Preliminary study on the use of perfluoropropane contrast agent in monitoring drug diffusion during fascial plane blocks.

objectivesThis research aims to preliminarily verify the feasibility of utilizing a novel perfluoropropane ultrasound contrast agent (UCA) for observing the spread of drugs within the fascial plane.We demonstrated the feasibility of this method by conducting transverse abdominis plane block(TAPB) using two-dimensional (2D) ultrasound.

methodsFirstly, to explore the optimal dilution ratio of UCA mixed with local anesthetics (LA), this study conducted in vitro simulation experiments by diluting the UCA with 0.375% ropivacaine hydrochloride(ROP) at various ratios (0, 10x, 30x, 100x, 300x, 1000x).The contrast of images under 2D ultrasound was observed and measured in a six-well plate. After selecting two relatively suitable doses, TAPB was performed using rabbits to determine the best dilution ratio. Next, 0.375% ROP was mixed with UCA at the selected optimal dilution ratio (with the addition of methylene blue). TAPB was performed, and the diffusion area of the contrast agent was recorded in real-time under 2D ultrasound. After dissection, photographs were taken to record the spread range of methylene blue, and the correlation and consistency between the two methods of observing drug diffusion were compared. Finally, we conducted in vitro and in vivo experiments to evaluate the muscular and neural toxicity of the novel UCA when combined with 0.375% ROP.

resultsUsing 2 ml of 0.375% ROP in combination with perfluoropropane UCA, without further dilution, produced stable and high-contrast 2D ultrasound images in an in vitro simulation experiment and TAPB in rabbits.This mixture ratio was subsequently used to observe drug diffusion and toxicity in further studies. A paired t-test analysis showed no statistically significant difference in the measured area between the spread of 0.375% ROP + perfluoropropane UCA in 2D ultrasound imaging and the spread of methylene blue (MB) after dissection.The area recorded by ultrasound images exhibited a strong correlation with the distribution range of LA as reflected by MB after dissection (R = 0.70, P = 0.02).Bland-Altman analysis showed that the mean difference in the measured area between the two methods was 0.65 cm2, and the 95% confidence interval (CI) of the difference was [-1.38 cm2, 1.16 cm2]. Only one data point was outside the 95% CI.Neither in vivo nor in vitro studies have found that perfluoropropane UCA increases the known muscular and neural toxicity of 0.375%ROP.

conclusionsOur preliminary study demonstrates the potential feasibility and safety of real-time monitoring of LA diffusion in rabbits using the novel perfluoropropane UCA under 2D ultrasound.