BRACHIAL PLEXUS ANESTHESIA

The brachial plexus is responsible for the innervation of the entire upper extremity deriving its nerve roots from C5-T1. For shoulder surgery C4 will also have to be blocked as will T2 for upper arm surgery. Brachial plexus blocks became popular in the 1960's when Alon Winnie first advocated the use of singe injection techniques. Prior to this anesthesiologists performed brachial plexus blocks by attempting to elicit numerous paresthesias corresponding to the multiple branches of the brachial plexus injecting local anesthetic with each paresthesia. This undoubtedly can be unpleasant for the patient. After performing cadaveric studies Winnie determined that the brachial plexus was invested by a fibrous sheath which could contain the spread of local anesthetic to the brachial plexus if a large volume single injection technique was used. Winnie's single injection technique however did not always prove itself reliable clinically as evident by lack of or delayed onset of block in one or more nerve distributions. A set of elegant cadaveric and image-contrast studies performed by Rorie and Thompson in the 1980's demonstrated compartmentalization of the brachial plexus sheath. Anesthesiologists continually strive to develop a 100 % success rate of brachial plexus anesthesia by developing new approaches. When blockade is attempted but there is no clinical analgesia/anesthesia this generally implies that the injection was not made within the brachial plexus sheath; partial blockade generally suggests that the performing anesthesiologist is at the mercy of anatomic compartmentalization. Not uncommonly, if one has the luxury to wait 30-40 minutes local anesthetic will redistribute itself within the brachial plexus sheath by either diffusing through septa or spreading longitudinally up and down compartments to eventually reach nerves within an isolated compartment.

There are three methods of ensuring one has positioned a block needle within the brachial plexus sheath: feeling the characteristic "click" as the needle pops through the sheath, eliciting paresthesias or by nerve stimulation techniques utilizing insulated block needles and a nerve stimulator. There are advantages and disadvantages of each technique. One of the greatest concerns of anesthesiologists is that of nerve injury. Debate continues in the anesthesiology literature over the use of nerve blocks in heavily sedated or anesthetized patients. Although intuition suggests otherwise, to date there is no overwhelming scientific evidence to suggest that nerve blocks performed in patients who are incapacitated by heavy sedation or general anesthesia (and thus unable to communicate pain as a result of nerve trauma) as having any higher incidence of nerve injury. There is also no overwhelming scientific evidence to support one technique of locating the brachial plexus as being safer than the other.

Brachial plexus blocks are divided into those performed above and below the clavicle, and those performed in the arm. A discussion of some of the common techniques will follow as well as a description of the advantages and disadvantages of each technique. In each situation, the patient is placed supine with the arm resting comfortably by their side, except in the axillary block where the arm is abducted to 90 degrees. The skin is prepared with an antiseptic solution and sterile towels placed on the periphery of the field. One percent xylocaine is used to raise a skin wheal with a 27 gauge needle at the intended block site. All patients must have EKG, pulse oximetry and blood pressure monitoring. If sedation is being used, supplemental oxygen is placed via face mask or nasal prongs.

INTERSCALENE: The patient is positioned supine with their arm resting comfortably by their side and the head turned gently away from the side being blocked. The cricoid cartilage in palpated and a line drawn laterally delineating the level of the C6 vertebral body. Next, the posterior border of the sternocleidomastoid muscle is palpated. Rolling the index finger posteriorly from the sternocleidomastoid muscle the operator will then feel the muscle bellies of the anterior and middle scalene muscles. The interscalene block is performed by entering the groove between the anterior and middle scalene muscles keeping the needle perpendicular to all planes. Once the brachial plexus sheath has been entered, the syringe containing local anesthetic is aspirated for evidence of blood or cerebral spinal fluid. If aspiration is negative, local anesthetic is incrementally injected while continuously monitoring for evidence of intravascular injection.

