J Korean Neurosurg Soc.  2014 Dec;56(6):455-462. 10.3340/jkns.2014.56.6.455.

A New Measure for Monitoring Intraoperative Somatosensory Evoked Potentials

• Jin SH
• Chung CK
• Kim JE
• Choi YD

• KMID: 2191129
• DOI: http://doi.org/10.3340/jkns.2014.56.6.455

Abstract

OBJECTIVE
To propose a new measure for effective monitoring of intraoperative somatosensory evoked potentials (SEP) and to validate the feasibility of this measure for evoked potentials (EP) and single trials with a retrospective data analysis study.
METHODS
The proposed new measure (hereafter, a slope-measure) was defined as the relative slope of the amplitude and latency at each EP peak compared to the baseline value, which is sensitive to the change in the amplitude and latency simultaneously. We used the slope-measure for EP and single trials and compared the significant change detection time with that of the conventional peak-to-peak method. When applied to single trials, each single trial signal was processed with optimal filters before using the slope-measure. In this retrospective data analysis, 7 patients who underwent cerebral aneurysm clipping surgery for unruptured aneurysm middle cerebral artery (MCA) bifurcation were included.
RESULTS
We found that this simple slope-measure has a detection time that is as early or earlier than that of the conventional method; furthermore, using the slope-measure in optimally filtered single trials provides warning signs earlier than that of the conventional method during MCA clipping surgery.
CONCLUSION
Our results have confirmed the feasibility of the slope-measure for intraoperative SEP monitoring. This is a novel study that provides a useful measure for either EP or single trials in intraoperative SEP monitoring.

Keyword

Intraoperative neurophysiological monitoring; Somatosensory evoked potentials; Slope-measure; Single trials; Temporary clipping

MeSH Terms

Aneurysm
Evoked Potentials
Evoked Potentials, Somatosensory*
Humans
Intracranial Aneurysm
Intraoperative Neurophysiological Monitoring
Middle Cerebral Artery
Retrospective Studies
Statistics as Topic

Figure

• 

  Fig. 1 Flow diagram of SEP detection and slope-measure application. Baseline value was determined before the main surgery, and when starting the surgery, the monitoring began. The slope-measure value of the EP was calculated after 100 trials, and the slope-measure values of the single trials (STs) were calculated for every single trial after applying a moving average filter. SEP : somatosensory evoked potentials, EP : evoked potentials.

• 

  Fig. 2 Analysis process at the left upper extremity from Subject 1. A : The raw SEP monitoring data along with the video capture of the temporary clipping from Subject 1. Baseline (the red signal at the bottom) was determined at 10 : 04 : 38, and the peak-to-peak amplitude value at baseline was 3.7 (the blue figure on the baseline signal). The significant change with the conventional method was detected at 10 : 20 : 29 (2.3/3.7, i.e., 37.84% decrease to the baseline). A temporary clip was applied between the times 10 : 19 : 07 and 10 : 19 : 11. B : EP signals as a function of time (upper subpanel). In the upper subpanel, blue and red colors mean negative and positive voltage, respectively, and baseline signal corresponds to the first EP trial. In the lower subpanels, slope-measure values as a function of the EP trial of the N20 and P25 components were plotted. In this case, a significant change in the slope-measure of the EP was detected at 10 : 19 : 41 (45.45% decrease to the baseline). C : Single trials signals as a function of time (upper subpanel). The noise in the single trials was remarkably reduced by applying filters. In the lower subpanels, slope-measure values as a function of the single trial of the N20 and P25 components were plotted. In this case, a significant change in the slope-measure of the single trial was detected at 10 : 19 : 22 (37.59% decrease to the baseline). SEP : somatosensory evoked potentials, EP : evoked potentials.

• 

  Fig. 3 Raw SEP data and video capture or comments showing the temporary clipping time at the contralateral upper extremity to the aneurysm from Subject 2 to Subject 7. The red signal at the bottom in each sub-graph corresponds to the baseline. The number in blue font on the baseline signal indicates the conventional peak-to-peak amplitude. The black arrow indicates a significant SEP change. SEP : somatosensory evoked potentials.

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