Paravertebral Nerve Block

Background

Paravertebral nerve block was a popular technique in the early 20th century. However, for some reason, paravertebral nerve block lost popularity and was almost extinct until the late 1970s, when there was a renewed interest in the technique. This technique is now considered safe and efficacious.[1]

A paravertebral block is essentially a unilateral block of the spinal nerve, including the dorsal and ventral rami, as well as the sympathetic chain ganglion. These blocks can be performed at any vertebral level. However, they are most commonly performed at the thoracic level because of anatomic considerations. Therefore, this topic primarily focuses on thoracic paravertebral blockade.

Indications

Paravertebral nerve blocks are indicated for surgical procedures requiring unilateral analgesia or anesthesia. Common cases benefitting from unilateral paravertebral blocks are breast surgery, thoracotomy, herniorrhaphy, open cholecystectomy, and open nephrectomy. Bilateral paravertebral blocks can be a viable option for midline abdominal surgery.[2]

The clinician may consider thoracic paravertebral blockade over thoracic epidural analgesia in patients for whom bilateral sympathectomy and subsequent hypotension would be especially detrimental.[3, 4, 5] For example, the use of thoracic paravertebral blockade in a patient with severe aortic stenosis has been reported.[6] In another study, thoracic paravertebral blockade resulted in more stable hemodynamics and equivalent analgesia when compared to thoracic epidural analgesia in thorocotomy patients.[7] However, because bilateral spread can occur[8] , which may cause hemodynamic compromise similar to epidural blockade.

Another unique feature of thoracic paravertebral blockade compared with thoracic epidural analgesia is the relative safety when performing these blocks on patients with a marginal coagulation cascade. This does not mean, however, that thoracic paravertebral blockade can be performed on patients with coagulopathy without caution. According to the American Society of Regional Anesthesia and Pain Medicine’s evidence-based guidelines, in the patient receiving antithrombotic or thrombolytic therapy, the exact same precautions should be taken when placing thoracic paravertebral blockade as when placing an epidural. However, if bleeding occurs in the thoracic paravertebral space, significant blood loss will be the likely complication rather than epidural hematoma and neurologic deficit.[9]

Contraindications

Contraindications to paravertebral nerve blocks include the following:

• Patient refusal

• Severe coagulopathy

• Local infection

• Allergy to local anesthetics (rare, usually the allergy is to the preservative)

• Severe hypovolemia (especially for bilateral blocks)

• Untreated sepsis

Anatomy

The thoracic paravertebral space is a triangular- or wedge-shaped space running the length of the thoracic vertebral column bilaterally (see the image below).

It is bounded posteriorly by the superior costotransverse ligament (a continuation of the internal intercostal muscle); anteriolaterally by the parietal pleura; and medially by the vertebral bodies, intervertebral foramina, and the intervertebral discs.

In contrast to cervical and lumbar regions, the thoracic paravertebral space is in continuity with adjacent vertebral levels, allowing for spread of local anesthetic. This anatomic property explains why the thoracic paravertebral space may have more utility than cervical or lumbar paravertebral blocks.

Complications

Complications of paravertebral nerve blocks may include the following:

• Failed block

• Hypotension

• Vascular puncture

• Pleural puncture

• Pneumothorax

Failure rate may be lower with ultrasound, but this has not been studied.

Patient education and consent

The patient should be consented for the procedure. The risks, benefits, and alternatives should be adequately discussed.

Equipment

All supplies and equipment should be gathered, including:

• Emergency airway supplies

• Emergency drugs, including 20% intralipid

• Ultrasound machine (if ultrasound guidance is planned) with sterile probe cover

• Local anesthetic to be used for the block

For continuous catheter insertion, the following equipment is needed:

• Surgical mask, hat, and sterile gloves

• Commercial epidural tray containing skin prep, lidocaine, drape, 25-G needle, 17-G Tuohy needle (see the image below)

  Epidural tray.

For single shot block, the following equipment is needed:

• Sterile gloves

• Skin prep solution

• Syringe with lidocaine and 25-G needle for local

• 22-G nerve block needle (see the image below)

  Supplies for single shot paravertebral block.

Note that 0.5% bupivacaine will last approximately 12-18 hours.

The thoracic paravertebral space is highly vascular and rapid systemic absorption can occur.

Use of epinephrine 1:200,000 may slow absorption and decrease the peak plasma concentration.[10]

Patient preparation

Anesthesia

The block may be done with local anesthetic infiltration and sedation or under general anesthesia.

Midazolam and fentanyl may be titrated to patient comfort.

Positioning

The patient may be positioned prone, lateral, or sitting.

Monitoring and follow-up

Patients should be monitored for at least 30 minutes after the block for signs of local anesthetic toxicity, hypotension, or other complications.

Approach considerations

Many techniques for accessing the paravertebral space have been described, including:

• Loss of resistance[11]

• Advancing the needle 1.5-2 cm beyond the transverse process[12]

• Nerve stimulation[13]

• Ultrasound guidance[14]

• Fluoroscopic guidance[15]

Examples of thoracic paravertebral block using sagittal and transverse imaging are shown in the following videos.

Ultrasound-guided block

Intravenous access should be obtained and standard monitors applied, including pulse oximetry, blood pressure, and electrocardiograph.

The patient is positioned, sedated, prepped, and draped, as shown in the image below.

A small curvilinear or high frequency linear probe is used for ultrasound guidance (see the image below).

A sagittal or transverse image can be obtained at the appropriate vertebral level. See the images below.

After image optimization, the skin is anesthetized with lidocaine.

The Tuohy needle is advanced in plane until the tip rests in the thoracic paravertebral space. Needle visualization is sometimes difficult due to the steep angle of insonation. Injection of small amounts of fluid (hydrodissection) will aid in needle tip location.

Saline or local anesthetic is injected through the Tuohy needle.

The endpoint for a successful block is anterior displacement of the pleura.

Both single injection and multiple vertebral level injection have been described.[14, 10]

The catheter is threaded through the Tuohy needle and its position is confirmed by injecting local anesthetic or small air bubbles. Pleural depression should again be noted.

The catheter is secured using a clear adhesive dressing

Loss of resistance technique

Intravenous access should be obtained and standard monitors applied including: pulse oximetry, blood pressure, and electrocardiogram.

The patient is positioned, sedated, prepped, and draped.

The spinous processes of the levels to be blocked are identified and marked.

The needle is inserted 2.5–3 cm lateral to the spinous process perpendicular to all planes of the skin.

The transverse process is contacted and the needle is then walked off the transverse process in a cranial or caudal direction. A cranial direction is preferred because the distance between the superior costotransverse ligament and pleura is longer than when using a caudal angulation; therefore, the margin of safety is greater.[16]

Using a low resistance syringe, a loss of resistance will be felt when the needle tip passes through the superior costotransverse ligament and enters the paravertebral space.

The local anesthetic is injected and, if desired, a catheter is threaded.