+ The interscalene approach blocks the brachial plexus high at the level of the roots permitting surgery of the shoulder. For shoulder surgery, a subcutaneous wheal of local anesthetic is generally needed to anesthetize the accessory nerve which may provide some innervation of the shoulder

- Some patients may not permit a needle entry into their neck or move their neck during critical points while performing the block. This approach can be used for forearm and hand surgery but blockade of the inferior trunk (C7-T1) is sometimes inadequate necessitating ulnar nerve supplementation if surgery is going to be performed in this nerve distribution. Although complications are rare they may be severe. Due to the large number of blood vessels in the neck there is added potential for intra-arterial or intra-venous injection with all its consequences. Injection into dural cuffs or nerve roots may produce an excessively high epidural or spinal block with cardiorespiratory collapse. There are case reports of the block needle entering the inter-vertebral foramen with injection into the spinal cord and consequent permanent spinal cord injury. The phrenic nerve is involved in 100 % of interscalene blocks causing paralysis of the ipsilateral diaphragm. This is rarely significant in healthy patients. Patients with respiratory illnesses may become compromised. Pneumothorax is another potential respiratory complication. Interscalene blocks frequently involve the cervical sympathetic nerves causing a temporary ipsilateral Horner's syndrome which is usually of no medical consequence but may be disturbing to the patient. Hoarseness of the voice may be produced with an accompanying sensation of fullness in the throat from involvement of the recurrent laryngeal nerve. In this situation patients should be instructed not to eat or drink until resolution of the recurrent laryngeal block in order to decrease the risk of aspiration

SUPRACLAVICULAR: The brachial plexus is most compact where it crosses over the first rib and under the clavicle lying just above and posterior to the subclavian artery. The midpoint of the clavicle is marked. The lateral boarder of the sternocleidomastoid muscle is identified and the interscalene groove palpated by rolling the fingers back from the muscle border over the anterior scalene muscle. A mark is then made 1.5 to 2.0 cm posterior to the clavicle at its midpoint. This mark should be within the interscalene grove. Palpation of the subclavian artery may also be possible at this point in thin individuals. The needle is gently advanced in a caudal, posterior and medial fashion until within the brachial plexus sheath. At the point where the supraclavicular block is performed the first rib is running predominantly in an anterio-posterior orientation and is short, flat and broad thus acting as a barrier to penetration of the cupola of the lung.

+ Due to the compactness of the brachial plexus at this site the block is very rapid in onset and extends to all components of the brachial plexus with infrequent need for peripheral nerve supplementation.

- The supraclavicular block is one of the most difficult to master and then to teach because of difficulty with determination of landmarks and in description of needle direction. The incidence of pneumothorax is described as ranging between 0.5-6 percent depending on the skill and experience of the operator. It may not be a wise choice in obese individuals because of difficulty with location of landmarks or in tall, thin individuals who characteristically have high apical pleura. There is a 50-60 % incidence of phrenic nerve paralysis. Recurrent laryngeal and cervical sympathetic nerve block may also occur.

INFRACLAVICULAR: The infraclavicular approach to brachial plexus block begins by marking a point 2.5 cm below the midpoint of the clavicle. The subclavian artery can usually be palpated where it exits between the anterior and middle scalene muscles and the axillary artery palpated high in the axilla. The course of the subclavian artery is then visualized between its route from the base of the neck to the axilla and the block needle advanced in a posterior, inferior and 30 degree angle laterally aiming for the subclavian artery.

+ The infraclavicular block offers a non-mobile site in which to approach the brachial plexus which may be of particular advantage in those individuals who have difficulty remaining motionless. It also is a clean non-mobile site which is well suited to placing and anchoring continuous brachial plexus catheters.

- The infraclavicular approach is ideally suited for all surgery of the hand and forearm but does not extend high enough for surgery of the shoulder. The risk of pneumothorax is unreported although in this author's hands there has never been a recognized incident of such. The incidence of phrenic nerve block is unknown but believed to be zero.

