New York School Of Regional Anesthesia - Continuous Interscalene Brachial Plexus Block

Indications: Shoulder, arm, elbow surgery
Landmarks:
- Clavicular head of the sternocleidomastoid muscle
- Clavicle
- External jugular vein
Nerve stimulation: Twitch of the pectoralis, deltoid, arm, forearm, or hand muscles at 0.2-0.4 mA current
Local anesthetic: 35-40 mL
Complexity level: Advance

An interscalene brachial plexus block relies on dispersion of a large volume of local anesthetic within the interscalene groove to accomplish blockade of the brachial plexus. In our practice, we approach this block closer to the clavicle, rather than a commonly described approach at the level of the cricoid cartilage. At this lower level, the interscalene grove is shallower, easier to identify and the distribution of anesthesia is also adequate for elbow and forearm surgery. This block has a substantial clinical applicability and it well may be the most commonly used block in our practice. In addition, the needle insertion is much more lateral, which makes vascular puncture rare and the performance of the block much easier for trainees. We use this block routinely for shoulder, arm, and forearm surgery. The most common indications for this block in our practice are shoulder surgery and insertion of arteriovenous grafts for hemodyalisis.

The brachial plexus supplies the shoulder and the upper limb and consists of a branching network of nerves derived from the anterior rami of the lower four cervical and the first thoracic spinal nerves. Starting from their origin and descending distally, the components of the plexus are named roots, trunks, divisions, and cords. The five roots of the cervical and the first thoracic spinal nerves (anterior rami) give rise to three trunks (superior, middle, and inferior) that emerge between medial and anterior scalene muscles to lie in the floor of the posterior triangle of the neck. The roots of the plexus lie deep to the prevertebral fascia, whereas 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 divisions combine to produce the three cords, which are named lateral, medial, and posterior, according to their relationships to the axillary artery. From there on, individual nerves are formed as these neuronal elements descend distally.

Organization and distribution of the brachial plexus.

The interscalene approach to brachial plexus blockade results in consistent anesthesia of the shoulder, arm, and elbow. The interscalene block is not recommended for hand surgery; more distal approaches to the brachial plexus should be used instead (e.g., infraclavicular, axillary). Note that the labeled areas without a color shade are not anesthetized consistently with the interscalene brachial plexus block.

The patient is in the same position as in the single-shot technique. However, it is imperative that the anesthesiologist be in the ergonomic position to allow for maneuvering during catheter insertion. It is also very important that all equipment as well as the catheter is immediately available and prepared in advance, because small movements of the needle while trying to prepare the catheter may result in needle dislodgement from its position in the brachial plexus sheath.

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
One 1½" 25-gauge needle for skin infiltration
A 5-cm long, insulated stimulating needle (Tuohy style or Quincke tip)
Catheter
Peripheral nerve stimulator

The landmarks for a continuous interscalene brachial plexus block are similar as those in the single-shot technique:

Clavicle
Clavicular head of the sternocleidomastoid muscle
External jugular vein

The subcutanoues tissue at the projected site of needle insertion is anesthetized with local anesthetic. The block needle is then attached to a nerve stimulator (1.0 mA, 2 Hz, 100 µsec) and to a syringe with local anethetic. With this technique, it is imperative that the palpating hand firmly stabilize the skin to facilitate needle insertion and insertion of the catheter. A 5-cm block needle is inserted at a slightly caudal angle and advanced until the brachial plexus twitch is elicited at 0.2-0.5 mA. Attention should be paid to avoid insertion of the needle through the external jugular vein because this invariably results in prolonged oozing from the site of puncture. This can be avoided by retracting the external jugular vein and inserting the needle slightly in front or posterior to the external jugular vein. Additionally, making a small skin nick before inserting the needle can be helpful in preventing uncontrolled needle insertion as the skin is penetrated. The initial volume of local anesthetic (20-40 mL) is always injected through the needle before advancing the catheter.

TIPS:

The most difficult aspect of this technique is stabilization of the needle for catheter insertion after the brachial plexus is localized. For patients in whom the needle encounters the brachial plexus at very shallow location, it best to have another person advance the catheter to assure that the needle does not move out of its original position.
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 that 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 needle through the skin.
Continuous nerve blocks require the use of larger needle gauges and thus intraarterial placement (e.g., carotid artery) has greater implications. For that reason, in patients with less than ideal landmarks, it may be prudent use a single-shot to localize the brachial plexus and determine the insertion needle point and proper angulation before inserting a large-gauge continuous block needle.

