Ultrasound-guided external oblique intercostal plane block versus thoracic erector spinae block for post-thoracotomy pain: A randomised double-blinded non-inferior clinical study

Abstract

Background and Aims:

Regional techniques are preferred for controlling post-thoracotomy pain due to lower complication rates. This study aimed to compare the analgesic efficacy and safety of ultrasound-guided external oblique intercostal block (EOIB) with thoracic erector spinae plane block (ESPB) for post-thoracotomy pain.

Methods:

This randomised, double-blind, non-inferior clinical study involved 60 cases scheduled for thoracic surgery. Cases were randomly allocated into two groups: ESPB and EOIB groups. Using 30 mL 0.25% bupivacaine at the level of the thoracic vertebrae 5, both blocks were performed after induction of general anaesthesia. The primary outcome was morphine consumption in the first 24 hours postoperatively. The secondary outcomes were time to first rescue analgesic request postoperatively, numerical rating scale (NRS) score during rest and with coughing, and occurrence of complications. The non-parametric Wilcoxon test was used for non-normally distributed variables, the Student’s t-test was used for normally distributed variables, and the Chi-square/Fisher’s exact test was used for qualitative variables. The significance level was set at P ≤ 0.05.

Results:

Patients who required intraoperative fentanyl, time of first request for analgesia, total morphine consumption, and pain score within the first 24 hours post-surgery were comparable between the two groups (P = 0.347, 0.085, and 0.354, respectively). Both groups exhibited comparable incidences of hypotension and bradycardia (P = 0.353 and P > 0.99, respectively). Local anaesthetic systemic toxicity (LAST) and pneumothorax did not occur in any patient in either group.

Conclusion:

The analgesic effect of EOIB was non-inferior to ESPB for post-thoracotomy pain, as evidenced by comparable total opioid consumption, time of first request for analgesia, and pain score in the first 24 hours post-surgery. Additionally, EOIB demonstrated the same level of safety as ESPB.

INTRODUCTION

Thoracotomy incision is one of the most extremely painful incisions experienced by patients.[1,2] Particularly in those with compromised immune systems, acute pain may hinder secretion clearance and respiratory function, increasing surgical complications.[3] The severity of immediate pain following thoracotomy surgery estimates the occurrence of post-thoracotomy syndrome with chronic pain.[4] Consequently, perioperative pain management is essential for reducing morbidity and death following thoracotomy.[5,6,7,8] The thoracic paravertebral block (TPVB) and thoracic epidural analgesia (TEA) represent the pain management standard prescribed treatments following thoracotomy. Nevertheless, both blocks exhibit considerable failure rates (15%).[5,6]

In 2016, Forero et al.[9] proposed the erector spinae plane block (ESPB). In the years that followed, the higher quantity of randomised controlled trials demonstrated that ESPB may be utilised to provide effective analgesic management after thoracotomy.[10,11,12] Elsharkawy et al.[13] described and discussed the external oblique intercostal block (EOIB) in 2021. Local anaesthetic (LA) is administered into the fascial plane beneath the external oblique muscle (EOM) and superficial to the sixth rib or external intercostal muscle. It targets the anterior and lateral cutaneous branches of the thoracoabdominal nerves, which originate from the ventral rami of the spinal nerves. A catheter can be placed in the external oblique intercostal (EOI) plane, allowing for postoperative pain management. Other benefits include simple sonoanatomy (even in obese individuals), supine positioning, and no anticoagulant concerns.[14]

Data is limited to whether EOIB is comparable to ESPB in managing acute post-thoracotomy pain. We hypothesise that EOIB is non-inferior to ESPB in managing acute post-thoracotomy pain. Therefore, this study aimed to evaluate the analgesic efficacy of ultrasound (US)-guided EOIB with thoracic ESPB for acute post-thoracotomy pain. The primary objective was morphine consumption in the first 24 hours postoperatively. The secondary objectives were the time to first rescue analgesic request postoperatively, numerical rating scale (NRS) score during rest and with coughing, and the occurrence of complications.

