Chapter 75 Brachial Plexus Blocks: Techniques Below the Clavicle Flashcards
KEY POINTS 1. There were no currently described techniques of brachial plexus block that rely upon blockade at the level of the divisions of the plexus until the advent of US guidance. 2. It has been demonstrated that the capacity of the axillary perivascular sheath is 42 ml. 3. Axillary and infraclavicular blocks of the brachial plexus are appropriate for surgeries of the upper extremity from the elbow to the fingers. 4. Paresthesias occur in up to 40% of cases of axillary perivascular
Brachial plexus blocks below the clavicle involve blockade
of the cords or peripheral nerves and include the infraclavicular block and axillary block approaches, which may be performed with peripheral nerve stimulation (PNS) or ultrasound (US)-guided, paresthesia-seeking, transarterial,
and fascial click techniques
As the plexus emerges from beneath the clavicle and crosses over the lateral aspect of the first
rib
the fibers from the anterior and posterior divisions recombine to form the three cords of the plexus
The lateral cord is formed by the union of
the anterior
divisions of the superior and middle trunks;
the medial cord is merely the continuation of the
anterior division of the inferior trunk
the posterior cord is composed
of
the posterior division of all three trunks
the medial and lateral cords give rise to nerves that supply the
flexor (volar or anterior) surface of the upper extremity
nerves arising from the posterior
cord supply the
extensor (dorsal) surface of the arm.
The lateral and medial cords are the origins of
the lateral and medial heads of the median nerve (C5–C8)
major terminal branch
The lateral cord continues on as
the musculocutaneous nerve (C5–C7) (major terminal
branch)
the medial cord continues on as the
ulnar nerve (C7–T1) (major terminal branch)
The posterior cord gives off the
axillary nerve as its branch (C5–C6) (major terminal branch) and then continues on as the radial nerve (C5–T1) (major terminal branch.
After the lateral cord gives off its contribution to the median nerve the musculocutaneous nerve
leaves the plexus and typically
dives into the substance of the coracobrachialis muscle, but
may also course in a fascial plane between the biceps brachii and coracobrachialis muscles. Then, it courses down
the arm between the biceps and brachialis muscles, sending motor fibers to the powerful flexors of the forearm.
lateral cord terminates as the
lateral antebrachial cutaneous
nerve.
Injury to the musculocutaneous nerve typically results in
paralysis of the coracobrachialis, biceps, and
brachialis muscles with resultant inability to flex the forearm.
the musculocutaneous
nerve must be routinely blocked by
a separate injection in either of these locations, either be in the coracobrachialis muscle or
within the fascial compartment between the coracobrachialis
and biceps brachii muscles
The median nerve consists of
motor fibers originating
primarily from C6–C8, with occasional contributions
from C5 and T1.Sensory fibers originate from C6–C8.
contributes to the lateral head
of the median nerve,
The lateral cord contributes to the lateral head of the median nerve, which joins the medial head contributed by the medial cord. Thus, this nerve may be considered as a branch of both the cords derived from the anterior
divisions. The two contributing divisions of the nerve, at their most cephalad point of origin, straddle the third part of the axillary artery before uniting on its ventral surface.
course of the median nerve
The nerve then continues its course along the brachial artery into the forearm, where it ultimately divides into muscular and cutaneous branches in the hand.
The median nerve provides motor branches to
most of the
flexor and pronator muscles of the forearm. It also supplies all the superficial volar muscles except the flexor carpi ulnaris, and all of the deep volar muscles except the ulnar half of the flexor digitorum profundus. The motor branches in the hand supply the first two lumbricals
and the thenar muscles that lie superficial to the tendon of the flexor pollicis longus.
The median nerve provides sensory branches to
Sensory branches
supply the skin of the palmar aspect of the thumb, the
lateral two and a half fingers and the distal end of the
dorsal aspect of the same fingers.
Injury to the median nerve results in
the so-called “ape hand deformity.
