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The Efficacy of Axillary Block for Surgical Procedures About the Elbow

Schroeder, Lawrence E. MD; Horlocker, Terese T. MD; Schroeder, Darrell R. MS

Regional Anesthesia and Pain Management

Surgical procedures to the distal humerus, elbow, and proximal ulna and radius are ideally suited to regional techniques.However, axillary block is usually not recommended for surgery about the elbow because blockade at this level may result in inadequate block of the terminal nerves that arise from the medial, posterior, and lateral cords, and provide sensory innervation to the upper arm. This study reports the success rates for interscalene, supraclavicular, and axillary blocks for surgery about the elbow. Three hundred thirty surgical procedures in 260 patients were reviewed retrospectively. Approach to the brachial plexus (interscalene, supraclavicular, axillary), anesthetic technique (paresthesia, nerve stimulator, transarterial), and local anesthetic solution were recorded. Success rate, defined as the percent of cases in which the block provided adequate surgical anesthesia, and the frequency of perioperative respiratory compromise were also determined. In 156 cases, the surgical procedure involved a bony structure. The surgery involved only soft tissue in the remaining 174 cases. Adequate surgical anesthesia was present in 283 cases, for an overall success rate of 86%. Adequate surgical anesthesia was present in 219 of 247 axillary (89%), 46 of 59 supraclavicular (78%), and 18 of 24 interscalene (75%) blocks (P < 0.025). Successful axillary block was achieved in 95% of blocks using paresthesia technique, 88% of blocks using a nerve stimulator/motor response, 94% of combination blocks (paresthesia or nerve stimulator combined with transarterial injection), and 81% of blocks performed exclusively with transarterial injection (P < 0.05). In addition, axillary blocks performed with mepivacaine had a higher success rate (93%) than those performed with bupivacaine (81%) (P < 0.01). There were no patients with perioperative respiratory compromise. These results demonstrate that the axillary approach to the brachial plexus may be successfully used for surgical procedures about the elbow.

(Anesth Analg 1996;83:747-51)

Departments of Anesthesiology and Biostatistics, Mayo Clinic, Rochester, Minnesota.

Section Editor: Denise J. Wedel.

Accepted for publication June 19, 1996.

Address correspondence and reprint requests to Terese T. Horlocker, MD, Department of Anesthesiology, Mayo Clinic, Rochester, MN 55905.

Surgical procedures to the distal humerus, elbow, and proximal forearm are ideally suited to regional anesthetic techniques. Selection of the preferred approach is determined by the innervation of the surgical site, risk of regional anesthesia related complications, as well as the preference and experience of the anesthesiologist. Historically, the supraclavicular block has been considered the most efficacious approach to the brachial plexus for surgical procedures about the elbow. Reliable and profound anesthesia of the entire upper extremity will result from injection of relatively small volumes of local anesthetic [1]. However, the risk of perioperative pulmonary complications renders the supraclavicular approach unsuitable for patients with significant pulmonary disease. Transient phrenic nerve paresis occurs in up to 50%, while pneumothorax develops in 0.5%-6% of patients after supraclavicular block [1,2]. In addition, the pneumothorax typically develops over 6-12 hours and therefore may not become apparent until after hospital discharge in outpatients [3]. The inconvenience of hospital readmission and chest tube placement after an outpatient surgical procedure makes supraclavicular block less desirable in this patient population.

The interscalene approach may also be used for surgical procedures about the elbow. However, anesthesia of the ulnar nerve is often incomplete, and requires that the block be supplemented. Interscalene block is also not recommended in patients who are dependent on bilaterally intact diaphragmatic function and who are unable to tolerate a 25% reduction in pulmonary function, since phrenic nerve paresis occurs in 100% of patients, even with dilute solutions of local anesthetic [4,5].

The axillary approach to the brachial plexus eliminates the risk of respiratory compromise due to pneumothorax or diaphragmatic paresis. Although axillary block is often recommended for distal forearm and hand surgery, many regional anesthesia texts do not advocate this approach for surgery to the distal humerus, elbow, or proximal forearm because blockade at this level will theoretically result in inadequate anesthesia of the terminal nerves that arise from the brachial plexus cords and provide innervation to the upper arm [1,3,6]. Injection of larger volumes (50 mL) of local anesthetic solution has been proposed to facilitate spread of local anesthetic proximally to the level at which the brachial cutaneous nerves exit the sheath [7]. While previous studies have examined the success rate for surgery to the forearm and hand, the efficacy of axillary block for surgery about the elbow has not been formally investigated [8,9].

