Advances in Anesthesia, Vol. 28, No. 1, 2010
ISSN: 0737-6146
doi: 10.1016/j.aan.2010.08.002
Single or Multiple Guidance Methods for Peripheral Nerve Blockade in Modern-Day Practice of Regional Anesthesia
Regional anesthesia has traditionally been performed with the help of a single modality, which has depended on the availability of technology at the time of performance of these blocks. The transitions from paresthesia-guided to nerve stimulation to ultrasound-guided nerve blocks have helped advance regional anesthesia as a science rather than an art, and have taken it to a higher level of sophistication. However, the visual information obtained with the use of ultrasonography remains subject to interpretation by the user and, consequently, is limited by the ability to optimize the sonographic image, variations in formal training of applied ultrasound physics, and overall experience in ultrasonography. Even though ultrasound visualization by itself is presumably associated with minimal risks, the safety claimed by ultrasound enthusiasts may not necessarily result in the safest clinical practice.
There is current debate as to whether the use of nerve stimulation or ultrasonography is superior as a nerve localization instrument for regional anesthesia; there is also a proposal that the use of dual or multiple guidance modalities may further expand the opportunities to employ regional anesthesia versus use of a single method. Regional anesthesia reliably works if the correct amount of the correct local anesthetic is placed within the correct fascial plane in correct proximity to the nerve. Nerve stimulation is generally able to provide one or two of these objectively, that is, depositing a local anesthetic near the nerve to be blocked. Anesthesiologists traditionally have used larger doses of local anesthetics with this technique to ascertain block success, as it is not possible to stimulate the nerve again after even a small dose of local anesthetic has been deposited. Ultrasonography does not solve all of these problems but it does provide extra information, such as direct visualization of nerve structures that need to be blocked, the appropriate spread of the local anesthetic around the nerve and within the correct fascial plane, and visualization of the surrounding perineural structures that need to be avoided. These advantages may improve success and reduce complications; however, experts have suggested that such claims may be premature [1]. The success rate and expertise of practitioner groups varies, making it very difficult to compare the results of studies from different institutions and operators. Use of one approach should not preclude the use of another, and the debate on the best methods needs to be more outcome-oriented than target-oriented. The guidance modalities used in each case must depend on the availability of equipment, the hospital setting, the individual patient’s needs, and the expertise of the practitioner. Current technologies aiding in block performance include feeling loss of tissue resistances with blunt needles, eliciting paresthesia, peripheral nerve stimulation (PNS), ultrasonography, and injection pressures [2,3]. However, addition of sophisticated modalities may not necessarily improve the success rate nor decrease the complication rate of peripheral nerve blocks, especially in the hands of experienced physicians.
In this review, the authors present the outcomes of randomized, controlled studies that compare single to dual guidance for regional anesthesia, concentrating on PNS in comparison with ultrasound guidance, or the combined use of the two technologies.
Evolution of regional anesthesia
In 1885, William Halsted performed the first brachial plexus block under direct visualization by applying cocaine directly to nerves that had been surgically exposed. Going forward, but before the invention of nerve stimulation, the nerves or nerve roots were recognized by the presence of paresthesia. Almost 100 years ago a German physician, Kulenkampff [4], used transcutaneous insertion of a needle and located nerves using the paresthesia technique. Paresthesia is a phenomenon whereby mechanical stimulation of a nerve results in a sensory feeling described as “an electric shock” in the sensory distribution of the nerve being contacted. Moore [5] stated “no paresthesias—no anesthesia,” which is still part of the controversy regarding the use of nerve stimulation. The knowledge of anatomy and its common variations are core to performing this technique, as is the ability to appreciate the fascial planes and tissue layers with the use of blunt needles. Patient understanding and cooperation greatly enhance success with this method. The success rate with these techniques is about 60% to 70% [6]. Moreover, paresthesia has been demonstrated to have poor sensitivity for needle to nerve contact [7].
