Intraoperative Visual Evoked Potential Monitoring Research Articles

Visual-Evoked Potentials for Intraoperative Neurophysiology Monitoring

Intraoperative monitoring of visual evoked potential: introduction of a clinically useful method Sasaki T, Imamura T, Suzuki K, Kasey H, Mankato R, et al. J Neurosurgery 112:273–284, 2010 Object: To obtain a clinically useful method of intraoperative monitoring of visual evoked potentials (VEPs), the authors developed a new light-stimulating device and introduced electroretinography (ERG) to ascertain retinal light stimulation after induction of venous anesthesia. Methods: The new stimulating device consists of 16 red light–emitting diodes embedded in a soft silicone disc to avoid deviation of the light axis after frontal scalp-flap reflection. After induction of venous anesthesia with propofol, the authors performed ERG and VEP recording in 100 patients (200 eyes) who were at intraoperative risk for visual impairment. Results: Stable ERG and VEP recordings were obtained in 187 eyes. In 12 eyes, stable ERG data were recorded but VEPs could not be obtained, probably because all 12 eyes manifested severe preoperative visual dysfunction. The disappearance of ERG data and VEPs in the 13th eye after frontal scalp-flap reflection suggested technical failure attributable to deviation of the light axis. The criterion for amplitude changes was defined as a 50% increase or decrease in amplitude compared with the control level. In 1 of 187 eyes the authors observed an increase in intraoperative amplitude and postoperative visual function improvement. Of 169 eyes without amplitude changes, 17 manifested improved visual function postoperatively, 150 showed no change, and 2 worsened (1 patient with a temporal tumor developed a slight visual field defect in both eyes). Of 3 eyes with intraoperative VEP deterioration and subsequent recovery upon changing the operative maneuver, 1 improved and 2 exhibited no change. The VEP amplitude decreased without subsequent recovery to 50% of the control level in 14 eyes, and all of these developed various degrees of postoperative deterioration of visual function. Conclusions: With the strategy introduced here it is possible to record intraoperative VEPs in almost all patients except in those with severe visual dysfunction. In some patients, postoperative visual deterioration can be avoided or minimized by intraoperative VEP recording. All patients without an intraoperative decrease in the VEP amplitude were without severe postoperative deterioration in visual function, suggesting that intraoperative VEP monitoring may contribute to prevent postoperative visual dysfunction.

Standard and limitation of intraoperative monitoring of the visual evoked potential

Visual evoked potential (VEP) has been installed as one of the intraoperative visual function monitoring. It remains unclear, however, whether intraoperative VEP monitoring facilitates as a real time visual function monitoring with satisfactory effectiveness and sensitivity. To evaluate this, relationships between VEP waveform changes and postoperative visual function were analysed retrospectively. Intraoperative VEP monitoring was carried out for 106 sides (eyes) in 53 surgeries, including two intraorbital, 36 parasellar and 15 cortical lesions in Shinshu University Hospital under total intravenous anaesthesia. Red light flash stimulation was provided to each eye independently. VEP recording and postoperative visual function were analysed. In 103 out of 106 sides (97%), steady VEP monitoring was recorded. Stable VEP was acquired from eyes having corrected visual acuity greater than 0.4. VEP was not recorded in one side with corrected visual acuity of 0.3 and two sides in whom sevoflurane was used incidentally for anaesthesia. Transient VEP decrease was observed in three sides, but visual function was preserved. Permanent VEP decrease was seen in seven sides, which presented visual impairment postoperatively. In one side, visual acuity improved but minor visual field defect was encountered postoperatively, though VEP unchanged throughout the surgery. Intraoperative monitoring of VEP predicts postoperative visual function: reversible change in VEP means visual function to be preserved. Visual field defect without decrease in the visual acuity may not be predicted by VEP monitoring. Intraoperative VEP monitoring will be mandatory for surgeries harbouring a risk of visual impairment.