AXILLARY: The axillary block is performed by placing the patient supine with the arm supinated and abducted 900 . The brachial artery is palpated and followed proximally to a point high in the axilla where is passes under the pectoralis minor muscle. The tips of the left index and middle fingers are used to stabilize the axillary artery against the humerus while the right hand is used to advance the block needle directly towards the artery. There are several types of short beveled or blunt tipped needles designed to accentuate the "pop" or "click" that is both heard and felt as the block needle pierces the brachial plexus sheath in the axilla. After passing through the characteristically fibrous brachial plexus sheath one can elect to use the "click" as confirmation of needle placement within the brachial plexus sheath or can elect to search for paresthesias or elicit nerve stimulation with a nerve stimulator.

The axillary approach lends itself well to a transarterial approach. In this technique, a 25 gauge needle is used to directly enter the brachial artery and is confirmed by aspirating bright red blood into the syringe. The needle is then further advanced until blood is no longer aspirated signifying passage of the needle through the posterior wall of the brachial artery. Local anesthetic is then deposited behind the brachial artery. The needle is then slowly withdrawn, once again aspirating blood into the syringe. When the needle is determined to have been withdrawn out of the anterior wall of the brachial artery another injection of the local anesthetic is made.

+ The axillary approach is very common and simple approach to use. It provides excellent anesthesia for surgery of the hand and forearm. Complications are rare and when they do occur they are generally attributable to intravascular injection, nerve injury and hematoma.

- Because of to compartmentalization of the brachial plexus sheath failed block of one or more of the peripheral nerves may occur at this level. The musculocutaneous nerve exits from the brachial plexus sheath high above the shoulder and thus is seldom blocked in the axillary approach. For surgery of the anteriolateral aspect of the forearm a separate injection into the belly of the coracobrachialis muscle is necessary to anesthetize the musculocutaneous nerve.

Several other approaches to brachial plexus block include the subclavian perivascular, "plumb-bob", coracoid and mid-humeral. They all have minor advantages and disadvantages but reflect anesthesiologists search for a fail-proof method of anesthetizing all branches of the brachial plexus. Different local anesthetics will provide varying lengths of surgical times and duration of postoperative analgesia. Surgical times are still limited by tourniquet pain; the mechanism of which is still not fully elucidated. Surgical times for brachial plexus blocks are within the range of 2 hours and may be shorter in the axillary approach as the upper arm is not extensively anesthetized. Chloroprocaine will produce approximately one hour of surgical anesthesia, lidocaine and mepivacaine 4-6 hours and bupivacaine 12-18 hours. Patients should be forewarned of the surgical discomfort that may occur with recession of the block. Some patients with prolonged anesthesia from bupivacaine will awaken later at night fearing a surgical catastrophe is occurring with the onset of discomfort from a receding block. Patients should be encouraged to begin oral analgesics with the onset of block recession.

CONTINUOUS BRACHIAL PLEXUS ANESTHESIA: Continuous brachial plexus techniques have several useful applications. They can provide for prolonged post-operative analgesia in patients undergoing painful procedures or who suffer from chronic pain syndromes. They are also useful in patients who are tolerant of opioids or suffer intolerable side effects from opioids or have medical conditions that preclude the use of opioids, i.e. sleep apnea, severe pulmonary disease, previous narcotic addiction. Another very useful role of continuous brachial plexus catheters is in re-implant and free-flap graft surgery. Continuous brachial plexus block interrupts sympathetic nerve function producing the vasodilatation that is necessary for implant and free-flap survival. Most continuous brachial plexus blocks will employ a catheter through needle insertion technique. Once the catheter is positioned correctly, it can be employed to establish surgical anesthesia or be combined with general anesthesia. Post-operative management is best managed by a dedicated anesthesiology based pain management service that will generally infuse dilute solutions of local anesthetics.

PERIPHERAL NERVE BLOCKS: Peripheral nerve blocks are useful when there is an anticipated limited surgical field, blocks of the brachial plexus are contraindicated or technically challenging, bilateral surgical procedures of the upper extremity are contemplated or for supplementing inadequate brachial plexus blocks. Peripheral nerve blocks of the upper extremity can be performed at the elbow or wrist. Innervation of the forearm arises from cutaneous nerves in the upper arm and will not be anesthetized by blocks at the elbow. Thus peripheral nerves blocks at the elbow or wrist are useful only for procedures of the wrist and hand. Peripheral nerve blocks will not provide anesthesia for tourniquet discomfort and thus will generally limit surgical time to less than one hour.