Nerve stimulation became common in the late twentieth century and changed the face of regional anesthesia. In 1912, a peripheral nerve stimulator was introduced by Perthes, but the technique did not gain popularity until 1962, when a smaller and portable instrument was devised [8]. PNS provides an accurate approximation of the proximity of the stimulating needle tip to a nerve or plexus by using an electric current to elicit an objective functional motor response. One obvious advantage is that PNS causes minimal discomfort to patients, because the low stimulating currents (0.3–1.5 mA) readily stimulate the larger A-alpha motor fibers more than C pain fibers when short pulse duration (0.1 ms) is used [9]; this is in contrast to the paresthesia technique, which by its nature causes varying degrees of discomfort. A second advantage of PNS is that patient cooperation is not needed during the procedure, so a block can be performed in a lightly or moderately sedated patient, providing an extra degree of comfort. In addition, the incidence of nerve damage may be decreased with PNS as compared with paresthesia techniques [10,12], and the success rate with PNS may be equal to or greater than that from eliciting paresthesias [13]. Problems with this technique, however, are that a motor response may not be elicited if the tip of the needle is in contact with just the sensory portions of a given nerve [14], and a response to a stimulating current less than 0.5 mA does not guarantee extraneural placement [3,7,15,16].
History of ultrasonography and its evolving use in regional anesthesia
Doppler and sonography became common for the placement of supraclavicular blocks as early as 1978 [17]. Ting and Sivagnanaratnam [18] first used ultrasound to confirm needle placement and observe local anesthetic spread during axillary nerve blocks in 1989. These investigators reported a 100% success rate with no complications during this pilot study, and that they were able to visualize the needle tip and axillary anatomy at all times. Subsequently, Kapral and colleagues [19] demonstrated that ultrasound-guided supraclavicular blocks resulted in safe and more effective anesthesia than axillary blocks for the brachial plexus distribution.
Marhofer and colleagues [20] demonstrated improved success of “3-in-1” lower extremity blocks performed under ultrasound guidance as compared with nerve stimulation. These investigators further showed a reduction in the volume of local anesthetic required to produce an effective block with ultrasound guidance than with nerve stimulation [21]. The use of ultrasound localization of nerves was further advanced when a group of researchers in Toronto demonstrated high-quality images of the brachial plexus with ultrasound [22]. This group also confirmed the findings by Urmey [23] that contact of a stimulating needle with the nerves does not necessarily initiate a motor response [14,22].
Within the past 6 years, Brian Sites and his colleagues [24–27] have developed and published core competencies training for ultrasound-guided regional anesthesia, and developed curricula focused on ultrasound physics and establishing appropriate learning metrics and behavior during ultrasonographic skill development. These guidelines for education and training in ultrasound-guided regional anesthesia have been adapted and published by the American and European Societies of Regional Anesthesia, and comprise formal guidelines and minimum expectations required of regional anesthesia practitioners, educators, and researchers in an attempt to create uniformity of practice in different parts of the world. The studies reviewed in this article lack this kind of consistency, but the authors hope that researchers in the future will follow these guidelines and that reviewers of their articles will have an easier time comparing studies from various countries.
Upper extremity blocks
Evidence for Interscalene and Supraclavicular Blocks
The upper extremity is especially well suited for ultrasound-guided regional anesthesia. High-frequency linear array transducers (10–15 Hz) provide very high-resolution images of the brachial plexus (Table 1) [28]. Supraclavicular blocks have regained popularity, because the dreaded complication of pneumothorax may be dramatically reduced with ultrasound-guided placement compared with the traditional landmark technique [17,19,29–32]. The interscalene and supraclavicular regions are rich in vessels and nerves, which helps allow clear identification of anatomic structures; conversely, it provides little room for error while performing regional blocks. Therefore, it seems likely that using ultrasound-guided regional anesthesia for the upper extremity may prevent severe complications (eg, vascular puncture and intravascular injection leading to local anesthetic systemic toxicity). However, differences between ultrasound-guided and PNS-guided blocks, as well as the combination of both techniques, are difficult to evaluate based on data available to date. Liu and colleagues [33] investigated ultrasound-guided and PNS-guided interscalene blocks in 219 patients, mainly to assess postoperative neurologic symptoms (PONS). These investigators found no difference in the failure rate, time to perform blocks, patient satisfaction, or postoperative neurologic outcome between techniques; however, they demonstrated fewer needle passes and quicker onset of motor block with ultrasound guidance [33]. This lack of difference in success (100% in both groups) could be attributed to the high volume of local anesthetic used in their study (55–65 mL mepivacaine 1.5% with sodium bicarbonate). In addition, this same group recently published a large prospective clinical registry of ultrasound-guided regional interscalene and supraclavicular blocks for shoulder surgery, demonstrating a 99.8% success rate of surgical anesthesia. The incidence of vascular puncture and permanent nerve injury was similarly low, at 0% (95% confidence interval [CI], 0%–0.3%), whereas the incidence of PONS was reported to be only 0.4% (95% CI, 0.1%–1%) [34].
