Nerve damage still occurs after regional anaesthesia. Permanent symptoms occur in approximately 1 in 2,500 patients. Factors implicated in nerve damage are the type of needle, intrasfascicular injection, trauma, high needle tip pressure and local anaesthetic toxicity. Perineural injection of vasoactive drugs such as epinephrine can reduce nerve blood flow. Surgical causes include poor positioning and prolonged tourniquet time.
Our 2014 NIAA BJA/RCoA PhD student scholarship was carried out at the University of Dundee and in the laboratory of Dr Christine Demore at Sunnybrooke Health Sciences centre, Toronto.
We used a high-resolution 40 MHz micro-ultrasound transducer (Vevo 2100; VisualSonics, Eglinton, Toronto, ON, Canada) to visualise the axillary nerves and sciatic nerves of anaesthetised pigs and rats respectively.
We visualised nerve anatomy, needles, and changes in nerve structure. Intra-neural injection was characterised by either central swelling, peripheral swelling, epineural rupture, or failure to return to pre-injection morphology on needle withdrawal. significant pressure changes occurred with different flow rates and needle location of the needle tip.
In order to investigate whether nerve damage is secondary to ischaemia, we used photo-acoustic imaging during conduct of regional anaesthesia on the sciatic nerve of anaesthetised rats. We generated acoustic waves by pulse emission of laser onto haemoglobin molecules. Images were superimposed onto B-Mode images. We will conduct nerve blood flow and oxygenation studies on anaesthetised pigs soon.
figure 1 shows sciatic nerve of rat with superimposed image (red areas) indicative of the presence of haemoglobin.
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