PERIPHERAL NERVE BLOCK

SOMATIC BLOCKADE OF THE UPPER EXTREMITY

• BRACHIAL PLEXUS BLOCK• SUPRACLAVICULAR (SUBCLAVIAN) BRACHIAL PLEXUS

BLOCK• INFRACLAVICULAR BRACHIAL PLEXUS BLOCK• AXILLARY BLOCK• INTERCOSTOBRACHIAL & MEDIAL BRACHIAL

CUTANEOUS NERVES• MUSCULOCUTANEOUS NERVE• RADIAL NERVE• MEDIAN NERVE• ULNAR NERVE• DIGITAL NERVE

AXILLARY BRACHIAL PLEXUS BLOCK

Overview• Indications: Forearm and

hand surgery • Landmarks: Axillary

artery pulse • Any of the following three

endpoints – Nerve stimulation: Hand

twitch at 0.2-0.4 mA current – Paresthesia: Hand – Perivascular: Arterial blood

aspiration (axillary artery) • Local anesthetic: 35-40

mL • Complexity level: Basic

General considerationsThe axillary brachial plexus block was first described by Halstead in New York City at St. Luke's-Roosevelt Hospital Center in 1884. The axillary brachial plexus block is a basic nerve block technique, and one of the most commonly practiced blocks by anesthesiologists in the United States. An axillary block is an excellent choice for forearm and hand surgery. However, it should be noted that because the musculocutaneous nerve leaves the brachial plexus sheath proximal to the site of injection, axillary brachial plexus block often results in incon-sistent coverage for tourniquet pain as well as anesthesia of the volar aspect of the skin below the elbow that extends to the thenar eminence.

Regional anesthesia anatomyThe brachial plexus supplies innervation of the upper limb. The plexus consists of nerves derived from the anterior rami of the lower four cervical and the first thoracic spinal nerves. The five roots (anterior rami) give rise to three trunks (superior, middle, and inferior) that emerge between the scalenus medius and scalenus anterior to lie on the floor of the posterior triangle of the neck. The roots of the plexus lie deep the prevertebral fascia. The trunks are covered by its lateral extension, the axillary sheath. Each trunk divides onto an anterior and a posterior division behind the clavicle, at the apex of the axilla. Within the axilla, the processes combine to produce the three cords, which are named the lateral, medial, and posterior, according to their relationships to the axillary artery. Each cord ends near the lower border of pectoralis minor by dividing into two terminal branches. Other branches of the plexus arise from the neck and axilla, directly from the roots, trunks, and cords. The anterior divisions form the lateral and medial cords, with branches that supply the flexor muscle of the arm, forearm, and hand, and the skin overlying the flexor compartments. The three posterior divisions unite to form the posterior cord. The cord branches supply the extensor musculature of the shoulder, arm, and forearm, and the skin of the posterior surface of the limb.

Musculocutaneous NerveThe musculocutaneous nerve is a terminal branch of the lateral cord. It pierces the coracobrachialis muscle and lies between biceps and brachialis, supplying both of these muscles. The nerve continues distally as the lateral cutaneous nerve of the forearm, which pierces the deep fascia between biceps and brachioradialis to lie superficially over the cubital fossa.

Median NerveThe median and ulnar nerves traverse the entire length of the arm, but neither gives any branches above the elbow joint. The median nerve derives its fibers from the lateral and medial cords. In the upper part of the arm, the nerve lies lateral to the brachial artery. However, at the midarm level, it crosses anterior to the vessels and finally lies medial to the brachial artery, a position in which it continuous its path through the cubital fossa. The median nerve enters the forearm from the cubital fossa between the two heads of the pronator teres. It crosses anterior to the ulnar artery and descends between the superficial and deep flexors. At the wrist, the median nerve is remarkably superficial, lying medial to the tendon of flexor carpi radialis and just deep to the palmaris longus tendon.

Ulnar NerveThe ulnar nerve is a terminal branch of the medial cord. Together with the medial cutaneous nerve of the forearm, the nerve initially lies medial to the brachial artery but leaves the artery at midarm through the intermuscular septum. The nerve enters the posterior compartment to lie between the septum and the medial head of triceps. The ulnar nerve passes behind the medial epicondyle and enters the forearm between the two heads of flexor carpi ulnaris. Lying on flexor digitorum profundus and covered by flexor carpi ulnaris, it traverses the medial side of the anterior compartment, accompanied in the lower part of the forearm by the ulnary artery. The ulnar nerve emerges near the wrist lateral to the flexor carpi ulnaris tendon and crosses super-ficial to the flexor retinaculum with the ulnar artery on its lateral side. The nerve terminates in the hand by dividing into superficial and deep branches. The ulnar nerve supplies the elbow joint and gives branches to the flexor carpi ulnaris and the medial part of flexor digitorum profundus. It also provides a palmar cutaneous nerve that supplies the skin on the medial aspect of the palm and dorsal cutaneous branches that innervate part of the medial part of the dorsum of the hand.

Radial Nerve

The radial nerve, a terminal branch of the posterior cord, leaves the axilla by passing below teres major and between the humerus and the long head of the triceps. The nerve passes between the medial and lateral heads of triceps in the posterior compartment. It then leaves the posterior compartment by piercing the lateral intermuscular septum to reach the lateral part of the cubital fossa in front of the elbow joint. In the arm, the radial nerve gives muscular branches to the medial and lateral heads of triceps and branchioradialis and extensor radialis longus. Cutaneous branches innervate the lateral aspect of the arm and the posterior aspect if the forearm. The branch to the long head of triceps usually arises in the axilla.

Distribution of anesthesia

An axillary brachial plexus block (including musculocutaneous nerve block) provides anesthesia to the to the arm, elbow, forearm, and hand. It should be noted that the unshaded areas are not covered by the axillary brachial plexus block.

