Functional anatomy of the brachial plexus sheath: implications for anesthesia

Anatomical study of the brachial plexus of 18 cadavers was undertaken to confirm the presence and significance of "septa" dividing the brachial plexus or axillary sheath. Dissection demonstrated that the sheath consists of multiple layers of thin connective tissue surrounding the various elements of the neurovascular bundle. These septa are incomplete, however, forming small bubble-like pockets when solution is injected. Single injections of methylene blue and Latex solutions into the axillary sheath resulted in immediate dye staining of median, radial, and ulnar nerves, despite the presence of septa. These data demonstrate that there are connections between compartments within the sheath and, therefore, do not support the need for multiple injections when performing an axillary block.     

Gross anatomy of the brachial plexus sheath in human cadavers

BACKGROUND AND OBJECTIVES: Major nerves and vessels run alongside each other in a "neurovascular bundle" kept together by connective tissue that is often referred to by anatomists, surgeons, and anesthesiologists as the "sheath." Our goal was to macroscopically demonstrate the brachial plexus sheath in embalmed and fresh cadaver dissections. METHODS: Systematic dissections were performed on 11 embalmed cadavers (6 females and 5 males), plus one fresh, unembalmed male cadaver. Dissections were started in the arm, and progressed proximally to the axilla and the supraclavicular area. Notes and photographic documentation were obtained. RESULTS: A sheath around the neurovascular bundle of the brachial plexus was visible to the naked eye in every dissection. The sheath had a fibrous external appearance, and was filled with loose connective tissue. No evidence of septa was found. CONCLUSIONS: We observed a macroscopic fibrous structure surrounding the plexus, which was filled with loose connective tissue lacking any apparent organization.     

Groin flap immobilization by axillary brachial plexus block anesthesia

Pedicled groin flaps are still widely used as soft tissue coverage in hand surgery. Various methods have been described for immobilization of flaps, such as Ace wraps, plaster, and external fixators. The hands of 5 females and 12 males, totaling 17 patients, with severe injury were reconstructed with groin flaps between 2001 and 2005. Patients were operated on under a combination of axillary block and general anesthesia. Motor block effect of axillary anesthesia was used for immobilization of the upper extremities at groin flap coverage. A combination of axillary brachial plexus block plus general anesthesia had advantages in the prevention of pedicle tension or torsion during the initial recovery period. Reduction of general anesthesia time and improvement of postoperative pain were also observed. Axillary brachial plexus block and general anesthesia are a preferred combination for patients undergoing groin flap operations.     

Endoscopic exploration of the brachial plexus: technique and topographic anatomy--a study in fresh human cadavers

OBJECTIVE: The indications for and timing of brachial plexus exploration in closed injuries are controversial. The time-consuming surgery proves its worth in some cases, whereas spontaneous regeneration might have been possible in others. The differentiation is difficult, because no investigational method reveals the exact morphological correlates of the nerve lesions. Minimally invasive, direct observation of the structures is a possible solution. Here we describe our surgical technique and the anatomic features of the normal brachial plexus appreciated with the endoscope. METHODS: Twenty-one brachial plexus in 11 fresh cadavers were investigated. Endoscopic exploration was performed at the supraclavicular and infraclavicular levels. The method involves insertion of an optic shaft-integrated retractor through a stab wound; retraction of landmark muscles produces a working space, into which other instruments are introduced for dissection. After completion of endoscopic surgery, open dissection was performed to verify the endoscopically identified structures and to assess iatrogenic injuries. RESULTS: The omohyoid muscle is a reliable landmark in the supraclavicular region, beneath which the suprascapular nerve can be observed. Following the suprascapular nerve proximally leads to the plexus trunks. Infraclavicular exploration first reveals the axillary artery. The plexus and its nerves are traced around this artery. The anatomic features were constant in all cases, with variations in fat accumulation depending on the corporeal constitution. We detected iatrogenic injuries to the medial circumflex humeral vessels in two cases. No nerve injuries were observed. CONCLUSION: The endoscopic technique combined with intraoperative nerve stimulation studies might provide important information on the type of morphological damage in closed brachial plexus injuries and thus might become an important tool for determination of the surgical treatment strategy. Clinical work is under way.     

Enhancement of axillary brachial plexus block anesthesia by coadministration of neostigmine.

BACKGROUND AND OBJECTIVES: The acetylcholinesterase inhibitor neostigmine has shown peripherally mediated analgesic action in recent preclinical and clinical studies. The present study investigates the effectiveness of adding neostigmine to a local anesthetic, mepivacaine, in patients receiving axillary brachial plexus block for upper extremity surgery. METHODS: In a double-blind, randomized study 34 patients were assigned to the treatment group: Neostigmine (NM) (500 microg) + mepivacaine (M) (500 mg) (NM, n = 17) as drugs for the plexus block, or to control group: mepivacaine (500 mg) + saline (0.9%, 1 mL) (M, n = 17). RESULTS: The onset and duration of sensory and motor block was similar in both groups. Patients receiving NM had significantly lower pain ratings [visual analogue scores (VAS): 14.7 +/- 9.9 vs 32.4 +/-23.5; P < .05] 24 hours after surgery, and a lower number of patients in the NM group needed supplemental analgesics during the first 24 hours postoperatively. No adverse events were recorded for either group. CONCLUSIONS: Peripherally administered neostigmine improves postoperative analgesia in axillary brachial plexus block.     

