Block of the Brachial Plexus and Its Branches

 

History

Brachial plexus block was first performed in 1885 by William Steward Halsted, who used cocaine and direct exposure in the roots in the neck to accomplish the block.  In 1911, Hirschel and Kulenkampff described the first percutaneous brachial plexus block by the axillary and supraclavicular routes, respectively.  Since these historic reports, the efficacy of brachial plexus block has been confirmed and the procedure now is commonly used to provide upper-extremity anesthesia.

 

Anatomy

The brachial plexus is formed by the ventral rami of C5-C8 and T1 (with minor contributions from C4 and T2).  From the proximal to the distal part of the plexus, it is subdivided as described below.

 

Roots and Trunks:  The nerve roots enter the interscalene groove between the scalenus anterior and scalenus medius muscles.  The nerve root of C7 continues as the middle trunk, while the nerve roots of C8 and T1 unite to form the lower trunk at the lateral border of the scalenus anterior muscle.  The trunks are ensheathed by the prevertebral fascia and lie in the same plane as the subclavian artery.  The upper and middle trunks lie superior to and the lower trunk lies posterior to the subclavian artery close to the first rib.  Each trunk branches off into anterior and posterior divisions.

 

Divisions:  The six divisions regroup over the first rib and behind the clavicle.  They separate first into the fibers destined for flexor or extensor surfaces and then unite into cords.

 

Cords:  The cords derive their designations of posterior, lateral or medial according to their relation to the second part of the axillary artery behind the pectoralis minor muscle.  The posterior cord is formed by the posterior division of all the trunks.  The lateral cord consists of the union of the anterior divisions of the upper and middle trunks, while the medial cord is comprised of the anterior division of the lower trunk.

 

Branches:  Anatomically, the branches of the brachial plexus can be divided into those derived from the roots, the trunks, and the cords.  From the roots, C5 contributes to the phrenic nerve and gives off a branch to the levator scapulae muscle, while C5-C7 send nerves to the serratus anterior and rhomboid muscles.  From the upper trunk, C5 and C6 send a nerve to the subclavius muscle, while the suprascapular nerve innervates the supraspinous and infraspinatus muscles.

The lateral cord gives rise to the lateral pectoral nerve, the musculocutaneous nerve and the lateral head of the median nerve.  The medial cord branches off into the medial pectoral nerve, the medial cutaneous nerve of the arm and forearm, the medial head of the median nerve and the ulnar nerve.  The posterior cord divides into the upper and lower subscapular nerves, the nerve extending to the latissimus dorsi muscle, the axillary nerve passing on to the shoulder joint and leading to the deltoid and teres minor muscles, and the radial nerve.

Except for the innervation of the skin over the upper aspect of the shoulder (C3, C4) and the upper part of the medial arm (T2), all motor and sensory innervation of the upper extremity is derived from the brachial plexus.  Sympathetic innervation is from the spinal segments T1-T5.  The T1 and T2 postganglionic fibers traverse the brachial plexus via the stellate ganglion, while the T3-T5 post ganglionic fibers join the vascular branches of the subclavian artery leading to the arm.

 

Approaches

There are four usual sites of approach for a brachial plexus:  the interscalene space and the supraclavicular, infraclavicular and axillary regions.  While all these approaches have certain limitations or disadvantages, they allow the anesthesiologist to select from a variety of techniques the one that is most appropriate for the intended surgical or therapeutic procedure.

In general, supraclavicular and interscalene blocks are used for surgery performed on the shoulder or above the elbow.  An axillary block is considered the best choice for surgery on the hand and medial side of the arm below the elbow.  The infraclavicular block may be preferable for operations on the forearm and elbow.

For a consistent motor block of the brachial plexus, the following agents are recommended:  bupivacaine 0.5%, chloroprocaine 3%, etidocaine 1%, lidocaine 1.5% or mepivacaine q.5%.  For sensory block alone, lesser concentrations of local anesthetic, such as chloroprocaine 2% or lidocaine 1%, may be used successfully.