Intraoperative monitoring of visual evoked potential: introduction of a clinically useful method

To obtain a clinically useful method of intraoperative monitoring of visual evoked potentials (VEPs), the authors developed a new light-stimulating device and introduced electroretinography (ERG) to ascertain retinal light stimulation after induction of venous anesthesia. The new stimulating device consists of 16 red light-emitting diodes embedded in a soft silicone disc to avoid deviation of the light axis after frontal scalp-flap reflection. After induction of venous anesthesia with propofol, the authors performed ERG and VEP recording in 100 patients (200 eyes) who were at intraoperative risk for visual impairment. Stable ERG and VEP recordings were obtained in 187 eyes. In 12 eyes, stable ERG data were recorded but VEPs could not be obtained, probably because all 12 eyes manifested severe preoperative visual dysfunction. The disappearance of ERG data and VEPs in the 13th eye after frontal scalp-flap reflection suggested technical failure attributable to deviation of the light axis. The criterion for amplitude changes was defined as a 50% increase or decrease in amplitude compared with the control level. In 1 of 187 eyes the authors observed an increase in intraoperative amplitude and postoperative visual function improvement. Of 169 eyes without amplitude changes, 17 manifested improved visual function postoperatively, 150 showed no change, and 2 worsened (1 patient with a temporal tumor developed a slight visual field defect in both eyes). Of 3 eyes with intraoperative VEP deterioration and subsequent recovery upon changing the operative maneuver, 1 improved and 2 exhibited no change. The VEP amplitude decreased without subsequent recovery to 50% of the control level in 14 eyes, and all of these developed various degrees of postoperative deterioration of visual function. With the strategy introduced here it is possible to record intraoperative VEPs in almost all patients except in those with severe visual dysfunction. In some patients, postoperative visual deterioration can be avoided or minimized by intraoperative VEP recording. All patients without an intraoperative decrease in the VEP amplitude were without severe postoperative deterioration in visual function, suggesting that intraoperative VEP monitoring may contribute to prevent postoperative visual dysfunction.

Intraoperative monitoring of cortically recorded visual response for posterior visual pathway

Intraoperative monitoring of visual evoked potentials (VEPs) has been regarded as having limited significance for the preservation of visual function during neurosurgical procedures, mainly due to its poor spatial resolution and signal-to-noise ratio. The authors evaluated the usefulness of cortically recorded VEPs, instead of the usual scalp VEPs, as intraoperative monitoring focusing on the posterior visual pathway. In 17 consecutive patients who underwent microsurgical procedures for lesions near the posterior visual pathway, cortical responses were recorded using 1-Hz flashing light-emitting diodes and subdural strip electrodes after induction of general anesthesia with sevoflurane or propofol. The detectability and waveform of the initial response, stability, and changes during microsurgical manipulations were analyzed in association with the position of electrodes and postoperative changes in visual function. Initial VEPs were detected in 82% of all patients. The VEPs were detected in 94% of patients without total hemianopia in whom electrodes were placed sufficiently near the occipital pole; in these cases the recordings were not significantly affected by anesthesia. The detectability rates of the negative peak before 100 msec (N1), positive peak approximately 100 msec (P100), and negative peak after 100 msec (N2) were 36, 50, and 100%, respectively. The mean latencies and amplitudes of N1, P100, and N2 were 90.0 +/- 15.9 msec and 61.0 +/- 64.0 microV, 103.9 +/- 13.5 msec and 34.3 +/- 38.6 microV, and 125.7 +/- 12.2 msec and 44.9 +/- 48.9 microV, respectively, showing great variability. In 11 patients, the initial waveforms of VEP remained stable during microsurgical procedures, and the visual status did not change postoperatively, while it disappeared in 2 patients who presented with postoperative hemianopia. Direct recording from the visual cortices under general anesthesia achieved satisfactory detectability of the visual response to a light-emitting diode flashing light. Although the initial waveforms varied greatly among patients, they were stable during microsurgical procedures, and the changes were consistent with postoperative visual function. Intraoperative cortical VEP monitoring is a potentially useful procedure to monitor the functional integrity of the posterior visual pathway.

