Continuous Thoracic Paravertebral Block

Continuous thoracic paravertebral blockade is an advanced regional anesthesia technique and adequate experience with the single-shot technique is a prerequisite.

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Overview

Indications: Breast surgery, pain management after thoracic surgery or rib fractures Landmarks: Spinal process at the desired thoracic dermatomal levels Needle insertion: 2.5 cm lateral to midline Target goal: needle insertion 1 cm past the transverse process Local anesthetic: 3-5 mL per level Complexity level: Advanced

General considerations

Continuous thoracic paravertebral blockade is an advanced regional anesthesia technique and adequate experience with the single-shot technique is a prerequisite. The continuous thoracic paravertebral block technique is more suitable for analgesia than for surgical anesthesia. The resultant blockade can be thought of as a unilateral continuous thoracic epidural, except that there are no significant hemodynamic changes. The technique is somewhat similar to the single-shot injection, except that the needle should be properly angled to allow for insertion of the catheter. This technique provides excellent analgesia and it is devoid of significant hemodynamic effects in patients after mastectomy and unilateral chest surgery.

Regional anesthesia anatomy

The thoracic paravertebral space is a wedge-shaped area that lies on either side of the vertebral column. Its walls are formed by the parietal pleura anterolaterally; vertebral body, the intervertebral disk, and intervertebral foramen medially; and the superior costotransverse process posteriorly. The spinal nerves in the paravertebral space are organized in small bundles submerged in the fat of the area. At this location, the spinal nerves are not enveloped by a thick fascial sheath. Therefore, they are relatively easily anesthetized by injection of local anesthetic. The thoracic paravertebral space is continuous, with the intercostal space laterally, epidural space medially, and the contralateral paravertebral space via the prevertebral fascia. The mechanism of action of a paravertebral blockade includes direct penetration of the local anesthetic into the spinal nerve, extension laterally along with the intercostal nerve, and medial extension through the intervertebral foramina.

Distribution of anesthesia

Thoracic paraverterbral blockade results in ipsilateral dermatomal anesthesia. The location of the resulting dermatomal distribution of anesthesia or analgesia is a function of the level blocked and the volume of local anesthetic injected.

Patient positioning

The patient is positioned in the supine or lateral decubitus position. Most of our patients with this block are patients undergoing various thoracic procedures. For practical reasons, most catheters are placed postoperatively, just before the patients emerge from general anesthesia. Since these patients are typically already positioned in the lateral decubitus position, this practice precludes the need for special patient positioning or premedication for the block placement. In addition, the risk of pneumothorax is nonexistent because the patients already have a chest tube inserted. However, the ability to clearly visualize spinous processes is of crucial importance.

Equipment

A standard regional anesthesia tray is prepared with the following equipment: Sterile towels and 4"x4" gauze packs 20-mL syringe with local anesthetic Sterile gloves, marking pen, and surface electrode One 1½" 25-gauge needle for skin infiltration A 5-cm long, insulated stimulating needle (Tuohy-style or Quincke tip) Catheter

Landmarks

The landmarks for continuous paravertebral block are identical to those in the single-shot technique: Midline (spinous processes) Paramedial line (2.5 cm lateral to spinous processes) TIP: For continuous paravertebral blockade, the catheter is ideally inserted 1-2 segmental levels below the thoracotomy incision line.

Technique

The subcutaneous tissues and paravertebral muscles are infiltrated with local anesthetic to decrease the discomfort at the site of needle insertion. The needle is attached to a syringe with local anesthetic and advanced in a saggital and slightly cephalad plane to contact the transverse process.
Once the transverse process is contacted, the needle is withdrawn back to the skin and reinserted with a 10º-15º cephalad angle to "walk off" 1 cm past the transverse process and enter the paravertebral space. As the paravertebral space is entered, a certain "give" is sometimes perceived, but it should not be relied upon as the target. Once the paravertebral space is entered, the initial bolus of local anesthetic (5-6 mL) is first injected through the needle. The catheter is inserted some 5 cm beyond the needle tip.
The catheter is then secured using a solution of benzoin and clear occlusive dressing and clearly labeled "paravertebral nerve block catheter." The catheter should be carefully checked for air, CSF, and blood before dosing a local anesthetic or starting the continuous infusion.

TIPS:

• Care must be exercised to prevent medial orientation of the needle (risk of intraepidural/spinal placement).
• If it is deemed that the needle is inserted too laterally (inability to advance due to the needle-rib contact), the needle should be reinserted medially rather than oriented medially (risk of spinal cord injury).
• A distinct "give" is often felt as the needle passes through the costovertebral ligament. However, advancing the needle geometrically 1 cm past the transverse process is more accurate.

Management of the Continuous Infusion

Continuous infusion is initiated after an initial bolus of dilute local anesthetic is administered through the catheter. The bolus injection consists of a small volume of 0.5% ropivacaine or bupivacaine (e.g., 8 mL). For continuous infusion, 0.2% ropivacaine, or 0.25% bupivacaine (l-bupivacaine) are suitable. The local anesthetic is infused at 10 mL/hr or 6 mL/hr when a PCA dose is planned (4 mL/q30 minutes).

TIPS:

• Breakthrough pain in patients on continuous infusion is always managed by administering a bolus of local anesthetic. Increasing the rate of infusion alone is rarely adequate.
• When the bolus injection through the catheter fails to result in blockade after 30 minutes, the catheter should be considered dislodged and it should be removed.
• Every patient receiving a paravertebral block infusion should be prescribed an immediately available alternative pain management protocol because incomplete analgesia and catheter dislodgement can occur. For inpatients, this is probably best done using a backup IV PCA.

Choice of local anesthetic

It is almost always beneficial to achieve longer acting anesthesia/analgesia in thoracic paravertebral blockade by using longer acting local anesthetic. Unless lower lumbar levels (L2-5) are planned to be blocked, paravertebral blocks do not result in motor block of an extremity and do not impair patient's ability to ambulate or take care of themselves. In addition, relatively small volumes injected at several levels do not present a concern for local anesthetic toxicity.

TIP: In patients receiving multiple level blockade, consider using alkalinized 3-chloroprocaine for skin infiltration to decrease the total dose of the more toxic long-acting local anesthetic. Chloroprocaine is rapidly metabolized by plasma cholinesterase on its absorption.

Block Dynamics and Perioperative Management

Placement of the paravertebral block is associated with moderate patient discomfort. Adequate sedation (midazolam 2-4mg) is always necessary to facilitate placement of the block. We also routinely administer alfentanyl 250-750 µg just before beginning the block procedure. However, excessive sedation should be avoided because the positioning becomes difficult when patients cannot keep their balance in the sitting position. The blockade depends on anesthetic dispersion within the space to reach the individual roots at the level of the injection. The first sign of the blockade is the loss of pin-prick sensation at the dermatomal distribution of the root being blocked. The higher the concentration and volume of the local anesthetic used, the faster the onset can be expected.

Complications and How to Avoid Them

Bibliography

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