The medial brachial cutaneous nerve
derived from C8–T1. It is the second collateral derivation of the medial cord. It supplies the medial portion of the upper arm as far distally as the medial epicondyle. High in the axilla, part of this nerve forms a loop with the intercostobrachial nerve, with which it shares a reciprocal size and innervation area relationship.
The medial antebrachial cutaneous nerve
derived from C8–T1. It is another branch from the
medial cord and arises just medial to the axillary artery. It
passes down through the arm medial to the brachial artery
to supply the skin over the entire medial aspect of the forearm to the wrist. A segment of this nerve may also innervate the skin over the biceps muscle to the elbow
ulnar nerve
the major terminal branch of the medial cord. It arises from the medial cord
after the medial head of the median nerve has branched off
the cord at the lower border of the pectoralis minor muscle.
course of ulnar nerve
It typically lies medial to the axillary artery at its origin
and continues down the arm medial to the brachial artery,
running parallel to and between the median and medial antebrachial cutaneous nerves. It passes distally through a groove on the medial head of the triceps and passes behind the medial epicondyle. It then passes down the medial aspect
of the lower forearm into the hand. Motor branches in the forearm supply the flexor carpi ulnaris and the ulnar head of the flexor digitorum profundus.
In the hand ulnar nerve motor branches supply
all of the small muscles
deep and medial to the long flexor tendon of the thumb
except the first two lumbricals.
ulnar nerve sensory branches supply
no sensory branches in the forearm, but in the hand the skin of the fourth and fifth fingers and the medial half of the hand are usually supplied by the ulnar nerve
Ulnar nerve injury typically results in
the deformity known as “clawhand.”
The posterior cord gives off one major terminal branch,
the axillary nerve, before continuing on as the radial
nerve.
axillary nerve
(C5–C6) leaves the plexus high
in the axilla through the quadrilateral space bounded by
the surgical neck of the humerus, the teres major and minor muscles, and the long head of the triceps.
axillary nerve sensory
fibers supply
the skin overlying the lower two-thirds of the lateral and posterior deltoid, and its motor fibers supply the deltoid and teres minor muscles.
An articular branch of axillary nerve supplies the
inferior, lateral, and anterior
structures of the shoulder joint.
Injury to the axillary nerve
results in
an inability to abduct the arm.
The radial nerve
the largest terminal branch of the entire plexus and is the
terminal continuation of the posterior cord.
Course of the radial nerve
It accompanies the profunda brachii artery as they course behind and around the humerus in the musculospiral groove.
using a combination of US and peripheral nerve
stimulation indicate that the radial nerve is most often
located
posterior (dorsal) and medial to the axillary artery.
Motor branches of the radial nerve supply
the triceps (the powerful extensor of the forearm), the anconeus, and the upper portion of the extensor-supinator group of muscles.
The motor branches of the radial nerve that supply the triceps muscles are typically located
more superficially in the axillary perivascular
compartment, and are separated from the main
trunk of the radial nerve by the ulnar nerve and
in some patients, by the axillary artery.
The major sensory
branches of the radial nerve include
the dorsal antebrachial cutaneous nerve that innervates the posterior aspect of the forearm as far as
the wrist, as well as the posterolateral aspect of the upper arm.
Radial Nerve Branches to the hand innervate
the dorsal aspect of
the lateral hand, including the first two and a half fingers
as far as the distal interphalangeal joint.
Injury of the radial nerve results in
“wrist drop.”
