Postoperative pain following lower abdominal surgery remains a major determinant of patient recovery, ambulation, and overall satisfaction. Inadequately controlled pain prolongs hospital stay, predisposes to pulmonary and thromboembolic complications, and increases the risk of chronic post-surgical pain. Traditional reliance on systemic opioids for postoperative analgesia is limited by side effects such as sedation, respiratory depression, nausea, vomiting, and ileus, and has raised concern regarding opioid-related morbidity, prompting calls for reconsideration of opioid-centred postoperative pain management (1). This concern has driven a shift toward multimodal analgesic regimens that combine systemic agents with regional anaesthetic techniques targeting the abdominal wall directly.

The anterolateral abdominal wall is innervated by the anterior rami of the thoracolumbar spinal nerves (T6-L1), which travel within the fascial plane between the internal oblique and transversus abdominis muscles before dividing into anterior and lateral cutaneous branches (2). This plane, known as the transversus abdominis plane (TAP), can be accessed and infiltrated with local anaesthetic to interrupt somatic nociceptive transmission from the abdominal wall while largely sparing visceral pain pathways (3). The TAP block was first described using anatomical landmarks via the lumbar triangle of Petit by Rafi (4), and its clinical efficacy in reducing postoperative morphine consumption after abdominal surgery was subsequently validated in a landmark randomized trial by McDonnell et al. (5). With the introduction of ultrasound guidance, the block could be performed under direct visualization of the fascial planes, needle tip, and spread of local anaesthetic, improving its reliability and safety compared with the original landmark-based technique (3).

Local wound infiltration, in which local anaesthetic is deposited directly into the surgical incision at the time of wound closure, has long served as a simple, inexpensive, and technically undemanding method of providing analgesia at the site of tissue trauma (6). Because it requires no additional equipment or specialized training, wound infiltration remains widely practiced, particularly in resource-limited settings. However, its analgesic coverage is restricted largely to the immediate incisional tissue and tends to be of shorter duration than a plane block, which bathes the nerve trunks supplying a broader dermatomal distribution before they branch into the subcutaneous tissue (7).

Several randomized trials and systematic reviews have directly compared the two techniques across diverse surgical settings, including caesarean section (8-11), total abdominal hysterectomy (12), and other lower abdominal procedures (7). A meta-analysis of fifteen randomized trials by Yu et al. found that TAP block produced a more effective and sustained analgesic effect than wound infiltration with conventional local anaesthetics, a longer time to first rescue analgesic, and higher patient satisfaction (7). Similarly, Grape et al. reported that TAP block reduced 24-hour cumulative opioid consumption and pain scores compared with wound infiltration when both were used within a multimodal regimen after laparoscopic cholecystectomy (13). However, not all individual trials have shown a clear advantage for TAP block; Chandon et al. found broadly comparable 48-hour pain control between TAP block and continuous wound infusion after caesarean delivery, suggesting that the magnitude of benefit varies with the surgical procedure, local anaesthetic volume/dose used, and the time point of pain assessment (11,14).

Given this persisting debate, and the practical relevance of selecting a reliable, cost-effective analgesic technique-particularly in centres without ready access to ultrasound-guided regional anaesthesia expertise-the present study was undertaken to prospectively compare the analgesic efficacy of ultrasound-guided TAP block with that of local wound infiltration in patients undergoing elective lower abdominal surgery. The primary objective was to compare postoperative pain scores at rest, while secondary objectives included assessment of time to first rescue analgesia, 24-hour cumulative opioid consumption, incidence of postoperative nausea and vomiting, and patient satisfaction.

