A double blind randomised comparative study of external oblique intercostal plane block versus subcostal transversus abdominis plane block for upper abdominal laparoscopic surgeries

INTRODUCTION

Various regional nerve blocks have been explored for patient comfort and minimisation of postoperative pain after laparoscopic surgery. As the demand for minimally invasive surgeries grows, there is a growing need to refine techniques that contribute to adequate pain management, decrease opioid consumption, and accelerate postoperative recovery. The selection of the most appropriate regional anaesthesia technique can play a pivotal role in achieving these objectives.^[1]

External oblique intercostal (EOI) block and subcostal transversus abdominis plane (TAP) block are both emerging as promising interfascial plane blocks in the realm of regional anaesthesia for laparoscopic upper abdominal surgeries. The EOI block is a novel interfascial plane block which involves the administration of local anaesthetics into the plane between the external oblique and internal oblique muscles, targeting the anterior cutaneous branches of the lower intercostal nerves. On the other hand, the TAP block entails the deposition of local anaesthetics into the plane below the subcostal margin, thus affecting the subcostal and lower intercostal nerves. Both techniques aim to provide effective analgesia in the upper abdominal region, thereby reducing the necessity for systemic opioids, which are associated with various adverse effects, including sedation, respiratory depression, and gastrointestinal complications.^[2-4]

The present study aimed to study and compare these two regional anaesthesia techniques and their clinical applicability in laparoscopic upper abdominal surgeries.

The primary objective was to compare the numerical rating scale (NRS) score among the two groups in the first postoperative 24 hours. The secondary objectives were to observe the total duration of analgesia and time to first rescue analgesia.

MATERIAL AND METHODS

76 patients of either gender, aged 20-70 years, undergoing elective upper abdominal laparoscopic surgeries were recruited for the study. Intervention was done with the EOI block, which was compared with the subcostal TAP block. Outcome was measured by comparing postoperative NRS scores, total duration of analgesia, total analgesic consumption, and side effects, if any. The time frame was first 24 hours postoperatively.

This randomised, controlled, double blind, comparative interventional study was conducted in a tertiary health care centre after receiving approval from the Institutional Ethics Committee (approval number GCSMC/EC/Research Project/APPROVE/2024, dated 30th January 2024) and Clinical Trials Registry-India (CTRI/2024/03/063563). The study was executed from March 2024 to November 2024. The study was carried out in compliance with the principles outlined in the Declaration of Helsinki (2013) and adhered to Good Clinical Practice guidelines. Seventy-six patients of either gender, aged 20-70 years, belonging to the American Society of Anesthesiologists physical status grades I and II, posted for elective abdominal laparoscopic surgeries and scheduled to receive general anaesthesia were included in the study. Patients with uncontrolled comorbid conditions, allergic to local anaesthetics, an altered coagulation profile, body mass index (BMI) >35 kg/m², and having an infection at the site of block were excluded.

The patients were recruited after obtaining written informed consent and divided into two equal groups (Group EOI and Group TAP), each having 38 patients [Figure 1]. Randomisation was done according to the sequentially numbered, opaque, sealed envelopes (SNOSE) technique, where the sealed envelopes were placed, and after the patient’s consent, the primary anesthesiologist opened the sealed envelope and prepared for the regional block as per the group allocated in the sealed envelope. The outcome assessor, data collector, and statisticians were unaware of the group allocation and did not participate in regional procedures.

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Figure 1:

CONSORT diagram. CONSORT: Consolidated Standards of Reporting Trials; Group EOI= External oblique intercostal block group; Group TAP = Subcostal transversus abdominis plane block group. Loss to follow up: Patients who were not stable haemodynamically due to causes like hypertension, bradycardia, or haemorrhage

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Group EOI received an ultrasonography (USG) guided external oblique block, and Group TAP received a USG guided subcostal TAP block. The patients were educated about the NRS on the evening before surgery. Inside the operating theatre, non-invasive blood pressure, electrocardiography, and peripheral oxygen saturation monitors were attached to the patients. They were preoxygenated with 100% oxygen. Intravenous (IV) glycopyrrolate 0.04 mg/kg, IV midazolam 0.02 mg/kg, and IV fentanyl 2 µg/kg were administered. Induction and endotracheal intubation were done with IV propofol 2 mg/kg and succinylcholine 1.5 mg/kg. The patient was maintained on air, oxygen, atracurium, and sevoflurane. In all the patients, the local port site was infiltrated with 0.25% bupivacaine. After completion of the surgery and just prior to extubation, as per group allocation, a USG-guided EOI block or subcostal TAP block was performed on the patient. The drug administered for either of the blocks was 20 ml of 0.2% ropivacaine (on each side). Thus, a total of 40ml of the drug was administered. The patients were extubated on satisfying all extubation criteria and then shifted to the postoperative care unit for observation as per institutional protocol.

The patients included in the study were blinded to the block they received. The anesthesiologist who collected the data postoperatively was unaware of the group allocation.

The time of administration of the block was taken as the baseline. The NRS score was observed at 2,4,6,8,10,12,16,18,20, and 24 hours postoperatively. The duration of analgesia was considered as the time from administration of the block to the time the patient’s NRS score was ≥4/10. IV paracetamol (PCM) 15mg/kg was administered for rescue analgesia.

