Comparison of the effect of different volumes ropivacaine on deep serratus anterior plane block in patients undergoing breast surgery: a prospective randomized double-blinded trial

BACKGROUND A larger volume of local anesthetic provides a wider range of blocked sensory but carries a greater risk. The purpose of this trial was to compare the effect of different volumes of ropivacaine injected to deep serratus anterior plane in patients undergoing breast surgery. METHODS In this randomized double-blind trial, 60 patients undergoing breast surgery were randomly allocated to R10, R20 and R30 groups (n=20), and received deep serratus anterior plane block with 10, 20 and 30 mL of 0.5% ropivacaine respectively. 30 minutes after block, the cutaneous sensory was tested by cold stimulus in the craniocaudal direction along the midaxillary line. We recorded the numerical rating scale pain scores over 24 h after surgery and estimated the area under curve by numerical rating scale pain scores. The cases of rescue analgesia and the prevalence of adverse events were also recorded. RESULTS The blocked dermatomes were 3 [3, 4], 6 [5, 7] and 7 [6, 8] in the R10, R20 and R30 groups, respectively (R10 vs. R20, P<0.001; R10 vs. R30, P<0.001; R20 vs. R30, P=0.005). The area under curve of R10 group was significantly higher compared with the R20 and R30 groups (P=0.014, P=0.003, at rest; P<0.001, P<0.001, on movement). CONCLUSIONS The blocked dermatomes increased with increasing volume when 10, 20 and 30 mL ropivacaine was used for deep serratus anterior plane block. The analgesic effects of 20 and 30 mL were similar to each other and better than 10 mL. Therefore, in breast surgery, volume of 20 mL ropivacaine is considered to be appropriate for deep serratus anterior plane block.