Table 1 Randomized control trials comparing ultrasonography, peripheral nerve stimulation, or both for nerve block of upper extremities
By contrast, Kapral and colleagues [35] performed interscalene blocks using ultrasound in 160 patients, using a much lower volume of local anesthetic (20 mL of 0.75% ropivacaine). This study demonstrated both a quicker onset of sensory blockade and a stronger motor blockade in all nerves of the upper extremity, and detected anatomic variances in 11% of patients in the ultrasound group. In addition, they demonstrated an increased success rate in the ultrasound group (99%) versus the PNS group (90%). As elegantly described in the accompanying editorial [36], this could be caused by the methodological flaws of the study. For example, they used multiple injections for the ultrasound-guided group to ensure complete circumferential spread, but only a single stimulation for the PNS group, especially targeting for a twitch for middle and lower trunks only. Kapral and colleagues also highlight the lesser-known anatomic variation of the brachial plexus that constitutes roots located within the anterior or middle scalene muscles.
A single study performed by Williams and colleagues [30] compared combined ultrasound and PNS with anatomically guided PNS in 80 patients. These investigators demonstrated a higher success rate in complete block (95% vs 85%) and surgical anesthesia in the ultrasound group. Less time was required to perform the block in the ultrasound group (5.0 ± 2.4 minutes vs 9.8 ± 7.5 minutes, P = .0001).
The addition of nerve stimulation to ultrasound may not offer any advantage in supraclavicular blocks because about 13% of patients have no twitch response even after needle nerve contact, but will have successful surgical anesthesia [3,37].
Authors’ opinion
Interscalene and supraclavicular blocks should be performed under ultrasound guidance not only to avoid vascular or intrathecal puncture but also for a more circumferential spread of the local anesthetic, which is likely to increase the success rate. Ultrasonography would identify the abnormal location of one of the trunks within the scalene muscles. However, based on only one study in both interscalene (160 patients) and supraclavicular (80 patients) areas, it is difficult to comment as to whether using ultrasound and nerve stimulation guidance in combination will improve block quality, speed of onset, or duration of regional anesthesia.
Evidence for Infraclavicular Blocks
Compared with the supraclavicular area where the divisions of the brachial plexus are in close proximity to each other, the brachial plexus divides into cords below the clavicle. These cords surround the axillary artery laterally, medially, and posteriorly. Thus, methods for this block that use multiple-injection techniques are likely to achieve higher success rates than single-injection techniques. Eight randomized controlled studies have compared ultrasound-guided and PNS-guided infraclavicular blocks in adult patients [38–42]. Overall, 370 patients were included in these comparisons, with 37 to 103 patients per study. All studies reported a high success rate with either ultrasound guidance or with nerve stimulation guidance, without being able to demonstrate a clear difference between the 2 modes of nerve identification [38–41]. However, visualization of major anatomic structures by ultrasound appears to shorten the time to achieve a successful block [38,39]. Most studies failed to demonstrate a better quality of nerve blockade with one method over the other [38,40], but there was a trend toward a higher success rate in the ultrasound-guided groups [40]. Although limited by his small sample size, Gurkan and colleagues [41] demonstrated that the complication rate (eg, vascular puncture) was lower in the ultrasound-guided than in the PNS-guided group.
In contrast to the previous studies, Dingemans and colleagues [42] compared the combination of nerve stimulation and ultrasound guidance with ultrasound guidance alone for infraclavicular blocks. The trainee performing the block in all patients visualized the spread of the local anesthetic posterior to and to each side of the axillary artery in the ultrasound-only group with the minimum number of injections. The combined group received a single injection of local anesthetic after obtaining a distal motor response to nerve stimulation. Dingemans and colleagues concluded that infraclavicular nerve blocks were performed faster with a higher success rate in the ultrasound-only group. Patients with single injections in both groups had a similar success rate (86%), which reinforces the improved success with multiple injections.
