Chapter 31B. Ultrasound-Guided Interscalene Brachial Plexus Block
Which of the following is true regarding interscalene block?
A. Interscalene block is indicated for surgery of the shoulder, elbow, and wrist.
B. Interscalene block is indicated for shoulder and upper arm procedures.
C. Interscalene block concerns the whole brachial plexus.
D. The ulnar nerve is blocked with an interscalene block.
B is correct. The interscalene block results in a spread of local anesthesia around C5-C7 and superior and middle trunk. This will cover all the peripheral nerves innervating the shoulder.
A is incorrect. Elbow and wrist are innervated by the lower trunk (C8-T1) of the brachial plexus which is not covered by an interscalene block.
C is incorrect. C8-T1 for the inferior trunk are typically missed.
D is incorrect. The ulnar nerve originates from the C8-T1 nerve roots that are typically missed with an interscalene block.
When an in-plane approach is used, why should the needle be positioned between the two scalene muscles at the level of C5 and C6?
A. This approach is the best way to avoid a puncture of the vertebral artery.
B. The C5-C6 nerve roots are the only contributions targeted by this block.
C. An in-plane approach definitely avoids direct trauma of collateral terminal branches.
D. The lateral-to-medial approach still presents a risk of puncturing the phrenic nerve.
A is correct. The vertebral arteries arise from the subclavian arteries and enter deep to the transverse process at the level of C6 or occasionally (in 7.5% of cases) at the level of C7.
The vertebral arteries run upward and backward between the Longus colli and the scalenus anterior.
This position at the posterior aspect of the anterior scalene muscle is essential: a needle located in the middle of the interscalene groove is away from the vertebral artery. The Doppler should be used to differentiate the vertebral artery from C7, with C7 being lateral to the vertebral artery.
B is incorrect. Depending of the level of punction, the needle is positioned between C5 and C6, between C6 and C7, or between the superior and the middle trunk. The local anesthetic solution will spread around these structures.
C is incorrect. If an in-plane approach is chosen, the needle will cross the middle scalene muscle. Two nerves are usually running in this muscle: the long thoracic nerve and the dorsal scapular nerve. A trauma ...