BLOCKS AT THE ELBOW: The radial nerve can be blocked at two sites at the elbow. The first is at a point 4 cm proximal to the lateral epicondyle where the nerve wraps laterally around the humerus on its course from a posterior position along the humeral shaft to its anterior destination at the elbow. A 25 gauge needle is used to enter the skin 4 cm proximal to the lateral epicondyle and advanced until the humerous is contacted. The needle is then withdrawn 5 mm and a field block fanning both cephalad and caudad is performed using 5 ml of local anesthetic. In the crease of the elbow, the radial nerve lies lateral and deep to the biceps tendon and can be blocked by passing a 25 gauge needle through the elbow crease lateral to the biceps tendon and injecting 5 ml of local anesthetic at a depth of approximately 2-3 cm. At the elbow the median nerve lies medial and superficial to the brachial artery. A study has demonstrated that 50 % of skin infiltrations for brachial artery arterial line insertion at the level of the elbow produce block of the median nerve. The brachial artery is palpated with the index finger of the left hand and a 25 gauge needle is inserted medially to the brachial arterial pulse taking precautions not to enter the artery. After negative aspiration 5 ml of local anesthetic is injected. The ulnar nerve passes through the ulnar groove on the posterio-medial aspect of the distal humerus and is easily blocked in this location.

BLOCKS AT THE WRIST: At the level of the wrist the radial nerve exists as the superficial radial nerve, a pure sensory branch innervating the dorsal surface of the hand, first three fingers and radial half of the fourth finger. Block of this nerve at the wrist is a field block fanning around the radial border of the wrist two cm proximal to the tip of the radial styloid. The median nerve is blocks by inserting a needle into the volar crease of the wrist at the ulnar boarder of the palmaris longus tendon. The needle is advanced distally deep into the hand towards the carpal tunnel. Firm injection of 3-5 ml of local anesthetic may help displace the median nerve from the path of the advancing needle lowering the risk of nerve injury. The ulnar nerve can be blocked by inserting a needle just radial to the flexor carpi ulnaris(FCU) tendon or can be injected transversely by placing the needle underneath the FCU tendon. The ulnar artery is radial to the nerve and if blood is aspirated form the needle it is necessary to replace the needle slightly to the ulnar side of the ulnar artery.

INTRAVENOUS REGIONAL ANESTHESIA - THE BIER BLOCK: Intravenous regional anesthesia was first performed by the German surgeon August Bier. This technique is very simple to perform with the major technical skill being placement of an intravenous cannula. A detailed knowledge of the anatomy of the upper extremity is not necessary, however meticulous attention to detail must be provided both during initiation of and maintenance of block, for inadvertent loss of local anesthetic into the central circulation may produce life threatening sequelae. The person performing the anesthetic block should dedicate his full attention to the anesthesia and should not himself perform the surgery. An intravenous cannula is first placed in an extremity not intended for surgery. This intravenous line may be used for delivering medications for sedation or during a need for resuscitation. A 22 gauge intravenous cannula is inserted into a vein on the surgical extremity and then secured with minimal amount of adhesive tape. One layer of soft material i.e. Webril is wrapped around the intended tourniquet site in order to prevent petechiae or other superficial skin damage from occurring. A single or double tourniquet is securely placed on the upper arm and inflated and deflated once to test for functioning of all components. After the tourniquet has been tested, the arm is elevated and a 3-5 inch Esmarch bandage is used to exsanguinate all blood from the arm. The tourniquet is then inflated and the Esmarch bandage removed. At this point the extremity should be blanched and without a pulse. Failure of either of these to occur should alert the anesthesiologist to possible technical malfunctioning of the tourniquet. Local anesthetic is then injected and the i.v.cannula removed holding firm pressure on the i.v. site for 2 minutes.

