The use of ultrasound guidance to perform infraclavicular brachial plexus block has gained popularity in recent years. This technique showed a good success rate associated with low incidence of complications.1–3 The visualization of local anesthetic spread around the axillary artery was described as a reliable end point for successful block and can be achieved with single or multiple injections.4 Local anesthetic distribution creating sonographic images defined as an U-shaped distribution, a double-bubble sign, or a doughnut sign provides a complete sensory block in more than 90% of patients.4–6 These clinical results can be explained by the anatomy of the brachial plexus at the infraclavicular level. A magnetic resonance imaging study showed that the three cords were positioned within 2 cm of the axillary artery and that the closest injection site to the three cords was posterolateral to it.7 Although a single injection of local anesthetic at the posterior level of the artery provides blockade of the entire brachial plexus, it is not known whether the onset time of a complete sensory block would be faster with multiple injections around the axillary artery. Several studies using nerve stimulation have demonstrated faster onset time when using multiple injections rather than single injection of local anesthetic.8–10
The objective of this study was to compare the rate of complete sensory block at 15 min of ultrasound-guided infraclavicular block performed with one or three injections of mepivacaine. We hypothesized that the triple injection technique would provide a higher rate of complete sensory block at 15 min.
This prospective, randomized, blinded, controlled study was conducted at the Centre Hospitalier Affilié Universitaire de Québec (Hôpital de l’Enfant-Jésus) after Research Ethics Board approval and written informed consent from all patients were obtained. One hundred consecutive adult patients, American Society of Anesthesiologists Class 1–3, scheduled for hand, forearm, or elbow surgery, and agreeing to a regional anesthesia technique were recruited. Exclusion criteria were allergy to any of the drugs used, coagulation disorder, local infection at the puncture site, systemic infection, preexisting neurological deficit in the operated limb, pregnancy, and body mass index >40 kg/m2.
Patients were randomized in two groups: Group S (single injection) and Group T (triple injections), following a computer generated randomization sequence (www.randomizer.org) sealed in prenumbered opaque envelopes by an administrative assistant not involved in the study. All blocks were performed by five certified anesthesiologists experienced in performing ultrasound-guided infraclavicular block. After applying standard monitoring, premedication was offered to the patient when necessary (midazolam 0–2 mg IV and/or fentanyl 0–100 μg IV). Standard skin asepsis was done and a sterile sheath covered the ultrasound probe. A 5–12 mHz linear probe was positioned in a parasagittal plane, medial to the coracoid process, and adjusted to give a transverse view of the axillary artery using an ultrasound device (Aloka, Model SSD-3500, Tokyo, Japan) (Fig. 1). Using an in-plane technique, a Tuohy needle (20 Ga, 8.89 cm; BBraun, Bethlehem, PA) was advanced to the posterior side of the axillary artery until a facial click was perceived11 (Fig. 2). If the facial click was not perceived, the needle was positioned at the very posterior aspect of the axillary artery. In Group S, 30 mL of mepivacaine 1.5% was then injected and the needle was withdrawn. In Group T, 10 mL of mepivacaine 1.5% was injected at the posterior site. After this injection, the needle was successively redirected toward the lateral and the medial side of the artery, where 10 mL of the solution were injected at each of these two sites (Fig. 2). If paresthesia was elicited during the procedure, the needle was withdrawn back 2–3 mm and the anesthesiologist ensured that no more paresthesia was elicited before injecting the local anesthetic. If blood aspiration occurred, the needle was repositioned before injection of local anesthetic. The block performance time was defined as time between the initial skin puncture and final needle withdrawal. The patient was not informed of his/her allocation group.
Immediately after the injection of local anesthetic, an investigator blinded to the group allocation evaluated the block. Sensory block was evaluated with sensation to cold elicited by applying ice cubes on the dermatomes of the ulnar (5th finger), median (palmar aspect of 2nd finger), radial (dorsum of the hand between thumb and 2nd finger), and musculocutaneous (lateral aspect of forearm) nerves. Patients quantified the sensory block on a scale score: 0 = normal sensation to cold, 1 = reduced sensation to cold, and 2 = no sensation to cold. Sensory blocks were evaluated every 3 min until 30 min or occurrence of a complete sensory block. A complete sensory block was defined as a score of 2 in ulnar, median, radial, and musculocutaneous dermatomes.
