Newly designed, self-coiling catheters for regional anesthesia--an imaging study.

BACKGROUND AND OBJECTIVES: A major concern with the use of continuous peripheral nerve block is the difficulty encountered in placing the catheters close enough to the nerves to accomplish effective analgesia. The aim of this study was to investigate if a self-coiling catheter would remain close to the sciatic nerve once introduced through needles placed under ultrasound guidance and if contrast dye injected through the pigtail catheter made direct contact to the nerves.

METHODS: First, Tuohy needles were placed anterior to the sciatic nerves under ultrasound guidance (needle-in-plane/nerve in short-axis approach). Next, the self-coiling catheters were blindly introduced through the needles. A total of 40 catheters were placed; 2 per sciatic nerve in the right and left legs of 10 human cadavers. To detect the exact catheter location, computer tomographic imaging of the legs was performed. Finally, the spread of injected contrast dye in relation to the nerves was assessed by magnetic resonance imaging.

RESULTS: There was direct contact of the coil with the nerve in 37 cases. In the remaining cases, the shortest distances from the coil to the nerves were 5, 6, and 7 mm. In all but 1 case, the contrast dye was directly in contact with the nerves. The median circumferential covering of the nerve by contrast dye was 50% (25-interquartile range of 40%).

CONCLUSIONS: By using self-coiling catheters, it is possible to blindly introduce the catheter through needles placed under ultrasound guidance with a low risk of catheter misplacement away from the targeted nerves.