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Estimation of equivalent threshold currents using different pulse widths for the epidural stimulation test in a
Ban C H Tsui1, Jeremy H Tsui, Gareth N Corry
1Department of Anesthesiology and Pain Medicine, University of Alberta, 8-120 Clinical Sciences Building, Edmonton, AB, T6G 2G3, Canada, btsui@ualberta.ca.
Canadian Journal of Anaesthesia = Journal Canadien D'Anesthesie
|December 19, 2013
Summary
Adjusting pulse width in epidural stimulation tests allows for lower current thresholds to elicit motor responses. This study in pigs found a linear relationship between current and pulse width, aiding in catheter placement verification.
Area of Science:
- Anesthesiology
- Neurology
- Medical Devices
Background:
- The epidural stimulation test is crucial for verifying correct catheter placement in the epidural space.
- Conventional methods often require high currents (up to 16 mA), exceeding the capacity of many peripheral nerve stimulators.
- Modulating pulse width offers a potential solution to achieve motor responses at lower, more accessible current levels.
Purpose of the Study:
- To investigate the impact of varying pulse widths on the threshold current required for eliciting motor responses during epidural stimulation.
- To establish a clearer understanding of the relationship between pulse width and current intensity for accurate epidural catheter placement.
- To develop practical guidelines for optimizing epidural stimulation tests.
Main Methods:
- A single-blinded study was conducted using a porcine model.
- An 18G insulated Tuohy needle and a 20G stimulating epidural catheter were used for epidural access.
- Electrical current was incrementally applied at pulse widths of 0.1, 0.2, 0.3, 0.5, and 1 msec to elicit motor responses, with catheter repositioning at 15 locations per animal.
Main Results:
- Threshold currents ranged from 0.36-9.5 mA at a 0.2 msec pulse width.
- A significant linear correlation was identified between the threshold current and the applied pulse width.
- These findings suggest that pulse width is a critical factor in determining the required current intensity.
Conclusions:
- The study provides valuable data for estimating equivalent threshold currents across different pulse widths during epidural stimulation tests.
- Nomograms derived from these findings can assist clinicians in interpreting results and ensuring accurate catheter positioning.
- Optimizing pulse width can enhance the efficacy and accessibility of the epidural stimulation test for catheter verification.