Patient positioning• The patient is in the supine position with the

head facing away from the side to be blocked. The arm on the side of the block placement should be abducted and form a roughly 90o angle in the elbow joint.

TIPS: • Excessive abduction in the shoulder joint

should be avoided because it makes palpation of the axillary artery pulse difficult.

• Excessive abduction can also result in stretching and "fixing" of the brachial plexus. Such stretching of the brachial plexus components increases the vulnerability of the plexus during needle advancement. Stretching may increase the risk of nerve injury because the plexus components are fixed and more likely to be penetrated by the needle rather than "roll" away from the advancing needle.

EquipmentA standard regional anesthesia tray is prepared with the following equipment:

• Sterile towels and 4"x4" gauze packs

• 20-mL syringes with local anesthetic

• Sterile gloves, marking pen, and surface electrode

• 1½" 25-gauge needle for skin infiltration

• 3-5 cm long, short bevel, insulated stimulating needle

• A three-way stopcock • Peripheral nerve stimulator

LandmarksSurface landmarks• Surface landmarks for the axillary

brachial plexus block include: • Pulse of the axillary artery • Coracobrachialis muscle • Pectoralis major muscle TIPS: In some patients, palpation of the

axillary artery may prove difficult; a common scenario in young, athletic men. In this case, the approximate location of the brachial plexus can be estimated by percutaneous nerve stimulation. The nerve stimulator is set to deliver 4-5 mA and a blunt probe or an "alligator" clip is firmly applied over the skin in front of the palpating fingers until twitches of the brachial plexus are elicited.

CONT. LANDMARKSAnatomic landmarks • After a thorough skin preparation, the pulse of the

axillary artery is palpated high in the axilla. Once the pulse is felt, it should be straddled between the index and the middle finger and firmly pressed against the humerus to prevent "rolling" of the axillary artery during block performance. At this point, movement of the palpating hand and the patient's arm should be minimized because the axillary artery is highly movable in the adipose tissue of the axillary fossa.

TIPS: • When the location of the artery and the plexus is

not immediately apparent, asking the patient to adduct the arm against resistance during palpation of the artery tenses the pectoralis and coracobrachialis muscles.

• This maneuver is helpful to identify the groove between coracobrachialis and pectoralis muscle where the arterial pulse is easily detected.

• The position of the brachial plexus can be also estimated using percutaneous nerve stimulation with a current output of 4-5 mA. A blunt probe or an "alligator" clip is applied over the skin in front of the palpating fingers until twitches of the brachial plexus are elicited. At this point, the probe is substituted by a needle directed toward the estimated direction of the brachial plexus sheath.

Technique• After cleaning the skin with an antiseptic solution, local

anesthetic is infiltrated subcutaneously at the determined needle insertion site. The anesthesiologist should assume a sitting position by the patient's side. This avoids strain and hand movement during block performance and facilitates axillary block placement.

TIPS: • Local anesthetic is best infiltrated tangentially rather than at a

single insertion point. This both ensures a superficial injection and allows for needle repositioning during block performance if required.

• Hand position: The index and middle fingers of the palpating hand should be firmly pressed against the arm, straddling the pulse of the axillary artery at the midaxillary fossa level. This maneuver shortens the distance between the needle insertion site and the brachial plexus block by compressing the subcutaneous tissue. Also, it helps to stabilize the position of the artery and needle during performance of the block. This hand should not be moved during the entire block placement procedure to allow for precise redirection of the angle of the needle insertion when necessary

Needle advancement• A needle connected to the nerve stimulator is inserted just in

front of the palpating fingers and advanced at an angle 45o cephalad. The nerve stimulator should be initially set to deliver l mA current. The needle is advanced slowly until stimulation of the brachial plexus, arterial blood, or paresthesia is obtained. Typically, this occurs at a depth of 1-2 cm in most patients. Once the sought response is obtained, 35-40 mL of local anesthetic is injected slowly with intermittent aspiration to rule out an intravascular injection.

• TIP: It has been suggested that the axillary brachial plexus sheath contains septae preventing local anesthetic from reaching all neuronal components contained within the sheath. While the clinical significance of these septae remains controversial, it does make sense to inject local anesthetic in divided doses at two different locations within the sheath (e.g., behind in front of the artery).

Goal

We use a nerve stimulator technique and look for a single nerve response, (hand twitch at 0.2-0.4 mA current output). We then inject the entire volume of local anesthetic on obtaining such a response. Although multiple stimulation techniques (stimulating and injecting each major nerve of the brachial plexus separately) may increase the success rate, it also increases the complexity and time required to complete the block. However, when the axillary artery is punctured before the plexus is stimulated (rare), we do not continue searching for stimulation but resort to the transarterial technique and inject one third of the total volume of the local anesthetic posterior and one third anterior to the axillary artery.

Failure to obtain axillary brachial plexus stimulation on the first needle pass

When insertion of the needle does not result in nerve stimulations, the following maneuvers should be made:

• Keep the palpating hand in the same position and the skin between the fingers stretched.

• Withdraw the needle to the skin, redirect the needle to angles of 15o and 30o laterally and repeat the procedure.

• Withdraw the needle to the skin, redirect the needle to angles of 15o and 30o medially and repeat the procedure.

Musculocutaneous nerve block• The musculocutaneous nerve is not

consistently blocked with the axillary brachial plexus block, because this nerve leaves the brachial plexus sheath proximally. Due to the large area covered by this nerve and its importance in achieving complete anesthesia of the forearm and biceps (see description in this chapter), a block of the musculocutaneous nerve is often necessary for complete anesthesia. This is achieved with a separate injection by inserting the needle above the artery and toward the coracobrachial muscle. Nerve stimulation is used to produce twitches of the musculocutaneous nerve (biceps twitch). When twitches are observed 5 mL of local anesthetic is injected.