Axillary nerve (C5–C6)
Muscle Group(s): Deltoid Function/Action: Abducts arm; flexes and medially rotates arm (anterior fibers); extends and laterally rotates arm (posterior fibers)
Musculocutaneous nerve (C5–C6)
Teres minor: Rotates arm laterally, adduction
Coracobrachialis: Flexes, adducts arm
Biceps (long head): Flexes arm and forearm
Biceps (short head): Supinates hand
Radial nerve (C5–C8)
Triceps (long head): Extends, adducts arm
Triceps (lateral head): Extends forearm
Triceps (medial head): Extends forearm
Brachioradialis: Flexes forearm
Extensor carpi radialis: Extends, abducts hand
Extensor digiti: Extends fingers
Extensor carpi ulnaris: Extends, adducts hand
Supinator: Supinates forearm
Abductor pollicis longus: Abducts, extends thumb
Median nerve (C6–T1)
Pronator teres: Pronates, flexes forearm
Flexor carpi radialis: Flexes, abducts hand
Palmaris longus: Flexes hand at wrist
Flexor digitorum superficialis: Flexes hand, first, and second phalanges
Flexor policis longus: Flexes hand, phalanges
Pronator quadratus: Pronates forearm
Ulnar nerve (C8–T1)
Flexor carpi ulnaris: Flexes, adducts hand
Flexor digitorum profundus: Flexes phalanges, hand at wrist
Intrinsic hand muscles: Flex, extend, abduct, adduct phalanges
Postganglionic sympathetic fibers are distributed
distally via
the somatic nerves of the plexus to the peripheral
vessels.
The proximal sympathetics arise directly from
the cervical sympathetic chain, particularly from the middle
and inferior cervical sympathetic ganglia
The postganglionic
sympathetic fibers pass directly to the
subclavian artery and are conveyed in a plexiform manner along the outer coat of the vessel and subsequently into the axillary artery.
proximal and distal innervation is the mechanism of
Whereas the proximal innervation is the mechanism
of sympathetic supply to the proximal third of the
arm, distal innervation through the sympathetic fibers
traveling with the somatic nerves of the brachial plexus
control the constrictor impulses to the resistance vessels in the extremity
Blockade of the brachial plexus, then, results
in
complete blockade of the vasoconstrictor fibers to the capacitance vessels (i.e., the veins), which allows blood to pool peripherally in the arm
The subclavian artery becomes the axillary artery
beneath
the clavicle at the lateral border of the first rib
The axillary artery lies central to the
three cords of the infraclavicular brachial plexus (medial, lateral,
and posterior). The cords are not truly medial, lateral, and
posterior with respect to their positions around the axillary
artery until they have passed beneath the pectoralis minor
muscle just medial to the medial border of the coracoid process.
Cords in relation to axillary artery
the posterior cord lies in between the lateral and medial cords. The lateral cord is the most superficially located cord and is typically located superior to the axillary artery. Just deep to the lateral cord is the posterior cord, which is typically located slightly cephalad and deep to the axillary artery. The medial
cord is typically located deep and slightly caudal to the
axillary artery.
the contents of the proximal axillary perivascular
space are enclosed by two muscles
the biceps brachii and coracobrachialis), and the humeral insertions (the conjoint tendon) of the latissimus dorsi and teres major muscles
contents of the proximal axillary perivascular space
two vessels (the axillary vein and artery) and three nerves (median, radial, and ulnar).
The axillary sheath
a collection of connective tissue surrounding the neurovascular structures,
is a continuation of the prevertebral fascia that separates the anterior and middle scalene muscles.
Within the neurovascular
space, the usual relationship of the structures
the axillary vein medial, the median nerve superior, the ulnar nerve anterior and inferior, and the radial nerve inferior and posterior to the axillary artery.
the axilla to be divided into 12 sectors of a clock face with the axillary artery at its epicenter
the nerve distribution around it
Typically, the median nerve is located superficial and lateral
to the axillary artery (between 10 and 11 o’clock), the ulnar nerve is located superficial and medial (between 1 and 2 o’clock), the radial nerve is located deep and medial (between 4 and 6 o’clock), and the musculocutaneous nerve is
located (between 8 and 10 o’clock) at an average distance of 1.03 cm lateral to the axillary artery
perform axillary brachial plexus block for
surgery of the arm at or below the elbow, including the
wrist and hand. The block is also useful for manipulating
fractures in adults and pediatric patients.
