Peripheral Nerve Block Facilitates Acute Inflammatory Responses Induced by Surgical Incision in Mice

Background and Objectives

Anesthesia with peripheral nerve block (PNB) improves the early recovery profile of patients undergoing surgery, including the control of postoperative pain, opioid consumption, and the length of hospital stay. However, the influence of PNB on wound inflammation and the repair process has not been fully investigated. Therefore, we evaluated the effects of PNB on local inflammation of incised tissue in the acute phase of postoperative pain development.

Methods

Sciatic nerve block with 0.5% ropivacaine was performed before plantar incision in mice. Pain behavior, neutrophil infiltration, phagocytosis of apoptotic cells, and gene induction of inflammatory mediators were assessed for 7 days postoperatively.

Results

Sciatic nerve block with 0.5% ropivacaine treatment transiently increased the withdrawal threshold to mechanical stimuli and thermal latency for 2 hours after surgical incision, whereas no changes were observed from 3 hours after incision throughout the postoperative period. However, Gr-1⁺ neutrophil infiltration and the number of CD68⁺ macrophages engulfing TdT-mediated dUTP nick-end labeling⁺ apoptotic cells were significantly increased after incision. Tumor necrosis factor α and prostaglandin E2 were up-regulated at the incised sites. In addition, the expressions of lipoxygenase-15 and heme oxygenase-1, which resolve inflammation and promote wound healing after the acute inflammatory phase, were increased.

Conclusions

Single PNB before incision promoted acute phase inflammation mediated by neutrophils and macrophages at the sites of incision, whereas postoperative pain was not altered. Peripheral nerve block might locally accelerate innate immune responses after surgical incision without altering the nociceptive profile.