Troubleshooting• Response ObtainedInterpretationProblemActionLocal twitch of

the arm musclesDirect stimulation of the biceps or triceps musclesThe needle is inserted in direction that is too superior or too inferiorWithdraw the needle and redirect accordinglyThe needle contacts bone at 2-3 cm depth; no twitches are seenThe needle is stopped by the humerusThe brachial plexus was missedWithdraw the needle to the skin and reinsert at an angle 15o-30o superiorly or inferiorlyTwitches of the handStimulation of the medianus, radialis, or ulnar nervesCorrect needle positionAccept and inject local anesthetic.Arterial blood noticed in the tubingPuncture of the axillary artery Needle entered the lumen of the axillary arteryInject 2/3 of the local anesthetic posterior to the artery and 1/3 anterior to the arteryParesthesia- no motor responseContact of the needle with the brachial plexus branchesEquipment malfunction (stimulator, needle, electrode)Carefully assess the distribution of the paresthesia and if typical, inject local anesthetic

Choice of local anesthetic

• The axillary brachial plexus requires a relatively large volume of local anesthetic (35-40 ml) to achieve complete anesthesia. The choice of the type and concentration of local anesthetic should be based on whether the block is planned for surgical anesthesia or pain management. Due to the highly vascular area and potential for inadvertent intravascular injection, the local anesthetic solution should be injected slowly, with frequent aspiration.

TIPS: • Always assess the risk-benefit ratio of using large volumes and

concentrations of long acting local anesthetic for this block. • We never use bupivacaine for this block due to its high cardio-

toxicity profile and potential for inadvertent intravascular injection with axillary block technique.

• Smaller volumes and concentrations can be used successfully for analgesia (e.g, 15-20mL)

Block Dynamics and Perioperative Management

• The axillary brachial plexus block is associated with relatively minor patient discomfort. Intravenous midazolam 1-2 mg with alfentanil 250 to 500 µg at the time of the needle insertion should produce a comfortable and cooperative patient during nerve localization. The onset time for this block is rather long (15-25 minutes). The first sign of the blockade is the loss of the coordination of the arm and forearm muscles. This sign can be seen usually sooner than the onset of sensory or temperature change. When this sign is present within 1-2 minutes after injection, it has a very high positive predictive value for a pending successful brachial plexus blockade.

• FEMORAL NERVE BLOCK• OBTURATOR NERVE BLOCK• LATERAL FEMORAL CUTANEOUS

NERVE BLOCK• SCIATIC NERVE BLOCK• POPLITEAL BLOCK• ANKLE BLOCK• DIGITAL BLOCK OF THE FOOT

SOMATIC BLOCKADE OF THE LOWER EXTREMITY

• SUPERFICIAL CERVICAL PLEXUS BLOCK

• INTERCOSTAL BLOCK• THORACIC PARAVERTEBRAL BLOCK• INGUINAL NERVE BLOCK• PENILE BLOCK

SOMATIC BLOCKADE OF THE TRUNK

Superficial Cervical Plexus Block

Overview• Indications: Carotid endarterectomy, neck

surgery • Landmarks:

– Mastoid process – Sternocleidomastoid muscle; posterior border of the

clavicular head – Transverse process of C6

• Equipment: 1½" 25-gauge needle • Local Anesthetic: 15-20 mL • Complexity level: Basic

Regional anesthesia anatomyThe superficial cervical plexus supplies innervation to the skin of the anterolateral neck through anterior primary rami of C2 through C4. The individual nerves emerge as four distinct nerves from the posterior border of the sternocleidomastoid muscle. The lesser occipital nerve usually is a direct branch from the main stem of the second cervical nerve. The larger remaining part of this stem then unites with a part of the third cervical nerve to form a trunk that arises as the greater auricular and the transverse cervical nerves. Another part of the third cervical nerve runs downward to unite with a major part of the fourth to form a supraclavicular trunk, which then divides into the three groups of supraclavicular nerves.

Distribution of anesthesia

• The superficial cervical plexus innervates the skin of the anterolateral neck.

Patient positioning

• The patient is in the same position as in the deep cervical plexus block. The patient's head should be facing away from the side to be blocked.

Equipment

• A standard regional anesthesia tray is prepared with the following equipment:

• Sterile towels and 4"x4" gauze packs

• 20-mL syringe with local anesthetic

• Sterile gloves, marking pen, and surface electrode

• A 1½" 25-gauge needle for block infiltration

Landmarks

Surface landmarks • The following surface anatomy landmarks

are helpful for estimating the location of the posterior border of the sternocleidomastoid muscle and for estimating the site of needle injection:

• Mastoid process • Chassaignac's tubercle of C6 • The fingers of the palpating hand should be

stretched to outline the posterior border of the clavicular head of the sternocleidomas-toid muscle and to help visualize the line connecting the mastoid process with the C6 transverse process.

Anatomic landmarks• A line extending from the mastoid to C6 is

drawn. The site of needle insertion is marked at the midpoint of the line connecting the mastoid process with Chassaignac's tubercle of C6 transverse process. This is the location of the branches of the superficial cervical plexus as they emerge behind the posterior border of the sternocleidomastoid muscle.

Technique

• After skin cleansing with an antiseptic solution, a skin wheel is raised at the site of needle insertion using a 25-gauge needle. Next, using a "fan" technique with superior-inferior needle redirections, the local anesthetic is injected alongside the posterior border of the sternoclei-domastoid muscle 2-3 cm below and above the needle insertion site. This injection technique should be adequate to achieve blockade of all four major branches of the superficial cervical plexus.

Goal• The goal of the injection is to infiltrate the local

anesthetic subcutaneously and behind the sternocleido-mastoid muscle. Attention should be paid to avoid deep needle insertion (e.g., less than 1-2 cm).