METHODS

This randomised, double-blinded, non-inferiority study was carried out on 60 patients between 21 and 65 years of age, of both genders, with American Society of Anesthesiologists (ASA) physical status I and II, scheduled for thoracic surgery operated through an open thoracotomy incision. The study was carried out after the Institutional Ethics Committee (approval code: 36059/22/11) and registration at the Pan African Clinical Trials Registry (8^th February 2023; ID: PACTR202302491451057) and conducted from February 2022 (first patient enroled: 15^th February 2023) to October 2023 (last patient completed: 21^st October 2023). The study procedures adhere to the guidelines outlined in the World Medical Association (WMA) Declaration of Helsinki and Good Clinical Practice guidelines. All study participants signed informed written consent.

The presence of infections at the injection location, cases with previous allergic reactions to local anaesthetics, opioid addiction, coagulation abnormalities, pregnancy, and body mass index (BMI) ≥35 kg/m² were excluded.

Random numbers were generated using the Research Randomiser version 4.0 (Urbaniak, G. C., and Plous, S., 2013; http://www.randomizer.org/), created by an independent staff member not involved in the study. Randomisation and allocation concealment were achieved through central randomisation, in a parallel manner, into two equal groups: ESPB and EOIB groups. Another researcher opened the sealed envelopes, having no further involvement in the trial. Patients and outcome assessors were blind to the group assignment. All blocks were performed after induction of general anaesthesia (GA) by one anaesthesiologist who did not participate in data collection or analysis using the same solution (30 mL plain bupivacaine 0.25%) administered at the thoracic vertebrae 5 (T5) level.

History was taken, a physical examination was performed, and various investigations were conducted, including a coagulation profile, complete blood count, liver and kidney function tests, and an electrocardiogram. During the pre-anaesthetic assessment, all cases were familiarised with a NRS, ranging from 0 to 10, with 0 indicating no pain and 10 indicating maximum intolerable pain.

Pulse oximetry, electrocardiogram, non-invasive blood pressure monitoring, capnography, and temperature probe were utilised for the standard monitoring of patients. All patients received intravenous (IV) midazolam 2 mg as a premedication after placement of peripheral IV cannulas. The conventional approach of general anaesthesia (GA) was employed for all procedures. IV propofol 1.5–2 mg/kg and fentanyl 2 µg/kg were administered to induce GA. Following the administration of IV atracurium 0.5 mg/kg, the tracheal tube was inserted. A double-lumen tube was used when indicated. Maintenance of GA was achieved with sevoflurane (2%) and 50% oxygen. IV atracurium was administered in increments of 0.03 mg/kg. The lungs were ventilated to sustain an end-tidal of 30–35 mmHg. Additional IV fentanyl bolus dosages of 1 µg/kg were administered if there was a greater than 20% increase in heart rate (HR) or mean arterial blood pressure (MAP) from the baseline value (after exclusion of other causes than pain). The same surgical staff conducted all surgical procedures.

Cases received blocks after induction of GA using 30 mL of 0.25% plain bupivacaine administered at the T6 level. The blocks were performed on the ipsilateral side of surgery after skin sterilisation using 10% povidone-iodine by an anaesthesiologist who did not contribute to other tasks in the present study. A US machine (Philips CX50, Amsterdam, Netherlands Extreme Edition) with a linear probe of 5–12 MHz. Next, 2% lignocaine 3 mL was subcutaneously administered. Local anaesthetic (30 mL bupivacaine 0.25%) was administered after gentle aspiration for the exclusion of blood and air with a 22-G echogenic needle (Pajunk, Geisingen, Germany).

The adverse effects were also assessed, including hypotension (a decrease in MAP of >20% compared to baseline or a MAP of <65 mmHg), which was treated with repeated IV fluids and/or IV boluses of ephedrine (5 mg per bolus), as needed. Patients with bradycardia (HR <50 beats/min) were administered IV atropine 0.5 mg.

We utilised the block method as outlined by Elsharkawy and collaborators[13] in the supine position of patients by the abduction of the ipsilateral arm, with the probe placed over the 6^th rib medial to the anterior axillary spine in parasagittal orientation. The external oblique intercostal plane is situated deep to the external oblique muscle and superficial to the intercostal muscles that are connected to the sixth and seventh ribs. The needle was inserted using an in-plane technique from the cephalic end of the ultrasound probe. The EOI plane was subsequently hydrodissected using 3 mL of saline [Figure 1].

