Understanding the local anesthetic spread in paraspinal blocks: A cadaveric study

Paraspinal fascial plane blocks have gained popularity in modern anesthesia, particularly in thoracic surgeries. Techniques like the erector spinae plane (ESP) block and intertransverse process (ITP) block are being explored as alternatives to the paravertebral (PV) block and thoracic epidural anesthesia. These blocks aim to provide effective pain relief by targeting specific regions in the thoracic spine. However, the exact mechanisms of action and the extent of local anesthetic spread in these techniques remain controversial.

Study objective and methods

The cadaveric study aimed to evaluate and compare the spread of local anesthetic in three types of paraspinal blocks: ESP, ITP, and PV. The focus was on how far the local anesthetic spread, particularly within the paravertebral space, and its effect on the dorsal and ventral rami of spinal nerves.

Fifteen fresh cadaver hemithoraces were used, divided into three groups corresponding to the ESP (n = 5), ITP (n = 5), and PV (n = 5) blocks. Each block was administered under ultrasound guidance by experienced anesthesiologists. The same volume (20 mL of 0.375% ropivacaine) was injected in all blocks.

The blocks were performed between T4 and T6, and the technique for each block was as follows:

1. ESP block: The local anesthetic was injected into the erector spinae fascial plane, just superficial to the transverse processes.
2. ITP block: The local anesthetic was injected deeper, between the intertransverse processes, crossing through the intertransverse ligament.
3. PV block: The local anesthetic was injected anterior to the costotransverse ligament but posterior to the pleura.

Dissections were performed after each block to evaluate the spread of local anesthetic in both anterior and posterior directions. The involvement of the dorsal and ventral rami was also documented.

Key findings

1. ESP block

• The spread of local anesthetic extended across eight vertebral levels in a cranio-caudal direction.
• Involvement of the dorsal ramus at each level was observed.
• No local anesthetic spread into the paravertebral PV space or involvement of the ventral rami.

Posterior and anterior spread in ESP block.

2. ITP block

• Local anesthetic spread was observed within the PV space (1-2 vertebral levels) and across seven vertebral levels within the erector spinae fascial plane.
• This block involved both the ventral and dorsal rami of the spinal nerves, suggesting a more comprehensive analgesic effect.

Posterior and anterior spread in ITP block.

3. PV block

• Local anesthetic spread extended over 2-4 vertebral levels, affecting both the ventral and dorsal rami.
• No spread to the ESP was noted.

Posterior and anterior spread in PV block.

Conclusion

This study highlights important distinctions in the spread of local anesthetic among the three blocks. The ESP block affects the dorsal rami, making it useful for treating pain in the dorsal region but less effective for surgeries involving the ventral thoracic region. In contrast, the ITP block offers broader coverage, affecting both the ventral and dorsal rami and extending into the PV space, suggesting it may provide more balanced and effective pain relief. The PV block remains the gold standard for comprehensive pain relief but lacks the reach into the ESP.

These findings can guide anesthesiologists in selecting the most appropriate block based on the type of surgery and required pain coverage.

Future research

While this cadaveric study offers valuable insights, future research should focus on clinical trials in living patients to validate these findings. Exploring the spread of local anesthetic in real-world scenarios with dynamic tissue pressures and blood flow will provide a more accurate understanding of the blocks’ effectiveness. Additionally, investigating the long-term outcomes and combining blocks or modifying current techniques may further optimize pain relief, reducing the need for systemic opioids.

For more detailed information, refer to the full article in RAPM. 

Varela V, Ruíz C, Montecinos S, Prats-Galino A, Sala-Blanch X. Spread of local anesthetic injected in the paravertebral space, intertransverse processes space, and erector spinae plane: a cadaveric model. Reg Anesth Pain Med. 2024;49(3):228-232. 

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