Comparison of Oblique Subcostal Transversus Abdominis Plane Block and External Oblique Intercostal Plane Block for Postoperative Pain Management in Laparoscopic Cholecystectomy

By Gamze Ertas¹, Hamiyet Senol Cakmak¹, Mehmet Alperen Avci², Kevser Uzunoglu Yildirim², Can Akgun², Serkan Tulgar¹

Affiliations

1. Department of Anaesthesiology and Reanimation, Samsun University Training and Research Hospital, Samsun, Turkiye
2. Department of General Surgery, Samsun University Training and Research Hospital, Samsun, Turkiye

doi: 10.29271/jcpsp.2025.12.1504

ABSTRACT
Objective: To compare the efficacy and safety of oblique subcostal transversus abdominis plane (OSTAP) block and external oblique intercostal plane (EOIP) block for postoperative pain management in patients undergoing laparoscopic cholecystectomy (LC).
Study Design: A randomised controlled trial.
Place and Duration of the Study: Department of General Surgery, Samsun University Training and Research Hospital, Samsun, Turkiye, between January and September 2024.
Methodology: Eighty adult patients undergoing elective LC were randomly divided into two groups: OSTAP block (n = 40) and EOIP block (n = 40). Blocks were performed at the end of surgery. The primary outcome was cumulative opioid consumption. The secondary outcomes included pain intensity measured by Numerical Rating Scale (NRS), time to first analgesic request, quality of recovery (QoR-15 score), and incidence of postoperative nausea and vomiting. Statistical analysis included the t-test, Mann-Whitney U test, and Chi-square test, with Bonferroni correction applied for repeated NRS measurements.
Results: Demographic characteristics and perioperative variables were comparable between the groups. The mean 24-hour tramadol consumption was similar in both groups (175 ± 98.79 mg vs. 184 ± 106.62 mg; p = 0.696). The pain scores were not significantly different at all measured time points (p >0.05). In addition, time to first analgesic request (p = 0.954) and QoR-15 scores (p = 0.269) were comparable. No major block-related complications were observed.
Conclusion: Effective postoperative analgesia was achieved in both groups with similar opioid consumption and pain scores. However, the EOIP block may be considered as a technically easier and safer alternative for regional analgesia in LC. Further research is needed to determine the long-term benefits and optimum clinical applications of these blocks in laparoscopic surgery.

Key Words: Laparoscopic cholecystectomy, Oblique subcostal TAP block, External oblique intercostal plane block, Regional anaesthesia, Postoperative pain management.

INTRODUCTION

Laparoscopic cholecystectomy (LC) has become the most preferred minimally invasive surgical method for treating gallbladder disease due to its favourable outcomes, including patient comfort, shorter hospital stays, and faster recovery. Although LC is associated with less pain, nausea, and vomiting compared to open surgery, inadequate management of postoperative pain may  lead  to  the  development  of  chronic  pain.¹

Pain after LC arises from peritoneal, visceral, and incisional origins, with the most intense pain typically reported at the port sites. Studies show that incisional pain is more prominent than visceral pain.² Given the undesirable side effects of opioids in the management of incisional pain, multimodal analgesia, including regional anaesthesia, is of great importance. To improve perioperative analgesia management, techniques such as transversus abdominis plane (TAP) block, erector spinae plane (ESP) block, and local anaesthetic infiltration at the port sites are recommended as part of procedure-specific postoperative pain management guidelines.³ According to the PROSPECT guidelines, TAP and ESP blocks are recommended as second-line options, not due to an increased postoperative pain risk in certain patients, but primarily because of concerns about potential systemic local anaesthetic toxicity, the need for technical expertise to perform these blocks effectively, and variability observed in ESP block techniques.³ Simpler alternatives, such as wound infiltration, may offer comparable efficacy in certain cases and are often preferred as first-line approaches.

