A prospective double-blinded randomized control trial comparing erector spinae plane block to thoracic epidural analgesia for postoperative pain in video-assisted thoracic surgery

Lung resection surgery causes considerable postoperative pain, which can interfere with deep breathing or coughing during the postoperative period, and it can lead to postoperative pulmonary problems, such as atelectasis, lung infection, and respiratory failure.1 Although video-assisted thoracic surgery (VATS) is typically regarded as less invasive and painful, moderate-to-severe postoperative pain is still to be expected.2 Recently, appropriate and efficient postoperative pain management has become a requirement for improved recovery after surgery in thoracic surgery.3 It can improve surgical outcomes, reduce complications, and reduce hospital stays. Thus, inadequate pain relief following VATS exposes the patients to postoperative morbidities and affects the quality of the patient’s recovery.

Thoracic epidural analgesia (TEA) and thoracic paravertebral blocks (TPVB) have been used widely to manage postoperative pain in thoracic surgery. However, these gold-standard analgesic techniques are often challenging to perform and may induce complications, including dural puncture, nerve injury, epidural hematoma, infection, hypotension for TEA or pneumothorax, local anesthetic toxicity, inadvertent spinal or epidural block for TPVB.4 Thus, various regional nerve blocks, including intercostal nerve block, serratus plane block, pectoral nerve block, and retrolaminar block can be performed as alternative analgesic methods.5 The erector spinae plane (ESP) block is a recently described interfascial procedure where local anesthetics (LA) are injected between the erector spinae muscle and the tip of the transverse process (TP).6 This block is simple to perform, and numerous studies have established the analgesic efficacy of ESP block in a variety of therapeutic settings.6-8 However, because most earlier published studies were case reports,they could not provide a clinical basis for the effectiveness and safety of ESP blocks.9 Therefore, we performed a comparative study to evaluate the analgesic efficacy between continuous ESP blocks and TEA in patients with lung cancer receiving VATS.

In this study, we examined the effectiveness of ESP blocks and TEA as postoperative analgesics in patients undergoing VATS. Continuous ESP block provided inferior postoperative analgesia to TEA regarding analgesic efficacy in the immediate post-operative period following VATS, as shown by the NRS score at rest and during coughing for 48 hours postoperatively. Furthermore, ESP block needed more opioid consumption than the TEA group. However, the NRS score difference between groups was smaller than 2/10, and the TEA group had a greater incidence of overall adverse events than the ESP block group.

Forero et al6 first described ESP block for thoracic neuropathic pain. Erector spinae plane block is an emerging regional block in which LA is deposited in the interfascial plane between the erector spinae muscle and the transverse process of the vertebra. Erector spinae plane blocks have been utilized for acute pain control following surgery and chronic pain control in several body areas and for various surgeries, owing to their simplicity and safety in the last 2 years.11 In many articles published describing the application of ESP blocks for VATS, the procedure is performed with a single injection or continuous infusion method at the 5th thoracic vertebra TP, which provides multi-dermatomal spread and lower pain score, and decreased opioid consumption.6,7,12-18 In our study, the ESP block group described a reasonable analgesic efficacy, cephalocaudal spread covering an average of 4 dermatomes, and an improved side effect profile.

Previous research has suggested that the ESP block may function by blocking the dorsal and ventral rami of the thoracic spinal nerves as well as sympathetic nerve fibers.6,19 Cadaveric data show heavy dye staining anterior to the erector spinae muscles and intercostal muscles, as well as around the costotransverse junction, indicating spreading in the paravertebral space in anatomical dissection.6 Following this evidence, the recent cadaveric study described that an ESP block with 20 mL of injectate provided neural foraminal and epidural spread across 2 to 5 vertebral levels in magnetic resonance imaging.20 In contrast with this evidence, other cadaveric research demonstrated that 20 mL of dye infused between the erector spinae muscle and the transverse process resulted in extensive cephalocaudal and medial-to-lateral spread but no anterior spread to the paravertebral space.21 Thus, local anesthetics of ESP block may spread into the paravertebral area through porous ligamentous tissues. However, the extent of distribution into this space could be more limited than that of TPVB.

Thoracic epidural analgesia and TPVB represent the gold standards for both open thoracotomy and VATS. Recently, these regional anesthetic techniques, as adjuncts to anesthesia, are considered one of the critical components in a thoracic enhanced recovery after surgery (ERAS) program because of the benefit for acute postoperative pain management.22 However, there are possible side effects and complications, including hypotension, respiratory depression, urinary retention, nausea and vomiting, incomplete or failed block, and in rare cases, permanent neurologic injury.4 Recently, TEA and TPVB have been shown to provide similar pain relief following VATS, but TPVB has fewer side effect compared to TEA.23 In addition, a network meta-analysis on regional analgesic techniques for VATS reported that TPVB is one of the best analgesic methods, and ESP block could reduce postoperative pain within 6 hours.24

However, continuous TEA has been our institution’s 1st regional analgesic option for thoracic surgery. In addition, it could reduce chronic postthoracotomy pain and provide effective acute pain relief.25 Thus we chose continuous TEA for Comparison with the ESP block in this clinical trial.

