Intraneural Injection in Regional Anesthesia: What Does the Literature Tell Us?

Abstract

The contemporary use of ultrasound-guidance for peripheral nerve block allows for direct imaging of the relationship of needle-to-nerve. In the past it was presumed a block needle did not penetrate the nerve, but it is now apparent that unintentional, and even intentional, needle placement deep to the outer epineurium may occur without pain, paresthesia, or stimulating motor response below 0.5 mA. It remains controversial whether needle placement just outside the outer epineurium is effective in producing block, and less likely to contribute to postoperative neurologic symptoms than intentional intraneural needle placement which may produce faster onset of blockade, and sometimes more complete or longer blockade. Since extraneural, circumferential injection of local anesthetic is effective, and since current ultrasound and other technology cannot reliably prevent an intraneural needle from penetrating a fascicle with a potential for nerve injury, the extraneural needle location is concluded to be a more appropriate location.