**4. Conclusions**

ropivicaine 0.375% [47]. Of note, local anesthetic concentration was shown to be the prin‐

Goebel et al conducted a randomized trial examining the use of ultrasound-placed ISB catheters in managing postoperative pain for major shoulder surgery [48]. Patient controlled infusions of ropivicaine 0.2% resulted in less concomitant pain medication administration in

With the performance of interscalene block over the past four decades, notable adverse effects have been established. Perhaps most notable, phrenic nerve (C3-5) paralysis occurs in nearly all patients receiving ISB that may lead to significant decline respiratory function, particularly in patients with underlying pulmonary disease [26], [31]. One ultrasound study found the anatomical separation between the brachial plexus and phrenic nerve lateral to the cricoid cartilage to be as little as 2 mm [49]. Other undesirable effects of regional anesthesia at this site may include blockade of the recurrent laryngeal nerve causing hoarseness, stellate ganglion causing Horner's syndrome, and increased local anesthetic spread rarely causing elements of epidural or spinal quality anesthesia [27]. Inadvertent needle placement during ISB perform‐ ance may lead to vasculature puncture and direct nerve injury, including reported cases of spinal cord injury [50]. As with other forms of regional anesthesia, systemic local anesthetic toxicity as well as block failure may occur [51]. Failure to anesthetize the distribution of the ulnar nerve is of particular propensity with ISB, as the lower trunk is often spared [24].

With the inclusion of ultrasound guidance for interscalene block, several studies have demonstrated an impact on previously reported adverse effects. Renes et al conducted a randomized trial in patients undergoing shoulder surgery, comparing general anesthesia combined with ISB performed with 10 ml ropivacaine deposited via ultrasound versus peripheral nerve stimulator technique [35]. The ultrasound group showed a significantly decreased incidence of diaphragmatic hemiparesis [35]. In addition, the use of ultrasound technique has allowed ISB studies that have revealed decreased incidence of phrenic nerve blockade and respiratory complications based on level of block performance (C7) and reduced volume of local anesthetic [27], [26]. Abrahams et al conducted a systematic review and metaanalysis of randomized trials for a variety of peripheral nerve blocks [6]. When comparing ultrasound guidance versus peripheral nerve stimulation, ultrasound guided blocks were shown to have significantly less risk of vascular puncture [6]. Despite direct visualization when using ultrasound-guidance for PNB, no significant difference in the incidence of neuronal injury or neurologic symptoms postoperatively has been shown [25], [24]. With regard to failure to anesthetize the brachial plexus inferior trunk with ISB, Kapral et al demonstrated improved ulnar nerve and median nerve blockade 30 min post-block when compared to PNS

the first 24 h postoperatively as compared to catheter infusions of normal saline [48].

ciple determinant of motor blockade [47].

130 Advancements and Breakthroughs in Ultrasound Imaging

**3.8. Adverse effects with interscalene block**

**3.9. Impact of ultrasound on adverse effects**

guidance [30].

Peripheral nerve blockade has become an ever-increasing tool in providing analgesia for patients undergoing focal surgical interventions. Advancements in ultrasound guidance for performance of these peripheral nerve blocks have allowed a parallel increase in this technol‐ ogy's utilization. The interscalene approach to brachial plexus blockade is a commonly employed peripheral nerve block that has demonstrated effectiveness in providing perioper‐ ative analgesia for patients undergoing shoulder surgery. The use of ultrasound guidance in performing the interscalene block has been shown to be effective in providing postoperative analgesia while decreasing specific respiratory side-effects [26], [27], [35], vascular puncture [6], and local anesthetic toxicity [53] as compared to non-ultrasongraphic, blind techniques. These benefits likely stem from the direct visualization of anatomical structures afforded by ultrasound implementation during block performance. Ultrasound guidance for peripheral nerve blockade remains an exciting advancement in caring for patients during the periopera‐ tive period, and this technology will likely continue to become commonplace with an increas‐ ing patient population and demonstrated effectiveness.
