Study of damage to peripheral nerves caused by anaesthetic needles during regional anaesthesia

Abstract

Background: Ultrasound guidance is strongly recommended for the safe conduct of regional anaesthesia procedures. It is safe, now has adequate spatial resolution and provides real time visualization of local anaesthetic spread. However, the risk of nerve trauma still remains. A recent meta-analysis of randomized controlled trials has described the incidence of transient neuropathy secondary to Ultrasound Guided Regional Anaesthesia (UGRA) in 7% of patients, probably related to nerve trauma. Limited acoustic contrast of tissues, poor visibility of the needle and the limited detail resolution of the ultrasound probe are contributory factors. Microultrasound techniques are increasingly used for high resolution small animal and human tissue imaging as anatomical structures may be visualized in greater detail compared to conventional B-mode ultrasound. However, microultrasound imaging of real time of UGRA has not been conducted and our hypothesis was that subepineurial and subperineurial tissue could be identified using this technology. Nevertheless, questions remain as to how well micro ultrasound imaging is able to visualize nerve anatomy and the tip of needle in real-time. The aim of this study was to investigate cadaveric nerve models and microultrasound imaging as effective tools for determining the mechanisms of nerve trauma caused by intraneural insertion of anaesthetic needles.

Methods and Materials: Nerves resected from Thiel, soft embalmed human cadavers (Thiel nerves) and fresh cadaveric human nerves (Fresh nerves) were used in the study as specimens. Microultrasound scanning using a 30 MHz and 45 MHz transducer, gave an image resolution approaching about 100 μm. The radiofrequency (RF) data obtained was processed in MATLAB software to generate 2D and 3D images of the nerves. The visualised anatomy was validated with histology sections, taking into consideration the size of the nerve, number and size of fascicles, their pattern and distribution in the nerve. Since the microultrasound images were being validated using histology, some optimization was needed in histology techniques as well. The optimization was necessary as, the specimens used were Thiel nerves and fresh nerves.

Results: The microultrasound images showed the external shape and size of the nerve and distinct fascicles of size greater than 0.5 mm. Statistical analysis of the repeated measurements of the nerve diameter was done. Anatomical features such as the size, and shape of nerves and fascicles as well as epineurium and perineurium were similar in microultrasound and histology images. Also it was found that fresh cadaveric nerves and the recently embalmed cadaveric nerves (< 12 months) can be used as models for the study of regional anaesthesia. Needle insertion experiments showed that the fascicles tend to move away or split when a needle is inserted into the nerve.

Conclusion: Microultrasound has been validated with histology sections as a means of imaging nerve cross sectional anatomy. The preliminary needle insertion experimental results demonstrate mechanical damage when a needle is inserted into the nerve. Data suggests that microultrasound has potential for real time imaging of the internal structure of the nerve during regional anaesthesia. The resolution of the images can be improved with optimization of the microultrasound imaging.

Date of Award	2014
Original language	English
Awarding Institution	University of Dundee
Supervisor	Christine Demore (Supervisor) & Graeme McLeod (Supervisor)