Total intravenous anesthesia for improvement of intraoperative monitoring of somatosensory evoked potentials during aneurysm surgery.

Two anesthetic regimens for monitoring somatosensory evoked potentials (SEPs) during intracranial aneurysm surgery were compared. Eighty-four sequential cases of intracranial aneurysms were operated on employing SEP monitoring. The first group of 22 cases was anesthetized with "balanced anesthesia" and the second group of 62 cases received total intravenous anesthesia (TIVA) consisting of propofol and alfentanil. In the TIVA group, the amplitude of early cortical SEP responses (N20-P25, or P40-N50) was significantly higher than that of responses in the balanced anesthesia group. In median nerve SEPs, the averaged amplitude of N20-P25 was 3.22 microV with TIVA and 1.69 microV with balanced anesthesia (P = 0.006). Similarly, posterior tibial nerve SEPs showed a P40-N50 response of 1.85 microV and 1.00 microV, respectively (P = 0.017). The superior signal-to-noise ratio obtained with TIVA allowed more frequent and reliable intraoperative SEP recordings than was possible with balanced anesthesia, resulting in rapid and reliable feedback for the surgeon. In 19% of median nerve SEPs recorded with TIVA, the cortical responses were over 5 microV in amplitude, so that reproducible N20-P25 responses were obtainable by averaging only 10 to 50 serial responses, that is, two to three recordings per minute. The higher amplitude of posterior tibial nerve SEPs recorded with TIVA made monitoring during surgery for anterior communicating artery aneurysms possible in all cases. This was not always the case with balanced anesthesia. The late deflection of median nerve SEPs (N30) was more frequently observed with TIVA.(ABSTRACT TRUNCATED AT 250 WORDS)     

Electrophysiological monitoring during basilar aneurysm operation

Intraoperative brain stem auditory evoked potential (BAEP) and somatosensory evoked potential (SEP) monitoring was evaluated in 16 patients each undergoing intracranial operation for basilar artery aneurysm. The 16 patients had 18 posterior circulation aneurysms, including 2 patients with 2 aneurysms. Fourteen aneurysms arose from the rostral basilar artery, 2 arose from the midbasilar artery, 1 arose from the vertebrobasilar junction, and 1 arose from the proximal segment of the posterior cerebral artery. Five aneurysms were classified as giant (i.e., greater than 25 mm), and 5 aneurysms were large (i.e., 15 to 25 mm). Ten patients had BAEP and SEP monitoring, 4 had BAEP monitoring only, and 2 had SEP monitoring only. Two patients showed significant abnormalities during operation, including 1 patient with transient changes in the BAEP when the lower pons and the 8th cranial nerve were retracted. Another patient had progressive increases in latency and decreases in amplitude and subsequent loss of the SEP cortical components during a period of intermittent temporary rostral basilar artery occlusion. Wave P13 was also lost during that period. The cortical components as well as Wave P13 returned after circulation was restored. The BAEPs were unchanged in the same patient during the period of temporary basilar artery occlusion. Fourteen patients had no significant abnormalities. There were no consistent changes during the various stages of operation. BAEP and SEP monitoring failed to identify ischemic events in 4 patients with neurological findings of brain stem ischemia immediately after operation (i.e., 25% false-negative studies).(ABSTRACT TRUNCATED AT 250 WORDS)     

Intraoperative monitoring of the somatosensory evoked potentials and cerebral blood flow during aneurysm surgery--safety evaluation for temporary vascular occlusion.

Somatosensory evoked potentials (SEPs) and cerebral blood flow (CBF) were monitored during temporary vascular occlusion in 67 aneurysm operations to evaluate the usefulness of SEP as an indicator for cerebral ischemia. The SEP N20 component completely disappeared during temporary vascular occlusion in 24 cases, 23 of which demonstrated complete recovery following recirculation and had no postoperative neurological sequelae. The only one with postoperative sequelae demonstrated rapid, within 1 minute, loss of N20 followed by no recovery. Another eight cases showed prolongation of central conduction time during vascular occlusion and had no postoperative sequelae. The SEP N20 attenuation reflected the CBF reduction in the middle cerebral artery (MCA) territory during MCA occlusion. However, CBF changes in the internal carotid artery (ICA) territory during ICA occlusion greatly varied. No detectable changes in SEP were found during anterior cerebral artery occlusion for anterior communicating artery aneurysms. This study indicates that intraoperative SEP monitoring is useful to detect ischemia in the MCA territory and that rapid disappearance of the N20 component is a danger signal.     