One of these techniques, the oblique subcostal TAP (OSTAP) block, involves the injection of a local anaesthetic into the fascial plane between the transversus abdominis and internal oblique muscles.^4-6 The thoracoabdominal nerves (T6–L1) lie within this plane and provide sensory information to the front wall of the abdomen, including the upper abdomen—a key site of pain following LC. The subcostal approach targets the anterior cutaneous branches of the thoracoabdominal nerves as they emerge medially, thereby ensuring adequate coverage of the epigastric and  hypochondriac areas.^4,7

In contrast, the external oblique intercostal plane (EOIPB) block works on the nerves between the ribs (T7–T11) in the fascial plane, which is located between the external oblique muscle and the superficial fascia. This method is different from the TAP block because it uses the superficial course of the intercostal nerves within the lateral abdominal wall. This method effectively relieves pain in the upper abdomen, potentially using a  different  anaesthetic  approach.⁸

Previous clinical studies have already  demonstrated the analgesic efficacy of both OSTAP and EOIP blocks in LC.^9,10 Therefore, this study was planned as a head-to-head comparison of these two techniques, rather than including a no-block control group. Since both methods are already used in daily practice, comparing them directly was observed as more meaningful for everyday clinical decisions.

Despite their effectiveness on similar body parts, these techniques differ in their mechanisms, their ability to relieve pain, and their technical application. Therefore, conducting a direct compa-rative study is necessary to determine the optimal application of these techniques in clinical practice.¹¹ This study aimed to look at the pain-relieving effects and safety of ultrasound- guided OSTAP block and EOIP block. This may help to better understand and guide  the  clinical  application  of  these  techniques  in  LC.

METHODOLOGY

This study was designed as a prospective, randomised, controlled and assessor-blind trial. It was registered at ClinicalTrials.gov (NCT 06172465) after obtaining approvals from the Local Ethics Committee of Samsun University Training and Research Hospital and the Ministry of Health (SUKAEK-2023 18/7 and TITCK: 23-AKD-72). Informed consent was obtained from the study  participants.

The study was conducted in the Department of General Surgery, Samsun University Training and Research Hospital, Samsun, Turkiye, between January and September 2024 in accordance with the Declaration of Helsinki. Patients aged 18 to 80 years scheduled for LC were included in the study. Eligible participants had a body mass index (BMI) below 35 kg/m² and an American Society of Anesthesiologists (ASA) physical status classification of I or II. Patients with allergies to local anaes- thetics or contraindications to regional anaesthesia, such as bleeding or clotting disorders, were excluded. Additional exclusion criteria included morbid obesity (BMI >35 kg/m²), ASA ≥III, cognitive disorientation, or the use of psychiatric medications. Patients whose surgeries lasted more than 90 minutes or required conversion to open surgery were also excluded.

Patients were randomised using a sealed envelope technique into two groups: the OSTAP group and the EOIP group. Each patient was assigned a randomisation ID, which was used for all follow-up procedures. The anaesthesiologist performing the blocks was not involved in postoperative assessments. The study was assessor-blinded; the postoperative data collection, including pain and analgesia requirements, was conducted by a different anaesthesiologist who was blinded to group allocation and not involved in the study design. To ensure standardisation, all blocks were performed by an experienced anaesthesiologist (ST) who had previously conducted at least 20 successful procedures  of  each  block  type.

All patients received the same general anaesthesia protocol. Standard ASA monitoring was applied, and vital signs were recorded. Premedication consisted of intravenous (IV) midazolam (1–2 mg) administered in the operating room. Anaesthesia was induced using propofol (2.5 mg/kg) and rocuronium (0.6 mg/kg), with additional doses of rocuronium (0.1–0.2 mg/kg) as needed. Anaesthesia was maintained with a mixture of oxygen and air (FiO₂ 0.40), sevoflurane at 1 MAC, and the infusion of remifentanil at 0.1–0.25 mcg/kg/minute. At the end of surgery, pneumoperitoneum was released, and neuromuscular blockade was reversed with neostigmine (0.05 mg/kg) and atropine (0.02 mg/kg). No local anaesthetic was applied at the trocar sites.