This study evaluates the success rates of interscalene, supraclavicular, and axillary approaches to the brachial plexus for surgical procedures about the elbow. This study also determines factors associated with successful axillary block.

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Methods

After approval of our institutional review board, the medical records of 260 patients undergoing 330 surgical procedures to the distal humerus, elbow, or proximal forearm were reviewed retrospectively. Demographic data including age, gender, weight, height, surgical procedure, and ASA physical status were recorded. A diagnosis of a preexisting respiratory condition such as asthma, chronic obstructive pulmonary disease, or restrictive pulmonary disease was noted. Pulmonary disease was classified on the basis of pulmonary function tests, and the use of bronchodilators or supplemental oxygen. The presence of any preoperative central neuropathy (myelopathy, radiculopathy) or distal neuropathy (mononeuropathy, generalized peripheral neuropathy) was documented. The approach to the brachial plexus (interscalene, supraclavicular, axillary), technique (paresthesia, nerve stimulator, transarterial, or combination), needle gauge and bevel, and local anesthetic solution and volume were recorded. These data are routinely recorded as part of our anesthesia block record. Supplementation of the plexus block distally by the anesthesiologist or surgeon was noted. Success rate, defined as the ability to proceed surgically without supplementation of additional local or general anesthesia, was determined. Total doses of intravenous drugs administered for sedation during performance of the regional technique and intraoperatively were noted. Infusion rates of propofol consistent with a general anesthetic (100-200 micro gram centered dot kg-1 centered dot min-1) were also considered failed blocks. Administration of nitrous oxide, volatile drugs, an induction dose (bolus) of propofol or thiopental, controlled ventilation with a mask, or endotracheal intubation constituted a general anesthetic and block failures. Postoperative disposition and the time to first analgesic were recorded. The postoperative course was reviewed for neurologic and pulmonary complications.

The rate of successful brachial plexus blockade was compared across groups using Fisher's exact test. Other statistical methods included use of one-way analysis of variance and the two-sample t-test. In all cases, two-tailed tests were used with P values <0.05 considered statistically significant. Data are expressed as mean +/- SD.

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Results

Demographic information and preoperative patient characteristics are described in Table 1. Preoperative neurologic deficits were documented in 102 patients; there were two brachial plexopathies, 71 mononeuropathies, and 29 generalized peripheral neuropathies. In 156 cases, the surgical procedure involved a bony structure (distal humerus, elbow joint, proximal radius or ulna), including 21 total elbow arthroplasties. The surgery involved only soft tissue in the remaining 174 cases. A tourniquet was used in 217 cases, mean total tourniquet time was 64 +/- 76 min.

Table 1

Table 1

An axillary block was performed in 247 cases, a supraclavicular block in 59 cases, and an interscalene block in 24 cases. Needle size ranged from 22 to 25 gauge. A short-beveled needle was used in 147 cases, a long-beveled needle in 177 cases, while in 6 cases the needle type and gauge was unspecified. Mepivacaine (0.75%-1.5%) and bupivacaine (0.25%-0.75%) were the most commonly selected local anesthetic solutions, and were used in 188 and 106 cases, respectively. Other local anesthetics included 2-chloroprocaine, lidocaine, and tetracaine. Epinephrine was added to the local anesthetic solution in 254 cases. Local anesthetic volume was significantly greater for the axillary approach (48 +/- 8 mL) than for the supraclavicular (39 +/- 7 mL) and interscalene (41 +/- 12 mL) approaches (P < 0.01).

Local anesthetic supplementation by the surgeon was required in seven cases. Adequate surgical anesthesia was present in 283 cases, for an overall success rate of 86%. Surgical site (bony structure/soft tissue) did not affect block success rate. However, mean total tourniquet time was significantly longer for failed blocks (84 +/- 47 min) compared to successful blocks (56 +/- 39 min) (P < 0.005). Successful blockade was highly dependent on approach to the brachial plexus. Success rate with axillary block was 89%, supraclavicular block 78%, and interscalene block 75% (P = 0.025).

