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Please confirm that an ethics committee approval has been applied for or granted: Yes: I’m uploading the Ethics Committee Approval as a PDF file with this abstract submissionBackground and Aims The serratus anterior plane block (SAPB) catheter provides analgesia during cardiac surgery; however, its effect remains inconsistent because of unclear local anesthetic distribution. Contrast-enhanced ultrasonography (CEUS) with Sonazoid® is positively correlated with the distribution of contrast in vivo and dyes in cadaver models for single-injection nerve blocks. This study aimed to evaluate the correlation between Sonazoid® distribution on CEUS and dye spread via SAPB catheters in predicting local anesthetic distribution in patients using Sonazoid®.Methods This study used nine sides of five cadavers. Under ultrasound (B-mode) guidance, an SAPB catheter was inserted into the deep layer of the serratus anterior muscle at the fourth-rib level. A total of 20 mL of injectate was administered, comprising 0.2 mL of Sonazoid® (diluted 100-fold), 2 mL of dye (diluted to 10%), and 0.25% levobupivacaine. CEUS was performed immediately after the injection ( figure 1), and the enhanced area was marked externally. The cephalad and caudal spreads (cm) from the catheter insertion site were measured starting from the cephalad direction. Anatomical dissection was performed to measure the dye spread in the same manner. The analysis used Spearman’s correlation coefficient.Results Spearman’s correlation coefficient for the cephalad spread was 0.46 (p=0.21), which suggests a moderate correlation, but no statistical significance, and for the caudal spread was 0.12 (p=0.77), indicating no statistical significance.Abstract P234 Figure 1Dual-display ultrasound image shows the same plane in B-mode (right) and contrast-enhanced ultrasound image (left) following Sonazoid® injection via a serratus anterior plane block catheter. The enhanced area is indicated by yellow double-headed arrowsConclusions Although statistical significance was not achieved, the findings suggest that CEUS with Sonazoid® may be useful for estimating cephalad spread.