Mechanism of Analgesia for Erector Spinae Plane Block
The ESP block provides analgesia by depositing local anesthetic in the fascial plane deep to the erector spinae muscle and superficial to the transverse processes, where it spreads cranio-caudally and penetrates anteriorly through the costotransverse foramina to reach the paravertebral space and block the dorsal and ventral rami of spinal nerves. 1, 2
Anatomical Basis of Action
The mechanism relies on an interfascial injection technique where local anesthetic is placed in a specific tissue plane:
- Local anesthetic is injected deep to the erector spinae muscle at the level of the transverse process 1, 2
- The injectate spreads within this fascial plane and tracks anteriorly to reach the origin of spinal nerves in the paravertebral space 2
- This anterior spread allows blockade of both dorsal and ventral rami of multiple spinal nerve levels 2
Clinical Evidence of Efficacy
The analgesic effect has been demonstrated across multiple surgical contexts:
- ESP block reduces 24-hour postoperative opioid consumption (mean difference -17.49 mg morphine equivalents) and pain scores at rest and movement compared to no block 3
- Pain relief is most pronounced during the first 6-8 hours after single-shot administration, with effects diminishing thereafter 4, 5
- The block provides comparable analgesia to paravertebral block for thoracic surgery during the first 48 hours postoperatively 4
Spread and Coverage Characteristics
The extent of analgesia depends on injection level and volume:
- When performed at T5 level, ESP block provides thoracic analgesia 6
- Lower thoracic injections (T8 level) extend coverage to abdominal regions because the erector spinae muscles extend to the lumbar spine 6
- The typical volume of 20 ml bupivacaine 0.5% produces multi-dermatomal spread 4
Duration and Limitations
Single-shot ESP block provides effective analgesia for 6-8 hours, after which supplemental analgesia becomes necessary 4, 5. This time-limited effect represents a critical clinical consideration when planning postoperative pain management.
Continuous catheter techniques can extend analgesic duration and serve as an alternative to epidural analgesia for major surgery 6.
Safety Profile Advantage
ESP block is performed in a more superficial plane compared to paravertebral block, avoiding proximity to major intercostal vessels and the spinal canal, which reduces the risk of clinically significant hematoma 7, 3. This makes it particularly valuable for patients on anticoagulation therapy.
Integration with Multimodal Analgesia
ESP block must be combined with baseline analgesia including NSAIDs and paracetamol to optimize pain control 4, 7. The block serves as an adjunct rather than a standalone technique, with opioids reserved for rescue analgesia only 7.