Ultrasound-guided regional anesthesia is increasing in popularity. Although a recent large registry (6950 patients) has been reported that included a variety of peripheral nerve blocks and techniques including ultrasound,1 there are few large prospective clinical registries to document efficacy and safety of specific ultrasound-guided blocks.2,3 This is in contrast to nerve stimulator–guided regional anesthesia for which several large-scale surveys (N >500) have been published to precisely document success and complication rates for specific block techniques.4,5 Regional anesthesia is especially popular for ambulatory shoulder surgery, because an interscalene block can provide both anesthesia and postoperative analgesia.6 Furthermore, interscalene block for ambulatory arthroscopic shoulder surgery may be more cost effective than general anesthesia.7 However, interscalene block can also be associated with significant risk. One systematic review noted that interscalene block has the highest incidence of permanent neurological complications of all peripheral nerve blocks,8 and this technique also has a 100% incidence of phrenic nerve paresis with resultant pulmonary compromise.9 Although ultrasound-guided interscalene block has been suggested to have a superior safety profile, there are no large-scale prospective surveys to precisely define success and complication rates. Finally, ultrasound-guided supraclavicular block has increased in popularity10 and is a novel alternative to interscalene block for arthroscopic shoulder surgery.11 Supraclavicular block is performed at a more distal site with potentially less anatomic risk for neurological injury12 and has a reduced incidence of phrenic nerve paresis.13 Again, there are no large-scale prospective surveys to document efficacy and safety of ultrasound-guided supraclavicular block for arthroscopic shoulder surgery. Thus, we formed this prospective clinical registry of ultrasound-guided interscalene and supraclavicular block for ambulatory shoulder surgery to precisely document success and complication rates.
After IRB approval, written informed consent was obtained from 1250 patients scheduled to undergo ambulatory arthroscopic surgery from November 2008 to November 2009. Figure 1 displays the patient flow of the study. Patients were excluded if general anesthesia was planned, an open shoulder procedure was planned, or if a research assistant was not available. Patient characteristics were recorded, and each subject had a standardized sensory and motor neurological evaluation and physical examination to determine baseline neurological function (Appendix 1).14 This tool was prospectively designed by our neurologist coinvestigator (TS) who subsequently trained 2 coinvestigators to administer this tool (PS and SW). After placement of standard ASA monitors, patients received sedation at the discretion of the anesthesia team. The type of block (interscalene versus supraclavicular) was selected at the discretion of the anesthesia team. Ultrasound was performed with a linear 10- to 13-MHz probe and an in-plane technique. Interscalene block was performed at approximately the level of C6 with the needle placed through the middle scalene muscle. Supraclavicular block was performed in the supraclavicular fossa with a lateral to medial approach. The needle was to be placed immediately adjacent to the neural target with avoidance of intraneural placement. Final needle path, end points for needle target, type of block needle, use of hydrodissection, and type and dose of local anesthetic were all at the discretion of the anesthesia team. A 1- to 3-mL test dose was initially injected. The needle was repositioned if there was a positive test dose, positive heme during aspiration after every 5 mL of injection, or if the patient complained of severe discomfort. Complications such as vascular puncture (heme on aspiration) or systemic toxicity were recorded. After completion of the block, the patient was then placed in sitting beach chair position for the surgical procedure. Intraoperative sedation was at the discretion of the anesthesia team. In the postanesthesia care unit (PACU) after surgery, all patients were queried in a standardized manner as to presence of hoarseness and dyspnea as subjectively noted. A verbal pain score (0–10) was obtained at discharge from the PACU, and need for rescue IV opioid analgesia in the PACU was recorded. Approximately 1 week after surgery (excluding weekends or holidays), all patients were followed up by the same coinvestigators (PS or SW) and the same standardized neurological questionnaire (Appendix 1) was administered. Any positive questionnaires were reviewed by our neurologist (TS) who was blinded to block technique. Postoperative neurological symptoms (PONS) were prospectively defined as neurological symptoms within the operative site brachial plexus that were related to brachial plexus irritation but were unrelated to the surgical procedure as determined by our neurologist, TS. Symptoms involving the axillary or suprascapular nerves were considered to be potentially related to the surgical procedure15,16 and were not considered to be PONS.14 Patients were asked to rate overall severity of PONS as mild = barely noticeable, moderate = definitely noticeable, and severe = very preoccupied with symptoms. Any patient with PONS at each follow-up was followed monthly by phone until resolution of symptoms. All patients with nonresolving PONS were offered a complete neurological evaluation and standard diagnostic testing (e.g., nerve conduction velocities, electromyography) by TS to define the cause and determine the prognosis of PONS. During the same phone follow-up, all patients were again queried on the presence and subjective duration of hoarseness, dyspnea, and pain at the injection site and at the surgical site. A verbal satisfaction score (0 = worst and 10 = best) for anesthesia was obtained. Finally, at the completion of this study, our hospital Quality Assurance database was queried for our subjects to check for any delayed filing of complications.