Haemodilution in neurosurgical operations (author's transl)]

The subject of this paper is an investigation of the usefulness of haemodilution in neurosurgical operations. The studies were carried out on 30 patients undergoing operations for intracranial aneurysms (17 patients) or intracranial tumours (13 patients). The control group consisted of 50 patients undergoing operations for intracranial tumours (25 patients) or cerebral aneurysms (25 patients). It was found that during haemodilution cerebral oedema did not occur during the operation, while in the control group cerebral oedema was observed in 28% operations of the cerebral aneurysms and in 56%-- of the cerebral tumors. The amount of transfused blood in the group with intracranial tumors was diminished by ca 150 ml and in the group with cerebral aneurysms blood transfusion was not necessary at all (in the control group the average transfusion was 310 ml). Described method in correlation with the controlled hypotension should be more widely used in the neurosurgical operations.     

Pitfalls in cortical localization by intraoperative recording of cortical somatosensory evoked potentials]

Cortical somatosensory evoked potential (SEP) recordings were made in 11 patients who had lesions located in or near the somatosensory or motor gyri to localize the central sulcus and sensorimotor cortex during neurosurgical operations. Cortical localization was successful in 7 of the 11 patients by recording phase reversal waveforms of N20 and P20 at electrode sites in the hand area on opposite sides of the central sulcus. There were 4 cases in which the cortical localization failed. Locations of craniotomy were far distant from the central sulcus retrospectively in 2 of the 4 patients. Cortical SEPs couldn't be recorded despite probable exposure of the hand area and apparently adequate stimulation and recording conditions in 2 patients who had showed no or low amplitude scalp SEP preoperatively. In one of these 2 patients only low amplitude negative waves were recorded at the cortex which was thought far field potentials originated from subcortical structures. In 2 patients cortical SEP was monitored during the removal of the tumors and was useful to estimate the effects of the operative procedures on the sensorimotor cortex. It is concluded that the localization of cortical functions using cortical SEP is useful for reducing risk associated with intracranial surgery. However, we must be aware that there are some pitfalls in this method.     

Monitoring of somatosensory evoked potentials during surgery for middle cerebral artery aneurysms

Somatosensory evoked potentials (SEPs) were monitored during 53 procedures for aneurysms of the middle cerebral artery (MCA). "Significant" changes were reported to the surgeon, who took corrective action when possible. Changes in the SEPs were categorized as follows: Type I, no change; Type II, significant change with complete return to baseline; Type III, significant change with incomplete return to baseline; Type IV, complete loss with no return; and Type V, no response at baseline. Only 1 of 37 patients with a Type I SEP had a new neurological deficit, and this was a patient who could not be examined for several days after surgery because he was in a pentobarbital coma. All 4 patients with Type III and IV changes had new postoperative neurological deficits. Perhaps of greater importance, 4 of 5 patients with Type II changes had no new deficit. These patients all had changes in SEPs that were completely reversible by clip adjustment (2), prompt removal of temporary clips (1), and inducing hypertension after aneurysm trapping (1). These cases may, therefore, represent instances in which SEP monitoring allowed the clinicians to prevent a neurological deficit. The MCA supplies the area of the somatosensory cortex that controls the hand. Median nerve SEPs are, therefore, a theoretically ideal monitor during surgery for MCA aneurysms. This study suggests that the results of MCA aneurysm surgery may be accurately predicted and improved with SEP monitoring.     

