Analgesic efficacy of ultrasound-guided erector spinae plane block versus ilioinguinal/iliohypogastric nerve block in patients undergoing unilateral inguinal hernia meshplasty – A randomised comparative study

INTRODUCTION

Open meshplasty remains the most common surgical approach in around 75% of patients requiring hernia correction.^[1] Pain after the surgery is multifactorial, comprising both somatic and neuropathic components. While the former is due to surgical insult or inflammation, the latter is usually due to direct nerve damage of the ilioinguinal (IIN), iliohypogastric (IHN), genital branch of the genito-femoral nerve, and the lateral femoral cutaneous nerve. Various interventions have been utilised to provide post-operative pain relief in patients undergoing this procedure. While the IIN/IHN block has been performed using the anatomical landmark technique, the direct visualisation of nerves and accurate deposition of local anaesthetic in their vicinity using ultrasound has been shown to provide a better effect.^[2]

Erector spinae plane (ESP) block, an ultrasound-guided interfascial plane block, has shown favourable outcomes in a variety of surgeries involving thoracic as well as abdominal regions, such as ventral hernia repair.^[3] However, the studies determining the efficacy of ESP block were quite limited in patients undergoing inguinal herniorrhaphy at the time of carrying out this trial. Therefore, the present study was undertaken as a randomised controlled trial to compare the efficacy of ultrasound-guided ESP block with ultrasound-guided IIN/IHN block for post-operative analgesia in patients who underwent elective unilateral inguinal hernia repair. We hypothesised that the ESP block would provide superior analgesia as compared to the IIN/IHN block, as assessed by the post-operative pain scores and cumulative opioid consumption in the post-operative period.

MATERIAL AND METHODS

The present study was undertaken in a tertiary health care centre as a prospective randomised controlled trial that was conducted after approval from the Institutional Ethics Committee (approval number IEC - GMCH/IEC/2019/231, dated 18th December 2019 ) and registration with the Clinical Trials Registry-India (CTRI No- CTRI/2020/03/024236, registered on 25/03/2020). The study was carried out in the period between January 2020 and December 2021, as per the principles outlined in the Declaration of Helsinki (2013), and Good Clinical Practice guidelines were adhered to.

The sample size was estimated by assuming a mean visual analogue scale (VAS) score of 4.0 ± 0.8 in Group E (ESP block) and 3.5 ± 0.8 in Group I (IIN/IHN block) with 80% power and 90% confidence interval.^[4] This was calculated to be 31 subjects in each group. Considering the possibility of attrition, it was decided to include 35 subjects in each group.

However, with the suspension of elective operating rooms during the first and second wave of the coronavirus disease (COVID) -19 pandemic, the prerequisite number of patients could not be enroled, subsequent to which the sample size was reduced to 35 with due permission from the hospital authorities. After written informed consent, 35 patients in the age group of 18-65 years belonging to American Society of Anesthesiologists (ASA) physical status class I and II, scheduled to undergo unilateral hernia meshplasty, were included in the study. Any patient with recurrent hernia, inguino-scrotal or sliding hernia, drug allergy, infection at the block site, opioid dependence, chronic pain, coagulopathy, pre-existing liver disease, severe cardiac or respiratory disease, pre-existing neurological syndrome, dementia, any contraindication to subarachnoid block, or failure to identify the plane of ultrasonography was excluded from the present study.

The participants were randomly assigned to either of two groups, I or E, using a computer-generated random sequence, with 1:1 ratios (18 each but 35 patients in total were included. Allocation was concealed using sealed envelopes prepared by an independent researcher not involved in recruitment or data collection. The envelope was opened by the anaesthesiologist administering either of the blocks, and the intervention was performed after confirming patient consent. Group I patients received the IIN/IHN block, and Group E patients received the ESP block at the end of the surgery. The anaesthesiologist performing the procedure could not be blinded due to the nature of the intervention. The principal investigator collecting the data was unaware as to which block had been performed.

A comprehensive pre-anaesthetic assessment was done in all the patients prior to the surgical procedure and enrolment into the study. VAS for pain (0- no pain, 10 – worst possible pain) and categorical scoring system (CSS) for nausea (0-none, 1- mild, 2- moderate, 3- severe) were explained to all the patients. The use of intravenous patient-controlled analgesia (IV PCA), demonstrating the demand-based requirement of opioids, was also explained to all patients in their vernacular language.

On the operation table, the patients were connected to a multichannel monitor (Aspire view, GE Healthcare, Helsinki, Finland) for the monitoring of electrocardiogram, non-invasive arterial blood pressure, oxygen saturation, respiratory rate, and end-tidal carbon dioxide. All the baseline parameters were recorded, and the same was continued at predefined intervals throughout the intraoperative period. An intravenous infusion of 0.9% normal saline @ 2 ml/kg/h was initiated through an 18 G peripheral venous cannula. All the patients received subarachnoid block as per the standard institutional protocol under aseptic conditions in the L3-4 or L4-5 space using a 26-G Quincke spinal needle with 0.5% heavy bupivacaine as per standard dose for the surgical procedure after achieving adequate motor and sensory block. After the completion of the surgical procedure, the patients received either an ultrasound-guided ESP block (Group E) or an IIN/IHN block (Group I) with 20 ml of 0.25% ropivacaine, as per the group allocation. A single experienced anaesthesiologist performed the block in all patients to maintain consistency. The blocks were performed using a high-frequency (5-10 MHz) linear array ultrasound probe (Sonosite, Inc., Bothell, WA 98021, USA) on the ipsilateral side of the surgical procedure. 0.25% ropivacaine was chosen as the agent of choice because of its better safety profile compared to bupivacaine in terms of cardiotoxicity and neurotoxicity, lower chances of motor blockade, local stock availability, and the routine institutional practice of using ropivacaine for regional anaesthesia at our centre.

