Oct 30, 2019, 15:45 PM by Vishal Uppal, MBBS, FRCA, EDRA, and Vivian H.Y. Ip, MBChB, MRCP, FRCA

Since the erector spinae plane (ESP) block was first described for the treatment of thoracic neuropathic pain by Forero et al. in 2016,^[1] more than 200 articles have been published about the procedure. Most are positive case studies or case series reporting its analgesic efficacy for clinical indications ranging from tension headache to transfemoral knee amputation.^[2],[3] This is reminiscent of the enthusiasm that initially existed with the introduction of the transversus abdominis plane (TAP) block.^[4],[5] The TAP block emerged amid a plethora of encouraging case reports and case series. However, after randomized, controlled trials (RCTs) and systematic reviews were conducted, its efficacy was found to be moderate at best.^[6] Based on clinical experience and medical literature reports, clinical indications remain for the provision of TAP, but the widespread application has certainly diminished.^[7]

The advantage of most, albeit not all, interfascial plane blocks is their superficial nature, which makes them a popular option for patients who are coagulopathic or those with a high chance of requiring postoperative anticoagulation. Therefore, they can be offered as a rescue when the gold standard (epidural analgesia) cannot be used. In those scenarios, an interfascial plane block may be somewhat superior in terms of analgesic efficacy than no regional technique. One such example would be for an obese individual with a history of pulmonary embolism on anticoagulant therapy who presents with multiple rib fractures and respiratory compromise. In this situation, the patient could be offered an ESP as part of a multimodal analgesic regimen that aims to reduce opioid doses as well as oxygen requirements and intensive care unit admission.

Providers may have a false sense of security that interfascial plane blocks are safer than potential alternative procedures, but bowel puncture,^[8] rectus sheath hematoma,^[9] and pneumothorax^[10] have all been described in TAP, rectus sheath, and ESP blocks, respectively. The risks of associated adverse events tend to be underreported.

Nonetheless, ESP blocks may be useful in certain situations in the era of minimally invasive surgery. Laparoscopic bowel surgery may be less painful than open laparotomy; therefore, when analyzing the risk-benefit ratio, the risk of performing an epidural may outweigh the benefit of its superior analgesic effect. Despite the possible risks with ESP blocks, they are likely less detrimental when compared to potentially catastrophic neurologic side effects from an epidural. Perhaps there is such a thing as “minimally invasive” regional anesthesia.^[11]

However, any novel intervention should be rigorously tested for efficacy prior to widespread application and adoption into clinical practice. Diminished risks of adverse outcomes or complications are not a good indication for use of novel techniques as an alternative to more time-tested interventions. In the setting of limited efficacy evidence, clinicians should question whether an intervention is necessary at all, considering that each intervention is associated with some risk and economic impact. In the case of ESP blocks, the cost may be in the form of valuable operating or block room time, staffing, equipment, and follow-up. ESP blocks are still an invasive procedure.

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Any novel intervention should be rigorously tested for efficacy prior to widespread application and adoption into clinical practice.

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The gold standard for testing the efficacy of an intervention is a well-conducted RCT.^[12] RCTs are challenging to conduct with ever-increasing regulatory requirements necessitating abundant personnel resources and funding. Further, ethical considerations are associated with randomization if patients might be randomized to placebo. However, a clinical equipoise should justify those efforts. Unfortunately, the scientific community sometimes gets carried away and accepts weaker levels of evidence such as cadaver studies, case reports, and observational studies when RCTs are possible and justified. Cadaver studies can provide proof of concept, case reports are associated with high publication bias, and observational studies suffer from confounding issues.

A literature search of key databases MEDLINE, Embase, and Cochrane CENTRAL for ESP block in July 2019 yielded 526 citations. Most were cadaver studies, case reports, and case series. However, we identified 16 RCTs investigating ESP block published in the past 5 years. The RCTs were fairly heterogeneous in terms of surgical population, ESP technique, dose and type of local anesthetic used, and the comparator. Table 1 shows the RCTs’ key findings.

Table 1: Randomized, controlled trials of erector spinae plane (ESP) block.