脳動脈瘤ｃｌｉｐｐｉｎｇ術における術中視覚誘発電位モニタリング

To clarify the usefulness of intraoperative monitoring of visual evoked potentials (VEPs) in aneurysm surgery, we examined the correlation between the VEP amplitude and postoperative visual function in patients who underwent aneurysmal clipping. We developed a new light-stimulating device and introduced electroretinogram (ERG) to ascertain retinal light stimulation under total venous anesthesia. The new stimulating device consists of 16 red light-emitting diodes embedded in a soft silicon disk to avoid deviation of the light axis after frontal scalp-flap reflection. Under total venous anesthesia with propofol, ERG and VEP were recorded in 50 patients who were at intraoperative risk for visual impairment. Stable ERG and VEP recordings were obtained in 98 eyes. In one eye, stable ERG was recorded but VEP could not be obtained, because the eye manifested severe preoperative visual dysfunction. In the another eye, the disappearance of ERG and VEP after frontal scalp-flap reflection suggested technical failure attributable to deviation of the light axis. The criterion for amplitude aggravation was defined as a 50% decrease in amplitude compared to the control level. Of 93 eyes without amplitude changes, 2 manifested improved visual function postoperatively and 91 showed no change. Of 3 eyes with intraoperative VEP deterioration and subsequent recovery upon changing the operative maneuver 3 exhibited no change. The VEP amplitude decreased without subsequent recovery to 50% of the control level in both eyes of 1 patient, and she developed homonymous quadrant hemianopsia postoperatively. With the strategy introduced here it is possible to record stable VEP in almost all cases without severe visual dysfunction. In some patients, postoperative visual deterioration can be avoided by intraoperative VEP monitoring. All patients without an intraoperative decrease in the VEP amplitude were without postoperative deterioration in visual function, suggesting that intraoperative VEP monitoring may help to prevent postoperative visual dysfunction in aneurysmal clipping.

71. Intraoperative monitoring of visual-evoked potential for temporal lesions – Correlation between VEP findings and postoperative visual field

71. Intraoperative monitoring of visual-evoked potential for temporal lesions – Correlation between VEP findings and postoperative visual field

脳動脈瘤クリッピング術における術中視覚誘発電位モニタリングの有用性

We intraoperatively monitored visual evoked potential (VEP) in 6 aneurysm clipping surgeries for 2 IC paraclinoid, 2 IC-posterior communicating artery (IC-PCoA) and 2 posterior cerebral artery (PCA) aneurysms, which had potential risk of optic pathway damage. Stable waveform was acquired throughout the procedures in all cases under total intravenous anesthesia with propofol. Reproducible transient VEP waveform decrease was observed during temporary artery occlusion, which recovered after release of temporary artery occlusion in 3 patients. No visual disturbance was encountered in this group postoperatively. On the contrary, VEP waveform decreased permanently during aneurysm dissection from the optic nerve in an IC paraclinoid aneurysm patient. The patient had severe visual dysfunction postoperatively. Our series revealed that transient ischemic dysfunction of the optic pathway caused from artery occlusion was detectable within a reversible time window; however, it seems difficult to detect mechanical damage of the optic nerve damage in a reversible time window. Intraoperative monitoring of VEP predicts postoperative visual function; reversible change in VEP means visual function is preserved, especially when the change is caused by ischemia that occurs when the artery that supplies the optic apparatus is temporarily occluded.

