**4.3 Guidance effect: erector spinae plane block cases**

Findings obtained in transversus abdominis plane block, rectus sheath block, and quadratus lumborum block cases suggested that use of a mixture of local anesthetics and low-molecular weight dextran can provide good analgesia as part of an erector spinae plane (ESP) block in the same manner [14]. Thus, we applied such a block with a dextran mixture in patients undergoing video-assisted thoracic surgery (VATS) to confirm clinical feasibility and investigate the technical benefits of performing a nerve block with adjuvant dextran.

Five patients scheduled for video-assisted thoracic surgery for lung cancer (age 63 ± 7 years, body weight 59 ± 7 kg, anesthesia time 295 ± 94 minutes) received a unilateral erector spinae plane block just prior to starting surgery (**Figure 9**). Targeting the transverse process at the level of the thoracotomy incision, 40 ml of 0.3% ropivacaine and 7% low-molecular weight dextran in a saline solution were injected under ultrasound guidance. General anesthesia was maintained with

#### **Figure 9.**

*Upper panel: Anatomical scheme for erector spinae plane (ESP) block at T8 level of spine. Lower left panel: Positions of ultrasound linear probe and nerve block needle (BN) for ESP block targeting of the transverse process of T8 level of spine in patient positioned in a lateral decubitus position just prior to starting videoassisted thoracic surgery (VATS) for lung cancer [14]. Lower right panel: Corresponding ultrasound image obtained during ESP block with use of linear ultrasound probe (8–13 MHz). A mixture of local anesthetic and low-molecular weight dextran (LA-LMWD) was shown spread on the compartment just above the transverse process. ESM: erector spinae muscles; TM: trapezius muscle; TP: transverse process.*

*New Application of Low-Molecular Weight Dextran as Local Anesthetic Adjuvant… DOI: http://dx.doi.org/10.5772/intechopen.98797*

desflurane and remifentanil. Acetaminophen (15 mg•kg−1) was also administrated at the end of surgery. For postoperative rescue analgesia, intravenous flurbiprofen (50 mg) was prepared.

During the first night after surgery, no additional rescue analgesic was given to any of the patients and the NRS pain score (0-no pain, 10-worst pain) was uniformly very low at 2.2 ± 1.1. No adverse effects were observed with use of the low-molecular weight dextran mixture, the same as seen in cases examined in our other nerve block studies that received a dextran mixture. As a control, we enrolled five patients who underwent our usual protocol for video-assisted thoracic surgery, general anesthesia combined with epidural anesthesia and 15 mg•kg−1 of acetaminophen, with postoperative continuous epidural anesthesia performed with 3 ml•hr.−1 of 0.25% ropivacaine. The first night, NRS pain score (0-no pain, 10-worst pain) for those patients was 2.1 ± 1.2, indicating that an ESP block with a mixture of ropivacaine and low-molecular weight dextran has nearly the same analgesia effect as epidural anesthesia.

It should be noted that use of low-molecular weight dextran significantly increases the viscosity of the injection preparation. Should such a high-viscosity mixture be injected into the wrong portion of parenchymal tissue or an area outside of the target compartment, extra high pressure will likely develop. A large increase in injection pressure related to the site of injection can be a great help to avoid missinjection, resulting in accurate compartment injection. This guidance effect may be related, at least in part, to the adjuvant effect of low-molecular weight dextran. In addition, the impact of injection pressure could be especially beneficial for novice practitioners learning nerve block procedures.

#### **4.4 Inhibition of unintended spread: mandibular nerve block cases**

Based on the above results obtained in our study of compartment nerve block cases, we also examined use of low-molecular weight dextran for cases with a single nerve block [15]. Patients undergoing a mandibular nerve block performed at a site close to the oval foramen from which the mandibular nerve appears were enrolled. In this target site, various nerves and vessels are closely assembled, thus accuracy is essential. However, a correct nerve block needle tip position alone is not sufficient for an accurate injection. In addition to that, spreading of the injected local anesthetic into the unintended surrounding area must be avoided for precision as well as safety, thus the high viscosity characteristic of a dextran solution may be best for such a procedure. Based on this speculation, we performed a study.

A mandibular nerve block was performed using a lateral extraoral approach with guidance using ultrasound imaging in 10 patients undergoing a parotidectomy under general anesthesia (age 60 ± 12 years, body weight 69.5 ± 14.6 kg, anesthesia time 227 ± 92 minutes). Following anesthesia induction, the head of the patient was turned according to the surgical site with the mouth open, then a convex ultrasound transducer was placed just below and parallel to the zygomatic bone (**Figure 10**). Next, a 23-gauge nerve block needle was inserted towards the dorsal edge of the plate, close to the mandibular nerve. When the needle touched the plate edge, 3 ml of a mixture of 0.3% ropivacaine and 7% low-molecular weight dextran in a saline solution was injected. The maxillary artery frequently appears in this section and should not be traumatized. Eighteen hours after surgery, the NRS pain score (0-no pain, 10-worst pain) was 1.2 ± 0.4 without use of a rescue drug, as compared to 2.7 ± 0.7 in our previous non-nerve block cases (P < 0.01). No side effects related to unintended spread of the injected ropivacaine were noted.

Performance of a mandibular nerve block using a mixture of ropivacaine and low-molecular weight dextran provided good postoperative analgesia, as well as

#### **Figure 10.**

*Upper panel: Anatomical relationships of mandibular nerve, lateral pterygoid plate, and maxillary artery. For a mandibular nerve block, the ultrasound probe is placed just below and parallel to the zygomatic bone [15]. Lower left panel: Typical color Doppler ultrasound image obtained at 4.5 MHz with curvilinear ultrasound probe placed as shown in the upper panel. The maxillary artery is frequently visualized in such cases. The mandibular nerve could not be seen with this view due to acoustic shadows from surrounding bone. Lower right panel: Ultrasound image obtained at the moment when 3 ml of a mixture of ropivacaine and low-molecular weight dextran (LA-LMWD) was injected to the site close to the mandibular nerve emerging from the oval foramen.*

safety. These findings validated our speculation that such a dextran mixture enables an accurate single nerve block for enhancing analgesic potency of an injected local anesthetic without unintended spreading of the injectant.

*New Application of Low-Molecular Weight Dextran as Local Anesthetic Adjuvant… DOI: http://dx.doi.org/10.5772/intechopen.98797*

#### **Figure 11.**

*Ultrasound probe positioning and block needle orientation during caudal block (left panel), and ultrasound longitudinal images obtained at the same moment (right panel) [2]. An ultrasound-guided caudal block procedure in adult patients is performed as follows. After prone positioning, the location and structure of the sacral hiatus are confirmed in ultrasound transverse and longitudinal images. Then, a 23-gauge nerve block needle is inserted in the direction of the sacral canal through the sacral hiatus while monitoring real-time ultrasound images. Next, the tip of the nerve block needle is inserted into the sacral canal approximately 0.5–1 cm ahead. After negative aspiration, a local anesthetic mixture is injected.*

#### **4.5 Advanced application of low-molecular weight dextran mixture**

A local anesthetic and low-molecular weight dextran mixture can be used for a caudal block. Based on their experience, most anesthesiologists consider that a caudal block procedure in adults is generally not feasible and unreliable. However, an ultrasound-guidance technique makes such a procedure possible in adults and is rather easy to perform [2] (**Figure 11**). We consider that use of a block with a mixture that includes dextran can lead to a longer analgesia duration, thus is well applicable for gynecological, urological, and lower abdominal surgery procedures.