The catheter is secured using a benzoin skin preparation, followed application of a clear dressing. The infusion port should be marked as: "continuous interscalene block" and the catheter should be checked for intravascular placement before administering larger volumes infusion of local anesthetics.

Continuous Infusion

Continuous infusion is initiated after an initial bolus of dilute local anesthetic is administered through the catheter. For this purpose, we routinely use 0.2% ropivacaine (15-20 mL). Diluted bupivacaine or l-bupivacaine are also suitable, but may result in more motor blockade. The infusion is maintained at 8 mL/hr or 5 mL/hr when a PCA dose is planned (4 mL/q30 minutes).

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 rarely 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 test the position of the catheter.
When the bolus injection through the catheter fails to result in blockade after 30 minutes, the catheter should be considered dislodged and it should be removed.
Every patient receiving a continuous interscalene block should be prescribed an immediately available alternative pain management protocol because incomplete analgesia and catheter dislodgment can occur. For inpatients, this is probably best done using a back-up IV PCA.

The following twitches all result in the same success rate:

Pectoralis muscle
Deltoid muscle
Triceps muscles
Biceps muscle
Any twitch of the hand or forearm

Stimulation of the brachial plexus with a current intensity of 0.2-0.4 mA

Failure to obtain brachial plexus stimulation on the first needle pass

When insertion of the needle does not result in upper extremity muscle stimulation, the following maneuvers can be followed:

Keep the palpating hand in the same position and the skin between the fingers stretched.
Withdraw the needle to the skin level, redirect 15º posterior, and repeat the needle advancement.
Withdraw the needle to the skin, redirect 15º anterior, and repeat the needle insertion.
Never insert the needle beyond 2 cm in slim and 3 cm in obese patients; the brachial plexus is invariably superficial.

TIPS:

When these maneuvers fail to result in motor response, carefully and methodically reposition the palpating hand 1-cm posterior or anterior using an intuitive approach and repeat steps 1 through 3.
Failure to stimulate after the above steps should prompt needle withdrawal and a reassessment of the landmarks.
Keep in mind that failure to obtain brachial plexus stimulation is most commonly a result of a too anterior needle insertion.
Do not forget to ascertain that the nerve stimulator is functional and properly connected.
Increasing the current intensity >1.0 mA is more likely to result in patient discomfort then in helping to localize the brachial plexus.

Interpreting Responses to Nerve Stimulation

Some common responses to nerve stimulation and the course of action to obtain the proper response.

Response Obtained	Interpretation	Problem	Action
Local twitch of the neck muscles	Direct stimulation of the anterior scalene or sternocleoidomastoid muscles	Needle pass is in the wrong plane; usually anterior and medial to the plexus	Withdraw the needle to the skin level and reinsert 15^o posteriorly
Needle contacts bone at 1-2cm depth; no twitches are seen	The needle is stopped by the transverse process	The needle is inserted too posteriorly; the needle is contacting the anterior tubercles of the transverse process	Withdraw the needle to the skin level and reinsert 15^o anteriorly
Twitches of the diaphragm	This is the result of stimulation of the phrenic nerve	The needle is inserted too anteriorly	Withdraw the needle and reinsert 15^o posteriorly
Arterial blood noticed in the tubing	Puncture of the carotid artery (most common)	The needle insertion and angulation is too anterior	Withdraw the needle and keep a steady pressure 2-3 minutes; reinsert 1-2cm posteriorly
Pectoralis muscle twitch	Brachial plexus stimulation (C4-5)		Accept and inject local anesthetic
Twitch of the scapula	Twitch of the serratus anterior muscle; stimulation of the thoracodorsal nerve	Needle position is posterior/deep to the brachial plexus	Withdraw the needle to the skin level and reinsert the needle anteriorly
Trapezius muscle twitch	Accessory nerve stimulation	Needle posterior to the brachial plexus	Withdraw the needle and reinsert
Twitch of: pectoralis, deltoid, triceps, biceps, forearm and hand muscles	Stimulation of the brachial plexus	None	Accept and inject the local anesthetic

The brachial plexus at the site of an interscalene block 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 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 concentration of long- acting local anesthetic for lumbar plexus block.
Smaller volumes and concentrations can be used successfully for analgesia (e.g.,15-20 mL).