The ESP block was performed in the lateral decubitus position with probe placement in the craniocephalad position to identify the transverse process in the lumbar region (T7-T10), and subsequently the drug was deposited between the transverse process and erector spinae muscle using a Sono Plex Stim cannula (21G 100mm, Pajunk, Germany) after negative aspiration.

Likewise, the IIN/IHN block was performed in the supine position with a linear high-frequency probe that was aligned in an oblique plane towards the umbilicus and then rotated superiorly and inferiorly to identify the fascial plane between the internal oblique and transversus abdominis muscle. The local anaesthetic was directly infiltrated around the IIN-IHN that were identified as ovoid hypoechoic structures using a Sono Plex Stim cannula (21G 100mm, Pajunk, Germany) after negative aspiration.

After transferring the patients to the post-anaesthesia care unit (PACU), haemodynamic variables, CSS and VAS scores were recorded at predefined intervals. All the patients were connected to an IV-PCA pump with morphine in the strength of 1 mg/ml, a lockout interval of 5 minutes, and a maximum dose of morphine of 0.2 mg/kg body weight in 4 hours. Rescue analgesia with 1 gram paracetamol was administered to patients in both the study groups in case the VAS score was more than 4, even after the maximal permissible dose of morphine over 4 hours. The observations were recorded by an anaesthesiologist unaware of the group allocation and randomisation code. All the observations were recorded in the prescribed proforma and were subjected to appropriate statistical analysis.

The data were analysed using Statistical Package for the Social Sciences version 21.0 (SPSS Inc., Chicago, Illinois, USA). The categorical variables were represented as frequencies and percentages, and the continuous variables were expressed as mean ± standard deviation (SD). The normality of data was tested by the Kolmogorov-Smirnov test. Non-parametric tests were utilised to analyse data in case the normality was violated. The quantitative variables among the groups were compared using an unpaired t-test or a Mann-Whitney test. Chi-Square test or Fisher’s exact test was used to compare the qualitative variables between the two groups. P value < 0.05 was considered to be statistically significant.

RESULTS

Though the study was planned to be conducted in 70 patients, the present study could enrol only a total of 35 patients due to the COVID-19 epidemic that led to the curtailing of the calculated sample size. Therefore, 17 patients received the IIN/IHN block while 18 patients received the ESP block after randomisation. Since no dropouts were observed and no patients were lost to follow-up, the same number of patients were subjected to statistical analysis [ Figure 1].

Close

Figure 1:

CONSORT diagram. CONSORT: Consolidated Standards of Reporting Trials, ESP: Erector spinae plane, IV-PCA: Intravenous patient-controlled analgesia; IIN/IHN: Ilioinguinal/iliohypogastric nerve, n: Number of patients

Export to PPT

Baseline demographic variables like age, weight, and ASA physical status were comparable in both groups. The groups were also similar to each other with respect to the location and type of hernia, as well as pre-operative haemodynamic variables.

The post-operative haemodynamic measurements did not differ significantly in both groups at the monitored intervals. However, the post-operative VAS scores at rest as well as on movement were observed to be lower in the group receiving the ESP block as compared to the group that was administered the IIN/IHN block [Table 1]. The cumulative morphine requirement was less in patients receiving ESP block up to 4 hours. The difference in cumulative mean analgesic (morphine) requirement in both groups was statistically significant at 4 hours after surgery. The total morphine consumption at the end of 4 hours after surgery was less in the ESP group as compared to the IIN/IHN group (0.17 ± 0.51 mg and 0.76 ± 0.97mg, respectively)

Participants receiving the ESP block experienced a longer delay before requiring their first supplemental analgesic dose compared to the other group, which was statistically significant on analysis [Table 2]. Both groups were comparable to each other in the incidence of post-operative nausea and antiemetic consumption. No side effects were observed with reference to the performance of the block or the local anaesthetic administered in both groups.

DISCUSSION

Mesh hernioplasty is a frequently performed surgical procedure for inguinal hernia, and post-operative pain often stems from injury to the nerve or entanglement in the surgical devices.^[5,6] Numerous strategies have been explored to mitigate acute pain and avoid the development of chronic post-operative inguinal pain syndrome, along with minimising other complications.^[7,8]

Though pharmacological methods with various classes of agents like opioids and non-steroidal anti-inflammatory drugs have been traditionally utilised for pain management, the introduction of ultrasound-guided interfascial plane blocks has gained popularity owing to their excellent analgesia, safety profile, as well as opioid sparing effects with fewer side effects. Amongst the interfascial plane blocks, the transversus abdominis plane block, IIN/IHN, and ESP block have been utilised for post-operative pain relief after open hernia surgery. These blocks have been sparingly compared to each other to ascertain the better modality providing adequate pain relief after hernioplasty. Therefore, the present trial was undertaken to compare the ESP block and the IIN/IHN block to ascertain which provides better post-operative analgesia.

