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REGIONAL ANESTHESIA

Stimulation of the Posterior Cord Predicts Successful Infraclavicular Block

Department of Anesthesia and Critical Care, Department of Medicine, Massachusetts General Hospital, Boston, Massachusetts; Department of Anesthesiology and Perioperative Medicine, Medical College of Georgia, Augusta, Georgia

Address correspondence and reprint requests to Carl Rosow, MD, PhD, Department of Anesthesia and Critical Care, Massachusetts General Hospital, 55 Fruit St., Boston, MA 02114. Address e-mail to crosow{at}partners.org.

	Abstract

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Infraclavicular (IC) block is often performed by localizing one cord within the brachial plexus sheath and placing all the local anesthetic solution at that location. We hypothesized that posterior cord stimulation would be associated with a greater likelihood of IC block success. We enrolled 369 patients scheduled for surgery to the lower arm or hand in a prospective, nonrandomized observational trial. All underwent IC blocks using a standard technique, and the cord stimulated immediately before drug injection was recorded. Motor and sensory functioning were evaluated 15 min after injection. Compared with stimulation of either the lateral or medial cord, stimulation of the posterior cord was associated with rapid onset of motor block in significantly more nerves, as well as a decreased likelihood of block failure (motor and sensory block inadequate to perform surgery). Failure rates were 5.8% for posterior cord, 28.3% for lateral (P < 0.05), and 15.4% for medial (P < 0.05). The differences were highly significant when adjusted for multiple possible confounders, such as gender, body mass index, location of the incision, and level of training of the individual performing the block (P < 0.001, lateral versus posterior; P = 0.003, medial versus posterior). A low failure rate was also predicted by stimulation of more than one cord simultaneously (P < 0.05). We conclude that injection after locating the posterior cord or multiple cords predicts successful IC block.

	Introduction

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A brachial plexus block using an infraclavicular/coracoid approach (IC block) can be used to provide excellent surgical analgesia for the lower arm and hand. The IC approach was first described by Labat in 1922 (1), and several variations have been reported that increase the likelihood of successful block while minimizing complications (primarily pneumothorax) (2–5).

Regardless of the specific approach used, IC block is frequently performed by using electrical stimulation and observing the activation of specific muscle groups (6). The cord first encountered (lateral versus posterior versus medial) depends on the position of the needle with respect to the neural bundle. Most published studies report that a single injection of local anesthetic produces an adequate block (5,7–10), although one group reported frequent failures using this technique (11).

The present study was based on the premise that localizing the posterior cord during a single-injection IC block would place the needle centrally within the infraclavicular portion of the brachial plexus and allow an even spread of local anesthetic. We therefore hypothesized that posterior cord stimulation would be associated with more frequent block success than stimulation of the lateral or medial cords. "Success" in this case was defined as rapid onset of motor block and sensory block adequate to perform surgery.

	Methods

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This was a prospective, nonrandomized observational trial involving all attending or resident anesthesiologists providing clinical care in the Same Day Surgical Unit of the Massachusetts General Hospital. The study was approved by our institutional Human Research Committee, and informed consent was obtained from all study subjects. The eligible study population included all adult same-day surgical patients scheduled to have IC block for elective surgery on the hand or forearm. Patients were excluded if they were unable to cooperate, had a history of brachial plexus surgery or injury, or had a previous adverse reaction to amide local anesthetics. We also excluded patients who were anticipated to require a block technique other than the standard technique planned for this protocol (described below).

Our standard IC block technique was similar to that described by Wilson et al. (7). After placement of an IV catheter and premedication with 1–2 mg midazolam and/or 50–100 µg fentanyl, patients were placed supine with the arm abducted to approximately 90º. The coracoid process was palpated and a point 2 cm inferior and 2 cm medial to the process identified. The skin overlying this point was cleaned and infiltrated with 1% lidocaine. A 50-mm short-bevel insulated needle connected to a neural stimulator (Stimuplex, B. Braun, Bethlehem, PA) was then inserted perpendicular to the skin. The stimulator was set to deliver rectangular direct current impulses with a frequency of 2 Hz and pulse width of 100 ms. The initial stimulator current was set at 1.0 mA. Once proximity to a cord was identified by visible contraction of an appropriate muscle group, the current was incrementally reduced, and the needle slowly inserted until muscle activity resumed. The cord was identified by observation of the specific muscles responding:

Lateral cord – flexor carpi radialis; forearm pronation and elbow flexion

Medial cord – flexor carpi ulnaris; wrist flexion, intrinsic hand muscle contraction

Posterior cord – triceps, extensor carpi radialis; elbow/wrist extension

Local anesthetics were injected when either (a) muscle activity was observed at a stimulator current of 0.3 mA or less or (b) the operator felt a loss of resistance as the needle entered the plexus sheath, and a motor response was visible at a stimulator current of 0.5 mA. At least one of the motor responses listed was required before injection. Other responses were not considered acceptable unless they occurred in combination with one of those listed.

