Transversus Abdominis Plane Versus Quadratus Lumborum Blocks for Abdominal Surgery: Where Are We Now?
The role of regional anesthesia in abdominal surgery is well established, with epidural analgesia being the gold standard in perioperative analgesia since the early 1900s. However, following the advent of enhanced recovery after surgery protocols, early mobilization, minimally invasive surgical techniques, and pharmacologic venous-thromboprophylaxis are now recognized as key components of efficient surgical recovery. The search for less-invasive, motor-sparing, safer, and efficacious alternatives to epidural analgesia has been prioritized.
Multiple novel analgesic techniques for abdominal surgery have been described in recent years, most of which make use of fascial planes, and their purported benefits would make them ideal candidates for a multimodal analgesic strategy for abdominal surgery. The ubiquity of ultrasound technology and ultrasound-guided techniques has been vital in cementing the role of fascial plane blocks in the analgesic armamentarium. However, the evidence base for many of those approaches remains limited.
Although the differences in analgesic consumption between QL and TAP may be modest, the increased duration of QL blocks is perhaps the most significant difference between the two approaches.
Two techniques that have been the subject of the most interest are the transversus abdominis plane (TAP) block and the quadratus lumborum (QL) block approaches. The TAP block was first described as a landmark-based technique in 2001 and has since undergone several iterations to become an ultrasound-guided technique. The QL block approaches were an evolution of the TAP block and have also been revised and adapted over the years. For the details of the technique, please refer to the previous ASRA News article. However, with similar indications, direct comparison between the two techniques is warranted.
Transversus Abdominis Plane Block
The TAP block targets the somatic nerves on the anterior abdominal wall, most commonly using a subcostal or lateral approach (see Figure 1). The subcostal approach delivers local anesthesia between the rectus abdominis and transversus abdominis muscles (along the subcostal margin), through to the transversus abdominis plane, between the internal oblique and transversus abdominis muscles. This targets the anterior cutaneous branches of T6–T10, although more reliably of T7–T9. It is therefore suitable for unilateral, midline, upper-abdominal incisions. The lateral TAP block delivers local anesthesia in the same plane, but at the mid-axillary level, providing cutaneous analgesia for lower-abdominal incisions (T10–12).
Numerous clinical trials have examined the role of the TAP block following a variety of surgical procedures. Until recent meta-analyses, its clinical efficacy was presumed. It is now increasingly apparent, however, that the cutaneous analgesia provided by TAP blocks is modest. Although several studies have reported a significant reduction in pain scores and opioid consumption with TAP blocks compared to epidurals, local infiltration analgesia, or placebo, the clinical magnitude of those differences may be limited. Regardless of type of surgery, TAP blocks reduce morphine consumption by a maximum of 1 mg/hour and visual analogue scale pain scores by less than 2 points for the first 6–12 hours.[7-9] The limited extent of blockade and lack of visceral analgesia means the clinical importance of the differences is debatable.
Quadratus Lumborum Block
QL blocks target both somatic structures covering the anterior abdominal wall, with suggestions of abdominal visceral coverage as well, most commonly using a lateral, posterior, or anterior approach., The lateral approach (previously QL1) involves depositing local anesthesia at the lateral border of the QL muscle, anterior to the aponeurosis of the transversus abdominis muscle and within the anterior thoracolumbar fascia. The posterior approach (previously QL2) involves injecting posterior to the QL muscle, in the middle thoracolumbar fascia. The anterior approach (also called the transmuscular QL block) involves injecting anterior to the QL muscle, between it and the psoas major muscle and in the anterior thoracolumbar fascia (Figure 1).
Meta-analyses data are insufficient for QL blocks. Although multiple case reports and case series describe the utility of QL blocks in a range of abdominal surgical procedures, few randomized controlled trials have been conducted in this setting. Significant clinical benefits associated with the use of QL blocks include reductions in morphine consumption and pain scores up to 48 hours postoperatively. In particular, posterior and lateral QL block approaches have been investigated in cesarean delivery and gynecologic surgery, demonstrating longevity in duration of block. Limited and heterogeneous data are available in other abdominal procedures.
Three studies have directly compared TAP to QL blocks in a range of abdominal procedures. In caesarean delivery, QL blocks reduce morphine consumption for up to 48 hours whereas TAP blocks provide more short-term analgesic benefits. Similarly, QL demonstrated a more sustained analgesic effect compared to TAP blocks in pediatric patients undergoing abdominal surgery. These results have been further supported in other patient populations., Although the differences in analgesic consumption between QL and TAP may be modest, the increased duration of QL blocks is perhaps the most significant difference between the two approaches.
Table 1: Comparative table of transversus abdominis plane (TAP) blocks and quadratus lumborum (QL) blocks.
|TAP Blocks||QL Blocks|
|Potential dermatomal coverage||T10-12||T6-10||T7-L1||T7-L2||T6-L2|
|Lumbar plexus involvement||Reported||Rare||Possible||Rare||Likely|
|Injection site||Between internal oblique and transversus abdominis at midaxillary line||Superficial to transversus abdominis at midclavicular line along costal margin||Lateral border of QL muscle||Posterior surface of QL muscle||Between QL and psoas muscles|
• Trauma to abdominal structures
• Trauma to abdominal structures
|Level of difficulty||
• Easy to perform
• Single injection covering supraumbilical and infraumbilical dermatomes
• Potential visceral analgesia
• Potentially longer duration of analgesia
• Multiple injections to cover supraumbilical and infraumbilical levels
• No visceral analgesia
• Limited duration of analgesia
• Variable evidence of benefit
• Moderately difficult visualization
• Lumbar plexus block
• Limited evidence base
Several proposed and potential differences exist in the mechanisms of action between the two blocks that might explain the different clinical outcomes (see Table 1). TAP blocks only deliver local anesthetic to the cutaneous branches of the intercostal nerves and therefore only provide somatic analgesia for a limited duration of time. However, the mechanism of analgesia for QL blocks is less clear. One common theory is that QL blocks, particularly the anterior approach, provide analgesia via spread of local anesthetic to the thoracic paravertebral space by way of the thoracolumbar fascia and then the endothoracic fascia. This mechanism has been supported by both cadaveric and clinical studies., QL blocks may also exert their effect by blocking the branches of the lumbar plexus, particularly when an anterior approach is used. This mechanism is supported by limited clinical data that demonstrate QL block analgesic efficacy in lower limb surgery and iliac crest bone graft donor sites. In addition, QL blocks are associated with lower-limb weakness.[18-20] Finally, the long duration of QL blocks may be related to a peripheral sympathetic field block effect because the thoracolumbar fascia is richly innervated with autonomic fibres. This remains a theoretical mechanism.
The TAP block has played a critical role in opening doors for fascial plane blocks. Its simplicity, safety, and presumed efficacy improved access to regional anesthesia for patients globally. However, evidence suggests that its efficacy might be more limited than presumed. On the other hand, the QL block appears to have a prolonged duration of analgesic effect when compared to TAP blocks. Evidence for the efficacy of QL blocks continues to emerge, but until more robust randomized, controlled, clinical trials come forth, the debate goes on.
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