**5. New local anesthetics with extended activities**

Liposomal bupivacaine has recently become commercially available for use in cases with local infiltration anesthesia or a brachial plexus nerve block [28, 29]. Although this agent has shown excellent potential, it is quite expensive, and systemic or local toxicity occurring long after administration has yet to be determined. Low-molecular weight dextran was first used as an adjuvant more than half a century ago and its long history of clinical use, though recently limited in application, provides evidence of its therapeutic safety. Furthermore, it is inexpensive and approaches with it are easy to perform. Therefore, we consider that use of low-molecular weight dextran as a local anesthetic adjuvant remains beneficial even when compared with newer local anesthetics such as liposomal bupivacaine, with clinical condition a key factor for choosing the best method.

#### **6. Conclusion**

Findings obtained in our studies have demonstrated that low-molecular weight dextran functions as an effective adjuvant for potentiation of local anesthetic analgesia in patients undergoing an interfascial compartment nerve block, such as a transversus abdominis plane block, under ultrasound guidance. Notably, use of an abdominal trunk block with a large amount of a mixture of local anesthetic and low-molecular weight dextran, which allows the injected mixture to remain for a longer period at the injection site, provides good analgesia comparable to epidural anesthesia. The high viscosity of dextran can cause extra-high injection pressure when injected into the improper area or portion, alerting the practitioner regarding improper injection, a guidance effect and another practical advantage. Also, use of a dextran mixture may inhibit unintended spread of the injected solution and increase the accuracy of the intended nerve block. As a pharmacological safety aspect, use of a dextran mixture reduces the risk of systemic toxicity related to local anesthetics by suppressing their systemic absorption. All of these factors are significant clinical advantages gained by use of low-molecular weight dextran as a local anesthetic adjuvant when performing various nerve block procedures.