A standardised perioperative and postoperative analgesia regimen was used for both groups. At the end of surgery, patients received IV dexketoprofen (50 mg) and IV paracetamol (1 g), followed by dexketoprofen every 12 hours and paracetamol every 8 hours. Patient-controlled analgesia (PCA) with tramadol was administered using 20 mg bolus doses, a 15-minute lockout, and a maximum dose of 100 mg within 4 hours. If the Numerical Rating Scale (NRS) score was ≥4 in the recovery room, 25 μg of IV fentanyl was given as rescue analgesia.

All blocks were performed aseptically at the end of surgery, while patients were still under general anaesthesia and prior to extubation. A high-frequency ultrasound (US) probe (MyLab Five Portable Ultrasound, UK) was used, with the depth set to 3–5 cm. In all blocks, a 21-gauge short curved needle (Stimuplex Ultra 360^®, Braun, Germany) was inserted using an in-plane technique.

In the supine position, a linear probe was placed obliquely just medial to the anterior axillary line. At the sixth to eighth rib levels, subcutaneous tissue, external oblique muscle, intercostal muscles, pleura, and lungs were visualised. The EOIB group was administered at two levels. Under real-time ultrasound guidance, local anaesthetic was injected between the external oblique and intercostal muscles with hydrodissection of the sixth to seventh rib plane. The needle was then advanced caudally toward the eighth rib. A total of 30 mL of 0.25% bupivacaine was injected on each side, resulting in a total volume of 60 mL, similar to  the  OSTAP  group.

The OSTAP block was performed bilaterally, following proper aseptic and antiseptic procedures prior to awakening. The US transducer was positioned horizontally below the xiphoid process and moved laterally until the transversus abdominis muscle was visualised under the rectus abdominis muscle. A total of 60 mL of 0.25% bupivacaine hydrochloride was used as the local anaesthetic. In the dual-injection technique, 30 mL was injected on each side—the first between the rectus abdominis and transversus abdominis muscles, and the second slightly laterally, between the transversus abdominis and internal oblique muscles.

All patients were monitored postoperatively in the recovery room for one hour before being transferred to the surgical ward. Postoperative follow-up, including all data collection up to 24 hours and administration of the Quality of Recovery-15 (QoR-15) questionnaire, was conducted by the same anaesthesiologist for all patients. This anaesthesiologist was blinded to the  block  technique  applied  to  each  patient.

The primary outcome measure was opioid consumption in the first 24 hours via PCA after surgery. The secondary outcomes included several parameters. Pain intensity was evaluated using the NRS. It was a unidimensional scale ranging from 0 to 10, where 0 indicated no pain, and 10 indicated the worst pain imaginable. The Turkish validated version of the QoR-15 questionnaire was used to assess patients’ post- operative recovery quality.¹² Nausea and vomiting were eva- luated with a five-stage verbal descriptive PONV scale, and patients scoring ≥3 received 4 mg of intravenous ondan- setron. The time to the first PCA request was recorded. In addition, complications including shoulder pain, local anaesthetic systemic toxicity, and allergic reactions were monitored.

The sample size was calculated using G*Power 3.1. While the 24-hour tramadol consumption in the OSTAP group was determined from the literature,¹³ the value in the EOIP group was based on the results of an unpublished study conducted by this team. The sample size was determined according to the cumulative tramadol requirement in 24 hours and was calculated as 199.4 ± 27.7 mg in the OSTAP group and 170 ± 27.56 mg in the EOIP group. Based on this effect size, the analysis performed with a 5% significance level (α) and 95% power (β = 0.05) showed that at least 24 participants per group were required. However, to increase the reliability of the findings and to account for potential dropouts, it was decided to include 40 patients in each group. This decision was supported by a review of similar studies in the literature.^1,9

