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Background
Regional anesthetic techniques are commonly employed in pediatric urology to reduce post-surgical pain and minimize opioid requirements. Recently, the ultrasound (US) guided transversus abdominis plane (TAP) block has gained popularity, potentially providing benefit over regional field infiltration (RFI). However, there is paucity of high-level evidence to support this trend, particularly for children. To further evaluate this issue, herein we present data of a prospective randomized controlled trial designed to evaluated the superiority of US-guided TAP block vs. surgeon delivered RFI for children undergoing open pyeloplasty at a major tertiary care referral center.

Methods
After obtaining Research Ethics Board approval and registration (ClinicalTrials.gov #NCT01243593), children aged 0-6 years of age with American Society of Anesthesiologists status 1-3 undergoing unilateral open pyeloplasty were recruited following parental consent. After simple block randomization, patients were segregated, in a concealed fashion, into two groups: TAP block vs. RFI. General anesthetic delivery, muscle-splitting surgical technique and other adjuvant scheduled postoperative analgesics, were standardized. A blinded assessor determined pain scores on admission (time=0), 5, 10, 15, 30 minutes, and every 15 minutes thereafter in the recovery room using the Faces-Legs-Activity-Cry-Consolability (FLACC) scale. The primary outcome, need for rescue morphine administration based on a FLACC score ?3, was assessed based on cumulative morphine requirements. Based on an effect size of 0.88, a superiority design in favor of TAP block enrolling at least 32 patients would provide a power of 0.8 with and alpha of 0.05.

Results
Two pediatric urologists performed 57 pyeloplasties over a 2.5-year period, achieving enrollment of 32 children (16 in each group, balanced for age and weight). Twenty-four patients were not included because of refusal to participate (n=6), missed screening opportunity (n=10), solitary kidney (n=2), re-do procedure (n=5) and malignant hyperthermia (n=1). There was a statistically significant difference in total morphine requirements in favor of surgeon-administered local anesthesia (TAP block=0.066 ± 0.051mg/kg and RFI=0.027 ± 0.040mg/kg, p=0.023), exceeding acceptable effect size differences between treatment arms, thus the trial was stopped due to lack of benefit. In addition, the number of children requiring rescue morphine administration in the recovery room was statistically significant, likewise favoring RFI (TAP block=12/16, RFI=5/16, p=0.016). No local anesthetic-specific adverse events were noted in either group.

Conclusions
US-guided TAP block is not superior to RFI with bupivacaine as a strategy to minimize early opioid requirements following open pyeloplasty in children. Conversely, our data suggests that surgeon-delivered RFI provides superior pain control.