Authors’ opinion
The majority of studies suggest that approaches using ultrasound guidance alone allow quicker performance and faster onset or surgical readiness of regional anesthesia, with fewer needle passes than nerve stimulation with or without ultrasound in the infraclavicular region. Thus nerve stimulation does not provide any additional benefit to ultrasound guidance in the infraclavicular region; however, ultrasound guidance seems to have a definite benefit over nerve stimulation alone in all aspects of regional anesthesia success as defined by onset time, success rate, and surgical anesthesia.
Evidence for Axillary Blocks/Single Nerve Blocks
Axillary brachial plexus block is performed at the level of terminal nerves surrounding the axillary artery in a sheath. Radial and musculocutaneous nerves are often missed with single-injection techniques. Multiple-injection techniques have been shown to provide a higher success rate and a shorter onset time compared with single-injection techniques, even though they take longer to perform [43]. If each of the 4 major nerves is blocked with localization by nerve stimulation rather than paresthesia, the success rate is more than 90%. Ultrasound techniques also have high success rates because it is possible to make multiple injections with visual confirmation around the 4 major nerves.
Multiple studies have focused on the effect of ultrasound on success rate, complications, and performance time of axillary brachial blockade. Morros and colleagues [44] demonstrated similar success rates with nerve stimulation–guided and combined ultrasound-guided and nerve stimulation–guided axillary plexus block, but the complication rate (eg, vascular puncture 8% vs 28%) dropped significantly as did the onset time of sensory and motor blockade with ultrasound-guided blocks. However, more time (350 seconds vs 291 seconds) was required to perform the procedure when nerve stimulation was combined with ultrasound.
The largest study conducted in axillary ultrasound-guided regional anesthesia by Chan and colleagues [45] (188 patients) had 3 groups (ultrasound alone, ultrasound with PNS, and PNS alone). The results clearly demonstrated that ultrasound, with or without PNS, was superior to PNS alone in terms of blockade of the 3 major nerves—radial, median, and ulnar. However, there was no clinical difference in terms of surgical anesthesia between groups (95%, 92%, and 86% in ultrasound, ultrasound with PNS, and PNS groups, respectively). In addition, complications such as postoperative axillary bruising and pain were less frequent in the groups in which ultrasound was used during block placement.
By contrast, Casati and colleagues [46] found no difference in success rate (100% in both groups) or time to onset of motor block with axillary blocks performed with ultrasound or nerve stimulation guidance with 4 separate injections. On the other hand, onset of sensory block was faster with ultrasound guidance compared with electrical guidance (14 minutes vs 18 minutes). Patient satisfaction was higher in the ultrasound group as well. In fact, almost 53% of patients with multiple nerve stimulations reported the procedure as painful [47], whereas 98% of patients receiving their blocks with ultrasound guidance reported high satisfaction and acceptance of their procedures [48]. Thus, ultrasound guidance may have an advantage in the performance of axillary plexus block in terms of patient comfort. Bloc and colleagues [49] confirmed this finding in their recent study comparing comfort of the patient during axillary block placement with PNS and ultrasound guidance.
Authors’ opinion
Overall patient comfort and satisfaction seem to be greater in patients receiving ultrasound-guided axillary blocks simply because nerve stimulation in this area is uncomfortable, requires more time, and use of ultrasound may be associated with a higher success rate. In terms of success rate, there is no evidence that dual guidance is superior to ultrasound alone in this region. Vascular puncture and bruising are likely to be reduced with use of ultrasound for axillary plexus block; thus, the authors recommend the routine use of ultrasound for this site.
Lower extremity blocks
Unlike the upper extremities, there are relatively few studies that compare ultrasound with nerve stimulation guidance for lower extremity blocks, and in those available the total number of study subjects is small, allowing for limited interpretation of the results (Tables 2 and 3). A recent evidence-based review summarized the benefits of ultrasound versus nerve stimulation for lower extremity nerve block [50]
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