Intraoperative flash VEPs are reproducible in the presence  of low amplitude EEG.
Flash visual evoked potentials (FVEPs) are often irreproducible during surgery. We assessed the relationship between intraoperative FVEP reproducibility and EEG amplitude. Left then right eyes were stimulated by goggle light emitting diodes, and FVEPs were recorded from Oz–Fz′ (International 10-20 system) in 12 patients. Low cut filters were ≤5 Hz in all patients; two patients also had recordings using 10 and 30 Hz. The reproducibility of FVEP and the amplitude of the concomitant EEG from C4′–Fz were measured. Nine patients had low amplitude EEG (<30 μV); reproducible FVEPs were obtained from all eyes with normal pre-operative vision. The other three patients had high amplitude EEG (>50 μV); FVEPs were absent from three of four eyes with normal pre-operative vision (the other normal eye had a present but irreproducible FVEP). Raising the low cut filter to 10 and 30 Hz (in two patients) progressively reduced EEG and FVEP amplitude, reduced amplifier blocking time and improved FVEP reproducibility. FVEPs were more reproducible in the presence of low amplitude EEG than high amplitude EEG. This is the first report describing the effect of EEG amplitude on FVEP reproducibility during surgery
Suite F118, Department of Medical Imaging, The Ottawa Hospital, Ottawa, ON K1Y 4E9, Canada. dhoulden@toh.on.ca
David A
DA
Houlden
Chantal A
CA
Turgeon
Thomas
T
Polis
John
J
Sinclair
Stuart
S
Coupland
Pierre
P
Bourque
Martin
M
Corsten
Amin
A
Kassam
D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D004569:Electroencephalography / Q000379:methods*; D005074:Evoked Potentials, Visual; D006801:Humans; D064795:Intraoperative Neurophysiological Monitoring / Q000379:methods*; D008875:Middle Aged; D019635:Neurosurgical Procedures / Q000379:methods*; D010775:Photic Stimulation / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D059629:Signal-To-Noise Ratio; D055815:Young Adult