Quality of axillary brachial plexus block

A perivascular catheter technique (PVT) and a nerve stimulator technique (NST) for axillary brachial plexus block were compared in terms of quality: complete, incomplete or failed blocks. In a randomised series, 30 PVT blocks and 30 NST blocks were performed by three staff anaesthetists. In the NST group, surgical anaesthesia was always achieved, whereas in the PVT group, four blocks required supplementation with general anaesthesia. In both groups eight patients needed supplementation with additional conduction blocks of 1-3 peripheral nerves. It is concluded that a nerve stimulator technique may increase the success rate of axillary brachial plexus block to some extent.     

Two approaches to the axillary brachial plexus

A new technique of cannulation of the axillary neurovascular sheath, using loss of resistance to saline, was evaluated and compared to the established technique of eliciting paraesthesiae with a short-bevelled needle. The cannulation technique produced a more reliable block of axillary, musculocutaneous and radial nerves, significantly fewer incomplete blocks and a lower incidence of accidental vessel puncture.     

Addition of fentanyl to bupivacaine prolongs anesthesia and analgesia in axillary brachial plexus block

BACKGROUND AND OBJECTIVES: To evaluate the analgesic and anesthetic effects of 40 mL bupivacaine 0.25%, 40 mL bupivacaine 0.25% plus fentanyl 2.5 microg/mL, and 40 mL bupivacaine 0.125% plus fentanyl 2.5 microg/mL for axillary brachial plexus block. METHODS: Sixty patients were randomly allocated to 3 groups and received axillary brachial plexus block with 40 mL bupivacaine 0.25% (group B), 40 mL bupivacaine 0.25% with fentanyl 2.5 microg/mL (group BF), or 40 mL bupivacaine 0.125% with fentanyl 2.5 microg/mL (group DBF). The onset times and the duration of sensory and motor blocks, duration of analgesia, hemodynamic parameters, and adverse events were noted. RESULTS: The mean duration of sensory block and analgesia were longer in group BF (10.1 hours and 20.9 hours) than group B (6.9 hours and 11.6 hours) and DBF (5.9 hours and 12.0 hours) (P < .01, P < .001, respectively). The mean duration of motor block was also longer in group BF (10.7 hours) than group B (4.9 hours) (P < .01). Only 2 patients experienced motor block in group DBF. The frequency of successful block was 35% in group DBF (P < .01). Hemodynamic parameters were similar in all groups. In group B, only 1 patient experienced dizziness. Nausea was observed in 1 patient in each fentanyl group. CONCLUSION: The addition of 100 microg/mL fentanyl to 0.25% bupivacaine almost doubles the duration of analgesia following axillary brachial plexus block when compared with 0.25% bupivacaine alone.     

Safety of supplementing axillary brachial plexus blocks

The incidence of failed local anesthetic axillary blockade varies but can be as high as 20-30%. The authors propose to evaluate the safety of supplementing an axillary block with mepivacaine 30 min after the initial injection. An axillary blockade was performed on 10 healthy patients scheduled for forearm or hand surgery using a new catheter technique. Mepivacaine 1% with epinephrine (7 mg/kg) was administered initially and followed 30 min later by half the original dose (3.5 mg/kg). Plasma levels of mepivacaine were estimated at frequent intervals for 5 h after the initial injection. There were no symptoms or signs of local anesthetic toxicity, and plasma levels of mepivacaine remained below those that usually caused symptoms. In conclusion, the authors conclude that mepivacaine 1% with epinephrine (10.5 mg/kg) can be safely administered in divided doses into the axillary sheath within a 31-min period.     

Single-injection brachial plexus anesthesia for arteriovenous fistula surgery of the forearm: a comparison of infraclavicular coracoid and axillary approach

BACKGROUND AND OBJECTIVES: The surgical site for the creation of an arteriovenous fistula at the lateral aspect of the distal forearm may be faster and more effectively blocked with the infraclavicular coracoid approach than with the axillary approach for brachial plexus block. METHODS: Sixty uremic patients scheduled for the creation of an arteriovenous fistula at the forearm were randomized to receive a single-injection brachial plexus block with 35 to 50 mL mepivacaine 0.95% with epinephrine using the infraclavicular coracoid approach (IC group) or the perivascular axillary approach (AX group). A distal muscular contraction elicited by a nerve stimulator at current <0.5 mA was used in all patients. RESULTS: At 30 and 45 minutes, complete loss of sensation was observed more often in group IC than AX in the cutaneous distribution of musculocutaneous nerve (62% v 30% [P < .05] and 69% v 40%, respectively [P < .05]), but at 60 minutes the difference was not statistically significant. In other areas, analgesia and motor block were achieved at a similar rate. In 3 patients surgery could not be performed under the block due to changes in schedule or the use of a brachial tourniquet. Patient satisfaction was equally high in both groups. CONCLUSIONS: Blockade of the musculocutaneous nerve developed faster with the infraclavicular coracoid approach than with the axillary approach. The infraclavicular coracoid approach may be preferable in patients scheduled for the creation of an arteriovenous fistula at the forearm.     

Reciprocal compression between the axillary artery and brachial plexus

Angiographic studies were performed on 60 of 394 patients diagnosed as having thoracic outlet syndrome. Ten of the patients studied angiographically presented with obstruction of contrast material in the axilla with refilling of the axillary artery through the external mammary and shoulder arteries. The obstruction was caused by lower trunk brachial plexus compression. This seldom known cause of hyperabduction syndrome occurred in 2.5 per cent of the patients examined for thoracic outlet syndrome. Surgical treatment consists of loosening the axillary artery by tying off the external mammary and circumflex arteries, followed by section and anastomosis of the axillary artery anteriorly to the brachial plexus. Angiography is considered a basic diagnostic procedure, mainly when concomitant compression occurs and gives good dynamic information on the location and importance of the compression.