Figure 26-1. Cadaver dissection of left supraclavicular area. The SCM muscle has been removed. The roots and trunks of the plexus are visible lateral to the anterior scalene muscle. The trunks are all supraclavicular. The suprascapular nerve is seen arising from the upper trunk just proximal to the origin of the anterior and posterior divisions of this trunk. The phrenic nerve is visible in front of anterior scalene muscle. Medial to it, the origin of the vertebral artery can be seen, and more medially the common carotid artery and vagus nerve. The first intercostal space is visualized below the clavicle.

This space becomes wider in the anteroposterior plane as the muscles approach their insertion on the first rib. The subclavian artery accompanies the brachial plexus in the interscalene triangle anterior to the lower trunk. Although the roots of the plexus are long, the trunks are almost as short as they are wide, soon giving rise to anterior and posterior divisions as they reach the clavicle. Figure 26-1 shows the anatomy of the brachial plexus and surrounding structures in the supraclavicular area.

The pleura can potentially be violated in two places (the pleural dome and the first intercostal space) during a supraclavicular block, which can lead to pneumothorax. The pleural dome is the apex of the parietal pleura (inside lining of the rib cage), circumscribed by the first rib. Each first rib is a short, broad, and flattened bone structure with the shape of a letter C. They are located on each side of the upper chest with their concavities facing each other. This concavity, or medial border, forms the outer boundary of the pleural dome. The anterior scalene, by inserting in this border of the first rib, comes in contact medially with the pleural dome. There is no pleural dome lateral to the anterior scalene muscle. The first intercostal space on the other hand, is for the most part infraclavicular (see Figure 26-1 ) and consequently should not be reached when a supraclavicular block is properly performed, as will be explained later.

Clinical Pearls

With the shoulder pulled down, the three trunks of the brachial plexus are located above the clavicle; therefore, the needle should never need to reach below the clavicle during a supraclavicular block.

The first intercostal space is located below the clavicle, thus its penetration is unlikely during a properly performed supraclavicular block.

The needle should never cross the parasagittal plane medial to the anterior scalene muscle because of risk of pneumothorax.

The pulsatile effect of the subclavian artery exerted mainly against the lower trunk could explain why the C8 through T1 dermatome is often spared if the injection is not performed in the vicinity of the lower trunk.

The SCM muscle inserts on the medial third of the clavicle, and the trapezius muscle on the lateral third of it, leaving the middle third for the neurovascular bundle. These proportions are maintained regardless of patient’s size. Bigger muscle bulk resulting from exercise does not influence the size of the muscle insertion area.

The brachial plexus crosses the clavicle at or near its midpoint. Because of the direction of the brachial plexus from medial to lateral as it descends, the higher in the supraclavicular area the more medial (closer to the SCM) the plexus is located.

LANDMARKS

The technique described in this chapter combines the simplicity of the original single-injection Kulenkampff technique with important anatomic principles, which should help make the technique safer than the original procedure. The main landmarks for this block are the lateral insertion of the SCM muscle in the clavicle, the clavicle itself, and the patient’s midline. These three landmarks are easily identifiable in the majority of patients.

EQUIPMENT

• Gloves

• Antiseptic solution for skin disinfection

• Marking pen

• Sterile gauze

• Two 20-mL syringes for local anesthetic solution

• One 1-mL syringe with a 27-gauge needle for skin wheal

• One 5-cm, short-beveled, 22-gauge insulated needle

• Surface electrode

• Nerve stimulator

TECHNIQUE

Ideally the block is performed in a room dedicated to regional anesthesia. However, whether the block is performed inside or outside the operating room, the location must include American Society of Anesthesiologists standard monitors, an oxygen source, suctioning, and resuscitation equipment and drugs. A contingency plan for emergencies must be in place to safely and expeditiously treat any emergency that might arise.

If not contraindicated, this block is best performed after appropriate, light premedication (eg, midazolam 1 mg (IV) plus fentanyl 50 meg IV for the average adult). In young and healthy patients this dose can be repeated as necessary. The patient is best kept sedated but cooperative.

A single-injection, nerve stimulator technique is pref- ered. The block is performed with the patient in a semisitting position with the head rotated to the opposite side as shown in Figure 26-2A. The semisitting position is more comfortable than the supine position both for the patient and the operator. Because patient positioning is very important in regional anesthesia, the operator should not try to recognize any landmarks until the patient has adopted the desired position. The patient is asked to lower the shoulder and flex the elbow, so the forearm rests on the lap. The wrist is supinated so the palm of the hand faces the patient’s face as shown in Figure 26-2B. This maneuver allows for detection of any subtle finger movement produced by nerve stimulation. If the patient cannot turn the wrist on supination, a roll is placed under it so the fingers are free to move.

The operator usually stands on the side to be blocked, so for a left side block the palpation is done with the left hand and the needle is manipulated with the right (see Figure 26-2B). For a right-side block we teach exactly the opposite: the operator manipulates the needle with the left hand and palpates with the right. Otherwise, the operator may choose to manipulate the needle always with his or her favored hand regardless of which side block is being performed. This is easily accomplished by standing on one side of the patient’s head while reaching to the other side when necessary.

Figure 26-2. A: Patient positioning. The patient lies in a semisitting position with the head turned away from the side to be blocked. B: The shoulder is down, the elbow is flexed, and the palm of the hand rests on the patient’s lap while it is turned toward his face.