After complete sensory block was achieved, sedatives and analgesics were administered during surgery at the discretion of the anesthesiologist (midazolam 0–2 mg or sufentanyl 0–15 μg). If a complete sensory block was not obtained at 30 min or if the patient complained of pain at the surgical site, a supplemental distal block was performed. If blockade was still insufficient to pursue the surgery, general anesthesia was performed.
The day after surgery, a phone interview was conducted to ensure complete block regression and to note any complications (hematoma, infection, dyspnea, persistent abnormal sensation of the upper limb). One month later, patients were contacted again to evaluate the incidence of late complications and their satisfaction with the anesthesia technique by stating whether they would choose the same anesthetic for a similar surgery in the future.
The following data were collected for every patient using a standardized form: age, weight, height, ASA status, type and length of surgery, and duration of tourniquet. Data recorded during the technique were amount of sedative and analgesic drugs administered, block performance time, procedure-related pain on a visual analog pain scale (0–10), incidence of vascular puncture or paresthesia. Administration of intraoperative sedative and analgesic drugs and need for complementary block or general anesthesia were also recorded.
The primary end point of this study was the percentage of complete sensory block at 15 min. Secondary end points were the percentage of complete sensory block at each evaluation time interval, the block performance time, the incidence of vascular puncture and paresthesia during the procedure, and the incidence of complications at 24 h and 1 mo. Using data from a small retrospective study of ultrasound-guided infraclavicular block with a single injection technique in our center (10 patients), we observed a mean success rate of 60% of complete sensory block at 15 min. A sample size of 50 patients per group was thus required to detect an increase in the success rate at 15 min from 60% in Group S to 85% in Group T, considering a β error of 20% and an α error of 5% using a two-sided analysis with a Fisher’s exact test. Statistical analysis was performed with the Student’s t-test for continuous data and the Fisher’s exact test for proportions. P < 0.05 was considered significant.
One hundred patients were randomized in this study: 49 in Group S and 51 in Group T. Patient demographics were comparable between groups (Table 1). At 15 min, the percentage of patients with a complete sensory block was comparable between the two groups (Group S: 84% [95% confidence interval: 72–92], Group T: 78% [95% confidence interval: 66–88], P = 0.61). The percentages of patients with a complete sensory block at each evaluation time interval up to 30 min was also comparable (Fig. 3). There was no statistically significant difference between groups in the progression of sensory block for each nerve over the first 30 min after performance of the block (Fig. 4). No patient with a complete block required general anesthesia or supplementary block for surgery. Because of pain at skin incision during elbow surgery or tourniquet-related pain, an infiltration of local anesthetic solution on the cutaneous nerves of the arm and forearm in the axilla was required in four patients (one in Group T and three in Group S).
There were three block failures in each group. In one patient from Group S, inability to correctly visualize the needle during the technique was encountered and the technique was abandoned after 20 min. In another patient from Group S, signs and symptoms of local anesthetic toxicity (lightheadness, slurred speech) were noted 3 min after the end of the technique. The patient was administered propofol and midazolam, and general anesthesia was induced for surgery. He recovered without any complication. Finally, one patient in Group S and three patients in Group T had incomplete sensory block after 30 min of evaluation and required a complementary block before surgery. These patients were included in the data analysis.
Blocks were more rapidly performed in Group S compared to Group T (124 ± 62 s vs 185 ± 72 s, P < 0.01). No statistically significant difference was observed for the incidence of vascular punctures between groups (one in Group S and three in Group T), and for transient paresthesia elicited during the technique (one in Group S and two in Group T). The difference observed in block-related discomfort was not clinically significant between groups with a median visual analog scale of one in Group S and two in Group T. At 24 h and 1 mo follow-up, none of the patients reported complications and 98% stated that they would choose the same anesthesia technique if they were to require the same surgery in the future.
