Erector Spinae Block: A Magic Bullet for Postoperative Analgesia?

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The erector spinae plane block was first described in 2016 for thoracic analgesia,¹ followed not long after by reports of its use for abdominal analgesia.^2,3 It has attracted much interest within the anesthesia community for both its relative simplicity and apparent efficacy. The mechanism by which the erector spinae plane block exerts its action remains controversial. Penetration of injected fluid into the epidural and paravertebral spaces has been demonstrated in several, but not all cadaveric studies.^1,4–6 The available evidence indicates that there are anatomical pathways that would permit local anesthetic spread from the fascial plane deep to the erector spinae muscle into the paravertebral and epidural spaces. What is less clear is how consistently and to what extent this occurs, which in turn determines the clinical efficacy of the erector spinae plane block in actual patients.

The erector spinae plane block has been described and promulgated enthusiastically, primarily through a vast volume of case reports. This is not unusual for newly described techniques. Randomized controlled trials evaluating regional anesthesia interventions are logistically challenging, labor intensive, and expensive. Methodological quality is often compromised as a result of these constraints. Nevertheless, high-quality controlled clinical trials with minimal risk of bias are essential for rational clinical decision-making and avoiding the possibility that patients might be exposed to procedures with no likely prospect of effectiveness. This is a real risk given the number of new ultrasound-guided techniques being described.

It is therefore encouraging to see that randomized controlled trials of the erector spinae plane block are beginning to emerge, including the publication by Abu Elyazed et al⁷ in this month’s Anesthesia & Analgesia. The authors performed bilateral sham or active single-injection erector spinae plane blocks at the T7 transverse process before general anesthesia for epigastric hernia repair through a midline incision. Patients in the active erector spinae plane group had significantly reduced intraoperative and postoperative opioid requirements, a significant reduction in pain scores during the first 12 postoperative hours, and prolongation of the time to first request for additional opioid analgesia.

The subjective nature of many of the outcomes in randomized controlled trials evaluating regional anesthesia techniques (eg, numerical pain scores) means that there is a real risk of bias if a robust placebo intervention and adequate masking of group allocation are not implemented. We recognize that the use of a placebo intervention in a trial may be ethically challenging for some clinicians, as this exposes patients in the control group to the additional risk of needle trauma without anticipated benefit. As clinicians, our first rule is “do no harm,” and thus, the concept of a deliberate additional intervention with inherent risk runs counters to deeply embedded responsibilities of care. However, we should not confuse the ethics of clinical practice with the ethics of clinical research. The ethics of research demand that a trial be designed to minimize bias to the fullest extent possible, in turn maximizing the validity of the results and reducing the risk that future patients are exposed to unnecessary or ineffective interventions. To this end, Abu Elyazed et al⁷ are to be commended for utilizing sham injections in the control group rather than simply omitting the block. Nevertheless, their methodology would have been significantly improved by using a placebo intervention that was otherwise identical to the active intervention, that is, 20 mL instead of 1 mL of saline. This would have provided effective blinding of patients and all the clinical and research personnel involved. The authors themselves acknowledge the problems with blinding in their trial and the real possibility that the study participants would have been able to distinguish between an injectate volume of 1 vs 20 mL. We cannot therefore exclude the possibility that this would have influenced the self-reporting of their pain scores (the primary outcome). Because of this risk of bias, it is likely that this trial, if included in a future meta-analysis, will be rated as being of low quality. An additional method of reducing uncertainty regarding blinding would have been to calculate a blinding index, as described by Bang et al,⁸ which is obtained by asking study participants what study group they thought they were allocated to.

So where do we stand with regards to the place of the erector spinae plane block in clinical practice? There is accumulating evidence that the erector spinae plane block is an effective technique for thoracoabdominal analgesia. In addition to the study by Abu Elyazed et al,⁷ there are at least 3 other recently published randomized controlled trials that describe its superiority compared to systemic analgesia alone in breast surgery,⁹ laparoscopic cholecystectomy,¹⁰ and median sternotomy for cardiac surgery,¹¹ although they too have methodological limitations with regard to blinding. The erector spinae plane block appears to be a relatively safer and simpler alternative to thoracic paravertebral and epidural techniques and, for these reasons alone, may be more appealing to both anesthesiologists and patients. In addition, the erector spinae plane block may be applicable in a wider range of clinical settings, including neonates¹² and anticoagulated patients.¹³ Comparative studies are needed to establish whether the risk-benefit profile is indeed more favorable; these are starting to appear, with a recent randomized controlled trial reporting that bilateral erector spinae plane catheters provided similar analgesia compared to a thoracic epidural after cardiac surgery.¹⁴

A related question is the place of the erector spinae plane block with regard to other fascial plane block techniques. Abu Elyazed et al⁷ propose that the erector spinae plane block may be advantageous over more peripheral truncal blocks such as the transversus abdominis plane block as it provides visceral as well as somatic analgesia. While their results do not provide direct evidence for the effect of the erector spinae plane block on visceral pain, this is supported by other reports in bariatric surgery³ and laparoscopic cholecystectomy.¹⁰ On the other hand, in surgical settings where visceral pain is not a significant component, the erector spinae plane block may not necessarily be advantageous as evidenced by a recent trial comparing the erector spinae plane and pectoral block in breast surgery.¹⁵

The maturation of ultrasound-guided regional anesthesia, and the accompanying resurgence in interest, has led to calls for the development of simple, safe, and reasonably effective techniques that are within the capabilities of most anesthesiologists.¹⁶ We believe the erector spinae plane block represents a new and potentially exciting step in the democratization of regional anesthesia, and further studies, such as this one by Abu Elyazed et al,⁷ are eagerly awaited.

DISCLOSURES

Name: Ki Jinn Chin, MBBS, FRCPC.

Contribution: This author helped draft and critically revise the final manuscript.

Name: Michael J. Barrington, PhD, MBBS, FANZCA.

Contribution: This author helped draft and critically revise the final manuscript.

This manuscript was handled by: Richard Brull, MD, FRCPC.