Given that a consistently good surgical block requires 10 ml of local anesthetic on each mixed peripheral nerve, the brachial plexus block requires 40 ml because it involves four major nerves.  The site of needle entry does not change the volume requirement.  A higher needle entry in the brachial plexus sheath, such as that used for the interscalene, supraclavicular or infraclavicular techniques, causes the motor block to appear earlier than the sensory block.  A more distal needle entry, such as that used for the axillary technique, is associated with greater sensory block and poorer motor block.  When choosing a local anesthetic for a brachial plexus block, one should select an agent that does not exceed safe plasma concentrations when used in the volume required to produce a consistently good block.

 

Complications

Vascular:  Since most major nerves occupy a neurovascular bundle, inadvertent intraarterial injection is always a risk.  Even an extremely low dose of local anesthetic (eg, a test dose) may precipitate a seizure if is it injected into an artery under high pressure and leads to reverse flow.

Although direct intravenous injection is more likely to occur than intraarterial injection, the volume or total dose of local aesthetic required to produce a seizure is much greater for intravenous than it is for intraarterial injection.  This allows the anesthesiologist to observe preseizure symptoms such as dizziness, tinnitus or disorientation.  Since toxic response to intravascular injection is immediate, resuscitation equipment and drugs must be available prior to the block.

Hematoma may occur after any nerve block.  Although most hematomas are not serious, they may cause complications.  The early effect of a hematoma is to compress the ischemic nerve.  If this occurs, the hematoma should be decompressed before irreversible neurologic damage occurs.  Calcification of a hematoma is a rare late complication. 

 

Pneumothorax:  The risk of pneumothorax is greatest with the supraclavicular approach to the brachial plexus.  Although extensive and usually symptomatic, pneumothorax may occur soon after the injury.  Most cases of pneumothorax take 24 hours to develop, are small to moderate in size and cause mild to no symptoms.

Pneumothorax should be suspected in patients who have undergone supraclavicular brachial plexus block and who later develop symptoms of dyspnea and chest pain that are aggravated when the patient breathes deeply or coughs.  The diagnosis can be confirmed after viewing the x-ray film of the chest.

 

Peripheral Nerve Damage:  Some studies have reported an increased risk of peripheral nerve damage when paresthesia is elicited during nerve block.  In other studies, the incidence of peripheral nerve damage was insignificant with any technique. 

 

INTERSCALENE APPROACH

Kappis in 1911 blocked the brachial plexus in the interscalene space by the posterior approach, followed by Mulley, who in 1919 performed the first interscalene approach by two injection methods.  Credit, however, is given to Etienne for describing the first true interscalene approach in 1925.  The popularity of the interscalene approach to the brachial plexus is due primarily to the eloquent descriptions and efforts of Winnie in 1970.

 

Anatomy

The brachial plexus in the interscalene region consists of roots and trunks covered by the prevertebral fascia and enclosed between the fascia of the scalenus anterior and medius muscles.

 

Technique

Position:  The patient lies supine with the head turned away from the anesthesiologist.  The arm is resting at the side with the hand pointing toward the knee.  The anesthesiologist stands on the side to be blocked at the level of the neck.

 

Landmark:  To ensure correct positioning of the needle, the following steps are taken:

…         The cricoid cartilage is palpated (at the level of C6).

…         The posterior border of the sternocleidomastoid muscle (clavicular head) is palpated.

…         -               The fingers are rolled posteriorly to the posterior border of the   sternocleidomastoid muscle in order to reach the interscalene groove.

…         The interscalene groove can be accentuated by raising the head against resistance.

…         The needle enters at the medial aspect of the jugular vein as it traverses to  sternocleidomastoid muscle at the level of C6.

 

Procedure:  The anesthesiologist stands at the dies of the neck and palpates the interscalene groove at the level of C6.  Subcutaneous local anesthetic infiltration is performed with a 27-g needle.  A 20-ml syringe with the appropriate local anesthetic solution is attached to an extension set and a 22-g needle.  The 22-g needle is inserted through a landmark, perpendicular to the skin and aimed at a point between the contralateral shoulder and nipple.  A nerve stimulator could be attached at this point to the needle with the ground electrode in the opposite shoulder.