For statistical analysis, sample size was based on previous randomized controlled trials (RCTs) that described an 8% to 11% incidence of PONS after interscalene block.14 A prospective registry of at least 500 subjects per block technique would allow determination of such complications rates with a 95% confidence interval (CI) of ±2%. Thus, we planned to enroll at least 500 patients undergoing each block (interscalene and supraclavicular) for a total of at least 1000 subjects. Descriptive statistics were used. Mean and standard deviation were used for continuous data. Median and mode were used for interval data. Ninety-five percent CIs were calculated for incidences based on a binomial distribution.
One thousand seven hundred sixty-one patients were available for recruitment during the study period. One thousand two hundred fifty patients were enrolled and 1169 patients completed follow-up in the registry. Figure 1 displays patient flow through the registry. Patients in the registry were fairly evenly divided between interscalene (44%) and supraclavicular (56%) block techniques. Patient characteristics and type of surgical procedures are displayed in Table 1 and were similar for both block types. Intraoperative and postoperative characteristics are displayed in Table 2 . During block performance, all patients received sedation with midazolam (5 mg mean) and a minority received fentanyl (34%) or ketamine (24%). Intraoperative sedation was provided with propofol (91%). Type of block needle was either a 22-gauge Stimuplex (B. Braun, Melsungen, Germany) (58%) or a 22-gauge Chiba (Hakko Corp., Tokyo, Japan) (42%). Mepivacaine 1.5% with or without epinephrine was used for the majority of blocks (99%) with a mean volume of 50 mL (range, 20–65 mL). Bupivacaine 10 to 15 mL was included in 62% of the mepivacaine blocks for postoperative analgesia. The majority of blocks (61%) were personally performed by an attending anesthesiologist, and the remainder by a supervised resident or fellow. There was a 0% incidence (95% CI, 0%–0.3%) of vascular puncture (positive heme aspiration in needle/tubing) or systemic local anesthetic toxicity. Block failure requiring conversion to general anesthesia was 0% (95% CI, 0%–0.7%) for interscalene block and 0.3% incidence (95% CI, 0.04%–1%) for supraclavicular block. In the PACU, verbal pain scores were a median and mode of 0/10. The requirement for rescue IV opioids in the PACU was 0.6% for both interscalene and supraclavicular block. The most common side effect in the PACU was hoarseness with a 31% incidence (95% CI, 27%–35%) for interscalene block and 22% incidence (95% CI, 19%–26%) for supraclavicular block. In the PACU, the incidence of dyspnea was 10% (95% CI, 7%–12%) for interscalene block and 7% (95% CI, 5%–9%) for supraclavicular block. At the 1-week follow-up, the incidence of PONS was 0.6% (95% CI, 0.1–2%) for interscalene block and 0% (95% CI, 0%–0.6%) for supraclavicular block. Table 3 displays characteristics of the patients with PONS. All episodes of PONS resolved within 3 months, and all patients declined formal neurological evaluation with our neurologist (TS). At the 1-week follow-up, patients reported an 11% incidence (95% CI, 8%–14%) of hoarseness during the past week for interscalene block with a mean postoperative duration of 2 days. Patients receiving supraclavicular blocks had a 6% incidence (95% CI, 5%–8%) of hoarseness with the same duration of 2 days. At the 1-week follow-up, patients reported the same incidences of dyspnea during the past week for interscalene and supraclavicular block (3%; 95% CI, 2%–4%), and the same 2-day duration. There were no patients with clinically appreciable pneumothorax at the 1-week follow-up. Patient satisfaction was a mean score of 8/10 (0 = none, 10 = best) for both blocks.
Our prospective clinical registry of ultrasound-guided regional anesthesia for ambulatory arthroscopic shoulder surgery documented excellent success rates (99.7%–100%) and low rates of complications at home (0%–11%) for both interscalene and supraclavicular techniques. Interscalene blocks with nerve stimulator guidance are already commonly performed for shoulder arthroscopy. Previous prospective surveys4,5 and RCTs2 have documented excellent success rates with a nerve stimulator (generally approximately 98%), and our data indicate that ultrasound guidance provides similarly excellent success rates for interscalene blocks (100%).
Our data indicate that ultrasound guidance for interscalene block has a low risk of PONS (0.4% with 95% CI, 0.1%–1%), which is less than that reported for nerve stimulators (typically 11%–14%). Furthermore, our incidence of permanent nerve injury (PONS >12 months) was 0% (95% CI, 0%–0.3%), which compares very favorably with an incidence of permanent nerve injury of 2.8% (95% CI, 1.3%–6%) for interscalene block reported in 1 systematic review.8 These lower incidences may be explained by the ability to visualize needle and local anesthetic injection throughout the block. Other recent prospective1 and retrospective17 registries of mixed peripheral nerve blocks also suggest a trend for decreased risk with use of ultrasound versus nerve stimulator (0%–0.02% vs 0.08%–0.09%).