For performing a USG-guided EOI block, the patient was kept in the supine position after completion of the surgery and before extubation.^[5,6] The surface landmark that was identified was 1-2 cm medial to the anterior axillary line. A linear ultrasound transducer was positioned sagittally between the midclavicular and anterior axillary lines at the level of the sixth rib.^[7] The local anaesthetic was injected between the external oblique and external intercostal muscles.^[8,9]

For performing a USG-guided subcostal TAP block, the patient was kept in the supine position after completion of surgery and before extubation.^[10] The surface landmark that was identified was between the lower costal margin and the iliac crest, on the anterior axillary line.^[11] A linear ultrasound probe was transversely placed, and the three muscles were identified: the external oblique muscle, the internal oblique muscle, and the transversus abdominis muscle.^[12] The local anaesthetic was injected in the fascial plane between the internal oblique and transversus abdominis muscles. The thoracolumbar nerves (T6 to L1), which supply sensory nerves to the anterolateral abdominal wall, were targeted.^[13]

The sample size was calculated using OpenEpi.com(version 3), an open-source calculator, based on a previous study.^[14] The minimum expected difference in time to rescue analgesia between the two groups was found to be 35%. For statistically significant results with an alpha error of 0.05 and a power of 80% with a 95% confidence interval, 38 patients were required in each group. Statistical analysis of the collected data was done using Statistical Package for the Social Sciences (SPSS) software (version 20, International Business Machines Corp., USA). Mean ± standard deviation was used to express quantitative data. An independent t-test was applied for the comparison of quantitative data. A P-value < 0.05 was considered significant.

RESULTS

Of the 76 patients who were recruited, three patients refused to participate, three patients underwent conversion to open surgery, and ten were lost to follow-up. Hence, the research was conducted on the remaining 60 participants [Figure 1].

Statistical analysis depicted comparable baseline characteristics between both groups with regard to the age and duration of surgery (P >0.05) [Table 1]. The NRS score was significantly low at 2,4,6,8,10,12,16,18,20 postoperative hours in Group EO compared to Group TAP (P value <0.05) at rest [Table 2]. The NRS score at movement was low at 2,6,24 hours in Group EO compared to the Group TAP [Table 3].

Time to first rescue analgesia (total duration of analgesia) was 7.6(1.86) hours in Group EO and 5.8(2.4) in Group TAP [Table 4].

The total PCM requirement was less in Group EO as compared to Group TAP(p=0.29) [Table 4].

DISCUSSION

The EOI block is a unique block that targets both anterior and lateral nerves, is superficial, convenient, and easy to perform under ultrasonographic guidance.

Both EOI and subcostal TAP blocks can be performed in the supine position, minimising the complex procedure of patient repositioning while performing the blocks. The findings of our study demonstrate that the EOI block provides superior analgesia compared to the subcostal TAP block in patients undergoing upper abdominal laparoscopic surgeries. This was evident from the significantly lower NRS scores at multiple time intervals postoperatively in the EOI group, indicating better pain control [Tables 2 and 3].

The EOI block, a relatively novel technique, targets the anterior and lateral branches of the thoracoabdominal nerves by depositing local anaesthetic in the plane between the external oblique and intercostal muscles. This anatomical approach may allow for more effective spread of the anaesthetic to the relevant nerves supplying the upper abdominal wall, thereby resulting in superior analgesia as seen in our study. Hemmerling et al. also emphasised its efficacy in upper abdominal procedures, especially in obese patients, where conventional approaches may be challenging.^[9] It has been found to be an innovative, safe, and effective block for providing postoperative analgesia in abdominal surgeries.^[9]

Subcostal TAP block provides analgesia to the anterolateral abdominal wall.^[15] In contrast, while the TAP block remains a well-established regional technique^[16] targeting the thoracolumbar nerves (T6-L1), its analgesic efficacy appears to be comparatively limited, particularly in the upper abdominal region. McDonnell et al.^[4] and Chin et al.^[2] have previously outlined the usefulness of TAP blocks, but our results suggest that the TAP block may not be as effective as the EOI block in minimising the intensity of postoperative pain during the early postoperative period.

Although the mean total PCM requirement over 24 hours was lower in the EOI group (0.8 ± 0.4) compared to the TAP group (0.93 ± 0.55), the difference was not statistically significant (p = 0.29). This could be attributed to the study’s sample size or the use of standardised rescue analgesia protocols, which may have minimised the differences in drug administration despite varying pain experiences. Furthermore, the number of patients requiring rescue analgesia was slightly lower in the EOI group (24/30) than in the TAP group (28/30), reinforcing the idea that the EOI block may reduce the need for additional analgesics. However, this difference did not reach statistical significance and warrants a future study with a larger sample size.

No major complications or adverse events related to either block technique were observed in the present study, affirming the safety profile of both regional anaesthesia approaches when performed under ultrasound guidance by trained anaesthesiologists.

One of the noteworthy observations was the ease and efficacy of EOI in the postoperative setting, particularly its utility in diverse patient populations, including those with high BMI. However, limitations remain, particularly in resource-limited settings where ultrasound machines and expertise may not be readily available, restricting the widespread application of such blocks outside tertiary care centres.

Our findings align with current literature supporting the utility of interfascial plane blocks in enhancing postoperative recovery and reducing opioid use.^[1] Given the growing emphasis on opioid-sparing techniques, the EOI block may represent a valuable addition to the armamentarium for postoperative analgesia in upper abdominal laparoscopic surgeries.

The present study has some limitations. It was carried out at a single centre, tertiary hospital, with a limited sample size and included only elective laparoscopic surgeries. The USG machine may not always be readily available at peripheral hospital setups. The clinical application of such studies requires a tertiary care setup with appropriate equipment and trained personnel.

CONCLUSION

The USG-guided EOI block appears to be better than the subcostal TAP block in reducing the postoperative pain intensity score and providing postoperative analgesia.