Study	Population	N	Intervention	Control	Findings	Analgesic benefit
Aksu et al., 2019[13]	Pediatric lower abdominal surgery	60	ESP block at L1 level using 0.5 mL/kg 0.25% bupivacaine (max 20 mL)	QLB transmuscular approach was performed preoperatively using 0.5 mL/kg 0.25% bupivacaine (max 20 mL)	No difference was seen in Face, Legs, Activity, Cry, and Consolability scores at 0, 1, 3, or 6 hours postoperatively. No significant difference was determined in times to first analgesia between the groups (p > 0.05).	No difference
Aksu et al., 2019[14]	Laparoscopic cholecystectomy	46	ESP block with 20 mL 0.25% bupivacaine	No block	Mean morphine consumptions at 24 hours postoperatively were 7.5 mg in the ESP group and 13.2 mg in the control group. The groups also had a significant difference for NRS scores at 12 and 24 hours.	Marginal reduction in opioid use and NRS score in the short term
Altlparmak et al., 2019[15]	Mastectomy	42	ESP block with 0.375% bupivacaine	ESP block with 0.25% bupivacaine	The mean tramadol consumption at 24 hours was lower in the 0.25% group. In the 0.375% group, the NRS scores were significantly lower at every time points compared with the 0.25% group.	Favors 0.375% bupivacaine
Altlparmak et al., 2019[16]	Radical mastectomy	38	ESP block	Modified PECS	Postoperative tramadol consumption was lower in the PECS group compared to the ESP group. Median NRS scores were significantly lower in the PECS group at 1, 2, 12, and 24  hours postoperatively compared to the ESP group.	Favors PECS
Altlparmak et al., 2019[17]	Laparoscopic cholecystectomy	68	ESP block	ScTAP	Postoperative tramadol consumption was lower in the ESP group (mean difference 60.29 mg). Integration of area under the curve revealed no time wise difference between groups even though NRS scores by itself and time-wise linear area under curve scores were higher in the ScTAP group compared to the ESP group.	Marginally favor ESP
Ciftci et al., 2019[18]	Video-assisted thoracic surgery (VATS)	60	ESP block	No block	Opioid consumption at 1, 2, 4, 8, 16, and 24 hours postoperatively and the active and passive VAS scores at 0, 2, 4, 8, 16, and 24 hours were statistically lower in the ESP block group.	Favors ESP
Gaballah et al., 2019[19]	Video-Assisted Thoracoscopy (VATS)	60	ESP block	SPB	The ESP group showed a significantly lower VAS pain scores (rest and movement) than the SPB group from 4–6 hours postoperatively. The time for first required analgesic was significantly longer in the ESP group.	Favors ESP
Gurkan et al., 2019[20]	Breast surgery	50	ESP block with 20 mL 0.25% bupivacaine at the T4 level	No block	24-hour postoperative morphine consumption was lower in the ESP group. No statistically significant difference was seen between the groups in terms of NRS scores.	No difference in pain scores; marginal reduction in opioid use
Krishna et al., 2019[21]	Adult cardiac Surgery	106	ESP block at T6 level with 3 mg/kg of 0.375% ropivacaine	No block	The ESP group had better pain control, lower opioid requirement, and earlier time to extubation.	Favors ESP
Oksuz et al., 2019[22]	Reduction mammoplasty	44	ESP block	Tumescent anesthesia (local anesthetic infiltration)	At 1, 2, 4, 6, 12, and 24 hours postoperatively, the pain scores and additional analgesic requirement were lower of the ESP group.	Favors ESP block
Singh et al., 2019[23]	Lumbar spine surgery	40	ESP block	No block	Pain scores (and morphine consumption) immediately after surgery (P = 0.002) and at 6 hours after surgery (P = 0.040) were lower in the ESP block group compared with the control group.	Favors ESP block
Singh et al., 2019[24]	Modified radical mastectomy	40	ESP block	No block	Postoperative morphine consumption and first 8-hour pain scores were significantly less in patients receiving ultrasound-guided ESP block.	Favors ESP
Tulgar et al., 2018[25]	Laparoscopic cholecystectomy	40	ESP block	ScTAP	No difference in NRS score between the block groups at any time point. Rescue analgesia requirements during the first 12 hours were statistically significantly higher in the control group.	No difference in pain scores; marginal reduction in opioid use albeit statistically significant
Tulgar et al., 2018[26]	Laparoscopic cholecystectomy	36	ESP block	No block	No difference was seen in NRS scores at any time points (except 3 hours). Tramadol consumption was lower in the block group during the first 12 hours.	No difference in pain scores; marginal reduction in opioid use in the short term
Tulgar et al., 2018[27]	Hip and proximal femur surgery	60	ESP block	QLB	ESP block and QLB have similar analgesia.	No difference
Yayik et al., 2018[28]	Lumbar discectomy	60	ESP block at L3 with 20 mL of 0.25% bupivacaine	Sham block	Postoperative fentanyl consumption and VAS scores were lower in ESP group. Time to first analgesic request was longer in the ESP group.	Favors ESP

