Intraoperative monitoring of identifiable visual evoked potentials during spine surgery under total intravenous anesthesia.

Abstract

Abstract: : Purpose:To determine whether VEPs during spine surgery under TIVA (total intravenous anesthesia) can produce consistently identifiable peaks throughout surgery. Methods:Three patients undergoing spine surgery under TIVA were consecutively consented and recruited. Pre–operative baseline VEPs were obtained on two of the three subjects. Intraoperative VEPs while under TIVA were obtained on all three subjects. The TIVA protocol called for induction with fentanyl, lidocaine, and propofol IV. Maintenance was with remifentanil supplemented by sevoflurane 0.1%–0.5% at 2–5 L/min as needed. Flash VEPs were obtained with binocular stimulation frequency of 1.0 to 3.0 hertz. The Nihon Koden "Sigma" intraoperative monitoring unit was used. Analysis time of 250 ms with 256 analysis points per trace were used. N1, P1, N2 and P2 wave peaks were reviewed by an observer (RT) and noted as either identifiable or not identifiable in each tracing for each subject. Results:Subject #1 and subject #2 had all four of the above wave forms identifiable in two out of two baseline readings each. Subject #3 was induced under anesthesia prior to obtaining a baseline VEP. Intraoperative readings for subject #1 produced 22 out of 23 tracings with all four wave peaks identifiable. Intraoperative readings for subject #2 produced 10 out of 10 tracings with all four of the wave peaks identifiable. Intraoperative readings for subject #3 produced 10 out of 12 tracings with all 4 of the wave peaks identifiable. Both tracings which showed an unidentifiable peak for this subject were due to a down–sloping P1. Conclusions: PION is a rare but devastating complication of spine surgery. Several previous attempts at intraoperative VEP monitoring during spine surgery gave unreliable results, partly attributed to physiologic interference associated with general anesthesia. Those studies demonstrated a high incidence of unidentifiable wave forms. One study with intraoperative VEP monitoring under TIVA was found in the medical literature. That study demonstrated an unacceptably high percentage of unidentifiable peaks in a majority of study subjects. Our findings show that a trend of identifiable peaks for N1, P1, N2 and P2 were obtainable for all three patients throughout all stages of their surgeries while under TIVA. Further studies are needed to confirm this finding in a larger sample size, and to determine whether amplitudes and latencies are reliable under these same conditions.

Keywords: electrophysiology: clinical • neuro–ophthalmology: optic nerve • visual impairment: neuro–ophthalmological disease