A Double-blinded Randomized Trial Comparing Surgeon-administered Transversus Abdominis Plane (TAP) Block With Placebo After Midline Laparotomy in Gynecologic Oncology

Multimodal opioid-sparing analgesia is recommended in order to prevent post-operative complications and shorten length of stay. While ultrasound-guided Transversus Abdominis Plane (TAP) block has been shown to reduce postoperative opioid use, the time and expertise needed to perform it can be a barrier to administering the procedure. A surgeon-administered TAP block has been described, but has yet to be evaluated with a randomized controlled study in gynecology oncology patients undergoing a midline laparotomy. The investigators hypothesize that surgeon-administered TAP blocks may decrease total opioid use in the first 24 hours.

Eighty women above the age of 18 and undergoing a midline laparotomy for a suspected gynecologic malignancy will be recruited to undergo bilateral surgeon-administered TAP blocks with either 40ml of 0.25% bupivacaine or an equal volume of saline administered equally over both sides, prior to fascial closure. Exclusion criteria include inability to give informed consent, presence of contraindications or sensitivities to drugs specified in the protocol, pre-existing truncal sensory disturbance, history of chronic opioid use, infections at the injection site, significant adhesions on the anterior or lateral abdominal wall preventing access to the injection site, patients receiving neuraxial anesthesia (Epidural, Spinal) or local wound infiltration. The primary outcome studied will be the total dose of opioid in morphine equivalents received in the postoperative period. Secondary outcomes including postoperative pain scores, postoperative nausea and vomiting rates, time to flatus, incidence of clinical ileus and time to discharge from hospital will also be recorded.

Sample size calculation was based on a meta-analysis by Johns for use of TAP blocks in abdominal surgeries, that reported morphine equivalents mean at 24h as 20.6mg for the TAP group and 44.3mg for the control group (mean difference of 23mg in 24h), with a standard deviation of 14mg. To find a clinically significant decrease in opioid use of 20%, our primary outcome, with a 2-tailed analysis and power of 80%; the investigators would need 36 patients in each group. To account for potential dropouts and protocol violations, as well as secondary analyses, the investigators will recruit a total of 80 patients (40 in the TAP block group and 40 controls).

Differences in characteristics between treatment and control groups will be analysed using the chi-square test for dichotomous data, independent samples Student's t-test for parametric continuous variables, and Mann-Whitney U test for non-parametric continuous data. Test of normality will be performed using the Shapiro-Wilk test. If there is significant (>10%) missing data, data will be imputed by predictive mean matching. Subgroup analysis by type of incision (infraumbilical vs supraumbilical) will be performed.

Missing data and patterns will be assessed monthly by the data manager. Remedial measures, including retraining of staff, will be used as needed to minimize missing data. The investigators plan for an intention-to-treat analysis.