The effect of transversus abdominis plane block on acute and chronic pain after inguinal hernia repair. A randomized controlled trial.

BACKGROUND: This prospective double-blind randomized study aimed at evaluating the short- and long-term postoperative analgesic efficacy of the ultrasound-guided tranversus abdominis plane (TAP) block in inguinal hernia repair under general anesthesia. METHODS: Sixty patients undergoing inguinal hernia repair were allocated to TAP block with either ropivacaine 0.75% 20 mL or placebo 20 mL. Postoperatively, they had access to a patient-controlled analgesia (PCA) device administering 1 mg doses of morphine as rescue analgesia. Pain was assessed at rest and during movement with the numeric rating scale (NRS) score 3,6 and 24 hs postoperatively. Other variables recorded were intraoperative dose of remifentanil required to maintain systolic arterial pressure within 20% of baseline, mg of morphine used in the Post Anesthesia Care Unit (PACU) and total dose of morphine administered via the PCA device. Six months after surgery, the occurrence of chronic pain was assessed with the NRS score at rest and during movement. Patients were also asked to fill in the DN4 questionnaire to estimate the development of neuropathic pain. RESULTS: Patients who were administered ropivacaine demonstrated significantly less pain at rest and on movement, as expressed by NRS scores in comparison to patients in the placebo group. The former group also required less remifentanil intraoperatively, less morphine during the PACU stay and had lower morphine consumption through the PCA device. Six months after surgery, pain scores at rest and during movement were comparable between the two groups. At the same time DN4 scores were low and comparable between the two groups. CONCLUSION: Ultrasound-guided TAP block provided better pain control than placebo in the acute setting after inguinal hernia repair. However, the incidence of chronic pain was low and not significantly affected by the performance of the block.