All patients in this study received 30 mL 1.5% mepivacaine with 3 mL 8.4% sodium bicarbonate, injected over 1–2 min with intermittent aspiration. This was followed immediately by 10 mL 0.75% bupivacaine injected over 1–2 min. Clinicians were not required to seek or avoid a particular cord. They were not limited as to the number of times cord stimulation could be performed, but all of the local anesthetic was injected at the same site. Fifteen min after injection, evaluation of motor and sensory function was performed to assess block of the radial, median, ulnar, musculocutaneous, medial brachial, and antebrachial cutaneous nerves. An assessment time of 15 min was chosen because it allowed ample time to detect block onset but did not unduly delay surgery. After transfer to the operating room (usually 20–30 min after block placement), any patient with a block that was felt to be inadequate for surgery was treated with supplemental local anesthetic or offered general anesthesia.

The primary independent variable was the specific cord stimulated immediately before the injection of local anesthetic. We used two primary outcome measures:

1. Extent of block – the number of nerves showing evidence of motor block by 15 min. For this assessment we considered only 4 nerves: musculocutaneous, radial, median, and ulnar. This measure was independent of the surgical procedure.
   
2. Clinical success of block – sensory block sufficient to tolerate surgical incision without supplemental anesthesia or analgesia. This measurement was made after transfer to the operating room and was obviously influenced by the specific site of surgery.
   

Demographic information was collected, including age, gender, height, weight, and operative procedure. We recorded the block "operator," indicating the level of training of staff performing the block (attending, resident, or attending taking over from resident). We did not specify criteria for an attending taking over a block. Assessments were made about the technical aspects of block placement (minimum stimulator current, sensing loss of resistance, elicitation of paresthesias, blood on aspiration). Because the experience of those performing blocks varied widely, we did not collect data on the total block time or the number of needle passes. Because the operative site could also influence the probability of block success, we broadly categorized the location of surgery as above the wrist versus wrist and below.

A review of our clinical database indicated that clinical success rate after posterior cord stimulation was approximately 90%, and we assumed (incorrectly) that the 3 cords of the brachial plexus would be stimulated with similar frequency. To demonstrate that stimulation of another cord resulted in a 15% decrease in success rate, a study population of 339 (113 per group) was required ( = 0.05, two-tailed; 1-ß = 0.8).

Patients were grouped depending upon the cord(s) stimulated. Demographic variables were compared using analysis of variance for continuous measurements and ² test for categorical variables. In most of the analysis, the block extent (number of nerves blocked) was prospectively dichotomized into 2 categories: 0–2 and 3–4. ² test was also used to compare the rate of successful block and the rate of high block extent (3 or 4 nerves blocked) among the 4 groups. Multiple ordinal regression models were used to evaluate the potential predictors of failure and to examine the difference between study groups adjusted for confounders. Adjusted odds ratios from these models are reported.

	Results

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The study population consisted of 369 patients, enrolled over 11 mo. Outcome data were not available for 5 patients, leaving 364 evaluable subjects for analysis. More than 40 resident and attending physicians performed blocks. The initial design incorporated three study groups corresponding to the three cords. However, we found 58 patients who had clear evidence that more than one cord was being stimulated simultaneously. Therefore, a fourth group was added ("multiple cords") to account for these subjects.

The demographic and clinical data for all groups are presented in Table 1. There were no statistically significant differences among the groups with respect to age, gender, height, weight, body mass index, site of surgery, or operator performing the block. There was a small, but highly significant intergroup difference in minimum stimulator current (posterior>multiple>lateral>medial). Because minimum current did not subsequently prove to be a predictor of outcome, it was not a confounder in our analysis.

Of the 364 blocks, 322 (88.5%) were judged as clinically successful, and 243 (66.8%) had evidence of motor block of all 4 nerves at 15 min (Table 2). The risk of block failure as well as incomplete motor block was strongly predicted by the cord stimulated. Both of these poorer outcomes were significantly more likely if the lateral or medial cord was stimulated rather than the posterior cord (all with P < 0.05). There was no significant difference in outcome between posterior versus multiple cord stimulation.

Multiple logistic regression models were used to identify other predictors for poor outcomes and to compare study groups adjusting for these predictors. Male gender was associated with a lower extent of motor block and more frequent clinical block failure. Greater body mass index was associated with more frequent clinical block failure whereas staff take-over from a resident was associated with a lower extent of motor block. When adjustment was made for these potential confounders, posterior cord stimulation was still a highly significant predictor of greater motor block and higher block success compared with the lateral and medial cords (Table 3).

	Discussion

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Our study confirms the clinical impression that stimulation of the posterior cord before local anesthetic injection is associated with increased likelihood of IC block success compared with stimulation of either the lateral or posterior cord. When the infraclavicular portion of the plexus is viewed from the angle taken by our needle, the posterior cord appears to lie central to both the lateral and medial cords. A "central" location is speculative because, even with a consistent vantage point, the relative positions of the cords change as they twist around the axillary artery (12). Instillation of local anesthetic at the posterior cord appeared more likely than a more peripheral injection to reach all three cords. The frequent success of multiple cord stimulation suggests that it, too, predicted good spread of local anesthetic. This study did not address the relative merit of stimulating and injecting the cords separately.