PATIENT AND ARM POSITION
FOR AXILLARY BLOCK
The patient lies supine with the arm abducted to approximately 90 degrees and externally rotated to permit the dorsum of the hand to lie flat on the gurney while supported on one or two pillows. The forearm is flexed approximately 90 degrees at the elbow and should be parallel to the long axis of the patient’s body.
Hyperabduction of the arm beyond 90 degrees is avoided
since it tends to
obliterate the axillary arterial pulse, a critical landmark in the successful performance of the technique. Reducing the degree of abduction sometimes makes palpation of the pulse easier as one proceeds more proximally.
Hyperabduction causes stretching,
torsion, and pinching of the subclavian–axillary vessels and
the brachial plexus at three distinct locations
where the subclavian vessels and plexus trunks pass between the clavicle and first rib, at the point where the cords and vessels pass
around the tendinous insertion of the pectoralis minor muscle to the coracoid process, and at the level where both vessels and plexus pass around the head of the hyperabducted
humerus.
The advantages cited with using a peripheral nerve stimulator include a
high success rate, the ability to perform the block on sedated or uncooperative patients, the avoidance of paresthesias and the potential for neurologic injury, and the avoidance of arterial puncture and subsequent vascular insufficiency or hematoma formation
Stimulation of the median nerve, typically located at the
superior border of the artery, results in
an EMR characterized
by pronation of the arm, wrist flexion, finger adduction,
flexion of the lateral two fingers, and thumb opposition
Stimulation of the main trunk of the radial nerve, typically
located inferior and posterior to the artery, results in
wrist
extension, supination of the arm, metacarpophalangeal extension,
and thumb abduction.
The ulnar nerve is typically situated
inferior and anterior to the artery, and its stimulation results in
deviation of the wrist in an ulnar or medial direction,
metacarpophalangeal flexion, and thumb adduction
triple-EMR (evoked motor response)
the distal radial EMR (deep to the axillary artery),
the median EMR (superficial to the axillary artery) (in close proximity to the ulnar nerve), followed by specifically targeting the musculocutaneous EMR (within
that separate anatomic location from the other three nerves)
provides the optimal balance between efficacy and efficiency.
The elicitation of paresthesias during axillary plexus block is probably of minimal consequence as long as LA is not injected
intrafascicularly
The optimal
US image of axillary nerve block will demonstrate
the round, pulsatile, and non compressible hypoechoic (will appear dark on the US
screen) axillary artery surrounded by the hyperechoic (will
appear brighter) median, ulnar, and radial nerves.
optimal imaging of the musculocutaneous nerve located either in the
coracobrachialis muscle or in fascial plane between the biceps and coracobrachialis muscles
The typical topographic appearance of the terminal nerves
in relation to the axillary artery is as follows
the median nerve is located superficial and lateral (between the
10 and 11 o’clock position);
the ulnar nerve is located superficial
and medial (between 1 and 3 o’clock position); the radial nerve is located deep to the ulnar nerve and axillary artery (between the 3 and 6 o’clock position) and often lies directly over the conjoint tendon, which appears as an obliquely oriented hyperechoic fascial plane located superficial to the teres major and triceps muscles.
the radial nerve is typically targeted initially by advancing the needle tip
deep to the axillary artery, just above the conjoint tendon-triceps muscle.
US location of the musculocutaneous nerve
Given the more
cephalad (lateral) location of the musculocutaneous nerve, the transducer may require a slight relocation more cephalad over the biceps muscle
One of the potential benefits of US-guided techniques
decrease in the minimum effective LA volume for axillary
brachial plexus block.
Bupivacaine vs. Ropivacaine
Plain bupivacaine 0.5% has been demonstrated to provide
prolonged anesthesia and analgesia versus plain ropivacaine
0.5% for axillary block
Clonidine as an adjuvant
prolonged the duration of postoperative analgesia, sensory block, and motor block.
