Transversus abdominis plane block in robotic gynecologic oncology: a randomized, placebo-controlled trial

Although robotic surgery decreases pain compared to laparotomy, postoperative pain can be a concern near the site of a larger assistant trocar site. The aim of this study was to determine the efficacy of transversus abdominis plane (TAP) block on 24-hour postoperative opiate use after robotic surgery for gynecologic cancer.

Sixty-four subjects with gynecologic malignancies who were scheduled to undergo robotic surgery were enrolled into the study. They were randomized to receive a unilateral TAP block to the side of the assistant port via ultrasound guidance. The block was comprised of 30 cc of 0.25% bupivacaine with 3 mcg/mL epinephrine or saline. Opiate use was measured and converted into IV morphine equivalents. Patient-reported pain was measured using the Brief Pain Inventory (BPI) and Visual Analog Scale (VAS).

The treatment group used a mean of 64.9 mg morphine in the first 24h compared to 69.3mg for controls (primary outcome, p=0.52). After age-adjustment, the treatment group used a mean of 11.1mg morphine less than controls (p=0.09). Postoperative pain scores assessed by the BPI (6.44 vs. 6.97, p=0.37) and the VAS (3.12 vs. 3.61, p=0.30) were equivalent. Block placement was uncomplicated in 98.4% of participants with mean BMI of 35.3 kg/m(2). Linear regression revealed an approximate 8.1mg decrease in morphine equivalents used per additional decade of life (p=0.0008). There was a positive correlation between the amount of opiates and BMI with an additional 8.8 mg of morphine per 10 kg/m(2) increase in BMI (p=0.0012).

TAP block is safe and feasible in this patient population with a large proportion of morbid obesity. Preoperative TAP block does not significantly decrease opiate use. However; based on these data, a clinically useful nomogram has been created to aid clinicians in postoperative opiate-dosing for patients based on age and BMI.