Paravertebral nerve block
Introduction: Paravertebral block was first described by Hugo Sellheim more than 100 years ago. After some initial enthusiasm, popularity of the block fell probably due to the widespread acceptance of epidural anesthesia and improvements in general anesthesia. In 1979, Eason and Wyatt published a percutaneous technique, 1 and over the ensuing 20 years use of the block gradually increased. 2 Ultrasound guidance for regional anesthesia has further increased the block's popularity (ultrasound-guided paravertebral block), in part because of the ability to visualise the pleura. Motivation for the use of paravertebral block has primarily arisen out of a desire to avoid the problems associated with epidural block; prinicipally, lower limb motor block, urinary retention and hypotension in addition to the very rare risks: spinal cord needle trauma, epidural abscess and epidural haematoma.
Several paravertebral block techniques have been described, often with different names (retropleural block, extrapleural intercostal block, continuous intercostal block). All essentially consist of local anesthetic placement in the extrapleural space containing the intercostal nerves and sympathetic trunk alongside the vertebral column. Through cephalo-caudal spread of local anaesthetic within this space, multiple intercostal nerves can be blocked, resulting in unilateral thoracic and upper abdominal wall anesthesia/analgesia. Surgical indications therefore include breast and thoracic surgery, and possibly also cardiac and abdominal surgery.
Skll level: Moderate because accurate needle tip visualisation is required to avoid pleural puncture.
Procedure time: 2-5 mins per segment
Common – Breast surgery as the sole anaesthesia technique or in combination with general anesthesia for postoperative analgesia. 3
Less common – Thoracic surgery 4 as an alternative to thoracic epidural analgesia. An alternative to the percutaneous technique for this surgery is direct placement of the catheter by the surgeon just before chest closure (Fig. 1). 5, 6 Because percutaneous paravertebral catheter placement may be unpredictable when using standard (stiff) catheters, direct surgical placement may be the preferred approach for this surgery. 7 Analgesia for fractured ribs.
Uncommon – Cardiac, 8 gall bladder, 9 and kidney surgery. 10
Fig. 1. Paravertebral catheter position following direct placement by the surgeon during thoracotomy (From Berrisford et al, Annals of Surgery 1990).
Sedation: Midazolam/alfentanil or following GA.
The paravertebral space is a wedge shaped area lateral to the vertebral column (Fig. 2).
Fig. 2. Transverse (coronal) section of the vertebral column, paravertebral space and related structures. This section lies between adjacent transverse processes as only the vertebral lamina/inferior articular processes are visible. Note the superior costotransverse ligament situated at the same depth as the lamina - the lamina is therefore a useful depth landmark (From Luyet et al, Anaesthesia 2012).
The anterior border is formed by the pleura; the posterior border by the ribs or the superior costotransverse ligament; laterally is the internal intercostal membrane (rarely visible), and medially the vertebral bodies, intervertebral discs and intervertebral foramen. The costotransverse ligament lies at the same depth as the adjacent lamina/inferior articular process and is used as a landmark for the loss-of-resistance technique (not described here). The paravertebral space contains the intercostal nerves, sympathetic chain, intercostal vessels and the vessels to and from the spinal cord. The dura mater extends into the paravertebral space ("dural sleeve"/"dural cuff"), therefore, the paravertebral space is sometimes considered part of the epidural space. The paravertebral space is widest medially and shallowest laterally. The deep fascia of the thorax, a fibroelastic structure termed the endothoracic fascia, is closely applied to the anterior vertebral body, and laterally the rib cage. It divides the paravertebral space into anterior and posterior compartments. The clinical relevance of this fascia is not clear, but the segmental spinal nerves are said to be located in the posterior compartment, and penetration of this fascia by needle or catheter may explain incomplete or "patchy" blocks. Caudally, the endothoracic fascia is continuous with the transversalis fascia of the abdominal cavity and this may explain why solutions injected into the paravertebral space may spread to the lumbar region. It is generally accepted that the caudal limit of the paravertebral space is at the origin of the psoas muscle at L1.
Surface landmarks: Mark out the required anesthesia dermatome, the relevant spinous processes and the side to be blocked. The lateral tip of the transverse process is approx. 2.5 cm from the midline.
Needle: Large calibre (e.g. 18G) Tuohy needle. N.B. Small calibre needles (e.g. 22G) carry a higher risk of inadvertent dural puncture, particularly when accompanied by a sharp needle tip.