In the present study, all the blocks were administered by a single investigator who was not involved in the data collection in the post-operative period. Likewise, the investigator collecting the data was unaware of the group allocation of the patient. All the blocks were performed on the ipsilateral surgical side after the administration of spinal anaesthesia and before the start of the surgical procedure. We observed that in spite of the smaller sample size, patients in the ESP group exhibited lower pain scores at rest and on movement, which was also associated with lower morphine consumption in the same group, with statistical significance in the observed time intervals. The VAS scores at rest in Group E were found to be lower and statistically significant than Group I at 30 min(0.17 ± 0.38 vs 0.65 ± 0.78), 1hour(0.33 ± 0.59 vs 1.47 ± 0.72, p<0.001) and 4 hours (0.83 ± 1.15 vs 2.23 ± 1.44, p = 0.001) respectively in the post-operative period [Figure 2]. Similarly, VAS scores on movement in Group E were also noted to be significantly lower statistically than Group I at 1hour(0.56 ± 0.98 vs 2.23 ± 0.83, p<0.001) and 4 hours (1.22 ± 1.31 vs 3.18 ± 1.51, p = 0.001) respectively in the post-operative period [Figure 3] which was consistent with the results of other authors who have employed ESP block.⁹ The total morphine consumption at the end of 4 hours after surgery was also observed to be less in ESP group as compared to IIN/IHN group (0.17 ± 0.51 mg and 0.76 ± 0.97mg respectively, p value = 0.021) that too was congruous to the studies conducted by Singh and Gurkan et al. ^[10,11] The better analgesia in ESP group may be because of the diffusion of local anaesthetic agent to block the dorsal and ventral rami of the nerves.^[12]

Close

Figure 2:

Comparison of VAS scores at rest. VAS: Visual analogue scale

Export to PPT

Close

Figure 3:

Comparison of VAS scores on movement. VAS: Visual analogue scale

Export to PPT

The mean time (in hours) to first morphine request was also observed to be more in patients receiving ESP block as compared to those receiving IIN/IHN block that was found to be statistically significant (9.38±3.93 vs 6.27 ± 3.13 hours; p = 0.01) that is in line with the research conducted by Hamed et al and Kamel et al where the authors advocate the use of ESP block for extended analgesia.^[13,14] Therefore, studies with larger sample sizes may depict significant results at all the time intervals and could be a reference for future research.

Similar to the study by Altun et al, the antiemetic requirement was less in the present study too, with less post-operative nausea and vomiting, which suggests the ESP block to be a good modality for post-operative pain relief.^[15]

No significant statistical difference was noted amongst the groups with respect to haemodynamic variables, viz.: heart rate, systolic & diastolic blood pressure, and saturation. This may be attributed to analgesia received from the blocks and background (IV PCA morphine availability that led to haemodynamic stability as demonstrated in other trials by Gaballah and Prasad et al.).^[16,17] The same may have been the reason for no rescue analgesia in the post-operative period, as IV PCA may have provided analgesia for any breakthrough pain.

No side effects pertaining to either of the blocks were noted, which may be due to better delineation of anatomical and neural structures that resulted in accurate placement of the needle and drug. Use of ultrasound greatly increases the accuracy of administering peripheral nerve blocks and can be credited for the avoidance of any adverse event.

Apart from general complications associated with regional anaesthesia such as infection, bleeding, local anaesthetic systemic toxicity, some of the specific complications associated with both the blocks that one needs to be watchful about include – vascular injection into the deep circumflex artery, bowel perforation, bladder injury in case of IIN/IHN block and pneumothorax, epidural injection and rarely intrathecal injection in case of ESP block.

Some limitations are associated with the present study. The sample size had to be decreased because of the unavailability of operating rooms in the study period. The reduction in sample size has reduced the statistical power of the study and increased the chance of errors, mainly type II error. The findings of the study may not be reliable. This is a major limitation of the study brought by the circumstances, especially the COVID-19 pandemic. Therefore, the study needs to be replicated in the future with a larger sample size for the derivation of significant results. Further, the residual effect from spinal anaesthesia may have had an overlapping effect on post-operative analgesia, hindering the ability to gauge the onset of the blocks. Nevertheless, the dermatomal levels were not assessed in the present study, and the serum concentration of local anaesthetics was not estimated. Also, the pre-operative administration of the blocks could have provided synergistic analgesia in the intraoperative period.

CONCLUSION

Overall, the ESP block performed under ultrasound guidance appears to be more advantageous over the IIN/IHN block in terms of being associated with better post-operative analgesia, lesser opioid consumption, and longer time to rescue analgesia in patients undergoing mesh hernioplasty or herniorrhaphy.