	Onset (min)	Anesthesia (hrs)	Analgesia (hrs)
3% 2-Chloroprocaine (plus HCO3 + epinephrine)	5-10	1.5	2.0
1.5% Mepivacaine (plus HCO3)	10-20	2-3	2-4
1.5% Mepivacaine (plus HCO3 + epinephrine)	5-15	2.5-4	3-6
2% Lidocaine (plus HCO3)	10-20	2.5-3	2-5
2% Lidocaine (plus HCO3 + epinephrine)	5-15	3-6	5-8
0.5% Ropivacaine	15-20	6-8	8-12
0.75% Ropivacaine	5-15	8-10	12-18
0.5% Bupivacaine (plus epinephrine)	20-30	8-10	16-18

When low-intensity current nerve stimulation and slow needle advanced are used, interscalene brachial plexus block is associated with minimal patient discomfort. Thus, excessive sedation is not only unnecessary, but also disadvantageous with this technique because patient cooperation during landmark assessment and block performance is beneficial. Besides, administration of midazolam tends to decrease the tonus of the interscalene and sternocleidomastoid muscles, making palpation and identification of these landmarks difficult. We typically use small doses of midazolam (e.g., 1-2 mg) to achieve a comfortable and cooperative patient during nerve localization.

The onset time for this block is short. The first sign of the blockade is the loss of coordination of the shoulder and arm muscles. This sign is seen sooner than the onset of sensory blockade or temperature change and when present within 1-2 minutes after injection, it has a very high positive predictive value for a pending successful brachial plexus blockade. In fact, this is the single test that we perform before allowing the surgeons to proceed with the preparation for surgery. In patients undergoing shoulder arthroscopic procedures, it is important to note that the arthroscopic portals can be inserted outside the cutaneous distribution of the interscalene block. Local infiltration at the site of the incision by the surgeon is all that is needed as the entire shoulder joint and deep tissues are anesthetized with the interscalene block.

Many patients will developed a hoarse voice, mild ipsilateral ptosis (Horner's syndrome), and nasal congestion after interscalene block. Proper explanation and reassurance is all that is needed by patients.
An interscalene block inevitably results in ipsilateral diaphragmatic paralysis (phrenic nerve block). The significance of this is often debated and avoidance of this block is suggested in patients with chronic respiratory disease, such chronic obstructive lung disease and bronchial asthma. Although unilateral diaphragmatic paralysis should be kept in mind when choosing an interscalene blockade, we avoid the use of this block only in patients whose breathing involves the use of accessory respiratory muscles.
Appropriate intravenous sedation, communication with the patient, lifting drapes off patient's face, and shielding the ears from the noise are all necessary ingredients to success with interscalene block in patients undergoing shoulder surgery.

Infection	- A strict aseptic technique is used
Hematoma	- Avoid multiple needle insertions, particularly in anticoagulated patients - Keep a 5-minute steady pressure when carotid artery is inadvertently punctured - Use a single shot needle to localize the brachial plexus in patients with difficult anatomy - In the absence of spontaneous bleeding, the use of anticoagulant therapy should not be regarded as a contraindication for this block
Vascular puncture	- Vascular puncture is not common with this technique - Steady pressure of 5 minutes should be maintained when the carotid artery is punctured (rare)
Local anesthetic toxicity	- Systemic toxicity due to absorbtion of local anesthetic after interscalene blockade is rare - Systemic toxicity most commonly during or shortly after injection of local anesthetic; this is most commonly caused by an inadvertent intravascular injection or channeling of forcefully injected local anesthetic into small veins or lymphatic channels cut during needle manipulation - Large volumes of long-acting anesthetic should be reconsidered in older and frail patients - Careful and frequent aspiration should be performed during the injection - Avoid forceful, fast injection of local anesthetic
Nerve injury	- Never inject anesthetic when pressure on injection is encountered - Local anesthetic should never be injected when patient complains of severe pain or exhibits a withdrawal reaction on injection
Total spinal anesthesia	- When stimulation is obtained with current intensity of < 0.2mA, the needle should be pulled back to obtain the same response with the current > 0.2mA befire injecting local anesthetic to avoid injection into the dural sleeves and the consequent epidural or spinal spread - Never inject local anesthetic when pressure on injection is encountered
Horner's syndrome	- Occurence of ipsilateral ptosis, hyperemia of the conjuctiva, and nasal congestion is common and it is dependent on the site of injection (less common with the low interscalene approach) and total volume of local anesthetic injected; the patients should be instructed on the occurence of this syndrome and reassured about its benign nature
Diaphragmatic paralysis	Invariably present; avoid interscalene blockade or the use of a large volume of local anesthetic in patients who have severe, chronic respiratory disease and use accessory respiratory muscled during breathing at rest

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