The use of ultrasound guidance for peripheral nerve blocks in regional anesthesia and pain management offers several advantages over traditional methods including the paresthesia technique and neural stimulation technique. Studies in regional anesthesia and pain medicine seem to indicate that ultrasound guidance can decrease the time required to perform a nerve block and hasten the onset of block, thus potentially improving efficiency between operative cases. Patient discomfort may also be reduced as ultrasound decreases the number of attempted needle passes while performing a block. Direct visualization of neural and vascular structures, including the use of Doppler and visual confirmation of local anesthetic spread around the target nerves, could decrease the risk of intravascular injection, intraneural injection, injury to the lung, or other nearby vital structures.
In this chapter, we provide an overview of the most commonly performed ultrasound-guided peripheral nerve blocks in regional anesthesia and pain medicine, along with their clinical indications.
Thoracic paravertebral block provides a viable alternative to intercostal nerve blocks and thoracic epidural catheter placement. Continuous paravertebral blockade using a catheter can provide a similar reduction in postoperative pain scores as thoracic epidural blockade, but is associated with less profound sympathetic blockade, resulting in less hypotension and urinary retention (especially when unilateral block is performed). Thoracic paravertebral blocks are indicated for surgical anesthesia and analgesia for thoracic, upper abdominal, cardiac, and breast surgeries, as well as chronic pain management for post-thoracotomy pain syndrome, rib fractures, intercostal neuralgia, and other painful conditions requiring analgesia of the trunk.
The paravertebral space is a wedge-shaped region demarcated by the superior costo-transverse ligament (posterior border), parietal pleura (anterolateral border), and lateral surface of the transverse process (medial border). It should be noted that the medial aspect of the paravertebral space communicates with the epidural space. The paravertebral space contains the intercostal or spinal nerves, blood vessels, rami communicantes, dorsal rami, and the sympathetic chain.
Scanning Technique and Ultrasound Appearance
The procedure is performed with the patient in sitting, lateral decubitus, or prone positions. The ultrasound transducer can be positioned in the longitudinal parasagittal plane or transverse (axial) plane. Insertion of the needle in-plane with the ultrasound transducer is highly recommended (if not mandatory) to allow for complete visualization of the entire needle at all times and avoid puncturing the pleura.
Using a linear, high-frequency (10–12 MHz) transducer, the ultrasound probe is placed parallel to the appropriate intercostal level, just lateral to the spinous process. The image is optimized by adjusting for the appropriate depth of field (usually within 3–5 cm), focus, and gain. The spinous process and the corresponding transverse process are visualized as hyperechoic lines with acoustic shadows underneath. The hypoechoic wedge-shaped paravertebral space is identified by scanning lateral to the transverse process. Care should be taken to identify the underlying pleura (Figure 15-1A, ...