Intensity of the Stimulating Current May Not Be a Reliable Indicator of Intraneural Needle Placement

Abstract

Specific response to nerve stimulation with currents <0.2 mA occurred only when the needle tip was positioned intraneurally. However, motor response could be absent with intraneural needle placement at a current intensity of up to 1.7 mA.

Various Possible Positions of Conventional Catheters Around the Femoral Nerve Revealed by Neurostimulation

“…These ineffective blocks in the 2 cases without stimulation were probably due to incorrect positioning of catheters. The other 5 effective blocks (despite the absence of motor response to block stimulation) were perhaps consistent with a transepineural position without elicitation of any response, as has been shown in animals by Tsai et al 15 and in clinical practice with ultrasound by Perlas et al 16 According to Johnson et al, 14 the absence of response may be due to a stimulating tip positioned too far from the nerve or due to intraneural position, in which case high intensity induces a propagation block responsible for the absence of motor response. Mistaking this for unsuccessful positioning as termed by Morin et al 4 and administering a large dose of potentially toxic local anesthetic could be deleterious.…”

“…Significantly more boluses of ropivacaine and more morphine supplementation were required to relieve pain to an acceptable level in the 91 mA group ( Table 4). The motor blockade of femoral nerve was greater in the e1 mA group at 30 mins after extubation, but no between-group difference was found 14 Recent experimental and ultrasound studies 15,16 have called into question the relationship between intensity of nerve stimulation and stimulating tip-to-nerve distance. Yet, these recent findings actually provide support for most of the results of this study, which in turn help us understand why many past and recent studies failed to find a difference between the 2 types of catheters in CFNB.…”

A Prospective, Randomized Single-blind Study of the Anesthetic Efficacy of the Inferior Alveolar Nerve Block Administered with a Peripheral Nerve Stimulator

“…The use of low amperage (<0.5 mA) currents indicates an extremely close position to the nerve. Tsai et al (17) and Robards et al (18) found currents of 0.2 mA occurred only when the needle tip was positioned intraneurally. Similarly, increasing current flow (amperage), as was done in the current study, increases the ability to stimulate the nerve without placing the needle intraneurally.…”

High Opening Injection Pressure Is Associated With Needle-Nerve and Needle-Fascia Contact During Femoral Nerve Block

“…These findings suggest that nerve stimulation is relatively insensitive for neurolocation, which is consistent with other studies. 23,24 Ultrasound-guided nerve blocks often entail several needle redirections and multiple injections of local anesthetic that may further decrease the sensitivity of nerve stimulation and/or paresthesia to detect needle-nerve contact or intraneural injection. In such cases, OIP can serve as a reliable indicator of injection into dense tissue media that is unaffected by patient level of sedation or multiple injections of local anesthetic.…”