Ultrasound guidance (USG) for brachial plexus blocks has been described for the supraclavicular (1,2), infraclavicular (3,4) and axillary (1) approaches. These reports have shown that USG brachial plexus blocks have high success rates and few complications. Supraclavicular USG blocks are performed in our institution, eliminating the occasional failed blocks previously observed using neurostimulation alone (2); however, imaging difficulties are occasionally encountered in patients with short, wide necks. Anatomically, the infraclavicular approach should be feasible in almost all patients. It also has the theoretical advantages of both the supraclavicular and axillary approaches: a compact anatomical distribution of plexus structures allowing single injection of local anesthetics and a diminished risk of pneumothorax. USG has the potential to reduce the traditional disadvantages of infraclavicular block, including patient discomfort and technical difficulty (5–7).
The present study was designed to compare USG infraclavicular and supraclavicular blockade of the brachial plexus. We hypothesized that ultrasound visualization of the brachial plexus in combination with neurostimulation at the infraclavicular level would result in shorter visualization and performance times, equivalent block quality, and the same degree of patient discomfort as the supraclavicular technique.
After IRB approval and written informed consent, 80 consecutive patients who presented for surgery of the distal arm, forearm, or hand were randomized into two groups: Group I (infraclavicular block) and Group S (supraclavicular block), both performed with the use of ultrasound localization and neurostimulation. Exclusion criteria included: clinically significant coagulopathy, infection at the injection site, allergy to local anesthetics, severe pulmonary pathology, age <18 yr, mental incapacity or language barrier precluding informed consent, a body mass index more than 35, preexisting motor or sensory deficit in the operative limb.
Light sedation (midazolam 0.5–2 mg and fentanyl 25–100 μg) was provided as needed before performance of the block. No other sedation was administered until the evaluation of the block was completed. When needed, intraoperative sedation consisted of a propofol infusion titrated up to 50 μg · kg−1 · min−1 to maintain constant verbal contact with the patient.
After application of standard anesthesia monitors, the blocks were performed with the use of a 50-mm, 22-gauge Teflon-coated needle (Pajunk, Geisingen, Germany, or B. Braun, Bethlehem, PA). The anesthetic solution consisted of 1:3 volumes of 0.5% bupivacaine and 2% lidocaine hydrocarbonate with 1:200,000 epinephrine. This solution was administered in a single injection of 0.5 mL/kg up to a maximum of 40 mL once wrist or hand motion had been elicited with the neurostimulator delivering a current of <0.6 mA. Supraclavicular and infraclavicular blocks were performed using the technique described in a review (8), with a 7.5-MHz ultrasonic linear scanning head (Aloka, Japan). For both blocks, the nervous and vascular structures were optimally visualized and the stimulating needle was inserted perpendicular to the skin surface, oriented towards the presumed nervous structures. Appropriate needle position was confirmed by neurostimulation before local anesthetic was injected. All blocks were performed by the same senior anesthesiology resident, who, before beginning the study, performed 22 blocks, 11 with each of the 2 research techniques, while supervised by a staff anesthesiologist.
For the purposes of the study, block performance time was defined as the interval between the first needle insertion and its removal at the end of the block. If 20 min elapsed without adequate visualization and stimulation being obtained, the block was abandoned and considered a failure with a performance time of 20 min. Time to acquire the ultrasonic image was calculated for the last 10 patients of each group. Block performance-related pain was evaluated immediately after removal of the needle by asking the patient to verbally quantify the level of pain using a score between 0 and 10, 0 meaning no pain and 10 meaning excruciating pain. Evaluation of sensory and motor block was performed by the principal investigator every 5 min in musculocutaneous, median, radial, and ulnar nerve territories over a 30-min period beginning when the stimulating needle was withdrawn from the patient. Sensory block was evaluated by comparing the cold sensation elicited by ice in the central sensory region of each nerve with the same stimulus delivered to the contralateral side. Patients quantified the quality of the block using any score between 0 and 1, with 0 representing no block, any score between 0 and 1 representing partial block, and 1 representing complete block. Motor block was evaluated using forearm flexion-extension, thumb and second digit pinch, thumb and fifth digit pinch, and fingers abduction and scored as follows: no loss of force: no block; reduced force compared with the contralateral arm: partial block; inability to overcome gravity: complete block. Surgical anesthesia was defined as surgery without patient discomfort or the need for supplementation of the block. If a part of the surgical territory was not completely anesthetized at the time of surgery, the block was supplemented at the elbow or wrist. If the patient still experienced pain despite supplementation, general anesthesia was induced by the attending anesthesiologist using his preferred technique.
