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Introduction: Due to application of ultrasound needle tip localization and the distribution of local anaesthetics during injection can be visualized when performing peripheral nerve blocks. Clinical data whether the injection in the intraneural space may cause neurological symptoms or particularly nerve injury are limited. The aim of this study was to challenge the hypothesis that the application of isotonic Ringer´s solution causes fewer nerve injury compared to the injection of local anaesthetics in the intraneural space due to major toxicity.
Material and methods: Intraneural injection was applied in 7 anaesthetized pigs to a total of 40 brachial plexus nerves. In each animal up to 6 exposed plexus nerves underwent an injection in the intraneural space. Either a volume of 2 ml of bupivacain 0.5% or Ringer´s solution was applied. After 48 hours of maintaining general anaesthesia 54 nerves including negative and positive controls were resected. The specimens were processed for visual examination and the detection of inflammatory cells (haematoxylin eosin, i.e. CD68-immunohistochemistry for visualisation of macrophages), myelin damage (Kluver-Barrera staining), and intraneural haematoma. Considering myelin, haematoma and inflammatory cells, the grade of nerve injury was scored ranging from 0 (no injury) to 4 (severe injury).
Results: Statistical analysis showed significant nerve lesions in the interventional groups compared to the negative controls (p=0.02). According to the applied injury score, there was no significant difference between the bupivacaine group [median (interquartile range) 1 (1–1.5)] and the Ringer´s group [1 (0.5–2) p=0.77]. The occurrence of posttraumatic regional inflammation was directly related to the applied interventions. Myelin damage (Score value 4) was found in 12.5% of the examined specimens irrespective of the applied substance.
Conclusion: In the present study, the magnitude of nerve injury following intraneural injection was not related to the applied type of substance. Posttraumatic inflammation and structural damage of nerve tissue were notable signs of nerve injury after intraneural injection. According to the present data a volutrauma due to intraneural injection can be designated an important trigger for nerve injury.