小儿硫喷妥钠／七氟烷麻醉及复合使用酮洛芬和芬太尼对刺激正中神经的体感诱发电位的影响

背景体感诱发电位（somatosensory evoked potentials,SEPs）常被用于外科手术中判断脊髓和脑功能。总的来说,SEPs对吸入性麻醉药物是敏感的,但有关小儿用七氟烷维持麻醉对sEPs的影响了解甚少。麻醉中常会使用镇痛药物,辅助用药也会影响SEPs。在这项前瞻性的临床试验中,共计27例3。8岁的健康儿童接受研究,对其静脉给予苯二氮革和巴比妥类药物麻醉诱导后,用七氟烷维持麻醉,并观察它们对正中神经SF2s的影响。此外,也观察了两种镇痛药物,酮洛芬和芬太尼对SEPs的影响。方法麻醉前静脉给予0．1mg／kg咪达唑仑,用呼气末浓度为2％的七氟烷维持麻醉,分别在给予咪达唑仑前,吸入七氟烷后15分钟、25分钟（给予或不给予酮洛芬）、35分钟（给予芬太尼）记录正中神经SEPs。结果与基础水平相比,应用七氟烷维持麻醉期间N20潜伏期延长（P=0．015）,中枢传导时间延长（P=0．001）;使用镇痛药物对N20潜伏期和中枢传导时间并没有影响。5-8岁儿童的平均皮层N20-P25的振幅显著降低（P=0．008）。此外,对于年长的儿童,复合用酮洛芬和芬太尼后N20-P25振幅比使用前明显减低（P=0．03）,而在年幼的儿童则没有这样的变化。讨论本研究发现,儿童使用2％七氟烷维持麻醉会延长正中神经的SEPs,与用其他吸入性麻醉药的报道相似。然而,吸入七氟烷时可以进行SEP的监测,但吸入的剂量应根据个体差异调整。复合使用酮洛芬和芬太尼不影响SEP的潜伏期,但posthoc分析结果提示,较年长的儿童皮层波幅会减低。     

Intra-operative localization of sensorimotor cortex by cortical somatosensory evoked potentials: From analysis of waveforms to dipole source modeling

Summary Intra-operative localization of sensorimotor cortex is of increasing importance as neurosurgical techniques allow safe and accurate removal of lesions around the central sulcus. Although direct cortical recordings of somatosensory evoked potentials (SEPs) are known to be helpful for cortical localization, source localization models can provide more precise estimates than subjective visual analysis. In addition to intra-operative analysis of waveforms and amplitudes of SEPs to median nerve stimulation in 20 neurosurgical patients, we used a spatiotemporal dipole model to determine the location of the equivalent dipoles consistent with the cortical distribution of the SEPs. The early cortical SEPs were modeled by 2 equivalent dipoles located in the postcentral gyrus. The first dipole was primarily tangentially oriented and explained N20 and P20 peaks. The second dipole was primarily radially oriented and explained P25 activity. We found consistent localization of the first dipole in the postcentral gyrus, which was always located within 8 mm of the central sulcus, with an average distance of 3 mm. This finding provides an objective basis for using the SEP phase reversal method for cortical localization. We conclude that dipole source modeling of the cortical SEPs can be considered as an objective way of localizing the cortical hand sensory area.     

Surgical and electrophysiological observations during clipping of 134 aneurysms with evoked potential monitoring

Somatosensory evoked potentials (SEPs) were monitored during 113 operations for the clipping of 134 cerebral aneurysms. Changes in peak latency and amplitude of early cortical SEP as well as central conduction time were evaluated. In 58 cases surgical occlusion of arterial vessels or other events occurred, and in 17 of these cases such events were associated with SEP changes or loss. Arterial occlusions resulted from temporary clipping of a feeding blood vessel (22), accidental clipping of a vessel (12), and intentional permanent vessel occlusion (8). A total SEP loss was seen in 2 cases of accidental vessel occlusion and in 6 cases of temporary vessel clipping. Significant SEP changes were found in 6 patients with temporary clipping, and once each with retraction of the cerebellum, retraction of the middle cerebral artery, and after intentional permanent vessel occlusion. Response to these changes included reapplication of aneurysm clips, repositioning of retractors, or removal of temporary clips. Stable SEP signals during 13 cases allowed the surgeon to proceed with the surgical course. Despite the limitations of SEP monitoring in certain anatomical locations, it has been found to be helpful in the operative management of some cases such as multilobed aneurysms of the middle cerebral artery, giant aneurysms, trapping procedures, and procedures requiring temporary vessel occlusion.     

Somatosensory evoked potential monitoring of temporary middle cerebral artery occlusion during aneurysm operation

Somatosensory evoked potentials (SEPs) in response to median nerve stimulation were used as a guide to cortical function during temporary occlusion of the distal M1 segment of the middle cerebral artery (MCA) in the surgical treatment of five large aneurysms of the MCA bifurcation. MCA occlusion times ranged from 8 to 19 minutes under moderate hypothermia at 28.8 degrees to 30.3 degrees C. SEPs were preserved for variable times during MCA occlusion, ranging from no increase in latency after 13 minutes of occlusion to severe deterioration after 6 minutes. In no case was MCA occlusion maintained for longer than 3 minutes in the presence of a severely disturbed SEP. Recovery of the SEP to its preoperative relationship with that of the nonoperated hemisphere was seen in all cases before the end of operation. All patients were awake after rewarming at the end of operation without any neurological deficit. Monitoring the SEP pertaining to the territory of a cerebral artery during its temporary occlusion can help avoid ischemic damage and will allow the surgeon to take advantage of the several benefits of this technique in aneurysm surgery.     

