Thoraco Lumbar Paravertebral Block

 Indications: Inguinal hernia surgery, lateral abdominal wall surgery

 Landmarks:

                     Spinal processes T9-L5 (the number and location of levels chosen for each indication)

                     Transverse process

 Needle insertion: 2 cm lateral to midline

 Target goal: Needle insertion 1 cm past the transverse process

 Local anesthetic: 5 mL per level

 Complexity level: Advanced

A paravertebral block is an advanced nerve block technique. Although in principle, the technique is similar to that of the thoracic paravertebral block, its anatomy and indications are sufficiently distinct to deserve separate consideration. It is paradoxical that this technique is one of the easiest and most time efficient to perform, yet it is one of the most difficult to teach. The technique involves stereotactic needle maneuvering. A certain "mechanical" mind or sense of geometry is very helpful in mastering it. The paravertebral block is a selective block of the nerve roots at the chosen levels. The resultant anesthesia or analgesia is conceptually similar to a "unilateral" epidural anesthesia. Higher or lower levels can be chosen to accomplish a band-like segmental blockade at the desired levels. However, the paravertebral block does not result in hemodynamically significant sympathetic blockade, therefore, hypotension is not commonly seen with this block. This block is used most commonly in our practice for surgical patients undergoing inguinal herniorrhaphy. For this indication, it is important to avoid blockade of the L2 level (femoral nerve), which affects the ability to ambulate. The technique is also well suited for pain management after hip surgery (T12-L5).

The walls of the paravertebral space in this region are formed by the parietal pleura or iliopsoas anterolaterally, vertebral body, the intervertebral disc and intervertebral foramen medially and the superior costotransverse process posteriorly (higher levels). The spinal nerves in the paravertebral space are submerged in the paravertebral adipose tissue. The paravertebral space is continuous with the epidural space medially and the contralateral paravertebral space via the prevertebral fascia. The mechanism of action of paravertebral blockade at this level includes direct penetration of the local anesthetic into the spinal nerve, and medial extension through the intervertebral foramina.

Thoraco-lumbar paraverterbral block results in ipsilateral dermatomal anesthesia. The location of the resulting dermatomal distribution of anesthesia or analgesia is the function of the level blocked and the volume of local anesthetic injected.

The patient is positioned in the sitting or lateral decubitus position and supported by an attendant. The back should assume kyphosis, similar to a position required for neuraxial anesthesia. The patient's feet should be rested on a stool to allow for greater comfort and a greater degree of kyphosis. This increases the distance between the adjacent transverse processes and facilitates advancement of the needle beyond the contact with the transverse process.

Anatomic Landmarks

Before attempting the block, all relevant landmarks should be outlined with a pen. These include:

 Midline

 2.5 cm lateral to the midline

Hand position

The fingers of the palpating hand should straddle the paramedial line and fix the skin to avoid medial-lateral skin movement. This hand is moved in the cranial-caudal position only during the block placement. The needle is inserted perpendicular to the skin with constant attention to the depth of needle insertion and the medial-lateral needle orientation.

The entire block procedure consists of five maneuvers:

 Contact the transverse process of the individual vertebrae and note the depth at which the process was contacted.

 Withdraw the needle to the skin level and reinsert at a 10° superior or inferior needle angulation.

 Walk off the transverse process 1 cm deeper to the transverse process and inject 4-5 mL of local anesthetic.

Some authors suggest using a loss of resistance technique to identify the paravertebral space. However, such a change of resistance, even when present, is very subtle and nonspecific at best. For this reason, we do not pay attention to the loss of resistance but carefully measure the skin-transverse distance and simply advance the needle 1 cm past the process. A certain "give" may be occasionally felt as the needle passes through the costotransveralis ligament, however, this is obviously not the case at the lumbar level.

Proper handling of the needle is important both for accuracy and safety. Once the transverse process is contacted, the needle should be regripped so that the fingers create allow 1 cm deeper insertion.

Unless lower lumbar levels (L2-5) are blocked, paravertebral blocks do not result in motor block of an extremity and do not impair the patient's ability to ambulate. In addition, relatively small volumes injected at several levels do not present a concern for local anesthetic toxicity. For these reasons, it is almost always beneficial to achieve longer acting blockade by using longer acting local anesthetic.

The onset time for this block is slightly longer than in other block techniques (15-25 min). 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 of the local anesthetic used, the faster the onset can be expected.

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