Lateral Versus Subcostal TAP Block for Drain-Site Analgesia in Laparoscopic Cholecystectomy

Introduction Laparoscopic cholecystectomy is one of the most frequently performed surgical procedures for the treatment of gallbladder diseases. Although it is considered a minimally invasive technique, patients may still experience significant postoperative pain. This pain has both visceral and somatic components, with somatic pain being particularly prominent at trocar incision sites and surgical drain entry sites.

Effective management of postoperative pain is crucial for enhancing patient comfort, promoting early mobilization, and shortening hospital stay. Therefore, multimodal analgesia protocols and opioid-sparing regional anesthesia techniques are increasingly being incorporated into perioperative care. The transversus abdominis plane (TAP) block is a widely used regional analgesia technique that targets the somatic innervation of the anterior abdominal wall and has demonstrated efficacy in reducing postoperative pain and opioid requirements following abdominal surgery .

The transversus abdominis plane (TAP) block can be performed using different ultrasound-guided approaches, including the lateral, posterior, and subcostal techniques. These approaches differ in their dermatomal coverage and duration of analgesia. The lateral TAP block is performed by injecting a local anesthetic into the fascial plane between the internal oblique and transversus abdominis muscles under ultrasound guidance. This technique aims to provide temporary blockade of the T6-L1 spinal nerve branches that supply somatic innervation to the anterior abdominal wall. It is widely used for postoperative pain management following lower and lateral abdominal procedures, including cesarean section, gynecological surgery, appendectomy, laparoscopic abdominal surgery, and inguinal hernia repair. Previous studies have demonstrated that TAP block can provide prolonged postoperative analgesia and significantly reduce both opioid consumption and pain scores, particularly during the first 12-48 hours after surgery.

Similarly, randomized controlled trials have demonstrated that TAP block techniques can reduce postoperative pain scores and decrease opioid requirements. Consequently, TAP blocks have become an important component of multimodal analgesia protocols in laparoscopic surgery. However, most studies in the current literature have focused on overall postoperative pain and opioid consumption, while specific sources of postoperative pain have rarely been evaluated separately.

In patients undergoing surgical drain placement, the drain insertion site has been clinically recognized as a distinct source of somatic pain, particularly involving the lateral abdominal wall. Despite its clinical relevance, studies specifically investigating analgesic strategies targeting drain-related pain remain scarce. Most available studies have evaluated global pain scores and opioid consumption, whereas localized outcomes such as drain-site pain have seldom been assessed.

Given the different dermatomal coverage provided by various TAP block techniques, the lateral TAP block may more effectively target the innervation of the lateral abdominal wall and therefore provide superior analgesia at the drain insertion site. In contrast, the subcostal TAP block primarily covers the upper abdominal wall and is more likely to reduce pain associated with trocar insertion sites.

Based on this rationale, the application of a lateral TAP block on the side of drain placement combined with a contralateral subcostal TAP block may represent a novel targeted analgesic strategy for the management of drain-site pain. Comparing this approach with the standard bilateral subcostal TAP block technique may provide valuable evidence regarding the optimal management of postoperative somatic pain following laparoscopic cholecystectomy. To the best of our knowledge, no randomized controlled trial has directly evaluated this hypothesis.

Objective This study aims to investigate whether a targeted asymmetric TAP block strategy consisting of an ipsilateral lateral TAP block and a contralateral subcostal TAP block provides superior postoperative somatic analgesia compared with the conventional bilateral subcostal TAP block technique in patients undergoing laparoscopic cholecystectomy with surgical drain placement. The primary focus is the reduction of drain-site pain, a clinically relevant but often underrecognized source of postoperative discomfort.

Materials and Methods This study was designed as a single-center, prospective, randomized, controlled clinical trial. The study will be conducted in accordance with the principles of the Declaration of Helsinki. Written informed consent will be obtained from all participants prior to enrollment.

Patients scheduled for elective laparoscopic cholecystectomy with planned surgical drain placement at the end of the procedure will be eligible for inclusion.

Inclusion Criteria: Patients aged 18-75 years, classified as American Society of Anesthesiologists (ASA) physical status I-III, with a body mass index (BMI) < 35 kg/m², undergoing elective laparoscopic cholecystectomy and requiring abdominal drain placement at the end of surgery.

Exclusion Criteria: Patients with known allergy to local anesthetics, coagulopathy or ongoing anticoagulant therapy, infection at the planned block site, chronic opioid use, chronic pain syndromes, pregnancy, severe hepatic or renal insufficiency, inability to communicate effectively or to perform pain assessment using the Numeric Rating Scale (NRS), previous upper abdominal surgery, or drain placement outside the lateral abdominal wall (e.g., subxiphoid location) will be excluded. Patients who require conversion to open surgery, postoperative intensive care unit admission, or who experience block failure will also be excluded from the final analysis.

Randomization and Blinding Participants will be randomly allocated to one of two study groups using a computer-generated randomization sequence. Group assignments will be concealed using sealed opaque envelopes.

The anesthesiologist performing the TAP block will be aware of group allocation due to the nature of the intervention. However, patients and the investigator responsible for postoperative pain assessment and outcome evaluation will remain blinded to treatment allocation. Therefore, the study will be conducted using a single-blind, assessor-blinded design.

Study Groups Participants will be randomly assigned to one of two study groups using a computer-generated randomization sequence.

Group S (Standard Group): At the end of surgery and prior to extubation, patients will receive an ultrasound-guided bilateral subcostal TAP block. A total of 40 mL of 0.25% bupivacaine (20 mL per side) will be administered into the right and left subcostal planes to provide standard analgesia of the upper abdominal wall.