TIPS:• The transverse process is never sought with the

superficial cervical plexus technique. • Paresthesia is occasionally elicited during

needle insertion. However, paresthesia is nonspecific and should not be routinely sought.

Choice of local anesthetic

• A superficial cervical plexus block requires 10-15 mL of local anesthetic (3-5 mL per each redirection/ injection). Most patients benefit from the use of a long-acting local anesthetic. Since motor block is not sought with this technique, some anesthesiologists suggest using a low-concentration of local anesthetic (e.g., 0.2-0.5% ropivacaine or 0.25% bupivacaine). Although a low concentration may suffice when the needle is ideally placed in the vicinity of the cervical plexus nerves, this is often not the case and the higher concentration results in both a higher success rate and a longer duration of blockade.

Block Dynamics and Perioperative Management

• This block is associated with minor patient discomfort. Small doses of midazolam 1-2 mg for sedation and alfentanil 250 to 500 µg for analgesia just before needle insertion should produce a comfortable and cooperative patient during nerve localization. Similarly to the deep cervical plexus blockade, the sensory coverage of the neck is complex and a degree of cross-coverage from the cervical plexus branches from the opposite side of the neck should be expected. The onset time for this block is 10-15 minutes and the first sign of the blockade is the decreased sensation in the area of the distribution of the respective components of the cervical plexus. Excessive sedation should be avoided before and during head and neck procedures because many procedures require a fully conscious, oriented, and cooperative patient during the entire surgical procedure. In addition, airway management, when it becomes necessary, may prove difficult because of the shared access to the head and neck with the surgeon.

TIPS: A subcutaneous midline injection of the local anesthetic extending from the thyroid cartilage distally to the suprasternal notch will block the branches crossing from the opposite side. This injection can be considered as a "field" block. It is very useful for preventing pain from surgical skin retractors on the medial aspect of the neck.

INTERCOSTAL BLOCK

INTRODUCTION• The intercostal nerves (ICNs) supply the major parts of the skin and

musculature of the chest and abdominal wall. The block of these nerves was first described by Braun in 1907, in the textbook Die Lokalanästesie.1 In the 1940’s, clinicians noticed that intercostal nerve blocks (ICNBs) could favorably effect a reduction in pulmonary complications and in narcotic requirements after upper abdominal surgery.1 In 1981, continuous ICNB was introduced to overcome the problems associated with repeated multiple injections.1 Today, ICNB is used in a great variety of acute and chronic pain conditions affecting the thorax and upper abdomen. Less commonly, it is also used for breast and minor chest wall surgery and, in combination with celiac plexus blockade, abdominal operations, usually with light sedation or general anesthesia. As with many other regional techniques, the advantages of ICNBs include superior analgesia, opioid-sparing, improved pulmonary mechanics, reduced central nervous system depression, and avoidance of urinary retention. It should be noted however, that supplemental systemic analgesia is also always needed. The disadvantages of the technique however, include the requirement for technical expertise, risks of pneumothorax, and local anesthetic toxicity with multiple levels of blockade.

INDICATIONS

• ICNB provides excellent analgesia for chest trauma such as rib fractures,7,8 and for after chest and upper abdominal surgery such as thoracotomy, thoracostomy, mastectomy, gastrostomy, and cholecystectomy.2 Respiratory parameters typically show impressive improvements upon removal of pain.7,8 Blockade of two dermatomes above and two below the level of surgical incision is required. ICNB does not block visceral abdominal pain, for which a celiac plexus block is required. It is inadequate for renal surgery as block from T5 to L3 are required. In itself, ICNB does not provide adequate intraoperative anesthesia, and supplemental analgesics and/or sedatives are usually required except for minor body surface surgery. Neurolytic ICNB may be used to manage chronic pain conditions such as post-mastectomy pain (T2) and post-thoracotomy pain.

Contraindications• When pneumothorax would be a disaster. ICNBs may help a

patient tethering on the brink of respiratory decompensation but if an unintended pneumothorax could have serious consequences, an alternative block should be considered unless a chest tube is in place.

• Hemostatic deficiencies. This contraindication is not as strong as in central neuraxial blocks but may become absolute if the degree of deficiencies is severe.

• Other contraindications typically associated with regional blocks. Local infection, lack of expertise and resuscitating equipments, and lack of any short-term plan to wean from the ventilator should discourage the use of this block.

FUNCTIONAL ANATOMY

• As thoracic nerves T1 to T12 emerge from their respective intervertebral foramena, they divide into (Figure 1):

• the paired gray and white anterior rami comunicans, which pass anteriorly to the sympathetic ganglion and chain;

• the posterior cutaneous ramus, supplying skin and muscle in the paravertebral region;

• the ventral ramus (ICN, the main focus of this chapter).

Figure 1. Clinical anatomy of an intercostal nerve with its surrounding structures.

• T1 and T2 send nerve fibers to the upper limbs and the upper thorax, T3-T6 supply the thorax, T7-T11 supply the lower thorax and abdomen, and T12 innervates the abdominal wall and the skin of the front part of the gluteal region, Figure 2. Carrying both sensory and motor fibers, the ICN pierces the posterior intercostal membrane about 3 cm (in adults) distal to the intervertebral foramen to enter the subcostal grove where it, for the most part, continues to run parallel to the rib, although branches may often be found anywhere between adjacent ribs. Its course within the thorax is sandwiched between the parietal pleura and innermost intercostals (alias intercostalis intimus) muscle (inwardly) and the external and internal intercostals muscles (outwardly) (Figures 3 and 4). Just anterior to the mid-axillary line, it gives off the lateral cutaneous branch. As the ICN approaches the midline, it turns anteriorly and pierces the overlying muscles and skin to terminate as the anterior cutaneous. There are notable variations. T1 has no anterior cutaneous branch, usually has no lateral cutaneous branch, and most of its fibers leave the intercostal space by crossing the neck of the first rib to join those from C8, while a smaller bundle continues on a genuine intercostal course to supply the muscles of the intercostal space. Some fibers of T2 and T3 give rise to the intercostobrachial nerve, which innervates the axilla and the skin of the medial aspect of the upper arm as far distal as the elbow. In addition, the ventral rami of T12 is similar to the other ICNs but is called a subcostal nerve because it is not in between two ribs.

