Effects of three forms of local anesthesia on perioperative fentanyl-induced hyperalgesia

Both local infiltration analgesia (LIA) and nerve block are common analgesic modalities for pain relief after surgery. The aim of the current study was to investigate the effects of those two modalities on pain behavior and the expression of pro-inflammatory cytokines such as interleukin (IL)-1β and IL-6 and tumor necrosis factor-α (TNF-α) in the spinal cord and dorsal root ganglion (DRG) in a rat model of perioperative fentanyl induced hyperalgesia. Rats were injected with fentanyl (60 μg/kg) 4 times and received a plantar incision after the second injection or they received pre-incision LIA and sciatic nerve block (SNB) or post-incision LIA with levobupivacaine (0.5%, 0.2 mL). Mechanical and thermal nociceptive thresholds were assessed using the tail pressure test and paw withdrawal test on the day before drug injection, 1 and 4 hours after injection, and 1-7 days later. The lumbar spinal cord and dorsal root ganglia were collected from rats in each group to measure IL-1β, IL-6, and TNF-α on the day before drug injection, 4 hours after injection, and 1, 3, 5, and 7 days later. Fentanyl and an incision induced a significantly delayed mechanical hyperalgesia in the tail and thermal hyperalgesia in both hind paws and up-regulation of pro-inflammatory cytokines in the spinal cord and dorsal root ganglia. Rats treated with pre-incision LIA and SNB or post-incision LIA had alleviated hyperalgesia and significantly reduced levels of IL-1β, IL-6, and TNF-α compared to the control group. LIA and SNB partly prevented perioperative fentanyl-induced hyperalgesia and up-regulation of pro-inflammatory cytokines in the spinal cord and dorsal root ganglia.