This prospective, randomized, observer-blinded, parallel-group comparative study was conducted in the Department of Anaesthesiology at [Institution Name], over a period of [study duration], after approval from the Institutional Ethics Committee (reference number: [insert]) and prospective registration with the Clinical Trials Registry (registration number: [insert]). Written informed consent was obtained from all participants prior to enrolment. Participants: Eighty adult patients of American Society of Anesthesiologists (ASA) physical status I or II, aged 18-60 years, scheduled for elective lower abdominal surgery (lower segment caesarean section, total abdominal hysterectomy, open appendicectomy, or inguinal herniorrhaphy) under spinal anaesthesia were enrolled. Exclusion criteria included known allergy to amide local anaesthetics, body mass index >35 kg/m², chronic opioid or analgesic use, coagulopathy, local infection at the proposed block/infiltration site, significant hepatic or renal impairment, and patient refusal. Sample size: Based on an anticipated difference in mean 24-hour VAS pain score of 1.2 ± 1.5 between groups, derived from prior comparative literature (7), with alpha = 0.05 and power = 80%, a minimum of 36 patients per group was calculated; this was rounded up to 40 per group to account for an anticipated 10% attrition. Randomization and blinding: Patients were allocated in a 1:1 ratio to Group T (ultrasound-guided TAP block) or Group W (local wound infiltration) using a computer-generated random number sequence, with allocation concealed in sealed opaque envelopes. The intervention was performed by an anaesthesiologist not involved in postoperative assessment; pain scores and other outcomes were recorded by an independent observer blinded to group allocation. Anaesthetic protocol: All patients received subarachnoid block with 0.5% hyperbaric bupivacaine at the L3-L4 interspace. Intraoperative monitoring included continuous electrocardiography, non-invasive blood pressure, and pulse oximetry. Intervention: In Group T, after completion of surgery, a bilateral ultrasound-guided TAP block was performed with the patient supine, using a high-frequency linear ultrasound probe placed in the midaxillary line between the costal margin and iliac crest. After identification of the external oblique, internal oblique, and transversus abdominis muscles, 20 mL of 0.25% bupivacaine was injected into the plane between the internal oblique and transversus abdominis on each side under direct visualization using an in-plane needle technique. In Group W, an equal total volume and concentration of local anaesthetic (20 mL of 0.25% bupivacaine per side) was infiltrated by the operating surgeon along the subcutaneous and subfascial planes of the wound edges prior to skin closure. Outcome measures: The primary outcome was postoperative pain intensity at rest, assessed using a 10-cm visual analogue scale (VAS; 0 = no pain, 10 = worst imaginable pain) at 0 (immediately after the block/infiltration), 2, 4, 6, 12, and 24 hours. Secondary outcomes included time to first rescue analgesic request (intravenous tramadol 1 mg/kg administered when VAS ≥ 4), total tramadol consumption over 24 hours, number of rescue doses, incidence of postoperative nausea and vomiting (PONV), haemodynamic parameters, patient satisfaction (5-point Likert scale), and any block- or infiltration-related complications. Statistical analysis: Data were entered and analyzed using SPSS software (version 26.0). Continuous variables were expressed as mean ± standard deviation and compared using the Student’s unpaired t-test or Mann-Whitney U test as appropriate; categorical variables were expressed as frequencies/percentages and compared using the chi-square or Fisher’s exact test. Time to first rescue analgesia was compared using the Kaplan-Meier method with log-rank test. A p-value <0.05 was considered statistically significant.

A total of 80 patients completed the study, with 40 patients in each group; no patient was lost to follow-up or withdrew consent.

Table 1. Demographic and baseline characteristics

SD = standard deviation; ASA = American Society of Anesthesiologists. There were no statistically significant differences between groups for any baseline parameter (p>0.05), confirming comparability of the two groups at enrolment.

Both groups were comparable with respect to age, sex distribution, weight, ASA grade, and duration of surgery (Table 1), confirming that any difference in postoperative outcomes could reasonably be attributed to the analgesic intervention rather than to baseline imbalance.

Table 2. VAS pain score at rest at various postoperative time intervals

Values are mean ± SD VAS score (0-10). VAS = visual analogue scale.

Pain scores at rest were comparable between groups immediately after the block/infiltration (0 hour), confirming adequate onset in both groups. From 2 hours onward, Group T showed significantly lower VAS scores than Group W at every time point up to 24 hours (p<0.001 for all comparisons), with the widest difference observed at 12 hours. This pattern is consistent with the TAP block providing a broader and more sustained field of analgesia than wound infiltration, whose effect appeared to wane more rapidly.

Table 3. Postoperative analgesic requirement

SD = standard deviation.

Group T required significantly more time before the first rescue analgesic dose was needed compared with Group W (approximately 5.7 hours versus 2.8 hours; p<0.001). Correspondingly, total 24-hour tramadol consumption and the mean number of rescue doses required were significantly lower in Group T (Table 3), indicating a clinically meaningful opioid-sparing effect of the TAP block.

