Transversus Abdominis Plane Block Versus Ilioinguinal-Iliohypogastric Nerve Block for Postoperative Analgesia Following Open Total Abdominal Hysterectomy

A Comparative Study Between Ultrasound-guided Transversus Abdominis Plane Block Versus Ultrasound-guided Ilioinguinal-Iliohypogastric Nerve Block for Postoperative Analgesia Following Open Total Abdominal Hysterectomy: A Randomised Comparative Trial

The investigators hypothesised that ultrasound-guided transversus abdominis plane (TAP) block would prolong the time to first rescue nalbuphine within 24 hours compared with ultrasound-guided ilioinguinal-iliohypogastric (IIH) nerve block, by virtue of its broader dermatomal coverage (T10-L1 versus T12-L1) of the Pfannenstiel incision. This hypothesis direction was established before unblinding and data analysis.

Aim of the work

the aim of the study is to compare between the analgesic effect of Transversus Abdominis Plane Block and Ilioinguinal-iliohypogastric block following open abdominal hysterectomy Objectives

• to compare between the analgesic effect of Transversus Abdominis Plane Block and Ilioinguinal-iliohypogastric block For Postoperative Analgesia following open abdominal hysterectomy
• to measure the incidence of complications following both blocks as hematoma, block failure, infection at injection site

Sample size:

Our primary outcome is the time to first rescue analgesia request. In a previous study, the meantime to first rescue analgesia was 10.58 ± 2.35 hours (6). The investigators calculated a sample size that could detect a mean difference of 20% between both study groups. MedCalc Software version 14 (MedCalc Software bvba, Ostend, Belgium) was used to calculate the sample size.38 patients( 19 patients per group) at least were estimated to have a study power of 80% and an alpha error of 0.05. This number will be increased to 42 patients (21 patients per group) to compensate for possible dropouts.

Sample size calculation was performed guided by the power of 80%, confidence level of 95%.

Statistical analysis:

For data analysis, the Statistical Package for Social Science (SPSS) software, version 23.0 for Microsoft Windows (SPSS Inc., Chicago, IL, USA) was used (version 23.0 was used in place of the registered version 26; no impact on any statistical result). Python (SciPy 1.7) was additionally used for area-under-the-curve computation and Holm-Bonferroni multiplicity correction.

Normality of continuous data was assessed using the Shapiro-Wilk test and graphical inspection. Parametric data are reported as mean (standard deviation) and were compared between groups using the independent samples t test. Non-parametric data are reported as median (interquartile range [range]) and were compared using the Mann-Whitney U test. Categorical data are reported as number (proportion) and were compared using the chi-square test or Fisher exact test as appropriate.

The primary outcome time from end of surgery to first rescue nalbuphine within 24 hours was analysed as a time-to-event outcome using the Kaplan-Meier method with log-rank testing, and Cox proportional hazards regression was used to estimate the hazard ratio with 95% confidence interval. Participants who did not require rescue nalbuphine were censored at 24 hours. This approach replaced the t-test framework implied in the original registration, as Kaplan-Meier survival analysis is the methodologically appropriate method for a time-to-event outcome with censored observations. This change was made before unblinding and before any outcome data were examined.

To address multiple comparisons across the eight postoperative pain assessment time points, cumulative pain burden was calculated for each participant as the area under the numerical rating scale pain score-time curve from 5 minutes to 24 hours using the trapezoidal rule (NRS-AUC₅ₘᵢₙ-₂₄ₕ, in score·hours) and compared between groups using the Mann-Whitney U test. Individual time-point comparisons were considered exploratory and p values were adjusted using the Holm-Bonferroni stepwise correction in place of the Bonferroni post-hoc ANOVA approach registered originally; this substitution is more statistically appropriate as it controls the familywise error rate with greater power. Cohen's d was calculated from group means and standard deviations as a supplementary standardised effect-size measure.

All tests were two-sided with α = 0.05. Exact p values are reported throughout rather than thresholds (e.g., p < 0.05). All 42 randomised participants completed 24-hour follow-up and were included in the analysis (intention-to-treat).

Inclusion Criteria:

• Participants will be adult patients (35-65 years)
• ASA I-III
• Scheduled for elective open TAH

Exclusion Criteria:

• Patient refusal
• BMI > 40 kg·m-²
• Pregnancy
• Chronic pain requiring daily analgesics
• Any known allergy to local anesthetic, nalbuphine, paracetamol, or diclofenac
• Patients with neurological, psychological disorders or those lacking cooperation
• Patients with anatomic abnormalities at site of injection, skin lesions or wounds at site of proposed needle insertion.
• Patients with bleeding disorders defined as (INR >2) and/ or (platelet count <100,000/µL)
• Patients with hepatic disease e.g. liver cell failure or hepatic malignancy or hepatic enlargement