Investigating the use of Micro-ultrasound for Visualising Nerve Structures during Epidurals and Peripheral Nerve Anaesthesia

Abstract

Background: Epidural blocks and peripheral nerve blocks are an integral component of enhanced recovery. While these are widely used to improve patient comfort and patient safety, the complications and incidence of nerve trauma during these procedures cannot be evaded. This thesis evaluated the clinical potential of microultrasound imaging to improve visualisation and precision of performing epidural blocks and peripheral nerve blocks.

Materials and Methods: The experiments presented in this thesis are independent studies. For the epidural block study, two operators imaged the epidural space of ex vivo pigs at different frequencies at different tissue layers. A feasibility study of identifying the epidural space using M-mode imaging was also performed. For the peripheral nerve block study, a 40 MHz micro-ultrasound transducer was used for imaging the intraneural injections performed on in-vivo pigs using 21G anaesthetic block needle. Also, inline fluid pressure was recorded at different tissue interfaces during intraneural injections performed at flow rates of 6 ml/min, 12 ml/min and continuous flow rate of 1 ml/min.

Results: The M-mode imaging demonstrated good potential to identify the epidural space and the tissue layers around it. Real-time micro-ultrasound imaging showed good potential to visualise the needle-nerve interaction to visualise the morphological changes to the nerve during intraneural injection. Highest peak pressure was recorded when the saline fluid was delivered on epineurium. The statistical analysis showed flow rates (P = 0.004) and location of the needle tip contributing significantly to the variation in the pressure change and contributing to mechanical nerve trauma.

Conclusion: M-mode imaging showed good potential for identifying the different layers of porcine tissue and epidural space. Micro-ultrasound enabled in vivo, real-time visualisation of the fascicle structure in 100% of attempted peripheral nerve blocks. Pressure could not be used as a reliable indicator to identify the needle tip. Flow rate between 1 ml/min -3 ml/min was recommended as a suitable flowrate to perform peripheral nerve blocks and to identify the onset of the change in anatomy of the nerve if intraneural injection occurs. micro-ultrasound imaging along with pressure monitoring and flow control was recommended to perform a successful and safe peripheral nerve block.

Date of Award	2022
Original language	English
Sponsors	National Institute of Academic Anaesthesia
Supervisor	Zhihong Huang (Supervisor), Graeme McLeod (Supervisor) & Christine Demore (Supervisor)