Thoracic paravertebral block

Thoracic paravertebral blockade is a technique involving the introduction of a local anesthetic in the region of the thoracic spinal nerves emerging from the intervertebral foramen with ipsilateral somatic and sympathetic nerves. The resulting anesthesia or analgesia is similar to the "one-sided" epidural anethosis. The block level is selected in such a way as to achieve a one-way, band-like, segmental blockage at the desired length without significant hemodynamic changes. Paravertebral blockade is one of the simplest and most cost-effective to implement, but the most difficult in training, because it requires complex spatial maneuvers when moving the needle. It requires some "mechanistic" or metric thinking. Paravertebral blockade is most often used for operations on the mammary gland (mastectomy, cosmetic surgery) and chest.

Indications

Paravertebral blockade is indicated for operations on the mammary gland, pain relief after thoracic operations or rib fractures.

Landmarks

• Spiny process at the level of the corresponding thoracic dermatomes
• Insertion of the needle: 2.5 cm lateral to the midline.
• Final goal. Insertion of the needle 1 cm deeper than the transverse process
• Local anesthetic: 3-5 ml per level.

Anatomy

Thoracic paravertebral space is a wedge-shaped region that is located on both sides of the spinal column. Its walls are formed by the parietal pleura anterolaterally, the vertebral body, the intervertebral disc and the intervertebral opening medially and the superior costo- lateral process from behind. In the paravertebral space, the spinal nerves are organized into small bundles immersed in adipose tissue. At this level, they do not have a thick fascial membrane, so they are relatively easily blocked by the administration of a local anesthetic.

The thoracic paravertebral space communicates with the intercostal space laterally, with the epidural space medially and paravertebrally from the opposite side by means of the pre-invertebrate fascia. The mechanism of action of the paravertebral block is the direct penetration of the local anesthetic into the spinal nerve, its spread laterally along the intercostal nerve and medially through the intervertebral foramen.

[1], [2], [3], [4], [5]

Anesthesia zone

The thoracic paravertebral blockade is accompanied by anisal anesthesia of the corresponding dermatome. The final picture of the dermatomal distribution of anesthesia is a function of the level of the block and the volume of the local anesthetic injected.

[6], [7], [8], [9]

Position of the patient

Paravertebral blockade is performed in a certain position of the patient. The patient is sitting or lying on his side, supported by an anesthesiologist. The back bends forward (kyphosis), similar to the position required for neuraxial anesthesia. The patient's legs are placed on the stool to create a more comfortable position for him and a greater degree of kyphosis. This increases the distance between adjacent transverse processes and facilitates the movement of the needle without contact with bone formations.

Equipment for paravertebral blockade includes:

• a set of sterile diapers and gauze napkins;
• 20-ml syringes with local anesthetic;
• Sterile gloves, marker and surface electrode,
• one-time needle with a diameter of 25 gage for infiltration of the skin, a spinal needle - 10 cm in length and 22 giges in diameter of the type of Quincke or Tuohi.

The paramedial line, located 2.5 cm lateral to the median line.

It should be noted that marking the position of each transverse process at the level to be blocked is, at best, roughly approximate. From a practical point of view, it is better to designate the middle line and draw a line 2.5 cm lateral to it. All needle insertion points are located on this line. Once the first two transverse processes have been identified, the others will follow them at the same distance.

How is the paravertebral blockade performed?

Infiltration of the skin and subcutaneous tissue. After treating the skin with an antiseptic solution, 6-8 ml of a diluted solution of a local anesthetic is injected subcutaneously along the indicated paramedial line. The solution is injected slowly to avoid pain when injected. Repeated needles should be inserted on an anesthetized area of the skin. The additional injection of the vasopressor helps prevent the leakage of the syrup at the injection site. When a paravertebral blockade of more than 5-6 levels is performed (for example, with a bilateral block), it is preferable to use chlorprocarin or lidocaine to infiltrate the skin to reduce the total dose of a long-acting local anesthetic.

Introduction of the needle. The needle is inserted perpendicular to the skin. You should always pay attention to the depth and medial-lateral orientation. It must be especially carefully monitored to avoid the medial direction (risk of epidural or intrathecal injection). After contact with the transverse process, it is pulled to the skin and redirected up or down so as to bypass it.