SPSS version 16.0 software (SPSS, Chicago, IL, USA) was used for statistical analysis, and DataTab was used for boxplot, Kaplan-Meier, and other figure creation. The Kolmogorov- Smirnov test was employed to determine if the data were distributed normally. Continuous variables were demons- trated as mean ± standard deviation or median (25^th–75^th percentiles). For analysis, a 2-sample, independent t-test was used for continuous variables with equal variances. The Mann-Whitney U test was used when the data did not follow a normal distribution. The Chi-square was used for categorical variables, such as gender. A p-value <0.05 was considered statistically significant. To account for the multiple measurements obtained at six distinct time points—recovery room, and at 3, 6, 12, 18, and 24 hours postoperatively—a Bonferroni correction was applied to the analysis of NRS scores, resulting in an adjusted significance threshold of p <0.008. The time to first analgesic requirement was analysed using Kaplan-Meier survival  analysis.

RESULTS

A total of 84 patients were recruited for the study, but only 80 patients were enrolled. Two patients were excluded due to anticipated surgical duration exceeding 90 minutes, and two were excluded due to conversion to open cholecystectomy. The remaining 80 patients were randomised into two groups, with 40 patients in each group, immediately prior to block performance. No patients were lost to follow-up. The flow diagram  of  the  study  is  presented  in  Figure  1.

There were no significant differences in the demographic and perioperative characteristics, including age, gender distribution, height, weight, and duration of anaesthesia or surgery, between the EOIP and OSTAP groups (p >0.05). Block application times were also comparable between the groups (p = 0.323). Postoperatively, the time to the first analgesic requirement was 85.64 ± 120.08 minutes in the EOIP group and 116.13 ± 225.71 minutes in the OSTAP group, with no significant difference observed (p = 0.954). Similarly, the total opioid consumption was 184 ± 106.62 mg in the EOIP group and 175 ± 98.79 mg in the OSTAP group (p = 0.696). The QoR-15 scores, reflecting quality of recovery, were also comparable between the EOIP group (116.18 ± 12.76) and the OSTAP group (119.43 ± 13.33, p = 0.269). All  these  data  were  presented  in Table I.

The patients' NRS scores ​​at the time of arrival to the recovery room were ≥4 in the overwhelming majority of the patients and were similar (p >0.05). Rescue analgesia with fentanyl was applied to the majority. This situation can be attributed to the fact that sufficient time had not yet passed for the onset of effect in both blocks. Pain scores at rest (sNRS) and with cough and movement (dNRS) were similar in both groups at all time frames (p >0.05). Comparisons regarding pain scores are presented in detail in Table II and Figure 2 and 3.

The groups were evaluated in terms of 24-hour tramadol consumption, which served as the primary outcome of the study. The mean tramadol consumption was 184 ± 106.62 mg in the EOIP group and 175 ± 98.79 mg in the OSTAP group, with no statistical difference between them (p = 0.696). Tramadol consumption values are presented as mean ± SD in Table I and illustrated as a boxplot in Figure 4.

Table I: Descriptive data, surgical duration, time to first analgesic requirement, and QoR-15 scores for each group, along with their statistical evaluation.

Variables	EOIP Group (n = 40)	OSTAP Group (n = 40)	p-values
Age (years)	50.05 ± 11.39	48.63 ± 13.17	0.606
Gender F/M	23/17	24/16	0.820
Length (cm)	164.88 ± 9.69	165.68 ± 6.91	0.672
Weight (kg)	77.47 ± 12.12	79.1 ± 12.36	0.554
Anaesthesia time (minutes)	78 ± 21.12	74.63 ± 18.91	0.454
Surgical duration (minutes)	63.13 ± 21.21	58.53 ± 18.06	0.370
Block application time (minutes)	5.85 ± 1.27	6.13 ± 1.2	0.323
First analgesic requirement time (minutes)	85.64 ± 120.08	116.13 ± 225.71	0.954
Total tramadol dose consumed (mg)	184 ± 106.62	175 ± 98.79	0.696
QoR-15 score	116.18 ± 12.76	119.43 ± 13.33	0.269
Data are expressed as mean ± standard deviation or frequency. p-values were calculated using the t-test and Chi-square test, and p <0.05 was considered statistically significant.

