T6 dermatomal distribution, together with an increase in MAP of less than 20% from baseline within 5 min after skin incision; otherwise, the response was considered negative. The MEC_{9 0} was estimated using isotonic regression, and the 95% confidence interval (CI) was calculated using 2000 bootstrap resamples in R.

Fifty-five patients were included in the MEC₉₀ analysis, and 56 patients who received PECS II block were included in the safety analysis. The MEC₉₀ of 30 mL ropivacaine for ultrasound-guided PECS II block in patients undergoing MRM was 0.23% (95% CI, 0.18% to 0.25%). Among the 56 patients, one puncture-site hematoma (1.79%) and one suspected anaphylactic shock attributed to cisatracurium were observed, with no local anesthetic systemic toxicity. Among the 55 patients who completed surgery and postoperative follow-up, postoperative nausea and vomiting occurred in 14 patients (25.45%), and postoperative delirium occurred in one patient (1.82%).

The MEC_{9 0} of a fixed volume of 30 mL ropivacaine for ultrasound-guided PECS II block in patients undergoing MRM was 0.23%. Nevertheless, the limited sample size and individual differences may preclude a comprehensive evaluation of uncommon adverse events.

Chinese Clinical Trial Registry (Registration Number: ChiCTR2300076311).