Interscalene Brachial Plexus Block

An interscalene brachial plexus block relies on dispersion of the larger 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 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.

Surface landmarks

The following surface anatomy landmarks are helpful for identifying the interscalene grove in patients undergoing interscalene brachial plexus block:

1. Sternal notch
2. Clavicle
3. Sternal head of the sternocleidomastoid muscle
4. Clavicular head of the sternocleidomastoid muscle
5. Mastoid process

TIP: Proportions of the shoulder girdle, size of the neck, prominence of the muscles and so forth, greatly vary among patients. For this reason, always perform a "reality check" when in doubt by estimating the three bony landmarks: sternal notch, clavicle, and mastoid process

Anatomic landmarks

When getting ready to perform the interscalene brachial plexus block, the following three landmarks should always be marked with a pen: Clavicle Posterior border of the clavicular head of the sternocleidomastoid muscle External jugular vein

There are four maneuvers that can be used to accentuate the landmarks for this block: Ask the patient to slightly face away from the side to be blocked. This maneuver tenses the sternocleidomastoid muscles and makes this landmark much more prominent. Ask the patient to reach the ipsilateral knee on the side to be blocked or passively pull the wrist toward the knee. This maneuver flattens the skin of the neck and helps to identify both the scalene muscles and the external jugular vein. Ask the patient to lift the head off the table while facing away. This maneuver tenses the sternocleidomastoid muscles and helps to identify the posterior border of the clavicular head of the sternocleidomastoid muscle. Ask the patient to forcefully sniff while palpating the interscalene groove. The sniffing tenses the accessory respiratory muscles (scalene muscles) and the fingers of the palpating hand often fall into the scalene groove with this maneuver.

TIPS:

• All anatomic landmarks outlined in the "surface landmarks section" are important in estimating the site for needle insertion. However, in patients with good anatomy the clavicle, clavicular head of the sternocleidomastoid muscle, and external jugular vein are all that is really important.
• An argument can be made that the external jugular vein is not a consistent landmark and that it has a highly variable course. While this is certainly true, we find that the interscalene groove is almost always immediately in front or behind the external jugular vein.
• In patients with difficult anatomy, the clavicle and external jugular vein often prove to be the most reliable landmarks.

Local anesthetic skin infiltration After cleaning the skin with an antiseptic solution, local anesthetic is infiltrated subcutaneously at the determined needle insertion site. This is the most uncomfortable part of the entire block procedure (provided that low-intensity nerves stimulation is used to identify the brachial plexus). TIPS: Care should be taken to infiltrate local anesthetic in the subcutanous tissue plane only because the brachial plexus is very shallow at this location. Deeper needle insertion may easily result in injection into the brachial plexus sheath and a consequent difficulty in obtaining the twitch response. Local anesthetic is best infiltrated tangentially rather at a single insertion point. This both ensures a superficial injection and allows for needle repositioning during block performance, if required.

Hand position The fingers of the palpating hand should be gently, but firmly pressed between the anterior and middle scalene muscles to shorten the skin-brachial plexus distance. The skin over the neck is highly movable and care should be taken to stabilize the fingers as well as to distend the skin between the two fingers to assure accuracy in needle advancement and redirections. The palpating hand should not be moved during the entire block placement procedure to allow for precise redirections of the angle of the needle insertion when necessary.

TIPS: To ensure proper position of the palpating hand, first feel the posterior border of the clavicular head of the sternocleidomastoid muscle. Asking the patient to lift the head up assures accurate palpating of this landmark. Then, slowly move the palpating fingers posteriorly until they fall in the interscalene groove muscles. The most common mistake made when identifying the interscalene groove is too anterior needle insertion. Whenever the insertion site seems to be too anterior, the chances are it is! Go back to the posterior border of the clavicular head of the sternocledimoastoid muscle and reassess the anatomy.

Needle advancement

A needle connected to the nerve stimulator is inserted between the palpating fingers and advanced at an angle almost perpendicular to the skin plane. The needle must never be oriented cephalad. Slight caudal orientation of the needle is the single best measure to take to prevent inadvertent insertion of the needle toward the cervical spinal cord. The nerve stimulator should be initially set to deliver 0.8 mA (2 Hz, 100µsec). The needle is advanced slowly until stimulation of the brachial plexus is obtained. This typically occurs at a depth of 1-2 cm in almost all patients. Once appropriate twitches of the brachial plexus are elicited, 35-40 mL of local anesthetic is injected slowly with intermittent aspiration to rule out intravascular injection.

TIPS:

• The needle should never be advanced beyond 2.5 cm to avoid the risk of complications (cervical cord injury, pneumothorax, carotid artery puncture).
• Never inject when resistance (high pressure) on injection of local anesthetic is met. In this scenario, do not move the palpating hand from its position, simply flush the needle and repeat the procedure.

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

TIPS:

• A controversy exists over whether nerve stimulation or a paresthesia technique is better, safer, and more precise in interscalene brachial plexus block. The truth is, due to the superficial position of the brachial plexus in the interscalene groove, either technique can be used. In our practice, however, we use only nerve stimulation technique. This allows for appropriate sedation and a much more pleasant experience for the patient.
• Stimulation of the brachial plexus with a higher current (e.g., >1.0 mA) results in an exaggerated response and unnecessary discomfort for patient. In addition, an unpredictably strong response often causes dislodgement of the needle position and withdrawal reaction by the patient.
• A controversy exists over the optimal motor response to nerve stimulation in the brachial plexus. In our large series, there is no difference in the success rate among various twitches as long as the stimulation is obtained using similar stimulating current intensity (0.2-0.4 mA).
• Never inject local anesthetic when stimulation is obtained at a current intensity < 0.2 mA. Coupled with forceful injection of large volumes of local anesthetic, this carries a risk of injection under pressure within the epidural sleeve and the consequent spread of local anesthetic toward subarachnoid space (total spinal anesthesia).
• Attention should be paid to avoid interpretation of the diaphragmatic and trapezius twitch as the stimulation of the brachial plexus. Misinterpretation of these twitches are among the most common causes of block failures.
• Whenever in doubt, palpate the muscle that appears to be twitching to ensure the proper response.

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:

1. Keep the palpating hand in the same position and the skin between the fingers stretched.
2. Withdraw the needle to the skin level, redirect 15^o posterior, and repeat the needle advancement.
3. Withdraw the needle to the skin, redirect 15^o anterior, and repeat the needle insertion.
4. 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 are shown in table below:

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).

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 horse 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.

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