Anesthetic induction with thiopental: its effect on scalp topography of median nerve somatosensory evoked potentials

The effects on median nerve somatosensory evoked potentials (SEPs) of analgesic doses of fentanyl, meperidine or morphine and of sodium thiopental (STP) anesthesia (4 mg/kg) were tested in 36 surgical patients. We also explored changes in SEP components as a function of their scalp location. Before and after medication, responses were recorded from the scalp overlying the parietal cortex (ipsi- and contralateral to the stimulated arm) and the precentral (contralateral) cortex. None of the three opiates affected SEP latencies or amplitudes. The barbiturate increased the amplitudes of subcortical and early cortical components (N18, N20, P22, P25), whose latencies, however, were not significantly modified. The effect of STP on later SEP cortical components depended on their scalp topography: parietal N33 and P45 underwent significant changes in both latency and amplitude, whereas precentral N30 showed a significant amplitude increase only. Thiopental anesthesia produces clearer short-latency SEP recordings, from both parietal (components N20-P25) and precentral (P22, N30) areas.     

Somatosensory evoked potentials as an aid in the diagnosis and intraoperative management of spinal stenosis

The use of somatosensory evoked potentials (SEPs) in localizing the level, extent, and laterality of nerve root entrapment is clinically important. In patients with lumbar spinal stenosis, this is especially true. This study defines a prospective investigation of 20 patients with preoperative SEPs of which 11 patients had intraoperative SEPs correlated with their computed tomographic (CT) scan and/or myelographic findings. The results confirm a high incidence of 4th and 5th lumbar and 1st sacral nerve root involvement. The posterior tibial nerve was abnormal in 95%, the peroneal in 90%, and the sural in 60% in the symptomatical lower extremity. Upper lumbar segments were barely affected as evident by the low incidence of saphenous nerve abnormality in only 12% of the patients. The posterior tibial nerve had the highest yield and was useful for screening. Bilateral lower extremity abnormalities were found in seven of 20 cases studied with two patients having bilateral symptoms and findings. Therefore, bilateral lower extremity SEP evaluation can reveal previously unsuspected pathology and is strongly recommended in preoperative evaluations. SEPs can serve as a useful intraoperative tool to guide the surgeon during a decompressive surgical procedure. SEPs are specifically helpful in spinal stenosis with a paucity of clinical findings and equivocal CT scan or myelographic studies. SEPs seem much more sensitive and effective than conventional electrodiagnostic tests in detecting spinal nerve root compression secondary to spinal stenosis.     

Correlation of transient neurological deficit and somatosensory evoked potentials after intracranial aneurysm surgery. Case report

A patient is reported in whom intraoperative somatosensory evoked potential (SEP) changes occurred in response to temporary clipping of the right middle cerebral artery. A period of 10 minutes elapsed before changes in SEP's in response to contralateral nerve stimulation were noted and, during the following 2 minutes, the waves decreased in amplitude and then were unrecordable. Waves of SEP, with amplitude similar to those recorded before clipping but with abnormal latency, returned within 45 seconds of removal of the clip, and the latency abnormalities persisted until the end of the operation. The patient awakened promptly at the end of the procedure with a dense left hemiparesis which resolved over 24 hours. At the end of 24 hours, the SEP's in response to median nerve stimulation were symmetrical in both latency and amplitude. This report demonstrates the accuracy of intraoperative evoked potential monitoring in demonstrating alterations of cerebral perfusion during aneurysm surgery. It also suggests that a prolonged period of observation may be necessary to assess the effects of temporary vessel occlusion during surgery on aneurysms or arteriovenous malformations.     

