Serial Somatosensory Evoked Potentials Research Articles

Early recovery after closed traumatic head injury: somatosensory evoked potentials and clinical findings.

To determine the ability of somatosensory evoked potentials (SEP) compared with clinical findings to monitor and predict recovery in patients suffering from closed head injury with predominantly diffuse axonal injury (DAI). Prospective cohort study. Neurologic intensive care unit (ICU) of a university hospital. Serial SEP recordings were obtained from 31 consecutive patients with closed head injury. The first SEP was recorded within 48 hrs after trauma, followed by recordings after another 2 days, after which the time interval for each consecutive recording was doubled. Clinical examinations were performed every 6 hrs during the ICU stay and daily after transfer to a general neurologic ward. None. Twenty-three of 31 patients demonstrated pathologic SEP findings at initial examination. Of these patients, 11 recovered clinically, two remained vegetative, and ten died. In all 11 patients with clinical recovery, SEP also recovered. In 8 of 31 patients, initial SEPs were normal and remained normal until discharge, all eight had a good outcome. Initial SEP findings were related with outcome at 6 months (p = .02), and follow-up studies increased the predictive value of SEP studies (p = .009). Other factors related to outcome included age, severity of DAI, and length of ICU/hospital stay. In the 11 patients with SEP and clinical recovery, early (day 2) and late (>or=2 months) recovery was documented. Early and reliable SEP indicators of improvement included N20-P25-Amplitudes (mean recovery, 8.5 days) and central conduction time (9.6 days). Pupillary light reaction (6.4 days), Babinski reflex (12.4 days), and Glasgow Coma Score (9.6 days) were the most valuable clinical findings. Recovery of the Glasgow Coma Score frequently coincided with reduction of sedatives. In most patients, recovery was detected with SEP before clinical recovery (7/11 patients, time difference 1 wk). Initial SEP findings correlate with long-term outcome in patients with closed head injury with DAI. Initial bilaterally absent cortical responses in the SEP reliably predicted death, whereas completely normal SEP findings predicted good long-term outcome. Early recovery after DAI can be detected with serial SEP recordings despite sedative medications. Electrophysiologic recovery frequently precedes clinical recovery.

Serial evoked potentials and outcome in cerebrovascular critical care patients.

Median-nerve evoked somatosensory evoked potentials (SEPs) and brainstem auditory evoked potentials (BAEPs), examined early in the course of patients suffering from cerebrovascular disease, correlate statistically significantly with outcome. Little is known about the changes of evoked potentials in the course of disease and their correlation to outcome. In a series of 215 patients (75 supratentorial infarctions, 36 infratentorial infarctions, 58 supratentorial hemorrhages, 18 infratentorial hemorrhages, and 28 aneurysmatic subarachnoid hemorrhages) requiring neurologic intensive care treatment, we prospectively examined the correlation between the findings of serial SEPs and BAEPs and outcome at 4 weeks. Evoked potentials were examined after admission, after 1 week, and after 2 weeks. The findings were classified in 4 categories (normal, unilateral or bilateral pathologic findings, unilaterally attenuated, and bilaterally attenuated). Clinical outcome was determined by classification according to the Glasgow Outcome Scale (death, persistent vegetative state, severely incapacitated, mildly incapacitated, and recovery). Statistical evaluation was performed using Fisher's exact test for all variables. In all subgroups, SEPs correlated statistically significantly with outcome at all three examinations. No correlation was found for BAEPs at first examination in infratentorial disease, nor at second examination in subarachnoid hemorrhages. In all other cases, SEPs and BAEPs were correlated statistically significantly with outcome at all three examination timepoints.

The role of somatosensory evoked potentials in the evaluation of spinal cord retethering.

Early detection of clinically significant spinal cord retethering is of paramount importance for the preservation of neurologic function in patients with repaired spinal dysraphic lesions. We retrospectively analyzed 90 children who were followed with serial peroneal somatosensory evoked potentials (SEPs) after a repair of their spinal dysraphic lesions with the objective of evaluating whether SEPs were a useful way of monitoring these children to facilitate early detection of clinically significant retethering. Three hundred and nine studies were performed on these children yielding a mean of 3.4 studies per patient. The median time between SEP studies was 13 months. A clinical examination was performed at the time each SEP was done. Sixty-one patients (68%) had a myelomeningocele; 25 (28%) had a lipomyelomeningocele while other types of dysraphic lesions were found in the remaining 4%. Nineteen patients (21%) had no change in serial SEPs; 7 of these 19 (37%) had a deterioration in clinical status while the SEPs were stable. Twenty-six patients (29%) showed improvement in serial SEPs, however, 3 of the 26 had clinical worsening at the time SEPs improved. SEPs deteriorated in 45 patients (50%); 13 of the 45 had an associated clinical deterioration, and the remaining 32 were stable clinically. Twenty-three patients (26%) had a clinical deterioration; of these only 13 had a corresponding deterioration in SEPs, 7 patients had stable SEPs while 3 had improvement in SEPs at the time of clinical deterioration. This results in a false-positive rate of 71% and a false-negative rate of 43%. We conclude that serial SEPs do not correlate well with clinical status and are not a useful modality for monitoring patients at risk for retethering.