Table II: NRS scores at rest and during movement/coughing in the first 24 hours.

At rest (static)	EOIP Group (n:40)	OSTAP Group (n:40)	p-values
Recovery room	5 (4-6.25)	5 (3-6.25)	0.622
3-hour	3 (2-4)	3 (1-4)	0.680
6-hour	2 (1-3)	2 (1-3)	0.404
12-hour	1 (1-2)	1 (0.75-2)	0.768
18-hour	1 (0-2)	1 (0-2)	0.793
24-hour	1 (0-1)	0 (0-1)	0.391
During movement/cough (dynamic)
Recovery room	6 (5-7.25)	6 (4.75-7.25)	0.907
3-hour	4 (3-5.25)	4 (3-5)	0.732
6-hour	3 (2-5)	3 (2-4)	0.628
12-hour	3 (2-3.25)	3 (2-3)	0.945
18-hour	2 (1-3)	2.5 (2-3)	0.598
24-hour	2 (1-3)	1 (1-2)	0.901
Data are expressed as median (percentiles 25th–75th). p-values were calculated using the Mann-Whitney test, with a Bonferroni correction applied for repeated NRS measurements. Results with p <0.008 were considered statistically significant.

Figure 1: Flowchart of the study.

The scores of the EOIP group and the OSTAP group were similar in terms of the patient recovery quality score (QoR-15), which is one of the important parameters in the feasibility of regional anaesthesia techniques (116.18 ± 12.76 vs. 119.43 ± 13.33; p = 0.269). These data are presented in both Table I and Figure 5. Additionally, in Figure 6, the time to first analgesic requirement is demons-trated with Kaplan-Meier survival analysis.

Figure 2: Static boxplot comparison of NRS across groups at different time points.

All patients received fentanyl once in the postoperative recovery room. Nausea occurred in one patient in the OSTAP group and in two patients in the EOIP group. No cases of vomiting were observed in either group. No complications related to the regional blocks, such as vascular puncture, local anaesthetic systemic toxicity, or allergic reactions, were encountered in any patient.

DISCUSSION

In this study, patients who underwent LC and received either EOIP or OSTAP blocks under general anaesthesia at the end of surgery had similar opioid requirements and pain scores at 24 hours postoperatively. Both techniques provided effective analgesia, and the groups were similar in terms of first analgesia times, block performance durations, or recovery quality as assessed by QoR-15 scores.

Figure 3: Dynamic boxplot comparison of NRS across groups at different time points.

Figure 4: Boxplot comparison of cumulative tramadol consumption at 24 hours.

Figure 5: Boxplot comparison of Group QoR-15 scores in both groups.

Figure 6: Intergroup tramadol demand.

Although the surgical incision in LC is smaller than the conven-tional technique, the port entry points are located across different parts of the abdomen, making it almost impossible to cover the entire surgical field with a single regional anaes-thesia technique.¹⁴ Techniques capable of providing compre-hensive cutaneous blockade in both the mid-abdomen and lateral abdomen are still under investigation. Approximately ten years ago, a cutaneous mapping study conducted by Chen et al. showed that the OSTAP technique effectively blocked the mid-abdomen but was inadequate in the lateral abdomen.⁷ Genc et al. determined and compared the cutan- eous blockade areas in the abdomen with EOIP and M-TAPA;¹⁵ they reported that EOIP blocked the lateral abdomen effectively but missed the mid-abdomen, which is relevant to the study. The present comparison involved two techniques that do not provide complete abdominal coverage; however, coverage is not always limited in this way.

