Feasibility study of real-time three-/four-dimensional ultrasound for epidural catheter insertion

Real-time two-dimensional (2D) ultrasound can be used to facilitate neuraxial anaesthesia. Four-dimensional (4D) ultrasound allows the use of multiple imaging planes and three-dimensional reconstruction of ultrasound data. We assessed how 4D ultrasound could be used to perform epidural catheter insertion in a cadaver model. We then also compared 4D ultrasound and a previously described 2D technique in real-time epidural catheterization. Epidural catheter insertion was attempted on four embalmed cadavers using a variety of 4D techniques. A feasible, 4D ultrasound-guided in-plane needle insertion technique was then compared qualitatively with the 2D technique in a further six cadavers. A feasible technique of real-time 4D ultrasound-guided epidural insertion used two perpendicular imaging planes to improve the orientation of the operator. It resulted in changes in the needle direction in half of the approaches. Using 4D ultrasound, the Tuohy needle could only be seen reliably in the primary imaging plane. In-plane needle visibility using 4D imaging was inferior to 2D imaging. Successful epidural catheterization was also aided by an acoustic window being present, which allowed visualization of the vertebral body. The study demonstrates that 4D ultrasound can be used for real-time epidural catheter insertion and has both advantages and limitations compared with the 2D technique. Four-dimensional ultrasound has the potential to improve operator orientation on the vertebral column. However, this comes at the price of decreased resolution, frame rate, and needle visibility. Prospective evaluation of the importance of an acoustic window in neuraxial anaesthesia is required.