Histological change of intraneural and peri-neural injection of the local anesthetic ropivacaine in the rat sciatic nerve

ABSTRACT

Neural damage is a possible complication during locoregional anaesthesia. Damage may be caused by direct trauma, toxicity of the local anaesthetic drugs or ischaemia from decrease in the nerve blood flow. These mechanisms may occur either alone or in combination. We have studied the histological findings of perineural and intraneural injection of ropivacaine in rat sciatic nerve. 60 male albino rats were assigned into two equal groups. Group I received intraneural ropivacaine [50 microl] on the right sciatic nerve and an equivalent volume of saline intraneurally on the left sciatic using an insulin needle. In group II, the same volumes of ropivacaine and saline were injected perineurally on the right and left sciatic nerves respectively. Each group was subdivided into three equal subgroups according to whether the animals were sacrificed at 10 minutes 7 days or 30 days after injection. Nerves were harvested, fixed and processed for light and electron microscopic examination. Nerves injected perineurally with ropivacaine showed intraneural disruption, edema and fibroblasts after seven days. Nerves injected intraneurally with ropivacaine or saline presented with disruptions, edema and hemorrhage immediately after injection. After 7 days, disruption, degeneration and regeneration were observed. Mitochondrial swelling was observed 7 days after intraneural and perineural ropivacaine but not after saline. In both groups, regeneration started early [after 7 days] to become more or less complete after 30 days. These results demonstrate the safety of the use of ropivacaine for peripheral nerve block even if inadvertent intraneural injection occurred. However, to avoid neuropathy, the use of nerve stimulator should be encouraged to avoid nerve trauma during repeated puncture in the search for paraesthesia. Injection should be stopped if painful to avoid intraneural injection