Several points warrant further consideration: The mechanism of action of Bier blocks are not fully agreed upon but believed to be a combination of retrograde flow of local anesthetic through the vasa venosum to large peripheral nerves and diffusion of local anesthetic through venous channels to peripheral nerve endings. Equipment: Tourniquets should be of the pneumatic orthopaedic type rather than the conventional sphygmomanomter type with accurate pressure gauges that are routinely maintained. Tourniquets must have a secure method of fastening rather than relying on a Velcro-type of adhesive which may slip. Tourniquet pressure: Single tourniquets will usually satisfactorily occlude arterial blood flow if inflated to a pressure 100 mm Hg above systolic pressure. Double tourniquets, believed by some to be safer, must be inflated to a level between 150-200 mm Hg above systolic pressure to adequately occlude arterial blood flow. Failure to satisfactorily occlude arterial blood flow will produce bleeding and loss of local anesthetic at the surgical site resulting in a painful bloody surgical field; a disaster for the surgeon and patient. Intravenous cannula: A small vein in the back of the hand will suffice as an i.v. site. The cannula is capped with a Heplock type of apparatus. Care must be taken not to dislodge the cannula during placement of the Esmarch bandage. Some surgeons prefer to prep around the Heplock and remove it at time of surgical incision. Tourniquet deflation: Upper arm tourniquets should be kept inflated for 30 minutes. After this time enough local anesthetic will have bound to tissues prevent a rapid rise in plasma local anesthetic level after tourniquet release. After the tourniquet is initially deflated it should be re-inflated within seconds to provide a test of "tolerability" of the anesthetic load into the central nervous system. It is recommended that this maneuver be repeated 3 times producing a gradual release of the local anesthetic back into the central circulation. Local anesthetic: Fifty milliliters of procaine 0.5%, lidocaine 0.5%, mepivacaine 0.5% or chloroprocaine 0.6% have all been used with good success. Bupivacaine must not be used due to its cardiac toxicity. Tourniquet pain: Most patients will notice tourniquet tightness at 30 minutes and complain of marked pain somewhere between 1-1.5 hours. Double tourniquets can be used alternating inflation and deflation of proximal and distal cuffs. Extreme caution must be taken not to deflate one cuff prior to inflating the second cuff. Contraindications: Contraindications include infection in the involved extremity, allergy to local anesthetic, situations in which local anesthetics may affect pre-existing cardiac conditions, i.e. untreated heart block and in those situations where the use of a tourniquet is contraindicated, i.e. sickle cell disease.

+ Bier blocks are safe, reliable(96-100% reported success rates), easily to learn, acceptable to patients, produce good muscle relation for fracture reductions and have rapid recovery of function.

- Painful conditions of the extremity or external fracture fixators may preclude exsanguination of the extremity. Tourniquet pain limits the duration of patient tolerance. There is no provision of postoperative analgesia.

CONTINUOUS BIER BLOCK: An indwelling intravenous catheter is placed in an antecubital vein. Anesthesia and surgery proceed as usual after establishment of the Bier block. At the point where the patient can no longer tolerate the tourniquet the surgeon prepares for tourniquet deflation. The tourniquet is then deflated for 10 minutes. The surgeon then re-exsanguinates the extremity with a sterile Esmach bandage and the anesthesiologist injects 1/3-1/2 the initial volume of local anesthetic into the i.v. cannula. This maneuver can be repeated several times producing anesthesia for up to 6-8 hours.

FOREARM BIER BLOCK: For short surgical procedures on the hand a single forearm tourniquet can be placed on the forearm with 20-30 ml of local anesthetic used to produce anesthesia. Surgical anesthesia usually has an onset of 10-15 minutes and thus the tourniquet can be immediately released at the end of surgery with little fear of a toxic reaction. One should always perform a test deflation with immediate re-inflation within a few seconds. Care should also be taken in forearm tourniquets not to place the tourniquet to far proximally over riding the humeral epicondyles. Poor arterial stasis will result in this situation.