Introduction
Intraoperative neurophysiological monitoring (IONM) has been widely used for the purpose of minimizing the risk of postoperative neurological deterioration in brain or spinal surgery. However, the standard for the quality of the baseline for securing the reliability of inspection has not been prepared yet. This study was conducted under the hypothesis that the intraoperative evoked potentials (ioEPs) with severely deteriorated baseline (SDB) would be inadequate for reliable IONM.
Methods
This retrospective cohort study screened a total 201 patients with SDB who underwent brain or spinal cord surgery under IONM, including intraoperative somatosensory evoked potentials (ioSEPs) and intraoperative motor evoked potentials (ioMEPs) between January 2016 and December 2019 in Gangnam Severance Hospital. The data of the amplitude and the latency of ioSEPs (ioSEPAmp and ioSEPLat), and the amplitude of ioMEPs (ioMEPAmp) were used in analysis. The ioSEPs of bilateral median and tibial nerves were monitored. The ioMEPAmp data was obtained from bilateral deltoid, abductor pollicis brevis, tibialis anterior, and abductor halluces. Patients with SDB were screened when any of the examined nerves/muscles met the following experience-based criteria; ioSEPAmp < 0.2 μV, ioSEP N20 latency > 24 ms or P40 latency > 48 ms, and ioMEPAmp < 20 μV. When the baseline was no response, it was classified as ‘no response’. Muscle strength and sensory function was examined in all patients a day before, at 48 hours and 4 weeks after surgery. With the screened data of SDB, the sensitivity, specificity, positive and negative predictive values (PPV and NPV) of each IONM parameter’s change were analyzed.
Results
Excluding 11 patients with follow-up loss, data of 190 patients were finally screened as having the SDB. The baseline values of IONM parameters, including the data of non-SDB from the other nerves/muscles, are listed in Table 1. The postoperative neurologic prognoses (PNP) are listed in Table 2 by each IONM parameter change.
Because the sensory change was observed only in 1 patient, the clinical significances of IONM parameters in predicting PNP were mainly analyzed on postoperative motor function. The sensitivities of IONM parameters (ioSEPAmp, ioSEPLat, ioSEPs, ioMEPAmp, and ioEPs) for postoperative motor deterioration 4 weeks after surgery (PMD4wk) were 88.89%, 0.00%, 61.54%, 59.09%, and 69.57% respectively. The specificities of the IONM parameters for PMD4wk were 0.00%, 100.00%, 37.84%, 45.24% and 35.33% respectively. The PPV of IONM parameters for PMD4wk were 14.81%, 14.81%, 12.38% and 12.90% respectively (Table 3).
Conclusion
Because of the low sensitivity, specificity or positive predictive values, the IONM parameters with SDB are not adequate to use for qualified examination. Thus, it is suggested that the IONM to be designed effectively by obtaining the baseline data through conducting the preoperative electrodiagnosis in advance of the IONM.
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