Adverse Effects of Clonidine
clonidine also produces clinically significant
hypotension, orthostatic hypotension or fainting, bradycardia,
and sedation, which may be severe
a-2 agonist, dexmedetomidine
inhibit lipid peroxidation in the case of anticipated ischemia-reperfusion injury, such as would occur with tourniquet application in cases of upper extremity surgery. This is manifest as a reduction in plasma hypoxanthine
production is the ischemic time period and a reduction of plasma malondialdehyde production during
reperfusion period.
the most important
determinant of block efficacy.
drug mass (i.e., volume ∞concentration)
intercostobrachial nerve and the medial brachial cutaneous nerve
The intercostobrachial nerve supplies cutaneous analgesia
to the superior portion of the axilla, and often extends
distally to the anterior border of the axilla and to the anterior
shoulder.
intercostobrachial nerve block
once the injection of the appropriate volume of LA has been accomplished, the needle is withdrawn until it lies in the subcutaneous tissue directly over the artery, and its orientation is changed so that it runs from the biceps to the triceps. At this point, 3 to 5 ml of LA are deposited. This is to block the intercostobrachial nerve and the medial brachial cutaneous nerve, if it lies outside the sheath. This supplemental block is suited for those individuals who require a tourniquet placed on the upper arm.
indications for infraclavicular block (ICB) of the brachial
plexus
surgery of the elbow, forearm, wrist, or hand
For hand and wrist outpatient surgery, ICB compared to general anesthesia has been shown to provide
timeefficient
anesthesia, faster recovery, fewer adverse events,
better analgesia, and greater patient acceptance
The major benefit of this approach, when compared to brachial plexus blocks above the clavicle,
the unlikely risk of encroaching upon the pleural space or lung parenchyma and causing a pneumothorax, while maintaining the high success rate of blocking the axillary and musculocutaneous nerves prior to their departure from the sheath of
the brachial plexus
The other major advantages of the
ICB approach include
lower likelihood of tourniquet pain during surgery, and a more reliable blockade of the
musculocutaneous and axillary nerves when compared to a single-injection axillary block.
advantage for selecting ICB block, as compared with supraclavicular
techniques.
negligible risk of clinically relevant hemidiaphragmatic
paralysis from the paracoracoid approach
The ICB approach is ideally suited for
continuous catheter
insertion and maintenance, since the patient may move the head and arm without dislodging the catheter, which is well situated within the bulk of the pectoralis
muscles
The major theoretical disadvantage of ICB
increased potential for pain during the block performance since the pectoralis major and minor muscles must be traversed by the needle before reaching the cords of the brachial plexus.
a major landmark
for ICB
coracoid process of the scapula
In ICB the initial needle insertion point is typically
located
within 1 cm to the medial border of the coracoid process. In its final position, the needle tip should be situated at the level of the distal cords, ideally located within a central location (closest to the posterior cord, just posterior to the axillary artery) within the brachial plexus
A double-stimulation technique in ICB
first, stimulation of the musculocutaneous
nerve, and subsequent stimulation of either the radial, median, or ulnar nerve using a modified coracoid approach.
INFRACLAVICULAR APPROACH
OF BRACHIAL PLEXUS BLOCK
TECHNIQUE
the patient lies supine with the head in
a neutral position or turned slightly toward the contralateral
(nonblocked) side. The arm may be adducted, abducted,
or extended out away from the body, but it is typically abducted at 90 degrees as for axillary block. This
helps localize the axillary arterial pulse, a useful landmark for completing this block. Using US, it has been noted that abduction of the arm brings the brachial plexus much
closer to the skin and farther away from the pleura, but does not change the position of the axillary artery relative to the coracoid process or the pleura
Using the classically described paracoracoid PNS technique, the initial needle insertion point is
2 to 3 cm medial and 2 cm caudal to the midpoint of the coracoid process on the anterior chest wall.
ICB block brachial plexus at what level
The parasagittal plane of needle insertion and advancement lie laterally to the rib cage and lung, and intersect the plexus at the level of the distal cords.