Successful blockade was also dependent on the technique used to locate the brachial plexus for axillary blocks. Axillary blocks performed using paresthesia and combination (paresthesia or nerve stimulator combined with transarterial injection) techniques had higher success rates than blocks performed exclusively with transarterial injection (P = 0.036 and P = 0.047, respectively) Table 2. Nerve location technique did not affect success rate with supraclavicular and interscalene approaches Table 3.

Table 2

Table 2

Table 3

Table 3

Selection of local anesthetic also affected success rate. Surgical anesthesia was achieved in 93% of axillary blocks performed with mepivacaine compared to 81% of blocks performed with bupivacaine (P < 0.01) Table 2. The highest success rate for axillary blocks was reported using mepivacaine with the paresthesia technique (36 of 37 blocks, or 97%), while the most failures occurred injecting bupivacaine transarterially (5 of 10 blocks, or 50%) (P < 0.001). Addition of epinephrine to the local anesthetic solution also increased the success rate for axillary blocks (P < 0.001) Table 2. Local anesthetic and addition of epinephrine did not significantly affect outcome with supraclavicular and interscalene approaches Table 3. Volume of local anesthetic injected did not differ between failed and successful blocks with all three approaches. Needle type and gauge did not affect success rate.

Blockade of the musculocutaneous nerve did not improve success rate with axillary block. The musculocutaneous nerve was blocked after actual localization with a nerve stimulator response or elicitation of a paresthesia, or with a field block in 101 of 224 (45%) successful and 10 of 23 (43%) unsuccessful axillary blocks.

Intravenous sedation was administered during performance of the regional block in 308 cases. Mean preoperative doses of midazolam (298 cases) and fentanyl (270 cases) were 1.5 +/- 0.8 mg and 64 +/- 32 micro gram, respectively. Intraoperatively, additional intravenous supplementation was administered in 307 cases. Midazolam (3.2 +/- 2.7 mg, 283 cases) and fentanyl (143 +/- 100 micro gram, 284 cases) were the most common intravenous drugs. Propofol was administered intraoperatively in 77 cases, with a mean infusion rate of 62 +/- 61 micro gram centered dot kg-1 centered dot min-1.

In 161 cases (49%), the patient was admitted to the postanesthesia care unit (PACU) for observation. Patients receiving an axillary block were less likely to be admitted to the PACU (and more likely to be transferred directly to their hospital room) than patients receiving a supraclavicular or interscalene block. PACU admission rates were 42% after axillary, 68% after supraclavicular, and 71% after interscalene blocks (P < 0.001). The patient was discharged from the hospital prior to block resolution in 101 cases. Time to first analgesia was determined for the remaining 229 cases, and did not differ between axillary (10 +/- 7 h), supraclavicular (8 +/- 6 h), and interscalene (9 +/- 6 h) approaches. Time to first analgesia was significantly longer for brachial plexus blocks performed with bupivacaine (13 +/- 6 h) than for those performed with mepivacaine (8 +/- 7 h) (P < 0.001).

Seven patients (2.1%) reported new neurologic deficits or worsening of preexisting deficits. Five were related to surgery or the patient's initial trauma or surgery. The remaining two cases were believed to be secondary to the regional technique (one supraclavicular block, nerve stimulator technique; one axillary block, paresthesia technique). All neurologic deficits completely resolved in 4 days to 5 mo. Two patients developed axillary hematomas at the site of needle insertion. There were no patients with perioperative respiratory compromise.

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Discussion

The interscalene, supraclavicular, and axillary approaches to the brachial plexus occur at different anatomical levels. The interscalene block is performed at the trunk level, supraclavicular block at the transition between divisions and cords, and the axillary block at the terminal nerve level. Surgery about the elbow requires anesthesia of the cutaneous nerves to the upper arm (medial brachial cutaneous, lateral brachial cutaneous, posterior brachial cutaneous). These nerves arise (and leave the neurovascular sheath) at the cord level. Traditionally, surgical procedures about the elbow have been performed under supraclavicular block, since adequate blockade of the upper arm is accomplished only with this approach to the brachial plexus.