Transcranial Doppler sonography and somatosensory evoked potential monitoring in carotid surgery

Ninety-seven patients undergoing 103 carotid operations were studied intraoperatively using somatosensory evoked potentials after median nerve stimulation (SEP) and transcranial Doppler sonography (TCD). SEP were recorded from the scalp (C3'-Fz or C4'-Fz) and from the second cervical vertebra. The amplitude of the primary cortical response (N20P25) was measured peak-to-peak. Central conduction time (CCT) resulted from the difference between the first negative cortical (N20) and cervical (N14) response. TCD was performed using a pulsed 2-MHz-Doppler device to record the mean blood flow velocity of the middle cerebral artery (Vm-MCA) transtemporally. TCD and SEP variables were registered prior to and after carotid clamping, at short intervals during the clamping period, and after declamping. Critical SEP alterations (N20P25 less than 50% and/or CCT greater than 20% compared to the preceding values) were regarded as significant indicators of cerebral ischaemia, and selective intraluminal shunting was generally based on SEP criteria. The incidence of critical SEP changes was compared to Vm-MCA reductions greater than 60% using the Chi2-test. With SEP always recordable, additional TCD monitoring was possible in only 78 patients in our series for technical or anatomical reasons. Vm-MCA reductions greater than 60% were associated with critical SEP alterations in six cases. In five patients, Vm-MCA was reduced greater than 60% without relevant SEP changes, whereas one patient with critical SEP findings had only a minor Vm-MCA reduction (33%). In the remaining 66 cases, carotid clamping was tolerated without critical SEP changes associated with Vm-MCA reductions not exceeding 60%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Brainstem origins of the n18 component of the somatosensory evoked response

Proposed generator sites for the N18 component of the somatosensory evoked potential (SEP) range in location from the medulla to the thalamus. Additional knowledge regarding the generators of the N18 will be important in interpreting the results of intra-operative monitoring during skull base surgery and providing the surgeon more specific information. The goal of this study was to use both intracranial electrical recording and the effects of acute brainstem ischemia in humans to further define the generators of N18. Monopolar electrodes were used to record SEP (after median nerve stimulation) from the brainstem surface in eight patients undergoing posterior fossa surgical procedures. Recordings were made from various locations, from the cervico-medullary junction to the level of the aqueduct of Sylvius. As the electrode moved rostrally on the brainstem surface, the difference in latencies between the scalp N18 potential and the electrode potential approached zero, suggesting an upper pontine-lower midbrain origin of the N18 potential. These findings were supported by the lack of change in the N18 potentials of ten patients with basilar tip aneurysms who experienced marked changes of their N20/P22 potentials during temporary occlusion of the distal basilar artery.     

Brainstem Origins of the N18 Component of the Somatosensory Evoked Response

Proposed generator sites for the N18 component of the somatosensory evoked potential (SEP) range in location from the medulla to the thalamus. Additional knowledge regarding the generators of the N18 will be important in interpreting the results of intra-operative monitoring during skull base surgery and providing the surgeon more specific information. The goal of this study was to use both intracranial electrical recording and the effects of acute brainstem ischemia in humans to further define the generators of N18. Monopolar electrodes were used to record SEP (after median nerve stimulation) from the brainstem surface in eight patients undergoing posterior fossa surgical procedures. Recordings were made from various locations, from the cervico-medullary junction to the level of the aqueduct of Sylvius. As the electrode moved rostrally on the brainstem surface, the difference in latencies between the scalp N18 potential and the electrode potential approached zero, suggesting an upper pontine-lower midbrain origin of the N18 potential. These findings were supported by the lack of change in the N18 potentials of ten patients with basilar tip aneurysms who experienced marked changes of their N20/P22 potentials during temporary occlusion of the distal basilar artery.     

Monitoring of somatosensory-evoked potentials during aneurysm surgery

Somatosensory-evoked potentials were recorded during and after 31 operations for intracranial aneurysms, and the changes in the central conduction times, namely, the interpeak latencies between the N14 and N20 peaks in response to bipolar stimulation of the median nerve, were studied. Neuroleptanalgesia and routine intracranial operative procedures such as opening the dura mater, drainage of the cerebrospinal fluid, gentle retraction of the brain, and microsurgical dissection of the circle of Willis, were found to have no significant adverse effect on the evoked responses, whereas the temporary clipping of the major cerebral artery or premature rupture of the aneurysm associated with hypotension or both, often caused significant prolongation of the central conduction time. Prolongation of the central conduction time exceeding 1.2 ms or disappearance of the N20 peak adversely affected the postoperative conditions in 8 of 13 patients (62%).     