Figure 2. Dermatomal distribution of the intercostal nerves.

Figure 3. Intercostal nerves (accompanies by intercostal artery and vein) shown in the intercostal sulcus as seen from within the open chest cavity in a cadaver. The red dye illustrates spread of solutions injected into the intercostal sulcus during intercostal block

Figure 4. Intercostal nerve: Course and division.

Lateral cutaneous branch• From their origins just anterior to the mid-axillary line, the lateral cutaneous branches of T2-T11

pierce the internal and external intercostals muscles obliquely before dividing into the anterior and posterior branches, Figure 4. These branches supply the muscles and skin of the lateral torso. The anterior branches supply of T7 to T11 supply the skin as far forward as the lateral edge of the rectus abdominis. The posterior branches of T7 to T11 supply the skin overlying the latissimus dorsi. The lateral cutaneous branch of T12 does not divide. Most of the ventral ramus of T12 joins that of L1 to form the iliohypogastric, ilio-inguinal and genitofemoral nerves; the rest pierces the transverse abdominal muscle to lie between it and the internal oblique muscle.

Anterior cutaneous branch• The anterior cutaneous branches of T2-T6 pierce the external intercostals and pectoralis major

muscles to enter the superficial fascia near the lateral border of the sternum to supply the skin of the anterior part of the thorax near the midline and slightly beyond, Figure 4. Smaller branches (T1-T6) exist to supply the intercostals muscles and parietal pleura and these branches may cross to adjoining intercostals spaces. The anterior cutaneous branches of T7-T12 pierce the posterior rectus sheath to supply motor nerves to the rectus muscle and sensory fibers to the skin of the anterior abdominal wall. Some final branches of T7-T12 continue anteriorly, and, together with L1, innervate the parietal peritoneum of the abdominal wall. Their anterior course continues and become superficial near the linea alba, to provide cutaneous innervation to the midline of the abdomen and a couple of cm beyond.

Mechanism of block and distribution of anesthesia

• ICNB blocks the ipsilateral sensory and motor fibers of the ICNs by a direct effect of the local anesthetic. Three mL of solution injected through a needle spreads some 4-6 cm easily along that single subcostal groove distally and proximally, Figure 3. If a catheter is inserted at the angle of the rib and directed medially 2-3 cm, the tip of the catheter will lie medial to the medial border of the intercostalis intimus muscle; 20 mL of solution can spread to the paravertebral space to contact 3-5 ICNs.

TECHNIQUES

• As with any regional block, there are some basic safety rules. The patient’s airway and breathing must first be assessed and monitored. An intravenous line should be established and resuscitation drugs should be readily available. Sedation and analgesia may be used in selected cases. Supplemental oxygen may be required. During the block, the clinician’s hand controlling the needle should be firmly in contact with the patient’s body. ICNB may be performed in an anesthetized patient, although spinal anesthesia has been reported in patients when ICNB was performed under general anesthesia,2 and there is a concern that if the patient is under positive pressure ventilation, the risk of pneumothorax may be increased. After the block, the patient should be monitored for potential complications. In the case of ICNB, they include pneumothorax, local anesthetic toxicity, hematoma, nerve damage, infection, and, rarely, spinal anesthesia.

• The ICN can be blocked anywhere proximal to the mid-axillary line, where the lateral cutaneous branch originates. In children, the block is commonly carried out at the posterior axillary line or, alternatively, at just lateral to the paraspinal muscles, at the angle of the rib. In adults, the most popular site for ICNB is at the angle of the rib (6-8 cm from the spinous processes, Figure 5). Blocking the ICN at this location is relatively easy, is unlikely to result in direct injection into the dural sheath, and ensures that the tissues innervated by the lateral cutaneous nerve are blocked. At the angle of the rib, the rib is relatively superficial and easy to palpate and the subcostal groove is the widest, theoretically reducing the probability of pleural puncture. Within this groove, the nerve is inferior to the posterior intercostal artery, which is inferior to the intercostal vein, Figure 6 (Mnemonics: VAN (vein/artery/nerve)). They are surrounded mainly by adipose tissue and are sandwiched in between the internal intercostals muscle and the interior intercostal (intercostalis intimus) muscle. The nerve often runs as three or four separate bundles, without an enclosing endoneural sheath, making it easily accessible to blockade. Blockade medial to the angle of the rib is not recommended because the nerve lies deep to the posterior intercostals membrane with very little tissue between it and the parietal pleura, while the overlying sacrospinalis muscle makes rib palpation difficult. Blockade distal to the anterior axillary line is more difficult because the nerve has left the subcostal groove and re-entered the intercostals space and lies in the substance of the internal intercostal muscle.

Figure 5. Palpation of the intercostal space and needle insertion to contact the inferior edge of the rib.

Figure 6: Intercostal block: Needle angle required to enter intercostal sulcus.

• ICNB can be performed with the patient in the prone, sitting, or lateral position (block side up), with due considerations given to age, mental, physical, and ventilatory statuses, and any other concomitant blocks contemplated. For the prone position, a pillow should be placed under the patient’s upper abdomen, and the arms are allowed to hang off the sides. The sitting patient should lean slightly forward holding a pillow and be supported. The arms should be forward. The position of the arm in either position is to pull the scapulae laterally and facilitate access to the posterior rib angles above T7 (Figure 5).