For the US-guided ICB technique the US transducer
should be oriented
perpendicular to the clavicle just medial
to the coracoid process
in ICB The optimal
short-axis US image should demonstrate
the axillary artery and brachial plexus cords located immediately deep to the pectoralis minor muscle and its accompanying clavipectoral fascia. The brachial plexus cords should appear as hyperechoic polyfasicular (honeycomb appearance) structures arranged around
the centrally located anechoic, pulsatile axillary artery
in ICB topographic arrangement
the lateral cord is located cephalad (9 to
11 o’clock position) to the axillary artery, the posterior cord is located immediatley deep to the lateral cord and axillary artery (6 to 8 o’clock position), and the medial cord is located caudal (3 to 5 o’clock) to the axillary artery. the posterior cord is always
located in between the lateral and medial cords. The position
of the axillary vein is also variable, but is typically located superficial and caudal to the axillary artery.
ICB Needle insertion is typically
1 to 2 cm cephalad to the transducer, just below the clavicle and medial to the coracoid process.
function of continuous catheter techniques.
Prolonging the duration of perioperative anesthesia and
postoperative analgesia
when performing catheterUS-guided blocks, the use of agitated D5W
shown to be a valuable adjunct to enhance observation of the tip
COMPLICATIONS
Axillary block is the technique of brachial plexus block
most likely to be associated with
intravascular injection. This is because it is the only site where the major, large vein
lies within the sheath. Hematoma is certainly a possibility
with axillary block, but, fortunately the area of injection is
readily compressible. case of axillary artery dissection and subsequent
thrombotic obliteration following axillary block without arterial puncture. Vascular insufficiency is not an infrequent accompaniment of the transarterial technique, and results in severe blanching of the skin of the hand and wrist.
Hematoma formation
needs to be considered in any patient with
neurologic
impairment following axillary or infraclavicular brachial
blocks.
Pseudoaneurysm formation
also complicate
axillary block and may occur in the artery as well as in the axillary vein. The consequences of pseudoaneurysm formation include
pressure-induced neural ischemia
arterial vasospasm
This likely results from
the intra-arterial injection of epinephrine-containing solutions,
producing profound vasoconstriction of the axillary artery. The phenomenon reverses itself when the increase in blood flow from the sympathetic nervous system block produced
by the axillary block results in effective dilution and washout of the locally injected epinephrine
Neural injury
following axillary block is gratefully a rare
occurrence. needle trauma and LA neurotoxicity were the etiologies of most neurologic complications
Ischemia
may be a mechanism contributing to damage
that follows intrafascicular injection of LAs. transient elevation in endoneural
fluid pressure may exceed capillary perfusion pressure for
up to 15 min, interfering with the nerve’s endoneural
microcirculation. Elevated pressures may also alter the
permeability of the blood–nerve barrier within the endoneurium,
possibly contributing to axonal degeneration,
Schwann cell injury, and fibroblast proliferation
In any case of suspected neural injury following axillary or infraclavicular block the following steps (“minineurologic
examination”) should be undertaken immediately
the median nerve may be tested by using a pinprick over the
palmar surface of the distal phalanx of the index finger; the ulnar nerve may be tested in similar fashion by pinprick testing of the palmar surface of the distal phalanx of
the fifth finger; the radial nerve may be tested by asking
the patient to extend the distal phalanx of the thumb; the
musculocutaneous nerve function can be assessed by asking
the patient to flex the forearm; and the axillary nerve
may be assessed by abduction of the arm.
following a suspected nerve injury, It is important
to obtain
electromyographic studies as quickly as possible following a suspected nerve injury, for the purposes of
establishing a time frame of when the injury might have occurred. Electrodiagnostic studies should be obtained as
expeditiously as possible to rule out the likelihood of preexisting lesions playing an integral part in the etiology of these processes
Techniques of brachial plexus block below the clavicle offer many unique advantages versus the supraclavicular approaches.
They spare diaphragmatic function and are not
associated with the higher risk of pneumothorax encountered
above the clavicle, recurrent laryngeal nerve block, Horner’s syndrome, or shoulder weakness