Table 4. Postoperative complications and patient satisfaction

Values are n (%). Categorical variables were compared using the chi-square test or Fisher’s exact test, as appropriate.

The incidence of postoperative nausea and vomiting and mild sedation was numerically lower in Group T, although these differences did not reach statistical significance, likely reflecting the modest opioid-sparing magnitude relative to the sample size. No clinically significant haematoma, visceral injury, or local anaesthetic systemic toxicity was observed in either group. Patient satisfaction, rated on a 5-point Likert scale and dichotomized as good/excellent versus fair/poor, was significantly higher in Group T than in Group W (p=0.005), consistent with the superior analgesia and reduced opioid requirement observed in this group.

In the present randomized controlled study comparing ultrasound-guided TAP block with local wound infiltration following lower abdominal surgery, the TAP block group demonstrated significantly lower VAS pain scores at all postoperative time points beyond the immediate post-block period, a longer time to first rescue analgesic request, lower 24-hour cumulative tramadol consumption, and higher patient satisfaction, with a comparable, though numerically lower, incidence of PONV. These findings corroborate accumulating evidence in the regional anaesthesia literature.

The superior and more sustained analgesic profile of the TAP block can be explained by its mechanism of action: by depositing local anaesthetic in the fascial plane through which the thoracolumbar nerve trunks (T6-L1) traverse before dividing into their terminal cutaneous branches, the block anaesthetizes a wider dermatomal field supplying the abdominal wall rather than only the tissue directly adjacent to the incision (2,3). Wound infiltration, by contrast, acts predominantly on free nerve endings and small terminal branches at the wound margin and is therefore likely to provide analgesia of shorter duration and more limited spatial coverage, particularly once the local anaesthetic is cleared from the relatively well-vascularized subcutaneous tissue (6).

Our findings are concordant with the meta-analysis by Yu et al., who pooled data from fifteen randomized trials and reported that TAP block produced a more effective and steady analgesic effect than wound infiltration with conventional local anaesthetics, together with a longer time to first rescue analgesic and higher patient satisfaction, although the two techniques performed similarly at the one-hour postoperative time point (7). Likewise, Grape et al., in a systematic review restricted to laparoscopic cholecystectomy, found significantly lower pain scores at 2, 12, and 24 hours and reduced morphine consumption with TAP block compared with wound infiltration (13). In the obstetric population, randomized trials by McDonnell et al. and Tawfik et al. similarly favoured TAP block over wound infiltration for post-caesarean analgesia in terms of opioid-sparing effect (8,10), although Chandon et al. found broadly comparable 48-hour pain control between TAP block and continuous wound infusion, suggesting that catheter-based continuous infiltration techniques may narrow the gap observed with single-shot wound infiltration (11).

The lower incidence of PONV observed in the TAP block group in our study, although not reaching statistical significance, is consistent with the opioid-sparing effect of regional techniques, since reduced systemic opioid requirement is a recognized determinant of lower PONV rates (13). No block-related complications such as visceral injury, haematoma, or local anaesthetic systemic toxicity were observed in either group in our cohort, supporting the generally favourable safety profile of ultrasound-guided TAP block reported elsewhere (14,15).

Our study has certain limitations. First, the single-shot nature of both techniques limited analgesic assessment to the first 24 postoperative hours; continuous catheter techniques might extend, and possibly equalize, the duration of benefit. Second, the study was not powered to detect differences in less common complications such as local anaesthetic systemic toxicity. Third, the heterogeneous surgical procedures included, although reflecting real-world lower abdominal surgical practice, may have introduced some variability in baseline pain intensity. Finally, since the TAP block requires ultrasound equipment and additional operator training, its analgesic advantage must be weighed against considerations of cost, availability, and expertise when wound infiltration is being considered as an alternative in resource-constrained settings (6).

Ultrasound-guided TAP block provided superior and more sustained postoperative analgesia compared with local wound infiltration in patients undergoing lower abdominal surgery, as reflected by lower pain scores, delayed and reduced requirement for rescue opioid analgesia, and greater patient satisfaction, without an increase in block-related complications. These findings support the incorporation of ultrasound-guided TAP block as a key component of multimodal postoperative analgesia protocols where the requisite expertise and equipment are available, while wound infiltration remains a reasonable, low-cost alternative where ultrasound-guided regional anaesthesia is not feasible.

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