Alarm criteria for motor-evoked potentials: what's wrong with the "presence-or-absence" approach?
Blair Calancie1, Maria R Molano
1Department of Neurosurgery, Upstate Medical University, Syracuse, NY, USA. calancib@upstate.edu
Study Design:
Combined prospective and retrospective.
Objective:
Evaluate 2 published criteria for interpreting motor-evoked potentials (MEP) in response to repetitive transcranial electrical stimulation (rTES) during surgery.
Summary Of Background Data:
There is controversy regarding how to interpret MEPs elicited by rTES. Many centers warn the surgical team only if the MEP is lost entirely ("Presence-or-Absence" method). Alternatively, we monitor the stimulus energy needed to elicit a minimal evoked EMG response; significant increases in this energy reflect impending motor tract injury and serve as the basis for warning the surgical team ("Threshold-Level" method).
Methods:
We documented target muscle thresholds for rTES throughout each subject's surgical procedure. The time (in hours) between intraoperative threshold change and (a) complete loss of response or (b) until the end of the surgical procedure was determined. Short-term postoperative motor status was documented by either direct physical examination or by chart review.
Results:
We enrolled 903 subjects, from whom intraoperative rTES-evoked responses could be elicited in 859 subjects. Of these, 93 subjects sustained intraoperative damage to central motor pathways. Significant increases in target muscle thresholds were often noted many minutes, and sometimes hours before complete signal loss. In other cases, thresholds increased significantly without ever losing the muscle response.
Conclusion:
The Threshold-Level method is highly sensitive and specific to deterioration in central motor function, and provides early warning of such an event. Conversely, in some cases the Presence-or-Absence method may fail to detect episodes of partial loss, and in other cases typically introduces a delay between the times when motor dysfunction begins to occur and when the response is lost (at which time an alarm is triggered). We conclude that use of the Presence-or-Absence alarm criteria for interpreting MEPs during surgery is often incompatible with the requirement for accurate and early warning of impending injury to central motor pathways, and should be avoided.
Insights
The Threshold-Level method for interpreting motor-evoked potentials (MEP) during surgery is more sensitive and specific than the Presence-or-Absence method. This approach provides earlier warnings of potential motor tract injury, improving patient safety during operations.
Area of Science:
- Neuroscience
- Surgical Monitoring
- Biomedical Engineering
Background:
- Interpreting motor-evoked potentials (MEP) elicited by repetitive transcranial electrical stimulation (rTES) during surgery remains controversial.
- Current methods include the
- Presence-or-Absence
- method (warning only upon complete MEP loss) and the
- Threshold-Level
- method (monitoring stimulus energy for evoked EMG response).
Purpose of the Study:
- To evaluate and compare two published criteria for interpreting MEPs during surgery.
- Assess the efficacy of the
- Presence-or-Absence
- and
- Threshold-Level
- methods in detecting motor pathway changes.
Main Methods:
- A combined prospective and retrospective study design was employed.
- Intraoperative rTES thresholds for target muscles were documented throughout surgery.
- The time between threshold changes and subsequent signal loss or procedure end was recorded, alongside postoperative motor status.
Main Results:
- Of 859 subjects with elicited rTES responses, 93 experienced intraoperative central motor pathway damage.
- Significant threshold increases often preceded complete signal loss by minutes to hours.
- Threshold elevations occurred in some cases without complete signal loss, indicating partial motor pathway compromise.
Conclusions:
- The
- Threshold-Level
- method demonstrates high sensitivity and specificity for detecting central motor function deterioration, offering early warning.
- The
- Presence-or-Absence
- method can miss partial motor pathway injuries and introduces delays in alarm triggering.
- The
- Presence-or-Absence
- criteria are often incompatible with the need for accurate and early warnings and should be avoided.
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