Possible utility of contrast-enhanced ultrasonography for detecting spread of local anesthetic in nerve block

Purpose: This study demonstrated the effects of perfluorobutane (Sonazoid^®) with contrast-enhanced ultrasonography (CEUS) to identify the spread of local anesthetics in ultrasound-guided nerve block. Methods: This study consists of simulation, cadaveric, and animal studies. In a simulation study, 1% lidocaine with 10- to 1000-fold diluted Sonazoid^®, a US-specific contrast agent to diagnose hepatic and breast cancers (0.5 mL), was injected into a resin-based phantom to determine the optimal concentration for ultrasound-guided peripheral nerve block. The enhanced area was measured by direct observation and ultrasonography (US). In the cadaver study, ultrasound-guided sciatic nerve block was performed at the popliteal fossa in the 9 extremities, and 5 mL of the optimally diluted Sonazoid^® defined in the simulation study with X-ray contrast medium and blue dye was injected. Longitudinal spread of the solution was measured by CEUS, X-ray imaging and anatomical dissection. In the animal study, the optimally diluted Sonazoid^® was injected around the sciatic nerve of rats (n = 6), and neuronal function and toxicity were evaluated by behavioral and histological estimation. Results: The simulation study proved that 100-fold diluted Sonazoid^® was the optimal concentration. In the cadaver study, CEUS and anatomical dissection (r = 0.90, P = 0.0020) or radiography (r = 0.84, P = 0.0072) showed high agreement and correlation with the longitudinal spread. CEUS clearly showed a fine intraneuronal injection image compared to the usual B-mode imaging. The animal study suggested no adverse effects by co-administration of lidocaine and Sonazoid^®. Conclusions: CEUS with 100-fold diluted Sonazoid^® could identify the spread of local anesthetic as well as radiography and anatomical dissection, and distinguish between intra- and extraneuronal injections without neurodegeneration.