Our study reports an overall success rate of 89% with the axillary approach, in spite of the fact that nearly half of the procedures involved bony structures. This high success rate compares to rates previously published for surgical procedures to the forearm and hand, surgical sites ideally suited to the axillary approach [2,8,10-13]. Several limitations associated with a retrospective brachial plexus study warrant discussion. Sensory block of the individual nerves was not formally assessed and recorded on these records, so it is possible that incomplete anesthesia of one or more nerves was present. Our end point was sufficient anesthesia to allow completion of the surgical procedure (without intravenous supplementation approaching general anesthetic levels). Dosing of intravenous and volatile drugs over time, as well as notation of patient comfort (or discomfort) in the anesthesia record, surgical dictation, or hospital progress notes were considered in determining the success or failure of a block. It is possible that some inadequate blocks were classified as successful, thereby overestimating the overall success rates. However, success rates of blocks for all regional anesthetic techniques would theoretically be equally affected, and our results regarding regional anesthetic approach, technique, and local anesthetic used would remain valid.

Successful blockade of the upper extremity was achieved less frequently with the other two approaches to the brachial plexus. Interscalene block provided adequate surgical anesthesia in only 75% of cases. This is not surprising, since supplemental ulnar nerve block was not performed at the axillary level, leaving the inferior roots incompletely blocked in many cases. The lower success rate with the supraclavicular block, despite this approach historically being associated with profound and reliable block of rapid onset is most likely due to several factors. The ease of performance and safety has made many anesthesiologists more proficient with the axillary approach. Likewise, the supraclavicular approach is more difficult to teach and many of the regional techniques were performed by residents. Interestingly, the success rates for axillary and supraclavicular blocks reported in our study are comparable to those in one of the earliest publications comparing the two approaches [2]. Those authors concluded that the "axillary approach to the brachial plexus is superior to the conventional supraclavicular approach. It had a higher success rate and a lower incidence of complications. The serious complication of pneumothorax is entirely eliminated by use of the axillary technique."

Successful axillary blockade was dependent on the method used to locate the brachial plexus. The statistically higher rate of success with the paresthesia technique compared to transarterial injection has not been previously reported [8,12,13]. Indeed, the prior lack of difference in the success rate between the two techniques, combined with the theoretical increase in the incidence of persistent paresthesias after axillary blocks performed with the elicitation of paresthesias, has led to the recommendation that nerve blocks should be performed without intentionally searching for paresthesias [14-16]. However, the higher success rate in blocks performed with the elicitation of paresthesias supports the continued application of this technique.

Selection of local anesthetic also remains largely unstudied as a potential factor for block success or failure. Initial investigations used lidocaine [2,7]. More recently mepivacaine, either alone or in combination with bupivacaine, is the most frequently selected local anesthetic [8-12]. While the onset time and duration of brachial plexus blockade with bupivacaine compared to mepivacaine has been well documented, their respective success rates have not been evaluated. We report a significant increase in the success rate in axillary blocks performed with mepivacaine (93%) compared with those performed with bupivacaine (81%), suggesting improved distribution within the axillary sheath with mepivacaine. The improved success rate for axillary blocks performed with mepivacaine may make it preferable to bupivacaine in patients who may be at increased risk of complications from general anesthesia.

Postoperative pulmonary dysfunction is a major cause of surgical morbidity and mortality. Patients with significant respiratory disease may experience a worsening of their pulmonary status after general anesthesia or brachial plexus block. Pneumothorax is a well-documented complication of supraclavicular block and phrenic nerve paralysis may occur with both interscalene and supraclavicular techniques. Our study involved 72 patients with a preexisting pulmonary condition, including 30 patients with moderate or severe chronic obstructive pulmonary disease (26 of whom underwent axillary block). Although there were no cases of perioperative respiratory compromise, the high success rate combined with the minimal risk of pulmonary complications with the axillary approach establishes the reliability and safety of the technique in this patient population.

In conclusion, successful blockade of the brachial plexus was achieved in 88% of patients undergoing surgery to the distal humerus, elbow, or proximal forearm. Success rate was greatest with the axillary approach (91%), and was not dependent on supplemental block of the musculocutaneous nerve. In addition, axillary blocks performed with a paresthesia or combination paresthesia/transarterial injection technique were more successful than those performed with transarterial injection only. Finally, mepivacaine was more dependable than bupivacaine in producing adequate surgical anesthesia. These results suggest that axillary block is the brachial plexus block of choice for surgical procedures about the elbow, and that regional technique and selection of local anesthetic may also influence block success rate.

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