Before initiating this protocol we were concerned that a preexisting bias (in favor of seeking the posterior cord) might influence our results. Only one attending physician stated that she specifically looked for that cord, and all participants agreed that we would accept other cords. Using this needle approach, however, the posterior cord was encountered much more frequently than expected by chance. It is entirely possible that our conclusions might not apply if the needle were inserted at a different angle.

This concept of placing a needle centrally to increase the success rate of IC block is not new. For example, Borgeat et al. (5) reported a 97% rate of IC block success when nerve stimulation elicited a distal response consistent with central placement. More recently, Porter et al. (13) described three cases using ultrasound for IC block placement and speculated that injection of local anesthetic posterior to the axillary artery (also a central placement) would predict a successful block for the same reason. Ultrasound may be a direct and reliable method of confirming central placement (14), but this technique is not yet as popular as nerve stimulation and requires additional equipment and training. Given the 88.5% rate of successful block we achieved overall, it is unclear how much improvement we could achieve with ultrasound.

In summary, we have shown that stimulating the posterior cord (or multiple cords) before local anesthetic injection is associated with a more frequent success rate for IC blockade than stimulation of either the medial or lateral cord. The results must be interpreted cautiously because the study was not randomized, and the occurrence of posterior nerve stimulation was much greater than expected by chance. The potential drawbacks of searching for a specific cord have not been investigated. We do not know whether deliberately seeking the posterior cord results in a significantly longer time for block placement, increased complications from needle reinsertion, or greater patient discomfort. These factors will need to be investigated prospectively before we can uniformly recommend the technique.

The authors wish to acknowledge the support and participation of the attending and resident anesthesia staff in the Massachusetts General Hospital Same Day Surgical Unit.

	Footnotes

 
Supported by departmental funds.

Accepted for publication January 12, 2006.

	References

Top Abstract Introduction Methods Results Discussion References

 

1. Labat G. Brachial plexus block: details of technique. Anesth Analg 1927;6:81–2.[Free Full Text]
2. Raj PP, Montgomery SJ, Nettles D, Jenkins MT. Infraclavicular brachial plexus block: a new approach. Anesth Analg 1973;52:897–904.[Free Full Text]
3. Whiffler K. Coracoid block: a safe and easy technique for brachial plexus block. Br J Anaesth 1981; 53:845–8.[Abstract/Free Full Text]
4. Sims JK. A modification of landmarks for infraclavicular approach to brachial plexus block. Anesth Analg 1977;56:554–5.[Abstract/Free Full Text]
5. Borgeat A, Ekatodramis G, Dumont C. An evaluation of the infraclavicular block via a modified approach of the Raj technique. Anesth Analg 2001;93:436–41.[Abstract/Free Full Text]
6. Borene SC, Edwards JN, Boezaart AP. At the cords, the pinkie towards: interpreting infraclavicular motor responses to neurostimulation. Reg Anesth Pain Med 2004;29:125–9.[Web of Science][Medline]
7. Wilson JL, Brown DL, Wong GY, et al. Infraclavicular brachial plexus block: parasagittal anatomy important to the coracoid technique. Anesth Analg 1998;87:870–3.[Abstract/Free Full Text]
8. Kilka HG, Geiger P, Mehrkens HH. Infraclavicular vertical brachial plexus blockade: a new method for anesthesia of the upper extremity: an anatomical and clinical study. Anaesthesist 1995;44:339–344.[Web of Science][Medline]
9. Jandard C, Gentili ME, Girard F, et al. Infraclavicular block with lateral approach and nerve stimulation: extent of anesthesia and adverse effects. Reg Anesth Pain Med 2002;27:37–42.[Web of Science][Medline]
10. Kapral S, Jandrasits O, Schabernig C, et al. Lateral infraclavicular plexus block versus axillary block for hand and forearm surgery. Acta Anaesthesiol Scand 1999;43:1047–52.[Web of Science][Medline]
11. Gaertner E, Estebe JP, Zamfir A, et al. Infraclavicular plexus block: multiple injection versus single injection. Reg Anesth Pain Med 2002;27:590–4.[Web of Science][Medline]
12. Sala-Blanch X, Carrera A, Morro R, Llusa M. Interpreting infraclavicular motor responses to neurostimulation of the brachial plexus: from anatomic complexity to clinical evaluation simplicity. Reg Anesth Pain Med 2004;29:618–20.[Medline]
13. Porter JM, McCartney CJ, Chan VW. Needle placement and injection posterior to the axillary artery may predict successful infraclavicular brachial plexus block: a report of three cases. Can J Anaesth 2005;52:69–73.[Web of Science][Medline]
14. Ootaki C, Hayashi H, Amano M. Ultrasound-guided infraclavicular brachial plexus block: an alternative technique to landmark-guided approaches. Reg Anesth Pain Med 2001;26:384–5.[Medline]

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