A Chinese research group has developed a single crystal ultrasound transducer and put it on the end of a stylet fitting inside a standard epidural needle. The ultrasound probe will let you visualise where the tip of the needle is when placing the epidural. With A-mode ultrasound, you’ll see the ligamentum flavum and dura mater approaching. It’s not for clinical use just yet, but a fascinating technology.
And below is an image synthesized from the A-mode ultrasound images. The image resembles an M-mode scan, and is showing the ligamentum flavum and dura mater, the two hyper-echoic lines clearly outlining the epidural space. The image also shows the subdural space clearly. Along the x-axis, the epidural needle and ultrasound transducer are approaching the epidural space and finally, towards the right edge, going through the ligamentum flavum and entering the epidural space:
Background: Epidural needle insertion is usually a blind technique where the rate of adverse events depends on the experience of the operator. A novel ultrasound method to guide epidural catheter insertion is described.
Methods: An ultrasound transducer (40 MHz, a -6 dB fractional bandwidth of 50%) was placed into the hollow chamber of an 18-gauge Tuohy needle. The single crystal was polished to a thickness of 50 μm, with a width of 0.5 mm. Tissue planes were identified from the reflected signals in an A-mode display. The device was inserted three times into both the lumbar and thoracic regions of five pigs (average weight, 20 kg) using a paramedian approach at an angle of 35-40°. The epidural space was identified using signals from the ligamentum flavum and dura mater. Epidural catheters were placed with each attempt and placement confirmed by contrast injection.
Results: The ligamentum flavum was identified in 83.3% of insertions and the dura mater in all insertions. The dura mater signal was stronger than that of the ligamentum flavum and served as a landmark in all epidural catheter insertions. Contrast studies confirmed correct placement of the catheter in the epidural space of all study animals.
Conclusions: This is the first study to introduce a new ultrasound probe embedded in a standard epidural needle. It is anticipated that this technique could reduce failed epidural blocks and complications caused by dural puncture.