Ultrasound Guidance for Interscalene Brachial Plexus Block

With patients in the supine position, a high-frequency (10-12 MHz) ultrasound transducer in a sterile sheath will be applied to explore the interscalene region and locate the brachial plexus. The transducer will be positioned so as to image the C5 and C6 roots in a single view. Visualization of the C7 root in the same scan will be sought, but will not be required. A 50-mm, 20 G needle will be advanced in-plane from the postero-lateral side of the transducer. Injection of the local anesthetic will be performed in small aliquots while repositioning of the needle in order to optimize spread of the injectate around the nerve roots. At the end of the injection, a catheter will be threaded through the needle. The catheter will be positioned to lie deep and close to the imaged nerve roots.

With patients in the supine position, the head will be rotated to the contralateral side. The interscalene groove will be palpated. A 35-mm, 20 G needle will be inserted at the estimated C6 level (cricoid cartilage) with a 30-45° angle to the skin. The needle will be advanced along a line joining the insertion site to the axilla. An electrical nerve stimulator will be used at an initial intensity of 1.0 mA (frequency: 2 Hz, pulse width: 0.2 ms). A musculocutaneous or axillary-nerve mediated twitch will be sought Injection of the local anesthetic will start with a visible motor response at a current \<0.5 mA. The catheter will be positioned to as to elicit a motor response at ≤0.4 mA.