Continuous Infraclavicular Brachial Plexus Block

A continuous infraclavicular block is an advanced regional anesthesia technique and considerable experience with the single-shot technique is necessary for its safe and successful implementation. The use of a catheter significantly increases the utility of infraclavicular block. The infraclavicular technique is especially suitable for insertion of catheters because the technique and course of the catheter are straightforward. The brachial plexus is encountered at a relatively deep location, which decreases the chance of inadvertent catheter dislodgement. Additionally, the catheter insertion site is easily approachable for maintenance and inspection. Typically, the initial dose of local anesthetic is injected through the needle, followed by infusion of a more dilute local anesthetic at a desired rate. This technique may be utilized for prolonged surgery on the hand, wrist, elbow, or distal arm and surgery at the same anatomic locations requiring pro-longed postoperative pain management or sympathetic block.

The landmarks are the same as for the single-shot technique:

1. Medial clavicular head
2. Coracoid process
3. Midpoint of line connecting 1 and 2

The point of needle insertion is labeled 3 cm caudal to the midpoint between the medial clavicular head and the coracoid process.

TIP: Attention should be paid to avoid a too medial insertion of the needle as well as a too steep angle of the needle, which carries a risk of pneumothorax.

The subcutanoues tissue at the projected site of needle insertion is anesthetized with local anethetic. The block needle is then attached to the nerve stimulator (1.5 mA, 2 Hz, 100 µsec) and to a syringe with local anethetic. The fingers of the left hand should be firmly positioned on the pectoralis muscle and the needle is inserted at a 45 degree angle to the horizontal plane and approximately parallel to the medial clavicular head-coracoid process line. The needle bevel should be facing up. As the needle is advanced beyond the subcutaneous tissue, direct stimulation of the pectoralis muscle is obtained as the needle enters the body of the muscle. Stimulation of the brachial plexus is encountered soon after the pectoralis twitches cease. The sought response is that of the medianus nerve, indicated by rhythmic flexion of the wrist and fingers.

Once the medianus response is obtained at a 0.5 mA current level or less, the initial dose of local anesthetic is injected (30-45 mL). The catheter then is inserted while making sure that the needle remains firmly seated in the position in which the stimulation of brachial plexus was obtained. The catheter tip should be advanced some 5 cm beyond the needle tip. The needle is then carefully withdrawn while simultaneously advancing the catheter to prevent its dislodgment. The most important aspect of this technique is stabilization of the needle for catheter insertion after the brachial plexus is localized. In patients in whom the needle encounters the brachial plexus at very shallow location, sometimes it best to have an assistant advance the catheter to assure that the needle does not move out of its original position.

TIPS: This block should be avoided in patients with abnormal coagulation because the combination of the large needle diameter and inability to apply pressure in case of accidental puncture of the infraclavicular vessels (subclavian or axillary artery and vein) carries a risk of hematoma. The stimulation characteristics of the current, Tuohy-style needles appear to be somewhat different from that of the single-shot needles. This likely is the effect of the larger needle diameter and the coating of the needle tip. A slight needle rotation or angle change can make a significant difference in the ability to stimulate. Slight caudal orientation of the needle may be required to facilitate the catheter insertion. Some needles currently on the market have particularly blunt tips and tend to get hung up on the skin advancement. For this reason, sometimes it is best to create a small skin "nick" with a scalpel or side of a sharp tipped, 18-gauge needle before attempting to insert such a needle through the skin.

The catheter is checked for inadvertent intravascular placement and secured to the chest. A number of techniques to secure the catheter to the skin have been proposed. We find that a benzoin prep followed by application of a clear dressing is the simplest and the most efficacious. The infusion port should be clearly marked as: "continuous infraclavicular block".

Management of a continuous infusion catheter

The catheter is activated by injecting a bolus of local anesthetic (10-15 mL) followed by an infusion at 8 mL/hr. A PCA (patient-controlled analgesia) dose of 3-5 mL every 30 minutes can be added for breakthrough pain, in which case the basal infusion should be decreased to 5 ml/min. For continuous infusion, we typically use 0.2% ropivacaine.

Patients should be seen and instructed on the use of PCA at least twice a day. During each visit, the insertion site should be checked for erythema and swelling. The extent of motor and sensory blockade should be documented. The infusion and PCA dose are adjusted accordingly. When the patient complains of breakthrough pain, the extent of blockade should be checked first. A bolus of dilute local anesthetic (e.g., 10-15 mL of 0.5% ropivacaine) should be injected to reactivate the catheter. Increasing the infusion alone will never result in improvement of analgesia. When the bolus failes to result in blockade after 30 minutes, the catheter should be labeled as migrated and should be removed. Every patient receiving a continuous nerve block infusion should be prescribed an immediately available alternative pain management protocol because incomplete analgesia and catheter dislodgment can occur. For inpatients, this is best done using a back-up IV PCA.

TIPS: Breakthrough pain in patients on continuous infusion is always managed by administering a bolus of local anesthetic. Increasing the rate of infusion alone is never adequate. With patients on the ward, a higher concentration of a shorter acting and epinephrine-containing local anesthetic (e.g., 1% mepivacaine or lidocaine with 1:300,000 epinephrine) is useful and safe to both manage the pain and test the position of the catheter.

Disposition of radio opaque dye in the brachial plexus sheath after injection of 2ml through the infraclavicular catheter

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 0.3 mA.
• 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:

1. Keep the palpating hand in the same position, with the palpating finger firmly seated in the pectoralis and the skin between the fingers stretched.
2. Withdraw the needle to the skin, redirect 10º cephalad, and repeat the procedure.
3. Withdraw the needle from the skin, redirect 10º caudal, and repeat the procedure.

TIPS:

• 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

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.

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, a midazolam 2-6 mg IV can be used to achieve sedation. A short-acting narcotic (e.g., alfentanil 250-750µg) 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 coordination 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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