Purpose: Clear visualization of ultrasound (US) images is crucial for successful US-guided nerve block. However, accurate determination of local anesthetic (LA) distribution from US images remains difficult. Sonazoid®, which comprises perflubutane microbubbles, is used to diagnose hepatic and breast tumors. This study aimed to investigate the visibility of Sonazoid® in perioperative US-guided nerve block. Methods: We performed rectus sheath block (RSB) in patients scheduled for laparoscopic abdominal surgery (n = 10). 10 mL of a mixture containing equal amounts of 0.75% ropivacaine and iohexol with the addition of Sonazoid® diluted 100-fold was administered. We investigated the correlation and agreement between Sonazoid® and iohexol distributions. The brightness of the solution and tissues was calculated: a grayscale value between 0 (dark) and 255 (bright) was measured in all pixels of the region of interest. Adverse events were also investigated. Results: Sonazoid® was clearly visualized and distinguished from the surrounding tissues both during and after RSB. The spread of Sonazoid® and iohexol was significantly correlated (spearman’s ρ = 0.53, p = 0.0004). Bland–Altman analyses revealed significant mean difference between two methods (15.6 mm; 95% confidence interval [CI]: 10.6, 20.6; standard deviation (SD) 15.65; p < 0.0001). Limits of agreement were − 14.94 to 46.24 mm. Sonazoid® significantly increased the mean grayscale values at the posterior rectus sheath (93.7 vs. 201.9, p < 0.0001). There were no complications. Conclusion: Sonazoid diluted 100-fold® was clearly visualized real-time, and the enhancement was sustained and measurable after RSB. Sonazoid® could potentially be used for the contrast agent of US-guided nerve block.
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