A post-block chest radiograph was obtained if a patient complained of respiratory distress. All patients were hospitalized or observed in a phase II recovery area for 1–2 h after their surgery, then discharged home with oral analgesics and a detailed care sheet that included contact information and data collection instructions. Patients were followed up in a telephone interview with the principal investigator 1 wk later. Four questions were asked:
1. “When was the first oral analgesic required?”
2. “Did any region of the arm remain insensible or weakened or generate abnormal sensations for a prolonged period of time?”
3. “Was there any respiratory difficulty encountered by the patients in the days following the block?”
4. “Does the patient have any other question or comment to report to the investigators?”
If a positive response was elicited by any of the last three questions, details were obtained. The duration of post-block analgesia was defined as the interval of time between block completion and ingestion of the first postoperative analgesic.
Data are expressed as mean ± 1 sd or proportions with 95% confidence intervals (CI) as appropriate. Student’s t-test and the Fisher’s exact test for 2 × 2 contingency tables were used for statistical comparisons. All comparisons were two-tailed. A P < 0.05 was considered significant. Based on our previous study (2) and assuming an α of 0.05 and β of 0.2, it was calculated that a sample size of 40 patients per group would be necessary to show a difference of 1.4 min in performance time between the 2 techniques, assuming a performance time of 5.0 min in the supraclavicular group and a standard deviation of 2.4 min for both groups.
The demographic characteristics of the two groups were similar (Table 1). Block quality was quantified by measuring surgical anesthesia rates, supplementation rates, subjective block quality, and the incidence of partial and complete blocks. In Group I, 80% of blocks achieved surgical anesthesia without supplementation compared with 87% in Group S (P = 0.39; difference = 7%; 95% confidence interval: −10% to 24%). The radial territory was supplemented significantly more often in Group I (18% versus 0% in group S; P = 0.006). Supplementation rates in the other nerve territories were not significantly different. Figure 1 shows the progression of the sensory block over time for each terminal nerve territory. The onset of motor blockade (not shown) paralleled that of sensory blockade. At 30 min, 80% of patients in Group I and 95% of patients in Group S had a partial or complete sensory block of all nerve territories (P = 0.05). The proportion of complete blocks at 30 min (Table 2) showed a significant difference only for the radial nerve territory.
Performance times were significantly shorter in the last 20 patients than in the first 20 patients of Group I (5.65 min versus 2.35 min; P = 0.001), whereas in Group S a similar trend towards shorter performance times was not quite significant (5.65 min versus 3.65 min; P = 0.06). Group I performance times also became shorter than those in Group S (P = 0.03). Block quality also improved in Group I as the study progressed. Radial block quality was significantly worse in Group I compared with Group S for the first 20 patients (0.77 versus 0.99, respectively; P = 0.02) but was not significantly different in any territory for the last 20 patients.
Adequate image acquisition time was significantly shorter in Group I compared with Group S (12 s versus 28 s, respectively; P < 0.0001). Block performance times were similar between groups (4.0 ± 3.3 min and 4.7 ± 4.0 min for Groups I and S, respectively; P = 0.22; difference = 39 s; 95% confidence interval: −58 to 136 s).
Technique-related pain scores were not different between groups (2.0 ± 2 versus 2.0 ± 2 in Groups I and S, respectively; P = 1.00) and there were no differences in the amount of sedation received before the performance of the block or intraoperatively (Table 1). One patient in each group received an additional 100 μg of fentanyl after block quality had been completely evaluated because of the need to take a skin graft off their thigh. No patient in either group underwent general anesthesia.
Failure of the block technique occurred in two patients in Group S because of an inability to visualize the subclavian artery and the brachial plexus after 20 min and in one patient in Group I because of an inability to obtain distal nerve stimulation after 20 min. These patients were included in the analysis of block performance time and they received an alternate technique of brachial plexus block.
At the 1-week follow-up, no complication related to the anesthetic technique (pneumothorax, neuropathy) was reported. The duration of postoperative analgesia was not significantly different between groups (I: 434 ± 167 min versus 471 ± 215 min in Groups I and S, respectively; P = 0.39; difference = 37 min; 95% confidence interval: −60 to 134 min). No patient was lost at follow-up.