As the needle enters the interscalene groove, paresthesia will be elicited in the shoulder, elbow or thumb.  Needle penetration should stop when elbow or thumb paresthesia is obtained.  The nerve stimulator will cause the biceps, forearm muscles or wrist and hand muscles to contract.  The needle is in the correct position if there is thumb paresthesia or if movements are seen in the wrist or fingers.  If there is shoulder or elbow paresthesia of the biceps is contracting, the C5-C6 nerve root may have been reached.  If the diaphragm contracts unilaterally, the phrenic nerve has been stimulated, in which case the needle is too anterior and medial. 

 

Confirmation of Block

Interscalene block is successful when there is anesthesia of the shoulder, elbow, forearm and hand.  There is usually no anesthesia of the inner aspect of the upper arm or elbow.  The ulnar nerve is blocked only 50% of the time.

 

Practical Aspects

…         Aspiration should be performed before injection of the local anesthetic to prevent spread to the cardiovascular system or CSF.

…         A test dose of 1-2 ml local anesthetic should be administered to watch for signs of CNS toxicity or total spine block.

…         The injection should be stopped if early signs of toxicity appear.

…         The block can be supplemented with sedatives if the block is adequate but the patient is agitated.

…         Narcotics can be given intravenously as a supplement if the block is partial but surgery is short and the pain is in the tourniquet.

…         A mixture of N2O and O2 (50:50) can be given if supplemental analgesia is needed.

…         If the block is not present, full general anesthesia with airway control should be administered.

 

Complications

Brachial plexus block by the interscalene approach is subject to a number of complications:

…         Total spinal block (can be prevented by aspiration prior to injection)

…         High epidural block (treated by airway control and O2 administration and maintenance of blood pressure)

…         Systemic toxicity with unconsciousness (vital functions should be maintained until toxicity is reduced)

…         Laryngeal nerve block (no treatment necessary; no oral intake until the patient can sip water)

…         Phrenic nerve block (adequate ventilation should be maintained)

 

SUPRACLAVICULAR APPROACH

Kulenkampff described the first percutaneous supraclavicular approach in 1911.  The first significant modification of the technique was achieved by Labat in 1922, when he advocated injection of the local anesthetic agent at three separate points.

In 1927, Livingston described a technique similar to what is now called the subclavian perivascular approach.  In 1940, Patrick described a new technique that made it possible to lay down a wall of anesthetic through which the plexus must pass.  Since then others have described various modified techniques.

 

Anatomy

As the trunks of the brachial plexus emerge from the interscalene space at the lower border of the scalene muscles, they continue anterolaterally and inferiorly to converge toward the upper surface of the first rib.  At the lateral edge of the rib, each trunk divides into anterior and posterior divisions which enter the axilla at the midpoint of the clavicle.  In its position between the scalenus anterior and medius muscles, the plexus lies superior and posterior to the second and third parts of the subclavian artery.  Anteromedial to the lower trunk and posteromedial to the artery lies the dome of the pleura.

 

Technique

Position:  The patient lies supine with a roll-shaped cushion between the scapulae.  The arms are at the patient's side with the hands pointing toward the knee.  The patient's head is turned away from the side to be operated on.  For accentuation of the sternocleidomastoid and scalene muscles, the head may be lifted 30 degrees off the table.

 

Landmarks:  The correct point of entry is determined by observing the following landmarks:

…         The midpoint of the clavicle is located midway between the acromial end (the prominence at the top of the shoulder) and the sternal end of the clavicle.

…         The point of entry is on the lateral border of the scalenus anterior muscle at the midpoint of the clavicle.

 

Procedure:  The needle is inserted at the point of entry above the midpoint of the clavicle in a backward-inward-downward injection (BID).  The needle thus appears to be at right angles to all planes at this level of the neck.  Even though the direction of the needle is toward the first rib, it is not necessary to touch the rib.  Paresthesia of the digits or wrist if sought.  If obtained, after negative aspiration for air or blood, inject 1-3 ml local anesthetic as a test dose. 