Eliminating diathermy-induced artifacts during intraoperative monitoring of somatosensory-evoked potentials: A hardware solution

Somatosensory-evoked potentials (SEPs) recorded intraoperatively are often contaminated by artifacts arising from unipolar diathermy. This increases variability in serial SEP recordings and decreases the reliability of SEPs for intraoperative monitoring. Rejection of single sweeps on the basis of a voltage criterion can only partially prevent the inclusion of sweeps containing artifacts. We describe a low-cost hardware system that will halt SEP acquisition automatically before diathermy becomes active. Activation of the diathermy switch will halt SEP acquisition by sending a digital inhibit signal to the evoked potential machine via a fiberoptic cable. A timer delays the activation of the diathermy until the last sweep has been completed. To allow the electroencephalographic amplifiers to recover from any overload condition resulting from the high-voltage/high-frequency input during diathermy, acquisition is resumed only after a user-selectable time interval. The system was evaluated in 50 patients. It effectively interrupted SEP acquisition each time diathermy was used. By eliminating diathermy noise from the averaged waveforms, the system will allow evoked potential monitoring even during periods of intensive use of diathermy.

Serial somatosensory evoked potentials in a patient with familial hypobetalipoproteinemia, and vitamin E deficiency.

Serial somatosensory evoked potentials (SEPs) to median and posterior tibial nerve stimulation in a case with familial heterozygous hypobetalipoproteinemia and vitamin E deficiency were investigated over a period of 4 years. In serial SEPs to posterior tibial nerve stimulation, interpeak latencies between N20 and P2 were delayed even in the early clinical stage, although the peak latency of N20 was normal. N20 latency was delayed when the patient noted paresthesia of the lower extremities. Interpeak latencies between N20 and P2 were progressively prolonged, and finally both peaks disappeared. Progressive dysfunctions of spinal posterior columns and peripheral somatosensory pathways were discovered by serial SEP studies.

Prevention of Reperfusion Injury of the Ischemic Spinal Cord: Use of Recombinant Superoxide Dismutase

We investigated the effect of recombinant superoxide dismutase, an oxygen free radical scavenger, on the prevention of reperfusion injury of the ischemic spinal cord. Somatosensory evoked potentials (SEPs) were obtained in 23 dogs. Spinal cord ischemia was produced by cross-clamping the descending thoracic aorta just distal to the origin of the left subclavian artery through a left thoracotomy. Mean proximal aortic blood pressure was maintained between 90 and 100 mm Hg by partial exsanguination. Serial SEPs were obtained at 60-second intervals until the SEP disappeared. Aortic cross-clamping was continued for 10 additional minutes after the disappearance of the SEP. In Group 1 (N = 8), no medication was given when the aortic cross-clamp was removed. In Group 2 (N = 8), a bolus of 25,000 units of superoxide dismutase was injected into the proximal aorta prior to removal of the aortic cross-clamp, and was followed by 5,000 units per minute for 10 minutes after release of the cross-clamp. In Group 3 (N = 7), 50,000 units of superoxide dismutase was administered as a bolus prior to removal of the aortic crossclamp, followed by an additional 10,000 units per minute for 10 minutes as in Group 2. The postoperative neurological status was assessed by Tarlov's criteria. There was no significant difference in aortic cross-clamp time among the three groups. Paraplegia developed in 4 animals in Group 1; the remaining 4 dogs had paraparesis. In Group 2, paraparesis developed in 2 of 8 dogs; the other 6 had no neurological injury. All the animals in Group 3 had complete recovery. Group 1 animals (control) had a significantly ( p < .001, Fisher's exact test) increased incidence of neurological injury compared with the superoxide dismutase–treated animals (Groups 2 and 3). There was no significant difference in the incidence of paraparesis between Groups 2 and 3. We conclude that (1) oxygen free radicals generated during reperfusion may compound the ischemic injury, (2) the ischemic spinal cord injury is limited by the use of recombinant superoxide dismutase, and (3) further studies are indicated to elucidate the dose-response phenomenon of recombinant superoxide dismutase in this animal model.

Somatosensory evoked potentials in abetalipoproteinemia

Visual brain-stem auditory, and somatosensory evoked potentials (SEPs) were obtained on a patient with known abetalipoproteinemia. Only the SEP was abnormal, and it correlated with the reported neuropathology of this disease. Serial SEP studies remained stable, as had the clinical condition of this patient on vitamin E therapy. The SEP may supplement clinical examination in follow-up of patients under treatment.