Neurophysiological effects of needle trauma and intraneural injection in a porcine model: a pilot study

Neurophysiological data are lacking in the research of nerve injury during regional anaesthesia. The aim of this pilot study was to establish a large animal model in order to test the hypothesis that needle trauma alone or in combination with intraneural injection would result in measurable nerve injury.

The experimental set-up was elaborated in four pre-test animals. In the remaining animals (n = 11), 22 sciatic nerves were randomly assigned to one of four groups: needle trauma (n = 5) generated by ultrasound-guided forced needle advancement; intraneural injection of 2.5 ml saline (n = 6); intraneural injection of 5 ml saline (n = 6); extraneural injection of 5 ml saline (n = 5) as control group. Compound muscle action potential (CMAP) amplitudes as well as latencies were taken as outcome parameter and monitored over 180 min. Sonographic assessments were performed simultaneously.

Following needle trauma and intraneural injection, CMAP amplitudes declined significantly over 180 min (P < 0.001). The control group showed no electrophysiological alterations. At 60 min, decreases in amplitude were significant after needle trauma (P = 0.04) and intraneural injection of 2.5 ml (P = 0.045), and highly significant after injection of 5 ml (P = 0.006) when compared to controls. Sustained nerve swelling was observed after intraneural injection, but not after needle trauma and perineural injection.

Isolated mechanical trauma caused by forced needle advancement alone or in combination with intraneural injection of saline was followed by a significant decline in CMAP amplitudes indicating conduction block due to disruption of myelin or axon loss (pseudo-conduction block).