Reversibility of cerebral function assessed by somatosensory evoked potentials and its relation to intracranial pressure--report of six cases with severe head injury.

The critical value and duration of intracranial pressure (ICP) causing cerebral function damage was evaluated in six head injury patients by monitoring the first negative cortical component (N20) of the somatosensory evoked potential (SEP). The SEP was elicited by stimulating the median nerve, and N20 (C3' or C4'-Fz on the affected side) and N13 (C2S-Fz) were monitored serially with a signal processor. The auditory brainstem response (ABR) was simultaneously recorded on the affected side (A1 or A2-Cz). A reversible loss of N20 occurred 7 times in six cases. In all cases, the N20 was restored by emergency decompression or hyperosmolar therapy. The minimum ICP at which N20 disappeared was 30 mmHg, and the N20 was restored when decompression was performed within 4.5 hours. However, when the disappearance persisted for more than 1.5 hours, the N20 latency was markedly prolonged after restoration. These changes appeared before the ABR showed definite abnormalities. These results show that the cerebral function may be damaged when ICP exceeds 30 mmHg, and that emergency decompression is required within 4.5 hours, preferably within 1.5 hours, to restore cerebral function. This critical ICP and duration should be of clinical value in patient management.     

Somatosensory evoked potentials over the unaffected hemisphere in patients with unilateral intracerebral hematoma

Somatosensory evoked potentials (SEPs) recorded from the unaffected hemispheres were studied in patients of less than one month after the onset of unilateral intracerebral hematoma. We examined 66 SEPs obtained from 49 patients with putaminal hemorrhage (midline shift 0-15 mm), 38 SEPs from 25 patients with thalamic hemorrhage (midline shift 0-8 mm), and 14 SEPs from 10 patients with subcortical hemorrhage (midline shift 0-12 mm). These examinations were made after electrical stimulation of the median nerve at the wrist by using square waves of 0.2 msec in duration delivered at a rate of 3 Hz. We analyzed the first cortical potential N 20 recorded from the contralateral scalp over the unaffected hemisphere with reference on Fpz. N 20 peak latency was compared with the maximum shift of the midline structure such as in foramen of Monro or third ventricle in computed tomogram. Also with the site of the hematoma and the disturbance of consciousness. N 20 peak latency was not correlated with the degree of the midline shift in all the patients. There was abnormal prolongation of N 20 peak latency in one SEP of one patient, and disappearance of N 20 in two SEPs of two patients with putaminal hemorrhage. Abnormal prolongation of N 20 peak latency was found in 3 SEPs of 3 patients with thalamic hemorrhage. There was no disappearance of N 20 in patients with thalamic hemorrhage. There was no abnormal prolongation or disappearance of N 20 peak latency in patients with subcortical hemorrhage. In two of five patients showing stuporous state, disappearance of N 20 was found.(ABSTRACT TRUNCATED AT 250 WORDS)     

Short latency somatosensory-evoked potentials in children--Part 1. Normative data

Spinal, subcortical, and short latency cortical somatosensory-evoked potentials (SEPs) following electrical stimulation of the median or tibial nerve were studied in 100 children aged 4 weeks to 13 years. Standard neurophysiological methods of recording surface SEPs were used in sedated and nonsedated children. The morphology of the SEPs was similar to that obtained in adults; however, the initial components of the cortical SEP following median nerve stimulation did show maturational changes in both interpeak latencies and morphology. The negative peak latencies recorded over Erb's point (N9 equivalent) and the second cervical vertebra (N13 equivalent) following median nerve stimulation, and over the lumbothoracic junction (N14 equivalent) following tibial nerve stimulation were directly related to patient age and limb length. There was no correlation between age and the latencies of either the initial negativity (N18 equivalent) or the initial positivity (P28 equivalent) of the cortical SEPs following respective median and tibial nerve stimulation. The central somatosensory conduction time decreased slowly during the first decade and attained adult values after 8 years of age. The lumbar spine to scalp transit time showed no direct relationship to age. Comparisons of SEPs recorded in the same subject when awake and under general anesthesia showed that the latencies of the subcortical, spinal, and N1-P1 complex of the cortical SEP are identical; however, the later components of the cortical SEP vary both in latency and amplitude with anesthesia. This study represents normative data against which SEP in children with disorders of the central nervous system may be compared.