Figure 1.

Technique of external oblique intercostal block. a) Pre-injection. b) Post-injection. LA=local anaesthesia, N=needle, EO=external oblique, IC=intercostal muscle, P=pleura, R=rib

In the lateral position, the probe was positioned with longitudinal alignment, 3 cm lateral to the T5 spinous process, to obtain a parasagittal view. From the probe’s distal end, the needle was introduced and advanced in the plane until the needle tip contacted the transverse process (TP); then, it was inserted deeply into the interfacial plane at the level of the erector spinae muscle. This plane was exposed after hydrodissection by the administration of 3 mL of saline; 30 mL of 0.25% bupivacaine was required for the block.

Anaesthesia was withdrawn after completing the surgery, and IV neostigmine 0.08 mg/kg and atropine 0.02 mg/kg were used to antagonise residual neuromuscular block, followed by tracheal extubation. When cases regained full consciousness, they were transported to the post-anaesthesia care unit (PACU). All cases in the trial received IV paracetamol 1 g every 8 hours. Cases received rescue doses of IV morphine 0.1 mg/kg if the NRS pain score was 4 or higher. Postoperative HR and MAP, as well as NRS, were determined before discharge from the PACU and at 6, 12, 18, and 24 hours in both groups.

The sample size and power calculations were performed using PASS software (version 11.0; NCSS, LLC, Kaysville, UT, USA). The primary outcome of this non-inferiority trial, was to assess the amount of morphine used postoperatively within the first 24 hours. The determination of the sample size took into account a 95% confidence limit, a 90% study power, an equal distribution between the two groups, and a standard deviation of 6.24 mg for total postoperative morphine usage, as observed in a prior study.[15] Additionally, the margin for non-inferiority was established at 5 mg. A total sample size of 30 participants was allocated to each group to account for potential exclusion due to protocol deviations.

The Statistical Package for the Social Sciences (SPSS) statistics software, version 21.0 (International Business Machines Corporation (IBM Corp.), Armonk, NY, USA), was used to conduct statistical analyses. The Shapiro-Wilks test was implemented to evaluate the normality of the data distribution. An unpaired student t-test was implemented to compare parametric quantitative data, which were expressed in terms of mean and standard deviation (SD). The variables included age, weight, height, BMI, duration of surgery, heart rate (HR), mean arterial pressure (MAP), time to first analgesic request, and total postoperative morphine consumption within the first 24 hours. Conversely, the Mann-Whitney test (NRS) was implemented to evaluate non-parametric quantitative data, which was expressed in terms of median and interquartile range (IQR). The Chi-square test (for gender, ASA physical status, and type of surgery) and Fisher’s exact test (for patients requiring intraoperative fentanyl) were employed to analyse qualitative variables, which were expressed in terms of frequencies and percentages. Statistical significance was defined as a two-tailed P value of less than 0.05.

RESULTS

Thirteen of the 81 cases that were checked for eligibility did not meet the inclusion criteria, while eight others refused to participate. The remaining cases were equally randomised (30 cases in each). A follow-up was conducted on all randomised cases, and the findings were statistically analysed [Figure 2].

Figure 2.

CONSORT flow chart of the enroled patients. ESB=erector spinae plane block, EOIB=external oblique intercostal block, CONSORT=Consolidated Standards of Reporting Trials

The patients’ characteristics, duration, and type of surgery were comparable between the two groups (P > 0.05) [Table 1]. Baseline, intraoperative (at 30 min, 60 min, 90 min, and at the end of surgery), and postoperative HR and MAP measurements (at T0, 6 h, 12 h, 18 h, and 24 h) were comparable between both groups (P > 0.05) [Figure 3].

Table 1.

