Introduction:
Paracervical blocks are nerve blocks that comprise a one-time injection of local anesthetic adjacent to the nerve or plexus to provide good intra and postoperative pain relief. Sellheim first described the paravertebral block (PVB) in 1905, and it has been extensively employed to treat both acute and chronic pain since 1978. The paracervical blocks (PVB) can be given unilaterally or bilaterally, using either a single-shot or continuous catheter technique. Regional anesthesia for pain relief in the first stage of labor has traditionally been limited to caudal and lumbar epidural anesthesia. Injecting the anesthetic solution into the loose cellular tissue at the side of the cervix is a much more straightforward way of obstructing pain sensation from the uterus.
It may appear promising that this obvious technique of paracervical nerve block has not been utilized more extensively. There are two possible explanations. One issue is the complexity of exposing the lateral vaginal fornix during labor. The other appears to be the difficulty of inserting a needle which must be long and pliable by necessity in the exact anatomical position without injuring the fetus or damaging the uterine vessels and ureter.
What Is the Anatomy of the Paravertebral Block?
The thoracic paravertebral space (TPVS) is a wedge-shaped area on either side of the vertebral column adjoining the thoracic spine. The thoracic paravertebral space (TPVS) is bounded anterolaterally by the parietal pleura, posteriorly by the superior costotransverse ligament (SCTL), medially by the vertebrae and intervertebral foramina, and superiorly and inferiorly by the rib heads. The endo thoracic fascia, a fibroblastic structure that lines the interior of the thoracic cage and separates the TPVS into anterior and posterior fascial compartments, is located between the parietal pleura and the SCTL. Between both the parietal pleura and the endo thoracic fascia is the subserous fascia. The SCTL is continuous with the internal intercostal membrane and can be observed with ultrasound. This is anatomically significant since the tip of the needle must pierce this ligament for the PVB to be successful. The SCTL, on the other hand, is believed to be highly porous, perhaps through gaps at the medial or lateral aspects or through fenestrations in the ligament itself, which can sometimes assist in understanding the mechanism of some of the newer paraspinal blocks. Fatty tissue, intercostal spinal nerves, intercostal vessels, dorsal rami, rami communicate, and the sympathetic chain is all found in the TPVS space. In the TPVS, the spinal nerves run freely, the sympathetic trunk is anterior, and the intercostal nerves and vessels are posterior to the endo thoracic fascia.
What Is the Technique of Paracevical Block?
There are numerous landmark and ultrasound-guided methods available. All of them can be employed for single-shot injections or catheter placement.
A. Landmark Technique:
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With the patient in a sitting or lateral position, a mark is made 2.5 to 3 centimeters lateral to the spinous process at the correct level of the vertebrae.
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A Tuohy needle is usually used, and a catheter can be inserted if necessary. The needle is perpendicular to the skin until it contacts the transverse process (TP).
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This depth is greatest in higher thoracic levels (first thoracic vertebrae to second thoracic vertebrae). Conversely, in the midthoracic region, it is the shallowest (fifth thoracic vertebrae to tenth thoracic vertebrae ).
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This depth is approximately four centimeters in the thoracic region, which means that needle placement beyond this point without bony contact requires caution because the needle may be between the transverse processes, and deeper insertion risks pneumothorax.
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The transverse process contacted must be that of the thoracic vertebrae below considering the spinous process angulation, that is, the fifth thoracic vertebrae spinous process is at the level of the sixth thoracic vertebrae transverse process.
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When the needle contacts the transverse process, it is walked off superiorly or inferiorly using a loss of resistance to air or saline. Conversely, the needle should be progressed no further than 1 to 1.5 centimeters past the transverse process. A pop is felt immediately as the needle passes through the superior costotransverse ligament.
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In contrast to epidural block, loss of resistance or pop in thoracic paravertebral space is highly subjective. Therefore, following gentle aspiration, a local anesthetic can be administered. If necessary, a catheter is advanced up to two to three centimeters of the thoracic paravertebral space.
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To avoid an accidental pleural puncture, sonographic measurements of the distances from the skin to the transverse process and parietal pleura can be used to determine the depth of needle insertion.
B. Ultrasound-Guided Technique:
1. Longitudinal Oblique, In-Plane Technique:
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The ultrasound probe is positioned caudocranially, approximately five centimeters from the midline, to identify the ribs and pleura.
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The probe is moved medially till the ribs transition (convex) to the transverse process (more squared and superficial) is visible. The probe is then rotated anticlockwise, so the cranial end is medial, and the caudal end is now lateral.
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Finally, the probe is gently tilted laterally to enhance the image. Then, the needle is advanced from caudal to cranial in the plane of the ultrasound beam.
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When the superior costotransverse ligament (SCTL) is perforated, the needle tip is in the paravertebral space, and a local anesthetic, when administered, will push the pleura downward.
2. Transverse, In-Plane Technique:
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To identify the rib, the ultrasound probe is inserted transversely (axially), just lateral to the midline. The probe is then moved caudally to view the intercostal space.
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The pleura and the internal intercostal membrane that is continuous with the superior costotransverse ligament (SCTL) should be visible.
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The needle is progressed from lateral to medial towards the transverse process until it pierces the internal intercostal membrane.
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After confirming that the aspiration is negative, a local anesthetic is administered, and the pleura is re-visualized, moving downwards.
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Visualization of structural anatomy, the shaft and the tip of the needle, local anesthetic spread, and catheter placement are all potential advantages of ultrasound-guided transverse paracervical vertebral block techniques.
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Using ultrasound results in a shorter onset time, a longer duration of the block, less local anesthetic volume required lower failure and complication rates, and less patient discomfort.
What Are the Indications of Paracervical Block?
1. Postoperative Analgesia:
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Surgeries in the thoracic region (open and thoracoscopic) (T4 to T5).
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Surgeries involving the breast (T2 to T6).
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Surgery involving the kidneys and ureters (T10 to L1).
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Cholecystectomy (T6 to T7).
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Herniorrhaphy is a surgical operation to correct the hernia (T10 to L2).
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Appendicitis removal (T12 to L1).
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Cardiovascular surgery with minimally invasive techniques (T1 to T7) and hepatectomy is the surgical resection of the liver (T6 to T7).
2. Surgical Anaesthesia:
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Augmentation of the breast.
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Herniorrhaphy is a surgical operation to correct the hernia.
3. Chronic Pain:
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Neuropathy of the abdominal region and thoracic and from malignant and benign causes.
4. Miscellaneous:
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Controlling hyperhidrosis therapeutically.
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Analgesia of the liver capsule following blunt abdominal trauma.
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Herpetic neuralgia (acute).
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Anesthesia for rib fracture.
What Are the Contraindications of Paracervical Block?
1. Absolute Contraindications:
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Allergy to local anesthetic drugs.
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The patient refuses the technique.
2. Relative Contraindications:
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Coagulopathy, bleeding disorders, or patients currently taking anticoagulant medication..
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Patients who are suffering from kyphoscoliosis or other spinal deformities.
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History of thoracic surgery.
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Sepsis is caused by empyema and other causes.
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A neoplastic mass occupies the paravertebral space.
Conclusion:
Thoracic PVB is an excellent analgesic method for abdominal and thoracic surgeries, with catheter placement and local anesthetic infusion allowing extended analgesia. Ultrasound-guided advances in the field have success rates and may lower the risk of complications. Newer paraspinal blocks also show great promise, but more research is needed to determine their effectiveness.