Procedure (only ultrasound guided approach described)
Several ultrasound-guided approaches to the paravertebral space have been described. Two approaches are popular – medial and lateral. The medial approach may be advantageous in that the paravertebral space is wider closer to the vertebral column thereby potentially reducing the pleural puncture risk. It has been shown that injection closer to the spinal nerves (using a nerve-stimulator-guided technique) is more likely to result in longitudinal spread of the injectate. The lateral approach is advantageous in that the dural puncture risk is reduced. On balance, the medial approach is preferred because pleural puncture is considered to be the most relevant complication.
Medial approach (Fig. 3 and 6-9) 7
1. A curved probe is placed so the plane of the beam is transverse to the vertebral column (i.e. in the coronal plane).
2. First, the transverse and spinous processes are visualised, appearing as a double bump (Fig. 3A + Fig. 4Right). When the probe is moved slightly caudally, the transverse process disappears and the inferior articular process/vertebral lamina is visible as a hyperechoic line (Fig. 3B,Fig. 4Left and Fig. 5). Immediately lateral to the lamina/inferior articular process is the superior costotransverse ligament (not visible), and deep to the ligament is the paravertebral space. Further laterally is the pleura (an often visible hyperechoic line lateral to the paravertebral space and at approx. the same depth as the lamina/inferior articular process) (Fig 3B).
Fig. 3. Medial ultrasound-guided approach to the paravertebral space for paravertebral block. Section A shows the spinous process ('1'), trasverse process and rib. Section B shows the spinous process ('1'), inferior articular process/vertebral lamina (hyoerechoic line) and lateral/deep is the paravertebral space ('*'). The hyperechoic line lateral to the space (and at the same depth as the lamina) is the pleura.
Fig. 4. Paravertebral block: CT scan of paravertebral space and related bony structures. Left illustrates the vertebral laminae; Right (slightly cephalad to the cut on the left) illustrates the spinous process, transverse process and rib.
Fig. 5. Paravertebral block (sonography) corresponding to the video below. Blue arrow=pleura; Red arrow=lamina/inferior articular process; Green arrow=paravertebral space.
3. First infiltrate the intended block needle path using a 22.25G hypodermic needle and lidocaine 1%. Block needle advancement is out-of-plane in a medial to lateral direction directly into the paraveretebral space, or until bony contact is made with the inferior articular process/vertebral lamina. If bony contact occurs, the needle is walked-off laterally over the edge of the bone and through the superior costotransverse ligament. If the needle has not been advanced sufficiently deep, local anaesthetic spread will be detected in the spinal muscles posterior (superficial) to the inferior articular process/vertebral lamina.
4. Appropriate needle (or catheter) placement should be confirmed by observation of pleural deviation following local anesthetic injection. Pleural scanning can also occur more laterally. Typically, local anesthetic spread can be detected at multiple levels.
Fig. 6. Ultrasound guided paravertebral block: transverse probe orientation just lateral to the midline.
Fig. 7. Ultrasound guided paravertebral block: out-of-plane "medial" (to lateral) needle orientation.
Fig. 8. Paravertebral block: "self coiling" catheter inside catheter introducer.
Fig. 9. Ultrasound guided paravertebral catheter placement. Note when using the self coiling catheter, ultrasound visualisation of the catheter is possible but not necessary.
Local anesthetic regimen: 15 mL ropivacaine 0.5% will block approx. 4 dermatomes.
1. Epidural abscess/haematoma and dural puncture (total spinal). Theoretically, all complications associated with epidural block (total spinal, epidural haematoma, epidural abscess) can occur with paravertebral block, albeit with reduced risk. Therefore, if a catheter is placed, a catheter test dose should be given before discharge to a non-monitored environment. Relative contraindications are similar to epidural block (related infection, concomitant anticoagulation) but with a higher contraindication threshold. Clinical judgement should be used according the assessed risk-benefit ratio.
2. Pleural puncture/pneumothorax.
1. To achieve satisfactory anaesthesia for surgery under paravertebral block alone (i.e. without general anaesthesia) a multilevel multi injection technique will be more reliable than a single injection technique or local anesthetic through catheter technique.
2. An alternative to using real-time needle guidance for paravertebral block is to estimate the transverse process and pleural location/depth with US, and then perform the block without US. Accurate depth assessment necessitates gentle probe-skin pressure and a beam orientation similar to the expected needle trajectory. This approach may be preferable for less experienced operators, the obese, or when subcutaneous emphysema makes US imaging difficult.
Video 1. Paravertebral block (sonography). Out-of-plane medial approach. Needle tip can be seen walking off the lamina/inferior articular process before entering the paravertebral space.
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