The results of our study demonstrate that the success rate of ultrasound-guided infraclavicular block at 15 min is not enhanced by a triple injection technique compared with a single injection technique. Our study also suggests that with either one of the two techniques, four of five patients had a complete sensory block of all major nerves of the upper limb at 15 min. Moreover, at 30 min, the block success rate approached 95% in both groups.
Our results are in accordance with previous studies having demonstrated excellent efficacy of ultrasound-guided infraclavicular block to provide reliable anesthesia for hand, forearm, and elbow surgery. In a large retrospective cohort study, Sandhu et al.1 achieved successful surgical anesthesia in 99.3% of patients using separate injections of local anesthetics on the medial, posterior, and lateral cords of the brachial plexus. Moreover, in a recently published study, an 89% success rate at 40 min was achieved by injecting 35 mL of local anesthetic posterior to the axillary artery using an ultrasound device.12 Finally, results from a prospective controlled study evaluating the success rate of ultrasound-guided infraclavicular block using either a combination of ultrasound and electrical nerve stimulation or ultrasound alone suggested no benefit to performing a combined technique.4 In this latter study, a 86% success rate at 30 min was observed when targeting a U-shaped distribution of local anesthetic posterior to the axillary artery using 1–3 injections. Thus, these three studies suggest that good success rates of ultrasound-guided infraclavicular block could be obtained independent of the number of injections, as confirmed by our results.
Contrary to these findings, results from a prospective controlled study using electrical nerve stimulation to perform infraclavicular block showed that a multiple injection technique provided an increased success rate and shorter onset time compared with a single injection technique.9 This discrepancy could be explained by two methodological differences. First, they did not always seek a posterior motor cord response during the single injection technique, although this response has been demonstrated to be superior to any other motor response when performing infraclavicular block using electrical nerve stimulation.13,14 In a small cohort study, Porter et al.15 observed that a solution of local anesthetic injected on a medial or lateral cord motor response distributed in front of the artery and lead to a higher failure rate when compared with an injection guided by a posterior cord motor response. Second, the use of ultrasound has recently improved our anatomic knowledge of the brachial plexus at the infraclavicular level by allowing visualization of the spread of local anesthetic during injection. For instance, the existence of septa on the posterolateral side of the subclavian artery that could limit the posterior spread of local anesthetics solution injected close to the lateral cord was recently described.16 Interestingly, we recently reported a feeling of “facial click” when advancing a large bore blunt needle from the lateral to the posterior side of the subclavian artery.11 When the local anesthetic solution was injected after the facial click, it was associated with a U-shaped distribution of the solution. Thus, the result of our study combined with these previous observations suggest that the three cords are probably contained in the same anatomical plane that could be reached by seeking this feeling of facial click using an ultrasound technique.
The main limitation of our study is that we chose to perform the study with injection targets based on a vascular structure (the axillary artery) instead of the cords. The use of the axillary artery as a target greatly simplifies the technique, especially for novice users. We chose to exclude patients with a body mass index >40 because the axillary artery is often difficult to visualize in this population, and we believe the performance of an ultrasound-guided supraclavicular block instead of an infraclavicular block should be favored in this patient population.
Our decision to use a 15 min time interval as the primary end point for the evaluation of the success of the block could be challenged. However, we deliberately chose this interval because a block with such a short onset time could be used to improve clinical efficiency by not delaying surgery or compromising operating room availability when a block room is not available.
In summary, the success rate and the time to obtain a complete sensory block with ultrasound-guided infraclavicular block was not improved by a triple injection technique compared with a single injection technique. Furthermore, the single injection technique was potentially faster to perform. Thus, a single injection ultrasound-guided infraclavicular block is an easy-to-perform technique and provides rapid and reliable anesthesia for upper limb surgery. Because of its simplicity and effectiveness, this technique should be preferred over a triple injection technique.
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