This prospective randomized study demonstrates that although ultrasonic visualization is more rapid in the infraclavicular region than in the supraclavicular region, block performance times were similar. USG infraclavicular brachial plexus block resulted in the same success rate for surgical block as USG supraclavicular block. However, the radial territory may not have been as reliably anesthetized using USG infraclavicular blockade.
In our study, using a 7.5-MHz probe, recognition of the neurovascular structures was easier for the infraclavicular approach, as evidenced by significantly shorter visualization times in Group I. This result is explained by the relative technical ease with which the ultrasonic probe could be applied in the infraclavicular region. Chan (9), using a high frequency probe at the infraclavicular level, was able to visualize the brachial plexus in only 27% of cases. In contrast, Sandhu and Chan (4) and Ootaki et al. (3), using lower frequency probes, did not report any difficulties in imaging the brachial plexus at this level. Taken together, these results may indicate that the use of higher frequency probes is not required for USG infraclavicular blockade.
In terms of surgical anesthesia, success rates in this study were comparable to those of our previously published series of USG supraclavicular blocks (2) and better than a series of neurostimulator-guided supraclavicular blocks using a slightly different anatomical approach, a different local anesthetic, and a different observation period (10). When evaluating complete anesthesia of all target nerves, the proportion of blocks in the present study in which all territories were completely anesthetized at 30 min was somewhat greater than in our previous series of USG blocks (2); this may be explained by slightly faster completion times resulting from the larger proportion of lidocaine in the anesthetic mixture used in the present study. These results compare favorably with the 40% success rate using similar criteria after an undefined time period described by Gaertner et al. (11) for single-shot neurostimulator-guided infraclavicular block. The difference between the proportion of complete blocks and the proportion of surgical blocks is attributable to completion of partial blocks after the evaluation period and the fact that not all territories were subjected to surgical intervention.
Block quality (in terms of partial or complete sensory block of all nerve territories) tended to be better in Group S than in Group I, mostly because of radial sparing in Group I. Although the cords of the brachial plexus are compactly arranged around the axillary artery, the posterior cord is deeper from the point of entry of the needle than the lateral or median cords, which may explain why a single injection technique, such as the one used in the present study, results in incomplete block of the radial nerve. Sandhu and Chan (4), using a triple injection USG infraclavicular block, achieved 90% surgical blocks without supplementation in 126 patients undergoing upper extremity surgery. However, quality of block for each nerve territory was not detailed in their study. Ootaki et al. (3), using a USG infraclavicular block, in which the anesthetic was placed using 2 injection sites to completely surround the axillary artery, achieved surgical blocks in 95% of patients and complete sensory block of the radial territory in 95% of patients.
Defining the flat portion of the learning curve for a regional anesthesia technique is difficult. Sandhu and Chan (4) have surmised that approximately 20 blocks are needed to achieve a high degree of proficiency with USG techniques. Our results support this assertion, with shorter performance times and better block quality observed in the last 20 patients of Group I despite using the same injection criteria throughout the study. However, the value of these post hoc analyses is limited and most likely indicates only that studies specifically designed to measure learning rates for all regional anesthesia techniques are needed.
It is thought that infraclavicular block has not gained clinical popularity because of uncertain surface landmarks (6) and the perception that it is a more painful block. In the present study, pain scores were similar for Groups I and S. This difference with previous results may be explained in part by the sedation offered to patients before the technique in this study (12). The reliability of ultrasonic landmarks may also have contributed to minimizing patient discomfort.
In this study, no pneumothorax was observed in either group. Our study was not powered to evaluate the incidence of pneumothorax (95% CI, 0%–9%). It is interesting that no pneumothorax has been reported in any study of supraclavicular or infraclavicular block using USG despite the incidence of 1%–4% (13) reported for “blind” supraclavicular block and the occasional report of pneumothorax during infraclavicular block even in experienced practitioners (14).
In conclusion, single injection USG infraclavicular block can be performed as rapidly and results in the same success rate for surgical block as USG supraclavicular block. USG results in supraclavicular and infraclavicular blocks that are both reliable and quickly performed.
The authors would like to thank Dominique C. Girard, Sylvie McKenty, and Roger Perron for their invaluable assistance.
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