Patients’ characteristics, duration of surgery, and type of surgery of the studied groups

	EOIB group (n=30)	ESPB group (n=30)
Age (years), mean (SD)	52.77 (8.56)	50.07 (10.92)
Gender: Male/female, n	20/10	18/12
Weight (kg), mean (SD)	77.9 (9.74)	75.5 (9.3)
Height (m), mean (SD)	1.7 (0.06)	1.72 (0.07)
BMI (kg/m2), mean (SD)	26.97 (4.03)	25.63 (3.7)
ASA physical status: I/II, n	9/21	11/19
Duration of surgery (min), mean (SD)	137.83 (21.88)	140.17 (24.62)
Type of surgery: Decortication/Lobectomy, n	17/13	16/14

Data are presented as mean (standard deviation) or frequency. BMI=body mass index. ASA=American Society of Anesthesiologists, EOIB=external oblique intercostal block, ESPB=erector spinae plane block

Figure 3.

a) Heart rate and b) mean arterial blood pressure measurements of the studied groups. T0=before discharge from PACU

Patients that required intraoperative fentanyl, time to first analgesic request, and total morphine consumption in the first 24 hours were comparable between both groups (P > 0.05) [Table 2]. NRS measurements at T0, 6 h, 12 h, 18 h, and 24 h were comparable between both groups (P > 0.05) [Table 2].

Table 2.

Intraoperative fentanyl, postoperative morphine consumption, and NRS measurements of the studied groups

	EOIB group (n=30)	ESPB group (n=30)	P	Mean/median difference/RR (95% CI)
Patients requiring intraoperative fentanyl, n	8	5	0.347	1.6 (0.59,4.33)
Time to first analgesic request (h), mean (SD)	7.13 (1.36)	7.8 (1.58)	0.085	−0.67 (−1.43, 0.1)
Total postoperative morphine consumption in the first 24 h (mg), mean (SD)	16.97 (5.92)	15.67 (4.79)	0.354	1.3 (−1.48, 4.08)
NRS
T0, median (IQR)	1 (0–2)	1 (0–1)	0.145	0 (−1, 0)
6 h, median (IQR)	3 (2–4)	2 (2–3.75)	0.284	0 (−1, 0)
12 h, median (IQR)	2 (2–2)	2 (2–3)	0.567	0 (0, 1)
18 h, median (IQR)	4 (2.25–5)	3 (2–5)	0.699	0 (−1, 1)
24 h, median (IQR)	3 (2–4.75)	3 (3–5)	0.089	1 (0, 1)

Data are presented as mean (standard deviation), frequency, or median (interquartile range). RR=relative risk, CI=confidence interval, NRS=numerical rating Scale. T0=before discharge from the PACU, EOIB=external oblique intercostal block, ESPB=erector spinae plane block

Bradycardia did not occur in any patient in the EOIB group, but it occurred in one patient in the ESPB group. Hypotension and bradycardia were not significantly different between the two groups (P = 0.353 and P > 0.99, respectively). Local anaesthetic systemic toxicity and pneumothorax did not occur in any case in both groups.

DISCUSSION

According to our results, both EOIB and ESPB were effective and safe as cases that required intraoperative fentanyl, first analgesic request, and total morphine dosage were comparable between both groups. In both groups, hypotension and bradycardia were comparable.

The incidence of significant postoperative pain is the most important risk factor for post-thoracotomy pain syndrome (PTPS) development. Regional anaesthetic is effective in preventing the occurrence of this difficult problem.[16,17,18]

Recently, Mostafa et al.[19] documented that ESPB exhibited an analgesic effect in patients following open liver resection, which supports our findings.

Moreover, our results are corroborated by Fiorelli et al.,[5] who documented that in cases involving mini-thoracotomy, ESPB was shown to provide better analgesia, fewer perioperative analgesic doses, greater patient satisfaction, and reduced weakening of the muscles used for respiration compared to intercostal nerve block (ICNB). Sobhy et al.[12] documented that US-guided ESPB has a notable analgesic impact on patients following thoracotomy.

Although previous studies have shown the effectiveness of ESPB in thoracotomy[20,21], a comparison with EOIB has not been previously investigated.