The analgesic effect of the ESP block may be comparable to or less than that of a TPVB. Turhan et al26 reported that dynamic pain scores were significantly lower in TPVB compared with ESP block for 24 hours postoperatively when a single injection method was done. However, Taketa et al27 showed that the analgesic effect of continuous ESP block was comparable to that of TPVB for VATS using a non-inferiority test. Our study demonstrated that the postoperative NRS score between groups was generally comparable, but the TEA group had a lower NRS score than the ESP block group in the immediate postoperative period when the greatest pain intensity was expected, and the TEA showed better patient satisfaction with pain control than ESP block. In addition, total rescue morphine consumption in the ESP block group was higher than in the TEA group. Therefore, continuous ESP block may be inferior to TEA for analgesia following VATS. Our findings are consistent with the previous study that postoperative pain at rest and coughing in continuous ESP block were significantly higher than TEA 24 hours after surgery.28 On the contrary, Nagaraja et al10 have reported comparable pain scores in both TEA and ESP block groups in the early postoperative period after cardiac surgery and that an ESP block might be superior to TEA at 24 h, 36 h, and 48 h, both at rest and while coughing.

Although ESP block patients had more morphine consumption than TEA patients (6 mg versus [vs.] 3 mg), the overall incidence of adverse events in TEA patients was higher than in ESP block patients in our study. Postoperative opioid use can increase the incidence of nausea and vomiting. However, the amount of morphine consumed in both groups was relatively low because all participants took multimodal analgesia, including regional analgesic techniques, regular parenteral analgesics, and rescue opioids. In addition, the high thoracic epidural blockade could cause hypotension and related symptoms, including nausea and dizziness. Furthermore, nausea and vomiting could be related to hyperperistalsis secondary to unopposed vagal activity after TEA.29 Therefore, the difference in adverse events between the 2 groups is presumed to be due to these factors.

An ESP block might be a simpler and safer option to standard techniques since the key structure (the tip of the transverse process) is easily identified with ultrasound, and the needle can be inserted using the in-plane method. Additionally, the injection site is distant from the spinal cord, pleura, and major vascular structures. It may be performed at any time during the perioperative period on prone or lateral patients. Therefore, this block could provide better analgesia in patients with morbid obesity, spinal deformities, or decreased respiratory depression and could reduce the risk for patients with coagulation disorders or current anticoagulation therapy.14,17 Our study showed a tendency toward shorter procedural times in the ESP block group (130 s vs. 145 s). Also, none of the ESP blocks failed.

Previous literature described spreading across 5 to 9 dermatomes when the ESP block was performed at the T5 level, and 20 mL of continuous local anesthetic infusion was administered at 8 mL/h.7,18 The dermatomal spread of our study was an average of 4 sensory segments, which was less extensive than in previous studies. The volume of local anesthetics and different delivery protocols might affect the dermatomal range. We used only 10 mL of saline to open the interfascial plane and injected the loading dose through a multi-orifice catheter. Moreover, the background PIBI provided a maximal flow rate of 250 mL/h, much slower than the manual injection, and was started 3 hours after the injection of 20 mL of the loading dose. We presumed this prohibited an extensive spread of local anesthetics compared to previous case reports.

We used different methods to deliver local anesthetics to each group. In the ESP block group, a background PIBI with PCA was administered, whereas in the TEA group, PCA was administered continuously. The difference in the delivery method might affect the analgesic efficacy between groups. However, we expected the PIBI to result in a more extensive spread of local anesthetic and to show a better analgesic profile than continuous infusion in the ESP group. These issues have been controversial, but recently TPVB with PIBI showed a superior analgesic profile compared to continuous infusion in patients undergoing VATS.30

Furthermore, PIBI with TEA increased hypotension incidence, although it reduced local anesthetic consumption in patients undergoing thoracic surgery.31 And the patients undergoing VATS usually received 0.2% ropivacaine 5-8 ml/h as either PIBI or continuous infusion combined with a PCA pump.30 Thus, we programmed 0.2% ropivacaine 15ml/3h with PIBI for pain management.

Study limitations

First, the differences in NRS between groups for the overall postoperative period were statistically significant, but we could not find them at a specific time. This result could be associated with statistical power. Thus, there is a need for further research in which sample size is added to increase statistical power. Second, 2 different analgesic procedures were performed with different positions (ESPB prone position vs. TEA lateral decubitus position). Thus this study had a weakness in the double-blinded method. However, the patients did not know which group they belonged to because it was based on their lack of prior knowledge in ESPB or TEA. Third, it was difficult to check the dermatomal sensory range, especially in the ESP block. We assessed dermatome sensitivity less than 1 h after surgery when the patient might not be fully conscious. Furthermore, the extent of the cutaneous block has some interindividual variability based on local anesthetic spread into the interfascial plane.6

Our results imply that ESP blocks could be an alternative to conventional techniques in patients with VATS due to their simplicity and safety, especially as a part of a multimodal analgesic strategy. Therefore, ESP blocks should be considered for routine use in patients undergoing thoracic surgery if TEA or TPVB are not considered or are contraindicated. However, further studies are necessary to confirm the efficacy of ESP blocks compared to other techniques and to establish the optimal dose and regimen.

In conclusion, continuous ESP block might be inferior to TEA; however, this technique may have tolerable analgesic efficacy and a better side effect profile than continuous epidural analgesia. Therefore, it could be an alternative to conventional regional analgesic techniques as a component of multimodal analgesia.

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