ESP, erector spinae plane; NRS, numeric rating scale; PECS, pectoral nerve block; QLB, quadratus lumborum block; ScTAP, subcostal transverse abdominal plane; SPB, serratus plane block; VAS, visual analog scale.

To summarize the RCT findings, the ESP block has been compared with either no block or another fascial plane block, such as pectoralis nerve (PECS) block, serratus plane block, subcostal TAP block, or quadratus lumborum block, for postoperative analgesia following various surgical procedures. All of the studies used a single injection technique. Most of the RCTs were single centered, had a small sample size, and had an uncertain or high risk of bias.

As with all new techniques, the possibility of publication bias cannot be ruled out. Studies with positive findings are more likely to be published and are likely to be published earlier than the studies with negative findings. When interpreting results, it is important to focus on patient-centered outcomes. Although a reduction in pain and opioid-related adverse effects are important outcomes from a patient perspective, reduction in short-term opioid use is a surrogate and should be considered less important. Smaller studies either tend to poorly report opioid-related adverse effects or are not powered to detect a difference between the groups for that outcome. In terms of analgesic efficacy, ESP blocks appeared to provide marginal analgesic benefit when compared to no block. The results of comparison of ESP block to other fascial plane blocks were somewhat mixed: some studies favored ESP block, others showed no difference, and one study favored PECS block. The efficacy data in comparison to epidural or paravertebral analgesia were lacking.

Recently, an interesting concept regarding an ESP block’s ability to affect the integrity and support of the spine has been proposed. Researchers suggested that large volumes of local anesthetic might spread across six to eight spinal levels, induce paraspinal muscle and interspinous ligament relaxation, and increase the risk of significant spinal instability.^[29]

Following a thorough evaluation of all the available literature, we recommend caution prior to offering an ESP block as an alternative for pain management when well-established and highly effective techniques such as epidural analgesia or paravertebral blocks are available. The limited documented efficacy of fascial plane blocks should be considered and disclosed to patients if a planned surgical procedure is known to be associated with moderate to severe pain. Furthermore, some of the fascial plane blocks like PECS, serratus plane, and subcostal TAP blocks are more conveniently performed with the patient in a supine position following the induction of general anesthesia, whereas ESP requires access to the back (ie, lateral or sitting position).

“You win some, you lose some” appears to be very true in ESP block efficacy, especially when comparing  ESP to traditional modes of analgesia with a better presence in the published literature. Patient preference and planned surgical approach are crucial to maximize the potential benefits of ESP blocks. Patients scheduled to undergo minimally invasive surgeries expected to produce minimal postoperative pain, or patients interested in receiving an ESP as a last resort rescue block may still benefit from an ESP block. Multimodal analgesic regimens are still required with ESP blocks in most case reports or case series and may represent the etiology for reported block efficacy. The mechanism of action of ESP blocks remains unknown, and the uncertainty extends to the pharmacodynamics of deposited local anesthetics. Could the marginal analgesic of ESP blocks be simply related to systemic absorption of local anesthetic? Therefore, caution is advised when determining the dosage of local anesthetic, especially for patients at elevated risk for the development of local anesthetic systemic toxicity (eg, patients with hepatic failure, low cardiac output).

As clinicians, we like to practice evidence-based medicine. We urge pain physicians to “stop before the block” and evaluate the risk-benefit ratio prior to performing an ESP block. Is less risk a justifiable reason to perform a block if it has little evidence of benefit? Just because it is easy to do, is not a good reason to do it!

References