Among these techniques, the OSTAP block applied in the perioperative period is one of the most popular techniques that provides effective analgesia in patients undergoing LC. The initially described single-injection technique was later modified into the double injection technique by Chen et al.^4,7 Although this technique seems easy when described, it should be considered as an advanced technique for practitioners. Contrary, block EOIP is a relatively newly defined technique that targets the potential space between the external oblique muscle and the sixth to eighth ribs. This approach is both easier and more reliable for practitioners with a bone barrier.^8,16 Since both blocks are routinely performed in the clinic by an experienced anaesthesiologist, block perfor-mance times were similar. The EOIP technique may offer a technical advantage due to the rib acting as a consistent anatomical barrier, which could contribute to safer needle advancement and easier identification of the target plane. However, this is a clinical observation and was not assessed with objective measurements. If a choice must be made between these two techniques, which show similar effects, it may still be premature to make conclusions based on a single study. However, the EOIP seems to be preferable due to being far from the port entry sites while providing similar effects.

In laparoscopic abdominal surgical procedures involving the upper abdomen, the port entry sites vary; however, the three-port technique remains the most common. There is also an entry site in the upper left lateral region for a drainage tube. Blocking such a large area with a single injection, or ensuring it with multiple injections, is a focus of interest for regional anaesthesiologists, and most innovations in the field of regional anaesthesia have focused on this area. BRILMA, EXORA, TAPA, M-TAPA, and recto-intercostal blocks are a few of the techniques developed for this purpose, each of which needs to be considered separately, and their effectiveness should be investigated.^17-19 Of these new techniques, M-TAPA is the most frequently studied, and its efficacy was investi-gated in a recent meta-analysis. It was reported to reduce opioid consumption in the LC compared to the control group.²⁰

There are some limitations to the generalisation of the results of this study. The most important is that tramadol consump-tion was not presented in different time frames, as cumulative tramadol consumption had already determined the primary outcome. The study design focused on strengthening the data by assessing the quality of recovery and demonstrating the effectiveness of the block from the patients’ perspective. Another limitation is that block performance was planned at the end of surgery. Since block onset had not yet occurred in patients who were extubated shortly after, most patients had an NRS score of ≥4 on arrival to the recovery room. Even if block onset had occurred, visceral pain would continue due to peritoneal tension and insufflation, necessitating short-acting opioids. In this way, it did not want the effective period of the block to overshadow the surgical time spent under anaesthesia, and the study aimed to prolong the duration of the effect.

CONCLUSION

Both EOIP and OSTAP blocks applied at the end of surgery in patients undergoing LC provided effective analgesia with similar opioid requirements and pain intensity. The techniques also showed comparable first-line analgesia duration, block performance times, and recovery quality according to QoR-15 scores. Given the ongoing development of new regional anaesthesia techniques aimed at achieving larger areas of cutaneous blockade in laparoscopic procedures, further research is needed to optimise both the analgesic effec- tiveness and safety of these approaches in this patient population.

ETHICAL APPROVAL:
The study was approved by the Local Ethics Committee of Samsun University Training and Research Hospital, Samsun, Turkiye (SUKAEK-2023 18/7) and the Ministry of Health of the Republic of Turkiye (TITCK: 23-AKD-72). It was prospectively registered at ClinicalTrials.gov (Identifier: NCT06172465) prior to patient enrollment.

PATIENTS’ CONSENT:
Written informed consent was obtained from all patients for publication of the data.

COMPETING INTEREST:
The authors declared no conflict of interest.

AUTHORS’ CONTRIBUTION:
GE, HSC, MAA, KUY, CA, ST: Conception and design of the study, acquisition, analysis, and interpretation of the data, drafting, and critical review of the manuscript for important intellectual content.
All authors approved the final version of the manuscript to be published.

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