Residency · Residency · Anesthesiology

Truncal Blocks: TAP, Quadratus Lumborum, and Erector Spinae Plane

The Fascial Plane Block Concept

Principles

Fascial plane blocks involve injecting local anesthetic between fascial layers to block nerves as they traverse those planes. The extent of blockade depends on the volume of injectate and its spread along tissue planes. These blocks are generally simpler to perform than targeted peripheral nerve blocks. However, the rapidly expanding landscape of fascial plane techniques demands critical appraisal of efficacy evidence for each specific block.

Thoracoabdominal Innervation

The abdominal wall receives sensory innervation from the anterior rami of T6-L1, carried by the intercostal and subcostal nerves. These nerves travel in the transversus abdominis plane (TAP) between the internal oblique and transversus abdominis muscles. Each nerve gives off a lateral cutaneous branch and an anterior cutaneous branch.

Transversus Abdominis Plane (TAP) Block

Anatomy

The anterolateral abdominal wall consists of three muscle layers: the external oblique (most superficial), the internal oblique, and the transversus abdominis (deepest). The TAP is the fascial plane between the internal oblique and transversus abdominis. The thoracolumbar nerves (T6-L1) course through this plane.

Approaches

Lateral (Classic) TAP Block

The probe is placed between the iliac crest and the costal margin at the midaxillary line. The three muscle layers are identified, and the needle is advanced in-plane from anterior to posterior. Local anesthetic is injected between the internal oblique and transversus abdominis. This approach covers T10-L1 (infraumbilical region) with a typical volume of 20 mL per side.

Subcostal TAP Block

The probe is placed obliquely along the costal margin, targeting the upper abdominal wall (T6-T10). This approach covers supraumbilical incisions, including upper midline and subcostal incisions. Full midline coverage may require both subcostal and lateral TAP blocks.

Posterior TAP Block

The injection is performed posterior to the midaxillary line near the triangle of Petit. This approach tends to produce broader dermatomal spread due to proximity to the nerve origins and may provide some component of visceral analgesia.

Evidence

TAP blocks have demonstrated effectiveness for cesarean delivery, appendectomy, hernia repair, and laparoscopic surgery. The benefit is most pronounced when used as part of multimodal analgesia and when neuraxial techniques are not employed. When epidural analgesia is already in place, TAP blocks add minimal additional benefit. Analgesic duration is 12-24 hours with a single injection, which can be prolonged with liposomal bupivacaine or catheter placement.

<image>Cross-sectional anatomical diagram of the lateral abdominal wall showing the three muscle layers (external oblique, internal oblique, transversus abdominis) with the transversus abdominis plane highlighted between the internal oblique and transversus abdominis. The thoracolumbar nerve is shown coursing through the TAP. An ultrasound probe and needle are positioned at the midaxillary line between the iliac crest and costal margin, with the needle tip in the TAP and local anesthetic spread depicted as a lens-shaped collection in the fascial plane.</image>

Quadratus Lumborum (QL) Block

Rationale

The QL block involves injection adjacent to the quadratus lumborum muscle, allowing local anesthetic to spread along the thoracolumbar fascia toward the paravertebral space. This potentially provides wider dermatomal coverage than the TAP block and may offer some visceral analgesia through paravertebral spread.

Anatomy

The quadratus lumborum is a posterior abdominal wall muscle that extends from the iliac crest to the 12th rib. It is enclosed within layers of the thoracolumbar fascia. The psoas major lies anterior to it, the transversus abdominis (via its aponeurosis) is lateral, and the erector spinae is posterior.

Types

QL1 (Lateral QL Block)

The injection is placed at the lateral border of the QL muscle. This approach is similar to a posterior TAP block and provides coverage of T10-L1.

QL2 (Posterior QL Block)

The injection is placed behind the QL muscle, between the QL and the erector spinae. This approach has greater potential for paravertebral spread, and coverage may extend from T8 to L2.

QL3 (Transmuscular/Anterior QL Block)

The needle traverses through the QL muscle, and the injection is placed between the anterior surface of the QL and the psoas major. This approach has the best potential for paravertebral and even epidural-like spread, with coverage potentially extending from T7 to L2 or broader. It is the most technically demanding of the three approaches.

Evidence

A growing body of randomized controlled trials examines the QL block for cesarean delivery, hip surgery, and colorectal surgery. These studies generally show reduced opioid consumption compared to no block. Comparisons with the TAP block suggest the QL block may provide longer duration and broader coverage, though some trials show equivalence. The optimal approach (QL1 vs. QL2 vs. QL3) remains debated, and cadaveric dye studies show variable spread patterns, which explains the inconsistency of clinical results.

Complications

Potential complications include femoral nerve weakness from anterior spread to the lumbar plexus (especially with the QL3 approach), renal puncture (with the anterior approach), and local anesthetic systemic toxicity from the large volumes required.

Erector Spinae Plane (ESP) Block

Anatomy

The erector spinae muscle group lies posterior to the transverse processes of the vertebrae. The ESP block involves injection between the erector spinae and the transverse process. The proposed mechanism is that local anesthetic spreads craniocaudally along the fascial plane and penetrates anteriorly through the costotransverse foramina to reach the ventral and dorsal rami.

