Supraclavicular Brachial Plexus Block

Fig. 20.1

Patient positioning and surface landmarks for supraclavicular block of the brachial plexus

The patient is positioned supine with the head turned approximately 45° to the contralateral side after general anesthesia has been induced. The operative arm extends down the patient’s side, parallel to the body. If necessary, the arm can be pulled down gently towards the knee. A comfortable ergonomic position should be planned to improve block performance. The block may be completed while positioned lateral to the side to be blocked at the level of the upper arm or at the head of the table looking towards the patient’s feet. Surface landmarks include:

Clavicle: the needle insertion site is approximately at the midpoint of the clavicle.
Subclavian artery pulsation: this serves as the principal landmark; the plexus is located immediately posterolateral to the subclavian artery.

20.3 Nerve Stimulation Technique (Tables 14.1 and 20.1)

Table 20.1

Responses and needle adjustments for use with nerve stimulation at the supraclavicular level

Correct response to nerve stimulation

The correct responses are similar to those observed when using the interscalene approach. At this location, the brachial plexus is starting to divide from trunks into anterior and posterior divisions. Twitches of pectoralis, deltoid, biceps (upper trunk), triceps (upper/middle trunk), forearm (upper/middle trunk), and hand (lower trunk) muscles with current intensity of 0.4 mA (0.1–0.3 ms) are acceptable. Distal responses (hand or wrist flexion or extension) are best to confirm needle placement within the fascia

Other common responses and needle adjustments

Muscle twitch from electrical stimulation

Diaphragm (phrenic nerve)

Explanation: unlikely as the needle plane is too anterior

Needle adjustment: withdraw needle to the subcutaneous tissue and reinsert in a 15° more posterior angle

Vascular puncture

Subclavian artery puncture: indicated with arterial blood withdrawal

Explanation: needle tip is deep to the plexus

Needle adjustment: withdraw completely for pressure treatment and reinsert carefully while observing the needle tip at all times using in-plane approach

Bone contact

Needle stops at a depth of 3 cm (first rib)

Explanation: needle is inserted too deep and well beyond the plexus. However, this scenario is unlikely with ultrasound guidance, unless tip of the needle is not visualized (needle not properly aligned with the ultrasound beam)

Needle adjustment: withdraw to subcutaneous tissue and reinsert

Pleural contact

Needle tip seen beyond the white line (first rib) and a pocket is observed to form beyond the bright line

Explanation: needle is inserted too deep, traversed the plexus and subclavian artery, and has entered the pleural space. However, it is unlikely with US-guided technique

Needle adjustment: withdraw needle to subcutaneous tissue and reinsert if there is a strong clinical indication

Nerve stimulation responses can be useful to minimize the risk of intraneural injection and to confirm proximity of the needle to the target trunk. Because of the high risk of pneumothorax and vascular puncture during supraclavicular blockade, the authors strongly recommend an ultrasound-guided approach. See “Ultrasound-Guided Technique” below for a description of anatomical landmark identification, patient positioning, and needle insertion technique.

20.3.1 Needle Insertion

Depth of insertion depends on age and weight of the patient. It is a nonlinear relationship, i.e., for a 10 kg child, the depth of insertion is about 10 mm. For every 10 kg increase in weight, the depth of insertion increases 3 mm until the child reaches 50 kg. After that, advance 1 mm for every 10 kg increase in weight. The maximum depth should not exceed 35 mm (see Table 20.2).

Table 20.2

Weight-dependent depth of needle insertion for supraclavicular brachial plexus block

Patient weight (kg)	Recommended depthof needle insertion (mm)
10	10
20	13
30	16
40	19
50	22
60	23
70	24

20.3.2 Current Application and Appropriate Responses

Figure 20.2 illustrates the procedure for employing nerve stimulation techniques for supraclavicular nerve block.

Fig. 20.2

Flowchart of the procedure for employing nerve stimulation techniques for supraclavicular nerve block

An initial current of 0.8 mA (2 Hz, 0.1–0.3 ms) is sufficient for stimulation of the plexus. After obtaining the appropriate motor response, the current is reduced to aim for a threshold current of 0.4 mA (0.1–0.2 ms). Motor response cessation at currents greater than 0.4 mA or less than or equal to 0.2 mA indicates that the needle may either be too distant from the nerve or may have breached the epineurium, respectively.
As the trunks of the brachial plexus begin to divide at this block location, twitches of the pectoralis deltoid, biceps (upper trunk), triceps (upper/middle trunk), forearm (upper middle trunk), and hand (lower trunk) muscles may be elicited, depending on the needle location.
Obtaining a distal response in the hand or wrist indicates optimal needle placement for a successful block.
In children, the spread of anesthetic solution may be greater than for adults since the fascia is less adherent to the nerve trunks. This increases the likelihood of a successful block with any motor response.