Interestingly, our incidence of PONS (0.6%) was less than we previously reported (6%–8% incidence) in an RCT with the same ultrasound methodology.14 This seeming disparity can be explained by the much larger size and greater precision of this clinical registry. The 95% CI for incidence of PONS in our previous RCT was rather broad at 2% to 11%, and the lower limit does overlap the upper limit of this registry's much more narrow 95% CI of 0.1% to 2%. Thus, these 2 estimates of true incidence of PONS do not contradict each other. Because our registry enrolled nearly 5-fold more patients than our RCT, our current incidence of PONS is likely more accurate and demonstrates the value of large numbers of patients to determine precise incidences of uncommon complications. In addition, improved operator skills on our part may also explain the lower incidence of PONS in this registry. There are no other similar prospective surveys with which to compare our results. Another recent survey of ultrasound-guided interscalene blocks is likely not comparable, because it used a different technique, larger needles, combined nerve stimulator, and placed perineural catheters.18
Other neurological complications from nerve stimulator– guided interscalene blocks include a 100% incidence of phrenic nerve block with resultant hemidiaphragmatic paresis9 and reduced pulmonary function,19 and potential block of the recurrent laryngeal nerve with resultant vocal cord paresis.20 We did not formally measure diaphragmatic or vocal cord function, but our patients undergoing ultrasound-guided interscalene block reported a low incidence of dyspnea after PACU discharge (3%) that lasted a mean of 2 days. The incidence of hoarseness was 11% after PACU discharge and lasted a mean of 2 days. The etiology of these symptoms was not formally established. It is possible that symptoms were due to prolonged block of the phrenic and recurrent laryngeal nerves. A previous study noted a dose-related relationship between diaphragmatic paralysis and volume of local anesthetic for interscalene block (5 vs 20 mL),21 and our volumes were much larger.
Our registry is unique in that we enrolled a substantial number of patients receiving supraclavicular blocks for shoulder arthroscopy. Ultrasound-guided supraclavicular block had excellent success rates for anesthesia that were comparable to interscalene block (99.7% vs 100%). Supraclavicular block has not been commonly used for shoulder surgery10 because of concern that the block is too distal from the cervical nerve roots to provide satisfactory shoulder anesthesia. However, anatomic studies with ultrasound and computed tomographic scanning demonstrate that local anesthetic injected at a supraclavicular block travels cephalad between the anterior and medial scalene muscles and can function as a more caudad approach to an interscalene block.22 A potential advantage of the supraclavicular versus interscalene approach is the typically easier visualization of the brachial plexus in the supraclavicular fossa. In addition, the supraclavicular block may have less risk of block of the phrenic nerve with resultant diaphragmatic paresis and respiratory compromise and lesser block of the recurrent laryngeal nerve and unilateral vocal cord function.13 We did not observe a difference in dyspnea, but supraclavicular block did cause a lower incidence of hoarseness, thus suggesting potentially less risk of unilateral vocal cord dysfunction with supraclavicular block.
An additional risk from supraclavicular block is pneumothorax because of the proximity of the pleura to the brachial plexus. Our registry did not note any patients with clinical signs of pneumothorax. We did not routinely perform chest radiographs to exclude pneumothorax because of concerns of unnecessary radiation exposure. A previous large survey of ultrasound-guided supraclavicular block for upper extremity surgery also noted a 0% incidence of clinical pneumothorax in 510 blocks.10 Thus, the ability to visualize the pleura during supraclavicular block may minimize the risk of pneumothorax.
There are limitations to this registry. Differences between interscalene and supraclavicular block are intended to generate hypotheses for future confirmatory RCTs. Selection of type of block was at the discretion of the operator, and it is unclear if the type of block was selected because of operator skill, patient characteristics, or scan image quality. Block techniques were per general guidelines and not strictly controlled for the 89 different operators performing our blocks. However, this same variability strengthens the general applicability of our findings.
In conclusion, ultrasound-guided regional anesthesia with interscalene and supraclavicular blocks is very effective for shoulder arthroscopy with a low incidence of complications, especially for PONS. Ultrasound-guided supraclavicular block is an effective alternative to interscalene block with a lesser incidence of postoperative hoarseness. The risk of clinically apparent pneumothorax after supraclavicular block was minimal in our prospective registry. Future RCTs are required to confirm the potential differences we observed between interscalene and supraclavicular techniques and between ultrasound and nerve stimulator techniques.
Spencer S. Liu is Section Editor of Pain Medicine for the Journal. The manuscript was handled by Peter S.A. Glass, Section Editor of Ambulatory Anesthesiology, and Dr. Liu was not involved in any way with the editorial process or decision.
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