The final goal is to hold the needle 1 cm deeper than the level of the transverse process. Some sense of "failure" can be determined at the time of passage through the costal-lateral ligament, but it can be taken into account as an anatomical landmark. The procedure essentially consists of three maneuvers:

1. Enter into contact with the lateral process of this vertebra and note the depth at which this contact is obtained (usually 2-4 cm).
2. Tighten the needle to the skin level and to the right 10 degrees caudally or cephoidally. 3). Bypass the transverse process, hold the needle 1 cm deeper and introduce 4-5 ml of local anesthetic.

The needle must be guided so as to "bypass" the transverse process from above or below. At the level of Th7 and below, it is recommended to "walk along the transverse process" in order to reduce the risk of intrapleural needle insertion. Correct paravertebral blockade and needle insertion are important for both accuracy and safety. Once contact with the transverse process is obtained, the needle is intercepted so that the fingers holding it allow the introduction to be limited by 1 cm relative to the present position of the needle.

The middle line connecting the spinous processes, the paravertebral line located 2.5 cm lateral to the midline, the lower angle of the scapula corresponds to the level of Th7.

Some authors suggest using a technique based on loss of resistance to identify the paravertebral space, but such a change in resistance, even at best, is very subtle and uncertain. For this reason, it is better not to stop paying attention to the loss of resistance, but carefully measure the distance from the skin to the transverse process and simply move the needle 1 cm deeper.

Never direct the needle medially because of the risk of holding its intervertebral foramen with subsequent injury to the spinal cord. Use common sense when moving the needle. The depth at which contact with the transverse processes is determined depends on the physique of the patient and the level of the paravertebral block. Deepest contact with the transverse process is noted on the high thoracic (T1-T2) and low lumbar levels L1-L5), where the patient of medium build is determined at a depth of 6 cm. The closest contact to the skin is at the mid-thoracic (T5- T10) about 2-4 cm. Never disconnect the needle from the syringe tube with a local anesthetic throughout the procedure. Instead, use a three-position valve to switch from one syringe to another.

Choosing a local anesthetic

Paravertebral blockade uses drugs with long-term action.

If an anesthetic of the lower lumbar segments is not planned, a paravertebral blockade is not accompanied by a motor block of the limb and does not affect the patient's ability to walk and maintain himself.

In addition, relatively small volumes introduced at several levels do not pose a threat in terms of the general-resorptive action of the local anesthetic. In patients who undergo extensive paravertebral blockade at several levels, alkalized chloroprocaine for skin infiltration is preferred to reduce the overall dose of a more toxic long-acting local anesthetic.

[10], [11]

Dynamics of the paravertebral block

Paravertebral blockade is associated with mild discomfort for the patient. Adequate sedation (midazolam 2-4 mg) is always necessary to facilitate the execution of the block. To anesthetize the procedure - fentanyl 50-150 mcg. It is necessary to avoid excessive sedation, since the paravertebral blockade becomes difficult if the patient can not keep the balance in a sitting position. The spread of paravertebral blockade depends on the distribution of the anesthetic within the space and the achievement of nerve roots at the level of injection. The higher the concentration and volume of the local anesthetic used, the faster the development of anesthesia is expected.

[12], [13], [14], [15], [16]

Complications and prevention measures

Infection. Strict compliance with asepsis rules is necessary.

Hematoma - Avoid multiple needle introductions in patients receiving anticoagulants.

Common-resorptive action - is relatively rare in the procedure such as paravertebral blockade. Care should be taken to introduce large volumes of long-acting anesthetics in elderly patients; for infiltration of the skin, use the chlorprocarin solution to reduce the total dose of anesthetic with long-term action.

Nerve damage - never inject an anesthetic solution if the patient complains of a sharp pain or shows a protective reaction at the time of injection.

Total spinal anesthesia - avoid the medial direction of the needle to prevent its epidural or intrathecal administration through the intervertebral foramen, always perform an aspirate test for blood or cerebrospinal fluid before administration.

Weakness of the quadriceps femoris - may occur if the level of the paravertebral block is not defined or a block below L1 (femoral nerve L2-L4) was performed.

Muscle pain in nature resembling a muscle spasm is sometimes noted (more often in young men with well-developed muscles) when using thick needles such as Tuohi. Preventive measures - the introduction of a local anesthetic into the muscles before carrying it, the use of needles of smaller diameter (22 gage) or the type of Quincke.

[17], [18], [19], [20], [21]