Point of Needle Entrance

With the patient in the described semisitting position and the shoulder down, the lateral (posterior) border of the SCM muscle is identified and followed distally to the point where it meets the clavicle. This particular point is marked on the skin over the clavicle, as shown in Figure 26-3. The lateral border of the SCM is usually clearly visible at the level where the external jugular vein crosses it. From this level the border can be traced caudally to the point where it meets the clavicle. A parasagittal line (parallel to the midline) is imaginarily drawn at this level to recognize an area medial to it that is at risk for pneumothorax. The point of needle entrance is always lateral to this parasagittal plane, separated by a distance we call “margin of safety.” This distance is about 1 in. (2.5 cm) lateral to the insertion of the SCM in the clavicle or one “thumb’s breadth” lateral to the SCM as shown in Figure 26-4. The margin of safety can be alternatively established using a distance equal to the width of the clavicular head of the SCM at its insertion on the clavicle.¹⁶ The palpating index finger is placed at this site as shown in Figure 26-5. We customarily draw two arrows at this location pointing to each other. The proximal arrow, above the finger, is used to localize the needle entrance point, the distal one shows the direction of the needle path.

Figure 26-3. Landmarks. The lateral insertion of the SCM in the clavicle is marked (arrow).

Figure 26-4. Margin of safety. A distance of approximately 1 in. (2.5 cm) is measured laterally from the SCM, away from the pleural dome.

Figure 26-5. Point of needle entrance. The point of needle entrance is located just cephalad to the palpating finger and one fingerbreadth above the clavicle. The arrows on each side of the palpating finger help visualize the direction of the needle parallel to the midline.

The needle is inserted immediately cephalad to the palpating finger and advanced first perpendicularly to the skin for 2 to 5 mm (depending on the amount of the patient’s subcutaneous tissue) and then turned caudally under the palpating finger to advance it in a direction that is parallel to the midline, as shown in Figure 26-6.

The block should take place above the clavicle, under the palpating finger. An isolated muscle twitch is elicited in all fingers either in flexion or extension, often mistakenly referred as “median nerve” and “radial nerve” responses, respectively (both nerves at this level are yet to be formed while their constituent fibers are traveling in all three trunks). Any other response carries a significantly lower success rate.

Figure 26-6. Needle direction. The needle is first introduced perpendicular to the skin and is then turned and advanced parallel to the midline in the direction of the two lateral arrows.

If reposition of the needle is necessary, the needle is withdrawn and the penetration angle is adjusted in the anteroposterior plane, either slightly more posterior or slightly more anterior, but always parallel to the midline.

Nerve Stimulator Settings

Modern nerve stimulators used in regional anesthesia are portable, accurate and easy to use. They should be checked periodically by the hospital engineering department to ensure proper function and be fitted with new batteries according to a schedule. The ground electrode should be fresh out of the package. If for any reason it needs to be relocated, it is better to use a new one to avoid the increase in impedance that comes with desiccation of the conductive gel. Its location in reference to the blocking site does not seem to have any significance. The negative electrode should be connected to the needle because less current is needed to produce a nerve response.¹⁷ We always use a 5-cm, short-beveled, insulated needle to perform this technique.

We start the technique with a current of 0.8 mA and a pulse width of 100 ps. Once the desired response is obtained— ie, a muscle twitch of the fingers that is clearly visible—we start the injection without reducing the nerve stimulator current. This is a unique characteristic of the supraclavicular block. In a recent study, the onset, duration, and success rate with a supraclavicular block was unaffected by reducing the nerve stimulator to 0.5 mA or less.¹⁸ Supraclavicular and lumbar plexus blocks are the only peripheral nerve blocks in which injecting at a higher current than 0.5 mA should be recommended.

Clinical Pearls

To improve patient comfort, removal of a cast or splint prior to performing the block is not necessary as long as the fingers are visualized.

The lateral border of the SCM muscle follows a straight line from the mastoid to the clavicle. Frequently a lateral deviation of this otherwise straight border can be seen in the proximity of the clavicle. This lateral extension should be disregarded because it usually represents the omohyoid muscle.

The needle is inserted in a direction that is parallel to the midline. No other landmarks (eg, nipples) should be used to direct the needle, as their position is highly variable.

Depending on the patient’s weight, the palpating finger exerts different amounts of pressure on the deeper tissues. This maneuver helps bring the plexus closer to the skin and makes the trajectory of the needle shorter.

The needle should never be inserted deeper than 1 in. (2.5 cm) if a twitch from the brachial plexus is not present.

Because the trunks are contiguous, elicited twitches from one trunk follow the other without interruption. If the twitches instead disappear before reaching the lower trunk, the needle is withdrawn to the point of the previous twitch and advanced with a slight change in the anteroposterior angle of insertion.

The margin of safety of about 1 in. (2.5 cm) lateral to the insertion of the SCM on the clavicle provides a safe d istance lateral to the outer boundary of the pleural dome for the needle to travel. Because of the steep downward direction of the trunks, increasing this distance laterally may prevent the needle from contacting the plexus above the clavicle or miss the short trunks altogether.

The risk of intraneural injection is minimized by using low injection pressures, meticulous technique, and possibly by avoiding blocks in heavily sedated or anesthetized patients.