• Under aseptic condition, the block sites are identified. Rib counting, if required, can be achieved by starting from the 12th rib, or from the 7th rib, which is the lowest rib covered by the inferior tip of the scapula. The inferior edges of the ribs to be blocked are marked just lateral to the lateral border of the sacrospinalis (paraspinous) muscle group (usually 6-8 cm from the midline at the lower ribs and 4-7 cm from the midline at the upper ribs), corresponding to the angles of the ribs, Figure 5. Next, palpate the inferior borders of the ribs one needs to block, and mark them (Figure 7).

• The sites of skin entry are infiltrated with a small volume of lidocaine 1-2%. A site of entry is well-placed when a needle introduced through it at 20° cephalad (sagittal plane, Figure 7) just scrapes underneath the inferior border of the rib and reaches the subcostal groove. The skin is first drawn cephalad with the palpating hand by about one cm, and a 4-5-cm 22G to 24G (for single shot injection) short-bevel needle is introduced through the chosen site of entry at a 20° cephalad angle and with the bevel facing cephalad (Figure 7). The needle is advanced until it contacts the rib at a depth of less than 1 cm for most non-obese patients. A small amount of local anesthetic may be injected to anesthetize the periosteum. With the palpating hand holding the needle firmly and resting securely on the patient’s back, the injecting hand gently walks the needle caudally while the skin is allowed to move back over the rib (Figure 8). The needle is now advanced 3 mm, still maintaining the 20° tilt angle cephalad (even a slight caudad pointing angle by the needle greatly reduces the chance of success). A subtle ‘give’ or ‘pop’ of the fascia of the internal intercostal muscle may be felt, especially if a short-bevel needle is used. As the average distance from the posterior aspect of the rib to the pleura averages 8 mm, advancement of the needle much beyond 3 mm increases the risk of pneumothorax.3

Figure 7: Intercostal block: Points of needle insertion.

Figure 8: Intercostal block: Advancement of the needle as the needle walks off the inferior edge of the rib and enters intercostal sulcus.

• Paresthesia, while not actively sought, confirms needle placement. Radiologic guidance is advised for neurolytic blocks. At this point, upon negative aspiration for blood, 3-5 ml of local anesthetic is injected. For a single ICNB, it is desirable to block at least one ICN cephalad and one caudad as some degree of overlapping innervation from adjacent ICNs is common. To ensure that the tip of the needle remains in the optimal location, unaffected by hand and chest movement, some clinicians prefer to connect an extension tubing between the needle and the syringe and have an assistant perform the aspiration and injection.

• When repeated injections at multiple levels are desired, patient comfort, the increased risk of complications and convenience become important issues, and a continuous intercostal nerve block should be considered. The technique is the same as for a single injection except that a Tuohy 17-G or 18-G needle (in adults) is used to facilitate the placement of a catheter. The site of entry should be the intercostal space midway between the dermatomes to be blocked. By orientating the bevel of the Tuohy needle medially or laterally, the epidural catheter is directed medially or laterally, respectively. A catheter tip threaded medially by 3 cm would effect a paravertebral block; the local anesthetic injected can spread to the adjacent spaces involving 3-5 intercostal spaces in total if sufficient volume (e.g., 20 mL) is used. In contrast, solution injected via a laterally directed catheter tends to stay mainly in the same intercostal groove. A lesser degree of spread may be possible because the intercostalis intimus muscle is flimsy and local anesthetic can pass in between the separate fascicles of that muscle to reach the subpleural space, from where it can spread between ribs and pleura to reach adjacent ICNs.3 It is usually difficult to thread a catheter much beyond 3 cm. Ability to pass a catheter beyond several cm suggests that the catheter may be interpleural. It is also common for continuous intercostal block catheters to be placed under direct vision by surgeons at the end of a thoracotomy, before wound closure.4

• Blockade of T1-T7 is made more difficult because of the scapulae and the rhomboid muscles. Fortunately, few surgeries require blockade above T7. These authors prefer to perform a thoracic paravertebral block or an epidural blocks when high thoracic blockade is required.

• ICNB, single-shots or continuous, may actually result in injection of local anesthetic and/or catheter placement into the interpleural space or pulmonary parenchyma. Great ease of catheter insertion beyond 3 cm may suggest interpleural placement. While analgesia may be provided with interpleural analgesia, it will not be the case with intra-parenchymal injection.

EQUIPMENTNeedle:• Single-shot: 20-22-G short beveled 4-5-cm

needle (adults); • Catheter placement: 18-20-G Tuohy needle

(adults) • Syringe and needle for local infiltration• Syringe with extension tubing• Sterilizing and resuscitation equipment and

drugs; drapes; marking pen; pillow; portable fluoroscope (for neurolytic blocks).

CHOICE OF LOCAL ANESTHETIC

• The choice of local anesthetic for single shot ICNB include bupivacaine 0.25-0.5%, lidocaine 1-2% with epinephrine 1/200,000-1/400,000 and ropivacaine 0.5-0.75%. 3-5 mL of local anesthetic is injected at each level during a multiple injection ICNB technique. The duration of action is usually 12±6 h. Addition of epinephrine to bupivacaine or ropivacaine does not significantly prolong the duration of block, but may slow the systemic absorption and increase the maximum allowable dose with a single shot by 30%.2 Maximum bupivacaine dose is 2 (for plain solution)-3 (with epinephrine) mg/kg/injection (total at one time)5 and 7-10 mg/kg/day. Maximum lidocaine dose is up to 5 (for plain solution) and 7 (with epinephrine) mg/kg/single injection5 and 20 mg/kg/day. Volunteers have been found to tolerate 30% more ropivacaine than bupivacaine before neurologic symptoms develop.6 The maximum single injection dose for ropivacaine is 2.5 mg/kg (for plane solution) and 4 mg/kg (with epinephrine),5 and the daily dose should probably be <9-12 mg/kg/24 h. The maximum single injection of epinephrine in stable patients is 4 μg/kg. Depending on the volume of local anesthetic required, a 1/400,000 instead of 1/200,000 concentration of epinephrine may be chosen. Richly supplied areas favor rapid local anesthetic absorption, and the blood levels of local anesthetics after ICNB are higher than any other regional anesthetic procedure. As such, it is advisable to leave a safety margin between the doses given and the maximum recommended dosages, especially in young children, the elderly, debilitated, and those with underlying cardiac, hepatic, or renal impairment. For continuous infusion, patients can usually tolerate a gradual build-up of plasma local anesthetic level better than acute rises. An apparently safe regimen is a loading dose of 0.3 mL/kg followed by an infusion of 0.1 mL/kg/h of either bupivacaine 0.25% or lidocaine 1%.3

