Intraoperative monitoring of flash visual evoked potential under general anesthesia

Abstract

In neurosurgical procedures that may cause visual impairment in the intraoperative period, the monitoring of flash visual evoked potential (VEP) is clinically used to evaluate visual function. Patients are unconscious during surgery under general anesthesia, making flash VEP monitoring useful as it can objectively evaluate visual function. The flash stimulus input to the retina is transmitted to the optic nerve, optic chiasm, optic tract, lateral geniculate body, optic radiation (geniculocalcarine tract), and visual cortical area, and the VEP waveform is recorded from the occipital region. Intraoperative flash VEP monitoring allows detection of dysfunction arising anywhere in the optic pathway, from the retina to the visual cortex. Particularly important steps to obtain reproducible intraoperative flash VEP waveforms under general anesthesia are total intravenous anesthesia with propofol, use of retinal flash stimulation devices using high-intensity light-emitting diodes, and a combination of electroretinography to confirm that the flash stimulus has reached the retina. Relatively major postoperative visual impairment can be detected by intraoperative decreases in the flash VEP amplitude.

Intraoperative monitoring of visual evoked potentials in patients undergoing transsphenoidal surgery for pituitary adenoma: a systematic review

“…VEP stability and reproducibility are also affected by non-patient factors and particularly important techniques to augment this are the use of total intra-venous anaesthetic (TIVA), the use of LED goggles or silicone discs for light stimulus delivery, a black shield patch placed over the eyes and braided electrode cables, [ 20 ] and the use of simultaneous electroretinography (ERG) monitoring [ 12 ]. One or more of these techniques were employed in all studies (Table 4 ).…”

“…However, given that all studies involved the surgeon temporarily halting surgical manipulation at the point of a VEP amplitude decrease there is an underlying assumption that all teams believed that this may indeed be a contemporaneous warning sign of optic injury. Prolonged latency has also been used as an indicator to the optic apparatus; however, latency is felt to be a parameter that is more difficult to reliably monitor with flash VEP [ 12 ] and reported to be difficult to evaluate in the presence of decreased amplitude [ 6 , 11 , 12 ]. Latency was monitored in six of the studies in this review, but no statistically significant conclusions were drawn from these.…”

Comparative analysis of pattern visual evoked potentials according to the type of diabetes mellitus in patients in different diabetic retinopathy stages

“…The distance to the monitor was 100 cm. The patients were [17][18][19]. The impedance between the recording and the ground electrode was less than 5 kX.…”

Intraoperative visual evoked potential monitoring for a safer endoscopic transsphenoidal surgery

“…Anna Teresa Mazzeo 1 , Deepak Kumar Gupta 2 The main goal of modern neurosurgery is removal of the lesion with preservation of neurological function. In order to reach this objective, intraoperative neurophysiological monitoring (IONM) has been introduced and evaluated with the aim to make the neurosurgeon aware of ongoing changes in neural function, allowing prompt corrective intervention to prevent postoperative deficits.…”

“…Intraoperative VEP is affected by various factors, viz, temperature (hypothermia attenuates VEP amplitude and latency gets extended, and waveforms disappear at 25-27 degree C), partial pressure of carbon dioxide in blood [hypocapnia causes changes in pH resulting in acceleration of conduction velocity of somatosensory evoked potential], hypoxia and hypotension (VEP amplitude is decreased and latency is extended), hematocrit values <15%, during turning of skin flap on forehead (may dislodge the LED stimulating electrode) and anesthetic agents. [2,3] In some cases, VEPs change not as a result of damage to the optic pathway or ischemia but due to the anesthetics. As anesthetic agents suppress synaptic transmission, reactions from polysynaptic pathways (e.g., cortical recordings) are affected by anesthesia to a much greater extent than those recorded from oligosynaptic pathways.…”