Minimal current intensity to elicit an evoked motor response cannot discern between needle-nerve contact and intraneural needle insertion

Thomas Wiesmann, Andreas Bornträger, Timon Vassiliou, Admir Hadzic, Hinnerk Wulf, Hans-Helge Müller, Thorsten Steinfeldt
Anesthesia and Analgesia 2014, 118 (3): 681-6

BACKGROUND: The ability of an evoked motor response (EMR) with nerve stimulation to detect intraneural needle placement reliably at low current intensity has recently been challenged. In this study, we hypothesized that current intensity is higher in needle-nerve contact than in intraneural needle placement.

METHODS: Brachial plexus nerves were exposed surgically in 6 anesthetized pigs. An insulated needle connected to a nerve stimulator was placed either with 1 mm distance to the nerve (control position), adjacent to nerve epineurium (needle-nerve contact position), or inside the nerve (intraneural position). Three pulse duration settings were applied in random fashion (0.1, 0.3, or 1.0 milliseconds) at each needle position. Starting at 0.0 mA, electrical current was increased until a minimal threshold current resulting in a specific EMR was observed. Fifty threshold current measurements were scheduled for each needle position-pulse duration setting.

RESULTS: Four hundred-fifty threshold currents in 50 peripheral nerves were measured. Threshold current intensities (mA) to elicit EMR showed small differences between the needle-nerve contact position [median (25th-75th percentiles); 0.1 milliseconds: 0.12 (0.08-0.18) mA; 0.3 milliseconds: 0.10 (0.06-0.12) mA; 1.0 milliseconds: 0.06 (0.04-0.10) mA] and the intraneural position (0.1 milliseconds: 0.12 [0.10-0.16] mA; 0.3 milliseconds: 0.08 [0.06-0.10] mA; 1.0 milliseconds: 0.06 [0.06-0.08] mA) that are neither statistically significant nor clinically relevant. Regardless of the pulse duration that was applied, the 98.33% confidence interval revealed a difference of at most 0.02 mA. However, threshold current intensities to elicit EMR were lower for the needle-nerve contact position than for the control position (0.1 milliseconds: 0.28 [0.26-0.32] mA; 0.3 milliseconds: 0.20 [0.16-0.22] mA; 1.0 milliseconds: 0.12 [0.10-0.14] mA).

CONCLUSIONS: The confidence interval for differences suggests minimal current intensity to elicit a motor response that cannot reliably discern between a needle-nerve contact from intraneural needle placement. In addition, an EMR at threshold currents <0.2 mA (irrespective of the applied pulse duration) indicates intraneural needle placement or needle-nerve contact.


You are not logged in. Sign Up or Log In to join the discussion.

Related Papers

Available on the App Store

Available on the Play Store
Remove bar
Read by QxMD icon Read

Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"