Pearls:• A relatively easy site for ICNB is the angle of the rib, about 7 cm lateral to midline in adults. • The ideal angle of entry into the subcostal groove is about 20° cephalad. • A continuous catheter may be better tolerated in cases that require repeated blocks at multiple levels. • ICNB provides excellent analgesia but is seldom adequate for intraoperative anesthesia. • Supplemental analgesia may be required in continuous ICNB especially if the area of pain is wide. • Epidural block should be considered as a better alternative to bilateral ICNBs because of the risk of bilateral

pneumothorax and the potential for local anesthetic toxicity due the increased amount of local anesthetic required.

• Absorption of local anesthetic from the intercostal space is rapid and toxicity is usually an important concern. • ICNB above T7 may be difficult because of the scapulae and an alternative technique such as paravertebral or

epidural block should be considered.

COMPLICATIONS• The foremost concern in a patient without an ipsilateral tube thoracostomy is pneumothorax, the rate of

occurrence of which, as detected by chest X-ray and not necessarily accompanied by signs and symptoms, is well below 1%. Tension pneumothorax and the need for tube thoracostomy are rare. The risks of pneumothorax and lung injury, however, are increased in patients who have had previous chest surgery. If an asymptomatic pneumothorax is detected, the best management is observation, reassurance, and, if necessary, supplemental oxygen.

• The peritoneum and abdominal viscera are at risk of penetration when lower ICNs are blocked and the incidence should not be greatly different from that of pneumothorax.

• Absorption of local anesthetic from the intercostal space is rapid. Peak arterial plasma concentration develops in <5-10 min, and peak venous plasma concentration peaks several min later. Because of this, toxicity is always a concern with multiple or continuous intercostal injections. Sometimes the dilemma comes when a frail old person has multiple fractured ribs. The concern over systemic anesthetic toxicity may at times necessitate the use of a different regional technique.

• Finally, as the dural sheath can extend up to 8 cm laterally, there is a rare chance of spinal anesthesia after an ICNB.

Pearls:• ICNB is indicated for management of acute and chronic pain involving the thorax and upper abdomen.• ICNB by itself is inadequate for most intraoperative anesthesia except for minor body surface surgery.• ICNB is contraindicated when pneumothorax would spell disaster, and in the presence of severe hemostatic

deficiencies, and when there are better alternatives.• In the presence of minor hemostatic abnormalities, ICNB may be an attractive alternative to neuraxial blocks.

Serious hemostatic deficiencies contraindicate all nerve blocks.• General anesthesia is not a contraindication to ICNB.

SUMMARY

• Intercostal nerve block is a very satisfying block for both the clinician and patient because it is technically easy to perform and effective in the controlling pain involving the thorax and upper abdomen. It avoids many of the problems associated with central neuraxial blocks. Although there is the risk of pneumothorax and local anesthetic toxicity they can be reduced with good technique and due consideration given to the maximum allowable drug dose and patients clinical condition. The proper use of this technique includes balancing its advantages and disadvantages against those of alternative techniques such as epidural and thoracic paravertebral block.

Thoracic Paravertebral Block

Overview

• Indications: Breast surgery, pain management after thoracic surgery or rib fractures

• Landmarks: Spinal process at the desired thoracic dermatomal levels

• Needle insertion: 2.5 cm lateral to midline

• Target goal: needle insertion 1 cm past the transverse process

• Local anesthetic: 3-5 mL per level

• Complexity level: Advanced

General considerations

• The thoracic paravertebral block is a technique of injecting local anesthetic in the vicinity of the thoracic spinal nerves emerging from the intervertebral foramen with the resultant ipsilateral somatic and sympathetic nerve blockade. The resultant anesthesia or analgesia is conceptually similar to a "unilateral" epidural anesthesia. Higher or lower levels can be chosen to accomplish a unilateral, band-like, segmental blockade at the desired levels without significant hemodynamic changes. This technique is one of the easiest and most time efficient to perform, but more challenging to teach because it requires stereotactic needle maneuvering. A certain "mechanical" mind or sense of geometry is necessary for mastering it. This block is performed in our practice most commonly for surgery in patients undergoing breast (mastectomy and cosmetic breast surgery) and thoracic surgery. A catheter can also be inserted for continuous infusion of local anesthetic, even in patients on anticoagulants.

Regional anesthesia anatomy

• The thoracic paravertebral space is a wedge-shaped area that lies on either side of the vertebral column. Its walls are formed by the parietal pleura anterolaterally, vertebral body, the intervertebral disk, and intervertebral foramen medially, and the superior costo-transverse process posteriorly. The spinal nerves in the paravertebral space are organized in small bundles submerged in the fat of the area. At this location, a thick fascial sheath does not envelop the spinal nerves. Therefore, they are relatively easily anesthetized by injection of local anesthetic. The thoracic paravertebral space is continuous, with the intercostal space laterally, epidural space medially, and the contralateral paravertebral space via the prevertebral fascia. The mechanism of action of a paravertebral blockade includes direct penetration of the local anesthetic into the spinal nerve, extension laterally along with the intercostal nerve, and medial extension through the intervertebral foramina.

