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Electrophysiologic effect of injectates on peripheral nerve stimulation
Ban C H Tsui1, Alese Wagner, Brendan Finucane
1Department of Anesthesiology and Pain Medicine, University of Alberta Hospitals, 3B2.32 Walter Mackenzie Health Science Centre, 8440-112 Street, Edmonton, Alberta, Canada T6G 2B7, USA. btsui@ualberta.ca
Regional Anesthesia and Pain Medicine
|May 13, 2004
Summary
Injecting normal saline (NS) near a nerve blocks muscle twitches during nerve stimulation by expanding the conductive area around the needle. This effect is reversible with dextrose in water (D5W).
Area of Science:
- Anesthesiology
- Neurology
- Medical Devices
Background:
- Electrolocation during nerve blocks uses low currents to elicit motor responses.
- Local anesthetics and normal saline (NS) can abolish muscle twitches during electrolocation.
- The mechanism behind this phenomenon requires elucidation.
Purpose of the Study:
- To investigate the hypothesis that injectate's effect on electrical current density at the needle tip causes twitch abolition.
- To determine if injecting normal saline (NS) or dextrose in water (D5W) affects muscle twitch during nerve stimulation.
Main Methods:
- Five pigs were studied, with needles inserted near brachial plexuses and femoral nerves.
- The effect of injecting 1 mL of NS and 5% dextrose in water (D5W) on muscle twitch was assessed at 20 sites.
- Gel electrophoresis was used to demonstrate changes in conductive area induced by injectates.
Main Results:
- Muscle twitches were immediately abolished by NS injection and recovered with D5W.
- Electrical resistance decreased with NS injection and increased with D5W.
- Gel electrophoresis showed saline expanded the conductive area around the needle.
Conclusions:
- Injecting a conductive solution like NS makes previously effective stimulation currents ineffective.
- The primary mechanism is the expansion of the conductive area around the needle, reducing current density.
- This effect is reversible with a non-conductive solution like D5W.