The infraclavicular block is a blockade of the brachial plexus below the level of the clavicle and in the proximity of the coracoid process. This is an intermediate nerve block technique. Experience with basic brachial plexus techniques and nerve stimulation is necessary for its efficient implementation. This block is uniquely well-suited for hand, wrist, elbow, and distal arm surgery. It also provides excellent analgesia for an arm tourniquet. As opposed to a supraclavicular block, an infraclavicular block is not a good choice for shoulder surgery.
The boundaries of the infraclavicular fossa are the pectoralis minor and major muscles anteriorly, ribs medially, clavicle and the coracoid process superiorly, and humerus laterally. At this location, the brachial plexus is composed of cords. The sheath surrounding the plexus is delicate. It contains the subclavian/axillary artery and vein. Axillary and musculocutanous nerves leave the sheath at or before the coracoid process in 50% of patients. Consequently, the deltoid and biceps twitches should not be accepted as reliable signs of brachial plexus identification.
Anatomic structures of importance.
Pectoralis muscle (shown cut to expose brachial plexus)
A typical distribution of anesthesia after an infraclavicular brachial plexus block includes the hand, wrist, forearm, elbow, and distal arm. The skin of the axilla and proximal medial arm (unshaded areas) is not anesthetized (intercosobrachial and medium cutaneous brachii nerves).
The patient is in the supine position with the head facing away from the side to be blocked. The anesthesiologist also stands opposite to the side to be blocked to assume an ergonomic position during the block performance. It is best to keep the arm abducted and flexed in the elbow to keep the relationship of the landmarks to the brachial plexus constant. When a certain level of comfort with the technique is reached, the arm can be in any position during block performance. Attention should be paid when the arm is supported at the wrist to allow clear unobstructed detection of the twitches of the hand.
The following surface anatomy landmarks are useful in identifying the estimated site for an infraclavicular block:
Medial end of the clavicle
Head of the humerus
Landmarks for the infraclavicular block include:
Medial clavicular head
Midpoint of line connecting 1 and 2 and 3cm caudal
The needle insertion site is marked approximately 3cm caudal to the midpoint of the line connecting points 1 and 2.
An x-ray demonstrating the relevant anatomy:
TIP: Palpation of the bony prominence just medial to the shoulder, while the arm is elevated and lowered, identifies the coracoid process. As the arm is lowered, the coracoid process meets the fingers of the palpating hand. This maneuver should be used to identify the coracoid process in each patient planned for an infraclavicular block.
The needle insertion site is infiltrated with local anesthetic using a 25-gauge needle.
TIP: Local anesthetic should also be infiltrated a bit deeper into the pectoralis muscle to decrease the discomfort during needle insertion as well as soreness after the completion of the block procedure.
A 10-cm long, 22-gauge insulated needle, attached to a nerve stimulator, is inserted at a 45-degree angle to the skin and advanced parallel to the line connecting the medial clavicular head with the coracoid process. The nerve stimulator is initially set to deliver 1.5 mA. A local twitch of the pectoralis muscle is typically elicited as the needle is advanced beyond the subcutanous tissue. Once the pectoralis twitches disappear, the needle advancement should be slow and methodical while looking for the twitch of the brachial plexus.
When the pectoralis twitch is absent despite appropriately deep needle insertion, the landmarks should be checked as the needle is most likely inserted too cranially (underneath the clavicle).
The bevel of the needle should be facing down to facilitate nerve stimulation and reduce the risk of vascular puncture (subclavian or axillary artery and vein).
Brachial plexus stimulation is typically obtained at a depth of 5 to 8 cm.
The goal is to achieve a hand twitch (preferably medianus) using a current of 0.2-0.3mA.
Twitches from the biceps or deltoid muscles should not be accepted, since the musculocutaneous and axillary nerve, respectively, may depart the brachial sheath before the caracoid process.
Hand stabilization and precision is crucial with this block as the sheath of the brachial plexus is very thin at this location and small movements of the needle may result in injection of local anesthetic outside the sheath. This in turn, results in a weak block with a slow onset.
A twitch of the pectoralis muscle is observed first and indicates a too shallow placement of the needle. As contractions of the pectoralis muscle cease, the needle is slowly advanced until the twitches of the brachial plexus are elicited. This usually occurs at a depth of 5-8 cm.
After the twitches of the pectoralis muscle cease, the stimulating current is lowered to below 1.0 mA to decrease patient discomfort. The needle is then slowly advanced or withdrawn until hand twitches are obtained at 0.2 - 0.3 mA.
The success rate with this block decreases when local anesthetic is injected after obtaining stimulation with a current intensity above 0.3mA.
In the absence of the medianus response, stimulation of the radialis or ulnar nerve can also be accepted, as long as the twitch of the hand is clearly visible.
The twitch of the biceps (musculocutaneous nerve) or deltoid (axillary nerve) muscles should not be accepted as these nerves often leave the brachial plexus sheath proximal to the coracoid process.
Failure to obtain nerve stimulation on the first needle pass
When insertion of the needle does not result in brachial plexus stimulation, the following maneuvers should be undertaken:
Keep the palpating hand in the same position, with the palpating finger firmly seated in the pectoralis and the skin between the fingers stretched.
Withdraw the needle to the skin, redirect 10o cephalad, and repeat the procedure.
Withdraw the needle from the skin, redirect 10o caudal, and repeat the procedure
When these maneuvers fail to result in motor response, withdraw the needle and assess the landmarks.
Check that the nerve stimulator is properly connected and delivering the set stimulus.
Consider inserting the needle 2-cm laterally and repeating the above steps.
Interpreting responses to nerve stimulation
Some common responses to nerve stimulation and the course of action to obtain the proper response.
Pectoralis muscle - direct muscle stimulation
Too shallow a placement of the needle
Continue advancing the needle
Too deep a placement of the needle
Withdraw the needle to skin level and reinsert in another direction (superior/inferior)
Needle placed too inferiorly
Withdraw the needle to skin level and reinsert with a superior orientation
Needle placed too superiorly
Withdraw the needle to skin level and reinsert with a light caudal orientation
The infraclavicular brachial plexus requires a relatively large volume of local anesthetic to achieve anesthesia of the entire plexus. 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 high vascular content of the area and potential for inadvertent intravascular injection, the local anesthetic solution should be injected slowly with frequent aspiration.
3% 2-chloroprocaine (+HCO3; + epi)
1.5% Mepivacaine (+HCO3; + epi)
2% lidocaine (+ HCO3 + epi)
TIP: Always assess the risk-benefit ratio of using large volumes and concentrations of long-acting local anesthetic for a lumbar plexus block.
Adequate sedation and analgesia are crucially important for this block to ensure patient comfort and to facilitate interpretation of responses to nerve stimulation. For instance, midazolam 2-6mg IV can be used to achieve sedation. A short-acting narcotic (e.g., alfentantil 250-750 µg) is added just before needle insertion. A typical onset time for this block is 5-15 minutes, depending on the local anesthetic chosen. Waiting beyond 20 minutes will not result in further enhancement of the blockade. The first sign of the impending successful blockade is loss of muscle coordina-tion within minutes after the injection. This loss can be tested easily by asking the patient to touch his nose, while paying attention that the patient does not miss the nose and injure his/her eye. The loss of motor coordination typically occurs before sensory blockade can be documented. In case of inadequate skin anesthesia despite the apparent timely onset of the blockade, local infiltration at the site of the incision by the surgeon is often all that is needed to allow the surgery to proceed. Before and after the surgery, both the patient and the surgeons should be informed about the expected duration of the blockade.
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