This is followed after 5 minutes if there are no systemic effects by the total calculated volume of the local anesthetic.  If paresthesia is not obtained and the needle touches the first rib, it is usually at the subclavian groove.  The needle should then be walked posteriorly to elicit paresthesia.  If paresthesia is not obtained, contact with the rib will be lost.  It is then necessary to regain contact with the rib and walk toward the vertebra.  If no paresthesia is obtained, at this point, repeat the procedure.  A nerve stimulator can be used to aid in locating the brachial plexus. 

 

SUBCLAVIAN PERIVASCULAR APPROACH

An alternative technique makes use of subclavian perivascular landmarks.

…         The needle enters at the level of C7 in the interscalene groove.

…         The needle is directly caudal, and the hub is in line with the ear.

 

A 22-g 3.75 cm needle is inserted through the skin weal perpendicularly and downward in the interscalene groove toward the clavicle at the level of C7.  Paresthesia is elicited, as with the classic supraclavicular technique.  When it has been confirmed that the needle tip is on the brachial plexus, the usual calculated volume of the local anesthetic is injected.

 

Confirmation of Block

The block is confirmed when there is anesthesia of the whole arm up to the shoulder, except for the inside of the upper one third of the upper arm, and sympathetic block in the same regions, together with increased temperature and no sweating.

 

Practical Aspects

…         Puncturing the subclavian artery or lung or entering the epidural and subarachnoid spaces should be avoided.

…         The stellate ganglion may be blocked, especially when large volumes of anesthetic are used.

…         The vagus nerve and its branches in the neck may be blocked.

…         It is advisable to supplement with thiopental (Pentothal), pentobarbital (Nembutal, or diazepam (Valium) if the block is adequate but the patient is agitated.

…         Narcotics may be given intravenously as a supplement if the block is partial but surgery is to be of short duration and the pain arises from the tourniquet.

…         A mixture of N20 and O2 (50:50) can be given if supplemental analgesia is needed.

…         Full general anesthesia with airway control should be administered if the block is not present.

 

Complications

Complications associated with this approach include hematomas of the neck and pneumothorax.  In the event of the former, watch closely and aspirate or evacuate if necessary; advise the patient the hematoma will take 2-3 weeks to disappear by itself.  For pneumothorax, conservative treatment is appropriate in fewer than 10% of cases, and chest tube insertion is advised for more than 20%.

 

References

…         Etienne J: Regional anesthesia: its application in the surgical treatment of cancer of the breast (in French).  Doctoral thesis, Faculty of Medicine, University of Paris, 1925.

…         Halsted WS:  Surgical papers, Burket WC Jr (ed):  Baltimore, MD, Johns Hopkins University Press, 1925.

…         Hirschel G:  Anesthesia of the brachial plexus for operations on the upper extremity (in German).  MMW 1911; 58; 1555-6.

…         Kappis M:  Uber Leitungsanasthesie an Bauch, Brust, Arm und Hals durch Injektion as Foramen intervertebrale.  MMW 1914, 1:794.

…         Kulenkampff D:  Anesthesia of the brachial plexus (in German).  Zentralbl Chir 1911, 38:1337-50.

…         Livingston EM, Wertheim H:  Brachial plexus block:  Its clinical application.  Anesth Analg 1927;6:149-54.

…         Winnie AP:  Interscalene brachial plexus block.  Anesth Analg 1970; 49:455-66.

…         Adriani J (ed):  Labat's Regional Anesthesia:  Techniques and Clinical Applications, 4th ed.  St. Louis:  Green; 1984.

…         Patrick J:  The technique of brachial plexus block anesthesia:  Br J Surg 1940;27:735-9.

…         Mulley K: A modification of Kulenkampff's brachial plexus block technique in order to avoid pleural injury (in German).  Beitr Z Klin Chir 1919:114;666-80.