Interscalene Plexus Nerve Blocks (PNB)

Interscalene Plexus Nerve Block refers to the placement of local anesthetic around the roots or trunks of the brachial plexus at the level of the C6 vertebral body between the anterior and middle scalene muscles. It is typically performed to provide anesthesia or analgesia for surgery of the shoulder and upper arm.

The supraclavicular branches of the cervical plexus, supplying the skin over the acromion and clavicle, are also blocked due to the proximal and superficial spread of local anesthetic. The inferior trunk (C8-T1) is usually spared unless the injection occurs at a more distal level of the brachial plexus.

Which Ultrasound Scanner is suitable for Interscalene Plexus Nerve Blocks?

The Mini Linear Handheld WiFi Ultrasound Scanner MLCD is highly recommended for our anesthesiologist clients. In which the PNB assessment needs a linear transducer of 10 to 14 MHz.

Ultrasound use can decrease risks such as misguided needle placement which can result in pneumothorax, nerve damage, epidural or intrathecal placement, and spinal cord trauma.

There are 2 commonly accepted techniques for finding the proper image. Firstly, the transducer is placed at the level of the cricoid cartilage medial to the sternocleidomastoid muscle, and the carotid artery is identified. The transducer is then slid laterally until the brachial plexus in between the anterior and middle scalene muscles are identified.

 The second method is to place the transducer just above the clavicle and identify the subclavian artery with brachial plexus (the image for a supraclavicular block). The transducer is then moved cephalad towards the patient’s neck while keeping the brachial plexus nerves in view until the “stop-light” image is seen.

 The needle is then inserted in-plane to the transducer entering lateral to medial. If preferred the needle can be inserted medially to lateral as well. Once the needle reaches the Interscalene groove, after careful aspiration, the local anesthetic is injected. If a nerve stimulator is used, the patient should exhibit a motor response of the shoulder and arm.

The goal is to identify the anterior and middle scalene muscles and the elements of the brachial plexus that is located between them. It is recommended to use the color Doppler to identify vascular structures and avoid them.

To sum up, Ultrasound guidance allows for visualization of the spread of the local anesthetic and additional injections around the brachial plexus if needed to ensure an adequate spread of local anesthetic, improving block success. The ability to visualize local anesthetic spread and to inject multiple aliquots also allows for a reduction in the volume of local anesthetic required to accomplish the block.

References: Interscalene Nerve Block, Interscalene Block,