Peripheral Nerve Blocks: A Color Atlas, 3rd Edition

33. Ultrasound Guided Interscalene Block

Paul Bigeleisen

Steve Orebaugh

Patient Position: Supine, with head turned to contralateral side, as far as is comfortable for the patient. The ipsilateral arm should be adducted at the shoulder.

Indications: Shoulder or proximal arm surgery.

Volume of Local Anesthetic: 15 to 25 mL.

Needle Size: 22-gauge, 50-mm needle.

Ultrasonographic Landmarks: The sternocleidomastoid muscle lies superficial to the anterior and middle scalene muscles (Fig. 33-1). The nerve plexus is sandwiched between the scalene muscles. The carotid artery and internal jugular vein lie deep to the sternocleidomastoid muscle and medial to the brachial plexus at this level. In some patients, the vagus nerve may be seen between the carotid and jugular vein and the phrenic nerve may be seen lateral to the carotid artery and jugular vein as it courses over the anterior scalene muscle.

Transducer Position: Axial oblique plane, at approximately C6 level (Fig. 33-1). The transducer can be moved cephalad and caudad from this starting point to obtain the best image of the plexus elements.

Technique: The skin should be prepped in sterile fashion, and the transducer sterilized or covered with a sterile probe cover. Sterile sonographic gel is placed on the skin over the block site. The transducer is then placed on the skin at approximately the C6 level, and moved slowly cephalad or caudad to obtain an optimal image. The plexus can usually be found 1.5 to 2.5 cm lateral to the border of the internal jugular vein. Ideally, two or three nerve roots or trunks can be imaged in vertical alignment (Fig. 33-1).

 

Figure 33-1. a, carotid artery; c, clavicle; IT, inferior trunk; L, lung; m1, anterior scalene muscle; m2, middle scalene muscle; MT, middle trunk; scm, sternocleidomastoid muscle; ST, superior trunk; v, internal jugular vein.

Since the position of the plexus is relatively constant and predictable at the supraclavicular fossa, some practitioners begin with the transducer at this site, in a sagittal oblique position. This allows imaging of the trunks of the plexus cephalad and posterior to the subclavian artery (see Figure 34-1 in Chapter 34 on ultrasound guided supraclavicular block). From the supraclavicular fossa, the trunks can be traced cephalad to the interscalene region.

Once the optimum view is obtained, the block needle can be inserted at the posterior or anterior margin of the transducer. The needle should be kept in view along its length by keeping it parallel to, and aligned with, the long axis of the transducer (in-plane technique). This allows constant assessment of the tip of the needle.

The tip of the needle is then advanced to the nerve root (or trunk) that has been selected as the target. The nerve stimulator may be turned on at this time to confirm the target, at a current of 0.4 to 1.0 mA. As soon as confirmation is obtained with motor or sensory stimulation, the stimulator can be switched off (alternately, it can be left on until injection begins, to confirm that the twitch disappears at this time). Local anesthetic solution is then injected under direct visualization, 1 to 3 mL at a time. The syringe should frequently be aspirated for blood. As injection proceeds, patient discomfort or paresthesia should be assessed, and the solution should be evident as it distends tissues at the tip of the needle on the ultrasound screen. Circumferential spread of the solution around the trunk should be noted. If not, the needle tip may be slowly moved to a position which allows this spread. Whenever the needle is moved, the assessment for paresthesias and aspiration for blood should again be carried out. Each root or trunk should be anesthetized unless the injection appears to be confined to a fascial space around all of the nerves.

Tips

1.   Occasionally during interscalene block with ultrasound guidance, “posterior” shoulder twitches will be elicited on stimulation of the presumed target nerve. This is most likely due to stimulation of the suprascapular nerve, which branches quite proximally from the plexus to innervate the supraspinatus and infraspinatus muscles. The needle should be moved to a different target nerve to ensure complete brachial plexus block.

2.   All interscalene blocks can produce hoarseness or Horner's sign, and all produce ipsilateral diaphragmatic paralysis. Appropriate patient selection is paramount, and patients should be warned of this side effect.

3.   Because of the high level of this block in the brachial plexus, and the injection of local anesthetic solution at the superior trunk or C5/C6 nerve roots, incomplete block of the inferior trunk or roots C8 and T1 may occur unless these structures are individually identified and anesthetized. When roots C8 and T1 or the inferior trunk are only partially anesthetized, there will be some sparing in the innervation of the median, radial, and ulnar nerves of the hand.

Suggested Readings

Chan VWS. Applying ultrasound imaging to interscalene brachial plexus block. Reg Anesth Pain Med 2003;28:340–343.

Gruber H, Kovacs P. Sonographic anatomy of the peripheral nervous system. In: Peer S, Bodner G, eds. High resolution sonography of the peripheral nervous system. Berlin: Springer-Verlag, 2003.

Perlas A, Chan VWS, Simons M. Brachial plexus examination and localization using ultrasound and electrical stimulation. Anesthesiology 2003;99:429–435.