Dermatomal spread following posterior transversus abdominis plane block in pediatric patients: our initial experience

Introduction: Several techniques for the transversus abdominis plane (TAP) block have been described. The extent of sensory changes using an ultrasound-guided posterior TAP block (pTAP) remains unclear in pediatric patients. The primary aim of this study was to report the extent of sensory changes achieved with pTAP; specifically the highest thoracic dermatome anesthetized. Secondary outcomes were pain scores (PS), opioid consumption, and complications. Methods: We retrospectively reviewed the medical records of patients less than 21 years of age undergoing abdominal surgery with a unilateral or bilateral pTAP(s) for postoperative analgesia. The local anesthetic was placed posterior to the termination of the transversus abdominis muscle where the thoracolumbar fascia overrides the quadratus lumborum muscle. The extent of sensory changes, pain scores, and opioid consumption were analyzed. Results: A total of 10 patients (15 pTAP blocks) met the inclusion criteria. The mean (sd; range) age and weight were 15 years (5 years; range 7–20 years) and 57 kg (21 kg; 27–97 kg), respectively. The cephalad dermatome levels achieved were: T7 in 6/15 (40%); T8 in 10/15 (67%); and T9 in 14/15 (93%). An inferior dermatome level of T12/L1 and sensory extension from midaxillary line to the midline was documented in 15/15 blocks. The mean intraoperative and postanesthesia care unit (PACU) opioid consumption in morphine equivalents were 0.34 mg·kg⁻¹ (sd = 0.12 mg·kg⁻¹) and 0.04 mg·kg⁻¹ (sd = 0.05 mg·kg⁻¹), respectively. PACU pain scores were mild (<4) in 60%, moderate (4–7) in 30%, and severe (>7) in 10% of patients. No complications were reported. Discussion: The current uncertainty regarding sensory blockade limits the clinical application of TAP blocks. While the midaxillary approach results in unpredictable sensory changes of the abdomen, we reliably achieved sensory changes up to a T9 level in 93% of the blocks. Conclusion: In this small series of patients, we demonstrate a high technical success rate of achieving cutaneous analgesia to the abdominal wall. These results should encourage clinical studies of the efficacy of this block for abdominal surgery in pediatric patients.