Group L (Targeted Group): Patients in this group will receive an ultrasound-guided lateral TAP block on the side of surgical drain placement (ipsilateral side) and a subcostal TAP block on the contralateral side. A total of 40 mL of 0.25% bupivacaine (20 mL at each injection site) will be administered. This approach is intended to provide more targeted and effective blockade of the lateral abdominal wall innervation (T10-L1) associated with the drain insertion site while preserving adequate analgesia of the upper abdominal wall and trocar insertion sites through the contralateral subcostal TAP block.

The total volume and concentration of local anesthetic will be kept constant in both groups. Patients in both groups will be compared regarding pain at the drain insertion site during the postoperative period. Pain assessment will be performed at specified time points using the Numerical Rating Scale (NRS).

The primary objective of the study is to compare the effects of a lateral TAP block applied on the drain side with a standard bilateral subcostal TAP block on drain-related somatic pain.

Anesthesia Protocol Standard intraoperative monitoring, including electrocardiography (ECG), noninvasive blood pressure monitoring, peripheral oxygen saturation (SpO₂), and end-tidal carbon dioxide (EtCO₂), will be applied to all patients. General anesthesia will be induced using propofol (2-3 mg/kg), fentanyl (1-2 µg/kg), and rocuronium (0.6 mg/kg).

Anesthesia will be maintained with sevoflurane at 1.0-1.5 minimum alveolar concentration (MAC). Additional intraoperative opioid administration will be provided when heart rate or blood pressure increases by more than 20% above baseline values and will be recorded for subsequent analysis. The total intraoperative opioid consumption will be recorded and compared between groups.

Block Administration All block procedures will be performed at the end of surgery, prior to extubation, under sterile conditions and ultrasound guidance. Bupivacaine 0.25% will be used as the local anesthetic agent. A volume of 20 mL of local anesthetic will be administered for each injection site, resulting in a total volume of 40 mL per patient. The total dose of local anesthetic will be maintained within recommended safety limits according to the patient's body weight.

Block success will be assessed by the demonstration of appropriate fascial plane separation under ultrasound guidance and by postoperative sensory testing using the pin-prick method.

Postoperative Analgesia Protocol and Outcome Measures All patients will receive a standardized multimodal analgesia regimen according to institutional clinical practice. In addition, intravenous fentanyl patient-controlled analgesia (PCA) will be provided for 24 hours postoperatively (demand dose: 15 µg; lockout interval: 10 minutes; no basal infusion). Total fentanyl consumption and the requirement for rescue analgesia during the first 24 postoperative hours will be recorded and compared between groups.

The primary outcome of the study is the drain-site pain score at rest at 6 hours after surgery. Pain intensity will be assessed using the Numeric Rating Scale (NRS), ranging from 0 (no pain) to 10 (worst imaginable pain). The 6-hour postoperative time point was selected as the primary endpoint because TAP block analgesia is expected to be fully established while the inflammatory response associated with surgery becomes clinically relevant.

Secondary Outcomes

• Pain Profile Over Time: Resting and dynamic (during movement or coughing) drain-site NRS pain scores measured at 1, 2, 12, and 24 hours postoperatively.
• Analgesic Efficacy: Total intravenous fentanyl consumption during the first 24 postoperative hours (µg) and time to first rescue analgesic request.
• Quality of Analgesia and Patient Satisfaction: The proportion of patients with clinically significant pain (NRS ≥ 4) and overall patient satisfaction assessed at 24 hours using a 5-point Likert satisfaction scale.
• Likert Scale:

1. = Very dissatisfied
2. = Dissatisfied
3. = Neutral
4. = Satisfied
5. = Very satisfied

• Functional Recovery: Time to first mobilization, time to return of bowel function (first flatus or bowel movement), time to drain removal, and total length of hospital stay.
• Safety Outcomes: Incidence of postoperative nausea and vomiting (PONV), sedation level assessed using the Ramsay Sedation Scale, pruritus, and block-related complications, including local anesthetic systemic toxicity, hematoma, and infection.

Statistical Analysis Statistical analyses will be performed using SPSS version 27.0 (IBM Corp., Armonk, NY, USA). The normality of continuous variables will be assessed using the Shapiro-Wilk test. Normally distributed data will be presented as mean ± standard deviation (SD), whereas non-normally distributed data will be expressed as median (minimum-maximum). For between-group comparisons, the independent-samples Student's t-test will be used for normally distributed continuous variables, while the Mann-Whitney U test will be used for non-normally distributed variables. Categorical variables will be analyzed using the chi-square test or Fisher's exact test, as appropriate. Changes in pain scores over time will be analyzed using repeated-measures analysis of variance (ANOVA). If the assumptions for repeated-measures ANOVA are not met, an appropriate nonparametric alternative will be used. All statistical tests will be two-tailed, and a p-value < 0.05 will be considered statistically significant.

Sample Size Calculation The sample size was calculated using G*Power software (version 3.1.9.7) based on the primary outcome measure, namely the postoperative drain-site Numeric Rating Scale (NRS) pain score at 6 hours. Based on available literature and a clinically meaningful difference of 1.5 points in the NRS score between groups, the effect size (Cohen's d) was estimated at 0.65. With a two-sided alpha error of 0.05 and a statistical power of 80%, the required sample size was calculated as 39 patients per group.

To account for an anticipated dropout rate of approximately 10% and potential technical failures, 44 patients will be enrolled in each study group, resulting in a total planned sample size of 88 participants.