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, A1).
(A) Paravertebral space, ultrasound image. (A1) Paravertebral space anatomy, ultrasound probe orientation (inset). Transverse process, PVS = paravertebral space, pleura, IIM = internal intercostal membrane, EIM = external intercostal muscle.
NOTE: The pleura is distinguished as a hyperechoic line that moves with respiration and has underlying hyperechoic air artifacts. This is to be distinguished from the rib, which contains an underlying acoustic shadow.
The use of color Doppler may aid in the identification of intercostal vessels in the paravertebral space. Care must be taken to avoid intravascular injection or injury.
In-plane Needle Insertion Approach
The patient’s posterior midthoracic area and the ultrasound probe are prepared with standard sterile precautions. The underlying skin is infiltrated with local anesthetic. A 20- or 22-gauge needle is inserted at the lateral end of the ultrasound probe and advanced slowly into the paravertebral space under direct visualization in the lateral to medial direction. It is advisable to turn the bevel of the needle upward, toward the transducer, to reduce the risk of inadvertent puncture of blood vessels, nerves, or pleura. To facilitate better visualization of the needle tip, the hydrodissection technique may be utilized by intermittently injecting small volumes of normal saline to dissect tissue planes while under direct visualization. Once the needle tip penetrates the internal intercostal membrane and enters the paravertebral space, a test dose of local anesthetic (3 mL) can be administered after ensuring negative aspiration for blood or air.
Clinical Pearls and Common Pitfalls
Injection of local anesthetic under direct visualization is highly recommended. If resistance to injection is encountered, the needle should be redirected either more laterally, or the bevel should be rotated into a different plane. Upon injection, the paravertebral space will distend and push the underlying pleura ventrally.
When performing the in-plane needle insertion approach, the needle tip should be visualized at all times in relation to the pleura to avoid the risk of pneumothorax. Frequent aspiration and incremental injection of local anesthetic are recommended to avoid inadvertent intravascular injection and systemic local anesthetic toxicity. Caution should be exercised in anticoagulated patients to avoid multiple needle passes and, thereby, decrease the risk of hematoma.
A 67-year-old woman with no significant past medical history presents with right-sided chest wall pain that started approximately six months ago. The pain is described as burning, pulling sensation, worse with movement. She describes no preceding rash or blister formation or trauma to the area. Chest x-ray imaging of the ribs and thoracic spine shows no abnormalities. On physical examination, the patient reports tenderness to palpation over the right T7 and T8 dermatomes, in the anterior and midaxillary line. Differential diagnosis includes intercostal neuralgia, and the patient is scheduled for a right T7 paravertebral block. The block is performed under direct ultrasound guidance using a mixture of local anesthetic and steroid. After the procedure, the patient reports greater than 75% decrease in pain intensity and an overall improvement in the activities of daily living. She is advised to return to the pain clinic for a repeat block in the future, if needed.