Loss of visual evoked potential following temporary occlusion of the superior hypophyseal artery during aneurysm clip placement surgery

✓The authors report a case in which a 62-year-old woman with a history of subarachnoid hemorrhage due to a ruptured aneurysm was found to have a de novo paraclinoid aneurysm in the right internal carotid artery during a routine medical examination. Surgical clip placement was performed via a contralateral pterional approach under visual evoked potential (VEP) monitoring. The superior hypophyseal artery (SHA) was found to originate from the aneurysm body. The artery was temporarily occluded prior to application of the clip to the aneurysm neck. The VEP signal was lost 3 minutes after the SHA was occluded, and the potentials gradually recovered 10 minutes after the artery was released. The disappearance of VEP signal was reproducible with SHA occlusion. The clip was applied to the aneurysm body to preserve the origin of the SHA. The patient did not have any deterioration of vision after surgery. Intraoperative VEP monitoring can be used to help determine whether the SHA can be sacrificed safely.

Loss of visual evoked potential following temporary occlusion of the superior hypophyseal artery during aneurysm clip placement surgery

The authors report a case in which a 62-year-old woman with a history of subarachnoid hemorrhage due to a ruptured aneurysm was found to have a de novo paraclinoid aneurysm in the right internal carotid artery during a routine medical examination. Surgical clip placement was performed via a contralateral pterional approach under visual evoked potential (VEP) monitoring. The superior hypophyseal artery (SHA) was found to originate from the aneurysm body. The artery was temporarily occluded prior to application of the clip to the aneurysm neck. The VEP signal was lost 3 minutes after the SHA was occluded, and the potentials gradually recovered 10 minutes after the artery was released. The disappearance of VEP signal was reproducible with SHA occlusion. The clip was applied to the aneurysm body to preserve the origin of the SHA. The patient did not have any deterioration of vision after surgery. Intraoperative VEP monitoring can be used to help determine whether the SHA can be sacrificed safely.

Efficacy of Intraoperative Neurosurgical VEP Monitoring

Visual evoked potential (VEP) had not been seemed to be suitable for intraoperative monitoring because of its long latency and needs for addition. Intraoperative visual VEP monitoring under the recent anesthetic and neurophysiological techniques are examined. Since May 2002, VEP monitorings using LED Goggles (1Hz stimulation) by Neuropack MEB2200 (Nihon Koden Co. Ltd.) were performed in 15 neurosurgical operation including 5 transsphenoidal surgery (3 pituitary adenomas and 2 others) and 10 craniotomy (9 brain tumors and an arterio-venous malformation). Propofol anesthesia was performed in 14 operations and an inhalation. Scalp recording with the screw electrodes were monitored in 13 operations, subdural electrodes for direct cortical recording were used in 4, and both 2 methods were used together in 2 operations. Most P100 wave was stably recorded even in intraoperative monitoring. Shorter latency waves in cortical recording than in scalp recording were seemed to be available in intraoperative VEP. In a transsphenoidal surgery for acromegaly, the shortening of the latency after the tumor resection agreed with postoperative improvement of visual symptoms. Intraoperative VEP monitorings were not successful in 5 among 15 operations. LED Goggles was not suitable for intraoperative use and the special light-stimulator for intraoperative monitoring is now prepared.

The use of VEPs for CNS monitoring during continuous cardiopulmonary bypass and circulatory arrest

Cerebral function was monitored with the use of visual evoked potentials (VEPs) in 16 infants (mean age 9.9±4.3 months) during surgery for congenital cardiac anomalies. While hypothermia was employed in all patients, half (8) remained on continuous cardiopulmonary bypass (CCB) while the rest were cooled to lower temperatures before the induction of circulatory stasis and venous exsanguination (CA), i.e., profound hypothermic circulatory arrest (PHCA). VEPs were recorded before, during and after surgical intervention. Latency changes occurred in both the N100 and P145 components of the VEP as a function of systemic temperature during cooling in both groups. Differences in the VEPs were found between the two groups post-operatively, with the most interesting result being a greater increase in P145 latency in the CA group after rewarming. To the extent that VEPs reflect neurological status, our findings suggested that CCB was associated with less perturbation in acute neurological status than PHCA, and shorter arrest times and lower temperatures during CA were associated with the most favourable post-operatuve VEPs. Hence, intraoperative monitoring of VEPs appeared to be useful as an objective measure of the short-term effects of various cardiopulmonary procedures on neurophysiological function.