Peripheral nerve injury caused by injection needles used in regional anaesthesia: influence of bevel configuration, studied in a rat model.

We have studied the immediate and long term (up to 28 days) effects of short and long bevelled needle impalement of the rat sciatic nerve. Three techniques were used to assess neural trauma and its consequences: stained longitudinal nerve sections were assessed by light microscopy and scored for injury; the extravasation of Evan's Blue dye, after antidromic electrical nerve stimulation, was used as a test of unmyelinated fibre function; the flexion withdrawal times from a noxious stimulus were measured. The results of all three experiments suggested that, should a nerve fascicle become accidentally impaled during regional anaesthesia, the lesions induced by short bevelled needles are more severe, more frequent and take longer to repair than those induced by long bevelled needles. Nerve injury induced by short bevelled needles was associated with persisting signs of injury 28 days after the injury. These results suggest that the current practice of using short bevelled needles to prevent nerve injury complicating regional anaesthesia be reassessed.