Distribution of anesthesia

• Thoracic paravertebral blockade results in ipsilateral dermatomal anesthesia. The location of the resulting dermatomal distribution of anesthesia or analgesia is a function of the level blocked and the volume of local anesthetic injected.

Patient positioning

• The patient is positioned in the sitting or lateral decubitus position and supported by an attendant. The back should assume kyphosis, similar to a position required for neuraxial anesthesia. The patient's feet are rested on a stool to allow for greater patient comfort and a greater degree of kyphosis. This increases the distance between the adjacent transverse processes and facilitates advancement of the needle beyond the contact with the transverse process.

Equipment

A standard regional anesthesia tray is prepared with the following equipment:

• Sterile towels and 4"x4" gauze packs

• 20-mL syringes with local anesthetic

• Sterile gloves, marking pen, and surface electrode

• One 1½" 25-gauge needle for skin infiltration

• A 10-cm long, 22-gauge, Quincke or Tuohy tip spinal needle

Landmarks

• The following surface anatomy landmarks are used to identify spinal levels and estimate the position of the transverse processes:

• Spinous processes (midline) • Tips of scapulae (corresponds to T7) • Paramedial line 2.5 cm lateral to the

midline TIPS:• It should be noted that labeling the

position of each individual transverse process at the level to be blocked is, at best, a rough estimation.

• It is more practical to outline the midline instead and simply draw the line 2.5 cm lateral to it. All injections will be along this line. Once two first transverse processes are identified, the rest will follow the same cranial-caudal spacing.

Technique

Local anesthetic skin infiltration • After cleaning the skin with an

antiseptic solution, 6-8 mL of dilute local anesthetic is infiltrated subcutaneously alongside the line where the injections will be made. The injection should be carried out slowly to avoid pain on injection. New needle reinsertions should be made through already anesthetized skin.

TIPS:• Addition of a vasoconstrictor helps

prevent oozing at the site of injection. • When more than 5-6 levels are

blocked (e.g., bilateral blocks), the use of alkalinized chloroprocaine or lidocaine for skin infiltration is suggested to decrease the total dose of long-acting local anesthetic.

Needle insertion• The needle is inserted perpendicular to the skin,

while constantly paying attention to the depth of needle insertion and the medial-lateral needle orientation. The utmost care should be paid to avoid medial needle direction (risk of epidural or spinal injection). After the transverse process is contacted, the needle is withdrawn to the skin and redirected superior or inferior to walk off the transverse process. The ultimate goal is to insert the needle to a depth of 1cm past the trans-verse process. A certain "give" occasional can be felt as the needle passes through the costotransverse ligament, however, this is nonspecific and should not be relied on.

TIPS : The block procedure essentially consists of three maneuvers (click figure on right):

• Contact the transverse process of the individual vertebrae and note the depth at which the process was contacted (usually 2-4 cm), needle #1.

• Withdraw needle to the skin level and reinsert at a 10o caudal or cephalad needle angulation.

• Walk off the transverse process 1 cm deeper to the transverse process and inject 4-5 mL of local anesthetic, needle #2.

• The needle can be redirected to "walk off" the superior or inferior aspect of the transverse process (figure below). At levels of T7 and bellow, "walking off" is recommended to reduce the risk of intrapleural placement of the needle. Proper handling of the needle is important both for accuracy and safety. Once the transverse process is contacted, the needle should be regripped so that the gripping fingers allow 1 cm deeper insertion.

TIPS: • While some authors suggest using a loss of resistance technique to identify the paravertebral space, such a change of resistance is very

subtle and nonspecific at best. For this reason, we do not pay attention to the loss of resistance but carefully measure the skintransverse distance and simply advance the needle 1 cm past the process.

• Never redirect the needle medially because of the risk of intra-foraminal needle passage and a consequent spinal cord injury. • Use common sense in advancing the needle. The depth at which the transverse processes are contacted vary with a patient's body

habitus and the level at which the block is performed. The deepest levels are at the high thoracic (T1,2) and low lumbar levels (L4,5) where the transverse process is contacted at a depth of 6-8 cm in average sized patients. The shallowest depth is at the mid-thoracic levels (T5,10) where the transverse processes are contacted at 2-4 cm in an average sized patient.

• Never disconnect the needle from the tubing or syringe with local anesthetic in while the needle is inserted. Instead, use a stopcock to switch from syringe to syringe during injection.

Choice of local anesthetic

• It is almost always beneficial to achieve longer acting anesthesia/analgesia in thoracic paravertebral blockade by using longer acting local anesthetic. Unless lower lumbar levels (L2-5) are planned to be blocked, paravertebral blocks do not result in motor block of an extremity and do not impair patient's ability to ambulate or take care of themselves. In addition, relatively small volumes injected at several levels do not present a concern for local anesthetic toxicity

• TIP: In patients receiving multiple level blockade, consider using alkalinized 3-chloroprocaine for skin infiltration to decrease the total dose of the more toxic long-acting local anesthetic. Chloroprocaine is rapidly metabolized by plasma cholinesterase on its absorption.

Block Dynamics and Perioperative Management

• Placement of the paravertebral block is associated with moderate patient discomfort. Adequate sedation (midazolam 2-4 mg) is always necessary to facilitate placement of the block. We also routinely administer alfentanyl 250-750 µg just before beginning the block procedure. However, excessive sedation should be avoided because the positioning becomes difficult when patients cannot keep their balance in the sitting position. The blockade depends on anesthetic dispersion within the space to reach the individual roots at the level of the injection. The first sign of the blockade is the loss of pin-prick sensation at the dermatomal distribution of the root being blocked. The higher the concentration and volume of the local anesthetic used, the faster the onset can be expected.