Technique

The block is performed with the patient sitting or in lateral position. A curvilinear or linear probe is placed in a parasagittal orientation. The target transverse process is identified (typically T5 for thoracic procedures, L3-L4 for lumbar procedures). An in-plane approach from cranial to caudal is used. The needle contacts the transverse process, and local anesthetic is injected deep to the erector spinae muscle. Craniocaudal spread is observed as the muscle lifts off the transverse process. A volume of 20-30 mL per side is typical.

Coverage

Coverage from the ESP block is highly variable, which is one of the main criticisms of the technique. Theoretically, it covers multiple dermatomes with both somatic and potentially visceral components. A single injection site commonly claims 4-6 dermatomal levels of coverage. The block has been used for thoracic surgery (thoracotomy, VATS), abdominal surgery, breast surgery, hip surgery, and rib fractures.

Evidence -- Critical Appraisal

Initial enthusiasm for the ESP block was based on case reports and small series. Randomized controlled trials are now emerging with mixed results: some show reduced opioid consumption and pain scores, while others show minimal benefit over placebo. Comparisons with established techniques reveal that the ESP block is generally inferior to paravertebral block and epidural analgesia for thoracic surgery. The key criticism is that the proposed mechanism of action -- paravertebral spread -- is inconsistent in cadaveric and radiologic studies. The block may function primarily as a posterior chest or abdominal wall block rather than providing true paravertebral or epidural-like analgesia. The current consensus is that the ESP block is promising but requires further study and should not replace established techniques such as epidural and paravertebral blocks in evidence-based protocols.

<image>Parasagittal anatomical illustration showing the erector spinae plane block. The erector spinae muscle group is shown overlying the transverse processes of the thoracic vertebrae. A needle is depicted contacting the transverse process with local anesthetic spreading craniocaudally in the plane deep to the muscle. Inset arrows show theoretical anterior spread through the costotransverse foramen toward the ventral rami and paravertebral space, with a question mark indicating the inconsistency of this spread pattern in clinical practice.</image>

Other Truncal Blocks (Brief Overview)

Rectus Sheath Block

The rectus sheath block involves injection between the rectus abdominis muscle and the posterior rectus sheath, targeting the anterior cutaneous branches of T9-T11. It is ideal for midline incisions such as umbilical hernia repair and laparoscopy port sites. A volume of 10-15 mL per side is typical.

Serratus Anterior Plane (SAP) Block

The SAP block is performed by injecting superficial or deep to the serratus anterior muscle at the midaxillary line at rib level 4-5. It covers the lateral cutaneous branches of the intercostal nerves and is indicated for rib fractures, breast surgery, and thoracotomy supplementation. A volume of 20-30 mL is used.

Pectoral Nerve (PECS) Blocks

PECS I involves injection between the pectoralis major and minor muscles, targeting the medial and lateral pectoral nerves. PECS II adds an injection between the pectoralis minor and serratus anterior, covering the intercostobrachial nerve and T3-T6 lateral cutaneous branches. These blocks are primarily indicated for breast surgery, including mastectomy and implant-based reconstruction.

Comparing Truncal Blocks

Clinical Pearls

TAP blocks are most useful when neuraxial analgesia is not being used; they add little benefit on top of a working epidural. The QL block likely provides broader and longer-lasting analgesia than the TAP block due to paravertebral spread, but the optimal approach (QL1, QL2, or QL3) is not settled. ESP blocks are easy to perform and safe (the needle contacts bone), but their efficacy is inconsistent, and they should not be relied upon as the sole analgesic technique for major surgery. Bilateral truncal blocks require large total local anesthetic volumes, and maximum doses must be calculated carefully to avoid LAST. For cesarean delivery analgesia when intrathecal morphine is not used, both TAP and QL blocks are effective options. Fascial plane blocks should be viewed as one component of a multimodal strategy, not as a replacement for proven techniques like epidural analgesia.

References

• Elsharkawy H, El-Boghdadly K, Barrington M. Quadratus lumborum block: anatomical concepts, mechanisms, and techniques. Anesthesiology. 2019;130(2):322-335.
• Forero M, Adhikary SD, Lopez H, et al. The erector spinae plane block: a novel analgesic technique in thoracic neuropathic pain. Regional Anesthesia and Pain Medicine. 2016;41(5):621-627.
• De Oliveira GS, Castro-Alves LJ, Nader A, et al. Transversus abdominis plane block to ameliorate postoperative pain outcomes after laparoscopic surgery: a meta-analysis of randomized controlled trials. Anesthesia & Analgesia. 2014;118(2):454-463.
• Chin KJ, El-Boghdadly K. Mechanisms of action of the erector spinae plane (ESP) block: a narrative review. Canadian Journal of Anesthesia. 2021;68(3):387-408.
• Uppal V, Retter S, Engelbrecht N, et al. Quadratus lumborum block for postoperative analgesia: a systematic review and meta-analysis. Canadian Journal of Anesthesia. 2020;67(11):1557-1575.

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