Visual Evoked Potential Monitoring Research Articles

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.

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.

脳動脈瘤手術合併症の回避と予防 種々の術中モニタリングを用いた脳動脈瘤術後の虚血合併症の予防

Postoperative ischemic sequelae are the most frequent complication of aneurysm surgery. We have performed various types of intraoperative monitoring to prevent postoperative ischemic complications. In this manuscript, we report methods and results of motor evoked potential (MEP), visual evoked potential (VEP) and fluorescence angiography (FAG) with representative cases. MEP monitoring enables us to predict the blood flow insufficiency of arteries that supply the corticospinal tract. We can detect the blood flow insufficiency of not only the perforating artery, such as the anterior choroidal artery or lenticulostriate artery, but also the cortical artery of the middle cerebral artery. VEP monitoring enabled us to detect the ischemia and mechanical damage of the visual pathway from the optic nerve to the occipital lobe. FAG by intravenous administration of fluorescein sodium made it possible to detect the patency of the arteries, such as the hypothalamic artery or posterior thalamoperforating artery, which could not be detected by various electrophysiological monitoring methods. Ischemic complications after aneurysm surgery were markedly reduced after introduction of these monitoring methods. We discuss the usefulness and limitation of these methods.

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.

Value of visual evoked potential monitoring during trans-sphenoidal pituitary surgery.

The visual outcome of 22 patients undergoing trans-sphenoidal excision of pituitary macroadenomas with intraoperative flash visual evoked potential (VEP) monitoring (Group A), was compared with a non-randomized group of 14 patients who had undergone similar operations without VEP monitoring (Group B). Tumour size, preoperative visual acuity, peripheral fields, and latencies and amplitudes of P1 and P2 were analysed to ascertain the best predictor of postoperative visual function. It was found that patients in Group A had a significantly greater improvement in field defects than those in Group B. There was no difference in postoperative improvement in visual acuity between the two groups. None of the variables analysed were good predictors of visual outcome.

Behavioral and electrophysiological aspects of nitrous oxide dependence

We examined the effect of 70% nitrous oxide (N 2O) on locomotion and visual-evoked potentials (VEP) in rats. The animals exposed to N 2O showed an initial decrease of locomotion, followed by development of tolerance and unaltered motor activity during N 2O withdrawal. Similarly, an initial decrease of VEP amplitudes was followed by tolerance to N 2O. In addition, some amplitudes (N2-P3, P3-N3, and N3-P4) exceeded the control values, indicating an increase of neuronal excitability of the visual system during a long lasting exposure to N 2O. The increase of VEP amplitudes was further potentiated by cessation of this gas. The VEP latencies after initial increase, returned to normal and remained unaltered during N 2O withdrawal suggesting that the speed of neurotransmission is not essentially changed during chronic exposure to N 2O. However, a significant increase of neuronal excitability during chronic N 2O exposure, which further increased by cessation of N 2O, could be of clinical importance. Therefore, monitoring of VEP, particularly the amplitude values, may significantly improve a detection of altered neuronal excitability during anaesthesia and drug withdrawal.

Anterior Fontanel Pressure and Visual Evoked Potentials in Neonates and Infants Undergoing Profound Hypothermic Circulatory Arrest

To determine the effects of cardiopulmonary bypass with profound hypothermic circulatory arrest (PHCA) on anterior fontanel pressure (AFP) and visual evoked potentials (VEPs), 21 neonates and infants undergoing cardiopulmonary bypass (CPB) with PHCA for surgical correction of congenital heart defects were studied. Mean (+/- SD) minimum nasopharyngeal, esophageal, and rectal temperatures of 16.4 +/- 2.2, 11.2 +/- 2.7, and 17.7 +/- 1.9 degrees C, respectively, were achieved for a mean duration of PHCA of 51.6 +/- 18.7 min. AFP increased significantly above pre-CPB values for the first 21.7 +/- 8.1 min of rewarming. The duration of this increase in AFP was related logarithmically and directly to the product of the nasopharyngeal temperature (NPT) at the end of PHCA and the duration of PHCA (r2 = 0.82, P less than 0.0001). Nineteen of these patients had simultaneous monitoring of VEPs. The latency of both the N70 and P100 components of the VEPs increased as temperature decreased. The cerebral perfusion pressure was linearly and inversely related to the AFP (r2 = 0.72, P less than 0.01). The VEPs disappeared as a nasopharyngeal temperature (NPT) of 18.9 +/- 2.8 degrees C and reappeared after 21.9 +/- 8.8 min post-PHCA at an NPT of 32.8 +/- 1.4 degrees C. There was no significant difference between duration of increased AFP (20.9 +/- 8.1 min) and the duration of absence of VEPs during the post-PHCA period. The duration of increased AFP correlated linearly and directly with the duration of absence of VEPs (r2 = 0.84, P less than 0.005). These data demonstrate that transient neurophysiologic dysfunction occurs after PHCA. This dysfunction is related to the duration of elevation of the AFP and cannot be explained solely by a temperature effect.

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.