Long-axis ultrasound imaging of the nerves and advancement of perineural catheters under direct vision: a preliminary report of four cases.

Background And Objectives: Ultrasound allows visualization of in plane needle insertion toward a nerve and the perineural spread of local anesthetic (LA) solution. However, advancement and final positioning of perineural catheters is difficult to visualize. We assessed the feasibility of long axis nerve scans for controlling perineural catheter placement.

Methods: Four orthopedic patients scheduled for continuous peripheral nerve blocks (interscalene, femoral, midfemoral sciatic, and popliteal sciatic), had perineural catheters inserted under ultrasound guidance. After obtaining adequate short axis images of the target nerves, the high frequency linear transducer was rotated 90 degrees to obtain long axis views. An 18-gauge epidural Tuohy needle was inserted tangentially to the nerve and the correct tip position was confirmed visually by small volume injections of LA. A rigid epidural catheter was inserted under the transducer's long plane and advanced into the desired perineural position. LA was then injected through the catheter and the spread was confirmed both on long axis and short axis scans.

Results: The catheters were captured on the long axis scans in all 4 patients, both exiting the needle tip, and during further advancement. They remained in situ for 3 to 5 days providing adequate postoperative analgesia and were removed uneventfully.

Conclusions: This short case series suggests that long axis imaging of the nerve, the needle, and the catheter allows visualization of a catheter's advancement. Using to-and-fro movements, and slight rotation the needle's bevel, the catheter may be maneuvered under the ultrasound beam, which facilitates correct positioning.