New York School Of Regional Anesthesia - 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.

A standard regional anesthesia tray is prepared with the following equipment:

Sterile towels and 4"x4" gauze packs
20-mL syringes with local anesthetic
Sterile gloves, marking pen, and surface electrode
One 1½" 25-gauge needle for skin infiltration
A 10-cm long, 22-gauge, Quincke or Tuohy tip spinal needle

Surface Landmarks

The following boney surface anatomy landmarks are helpful to identify spinal levels and to estimate the position of the transverse processes:

Iliac crest (corresponds to L3-4 or L2-3)
Spinous processes (midline)
Tips of scapulae (corresponds to T7)

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

TIPS:

It should be noted that labeling the position of each individual transverse process at the level to be blocked is at best a rough estimation.
It is more practical to outline the midline instead and simply draw the line 2.5cm lateral to it. All injections will be along this line. Once two first transverse processes are identified, the rest will follow the same cranial-caudal spacing.
When lower lumbar levels are planned, keep in mind that the needle insertion should be closer to 2-cm lateral to the midline because the transverse processes of the lower lumbar vertebrae are shorter and smaller than at the higher lumbar or thoracic levels.

Local anesthetic skin infiltration

After cleaning the skin with an antiseptic solution, 6-8 mL of dilute local anesthetic is infiltrated subcutaneously alongside the line where the injections will be made. The injection should be carried out slowly to avoid pain on injection and new needle reinsertions should be made through already anesthetized skin.

TIPS:

Addition of a vasoconstrictor helps prevent oozing at the site of injection.
When more than 5-6 levels are blocked, use alkalinized chloroprocaine for skin infiltration to decrease the total dose of long-acting local anesthetic.

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 10º 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.

TIPS:

The needle should not be directed medially because of the risk of intraforaminal needle passage and a consequent spinal cord injury. Medial needle redirection leads to a needle pass identical to that in the paramedical approach to epidural/spinal block.
Use common sense in advancing the needle. The depth at which the transverse processes are contacted vary with the patient's body habitus and the level at which the block is performed. The deepest levels are at the high thoracic (T1,2) and low lumbar levels (L4,5) where the transverse process is contacted at a depth of 6-8 cm in averaged size patients. The shallowest depth is at the midthoracic levels (T5-T10) where the transverse processes are contacted at 2-4 cm in average sized patients.
Never disconnect the tubing from the needle (e.g., syringe change) during the block procedure when performing blocks at the thoracic levels. In cases when the needle tip is inadvertently placed in the chest cavity, a pneumothorax should not occur as long as the needle opening is sealed (no communication between the chest cavity and air outside).
Needles with depth markings are particularly well-suited for this block.

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.

	Onset (min)	Anesthesia (hrs)	Analgesia (hrs)
1.5% Mepivacaine (plus HCO3 + epinephrine)	10-20	2-3	3-4
2% Lidocaine (plus HCO3 + epinephrine)	10-15	2-3	3-4
0.5% Ropivacaine	15-25	3-5	8-12
0.75% Ropivacaine	10-15	4-6	12-18
0.5% Bupivacaine (plus epinephrine)	15-25	4-6	12-18
0.5% I-Bupivacaine (plus epinephrine)	15-25	4-6	12-18

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

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.

TIPS:

Local infiltration at the site of the incision by the surgeon sometimes is helpful to allow some additional time for the block onset. It is interesting that few patients have any discomfort on peritoneal stimulation with this block.
Weakness of the ipsilateral quadriceps muscle and inability to bear weight may occur in the occasional patient. It is due to the injection of local anesthetic at the L2 level. For this reason, it may be advisable to use a shorter acting local anesthetic (e.g., 1.5% mepivacaine or lidocaine) for blockade of the L1 segment.

Infection	- A strict aseptic technique should be used
Hematoma	- Avoid multiple needle insertions in anticoagulated patients
Local anesthetic toxicity	- Rare - Large volumes of long-acting anesthetic should be reconsidered in older and frail patients - Consider using chloroprocaine for skin infiltration to decrease the total dose/volume of the more toxic, long-acting local anesthetic
Nerve injury	- Local anesthetic should never be injected when the patient complains of severe pain or exhibits a withdrawal reaction on injection
Total spinal anesthesia	- This should be rare - Avoid medial angulation of the needle, which may result in an inadvertent epidural or subarachnoid needle placement - Aspirate before injection (for blood and CSF)
Quadriceps muscle weakness	- This may occur when the levels are not accurately determined and the levels below L1 are blocked (femoral nerve; L2-4)
Paravertebral muscle pain	- A paravertebral muscle pain, resembling a muscle spasm, is occasionally seen, particularly in young, muscular men and when a larger gauge Tuohy needle is used - Injection of local anesthetic into the paravertebral muscle before needle insertion and the use of a smaller gauge (e.g. 22 gauge) Quicke tip needle is suggested to avoid this side effect

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