The possible mechanism of EOIB is demonstrated by the spread of dye to the anterior and lateral cutaneous branches of the intercostal nerve.[13]

Hamilton et al.[22] revealed that T6 injection, either superficially or deeply, to the EO muscle around the middle of the chest resulted in only the T6–T11 cutaneous lateral branches being coloured. Tulgar et al.[23] defined thoracoabdominal nerve block by perichondria technique (TAPA), as it involves injecting a local anaesthetic beneath the skin and just above the costal cartilage to numb the area around the EO muscle, followed by a second, needle positioned between the internal oblique and the origin of transverse abdominis muscles, deeper (posterior) to the costal cartilage. This led to T5–T6 dermatome exposure, extending from 4 to 5 cm in front of the axilla to the side of the sternum, and also T7–T12 dermatome involvement from the frontal axillary line to the midline. In addition, Wilkinson-Maitland et al. 2023[24] used EOIB catheters bilaterally in a neonate undergoing Kasai portoenterostomy. EOIB managed pain successfully with comparable consumption of opioids and postoperative outcomes to epidural analgesia in the previous reports. Moreover, a case series[25] reported that EOIB was an easy technique that provided adequate postoperative pain management after hepatic surgeries.

Based on this dermatomal map, only the anterior and lateral branches of the T7–L2 intercostal nerves, as well as the lateral branches of the T5–T6 intercostal nerves, were blocked during this procedure. As mentioned, the TAPA block requires two injections: one to access the lateral cutaneous endings (in the vicinity of the costal cartilage) and another to reach the anterior cutaneous ramifications (at the level of the costal cartilage). The EOIB represents an example of ongoing progress, as demonstrated by Elsharkawy and colleagues’ case series and anatomical investigation.[13] As a result of its modification of a previously published technique, it now successfully covers both the anterior and lateral branches.

Our findings corroborate the findings of Hamilton and colleagues’ initial cadaver investigation.[26] However, when considering obesity, the EOI plane is superficial and readily recognisable. EOIB is a compressible fascial plane block with a safety profile comparable to that of ESPB.[27] EOIB produces pain control of the lateral and anterior dermatomes of the abdominal wall, from T7 through T11.[28,29]

Recently, Petiz et al.[30] presented convincing evidence that continuous epidural infusion of bupivacaine (EOIB) is an effective strategy for delivering postoperative pain management following open nephrectomies.

In laparoscopic cholecystectomy, Korkusuz et al.[31] and Kusderci et al.[32] reported that EOIB reduced postoperative opioid usage relative to the control group.

EOIB is a potential method for perioperative analgesia in subcostal incision procedures. This method decreases the need for perioperative opioids and improves early mobilisation and recovery.[33]

We chose to administer 30 mL of 0.5% bupivacaine in each block after inducing general anaesthesia. Previous studies showed that 0.25% bupivacaine has nearly the same analgesic efficacy as 0.5% bupivacaine. No significant difference was found between the concentrations and visual analog score (VAS) scores or between the concentrations and duration of action.[34] We chose 30 mL of bupivacaine as the high volume (30 mL) has been shown to have higher efficacy and spread than the lower volume (20 mL) in ESPB, according to several studies,[35,36] and according to a previous study,[13] We used a 30 mL volume in the EOIB. Administering blocks after induction, not at the end of surgery, had some advantages, such as pre-emptive analgesia and opioid-sparing anaesthesia.[37]

The advantages of this technique include easy sonoanatomy, a bony backstop, easy catheter placement, no resistance during insertion, and no concerns regarding anticoagulation.

The study’s limitations include a relatively small sample size and collection at a single site. Follow-up was restricted to a rather brief duration. To generalise the findings, large-scale multicentre investigations with extended follow-up durations are required.

CONCLUSION

The analgesic effect of external oblique intercostal block was non-inferior to erector spinae plane block for post-thoracotomy pain as evidenced by comparable total opioid consumption, time to first rescue analgesic demand after surgery, and pain score in the first 24 hours after surgery. In addition, external oblique intercostal block exhibited the same safety as erector spinae plane block as both groups were comparable in terms of complications.

Study data availability

De-identified data may be requested with reasonable justification from the authors (via email to the corresponding author) and will be shared upon receipt of such a request.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.