The use of evoked potentials in the management of patients with severe cerebral trauma

Predictive value of somatosensory evoked potentials for awakening from coma

OBJECTIVES

A systematic review of somatosensory evoked potentials performed early after onset of coma, to predict the likelihood of nonawakening. The pooled results were evaluated for rates of awakening, confidence intervals, and the possibility of rare exceptions.

DATA SOURCES

Forty-one articles reporting somatosensory evoked potentials in comatose patients and subsequent outcomes, from 1983 to 2000.

STUDY SELECTION

Studies were included if they reported coma etiology, age group, presence or absence of somatosensory evoked potentials, and coma outcomes.

DATA EXTRACTION

We separated patients into four groups: adults with hypoxic-ischemic encephalopathy, adults with intracranial hemorrhage, adults and adolescents with traumatic brain injury, and children and adolescents with any etiologies. Somatosensory evoked potentials were categorized as normal, abnormal, or bilaterally absent. Outcomes were categorized as persistent vegetative state or death vs. awakening.

DATA SYNTHESIS

For each somatosensory evoked potential result, rates of awakening (95% confidence interval) were calculated: adult hypoxic-ischemic encephalopathy: absent 0% (0%-1%), abnormal 22% (17%-26%), normal 52% (48%-56%); adult intracranial hemorrhage: absent 1% (0%-4%), present 38% (27%-48%); adult-teen traumatic brain injury: absent 5% (2%-7%), abnormal 70% (64%-75%), normal 89% (85%-92%); child-teen: absent 7% (4%-10%), abnormal 69% (61%-77%), normal 86% (80%-92%).

CONCLUSIONS

Somatosensory evoked potential results predict the likelihood of nonawakening from coma with a high level of certainty. Adults in coma from hypoxic-ischemic encephalopathy with absent somatosensory evoked potential responses have <1% chance of awakening.

Does wave VI of BAEP pertain to the prognosis of coma?

OBJECTIVES

The significance of brainstem auditory evoked potential (BAEP) wave VI for the outcome of comatose patients was assessed and compared to the prognostic impact of median nerve evoked somatosensory potential (MSEP) recording.

PATIENTS AND METHODS

One hundred sixteen patients in a comatose state due to traumatic brain injury (n = 57) and to intracerebral hemorrhage or tumours (n = 59) were investigated prospectively. Outcome was assessed 3 months after the onset of coma using Glasgow Outcome Score (GOS). Standard BAEP and MSEP recordings were obtained within 24 h after coma onset. The frequency of findings was correlated with outcome by means of non-parametric statistical analysis. Additionally, 27 healthy volunteers were studied to confirm the constant presence of wave VI in normal BAEP.

RESULTS

In healthy controls, wave VI was present in 53/54 ears stimulated. Outcome correlation analysis revealed a significantly (p < 0.01) higher frequency of abnormal wave VI in patients with unfavourable outcome (GOS 1-3) irrespective of the underlying pathology. Similarly, abnormal MSEP findings were significantly more frequent in this outcome group. Diagnostic sensitivity for an unfavourable outcome was low for both parameters, whereas specificity and positive predictive value of abnormal wave VI as well as of abnormal MSEP were equally high.

CONCLUSION

Abnormal BAEP wave VI bears prognostic information in comatose patients.

Review of the use of somatosensory evoked potentials in the prediction of outcome after severe brain injury

OBJECTIVE

Review the predictive powers of somatosensory evoked potentials (SEPs) in severe brain injury.

DATA SOURCES

Publications in the scientific literature, manual review of article bibliographies, and questioning workers in the field.

STUDY SELECTION

Studies addressing the prediction of outcome after severe brain injury using SEPs.

DATA EXTRACTION

To determine the outcome of patients with either normal or bilaterally absent SEPs as categorized using the Glasgow Outcome Scale into favorable outcomes (good or moderate disability) or unfavorable outcomes (severe disability, vegetative, or dead). Studies were included if they were in English and allowed the determination of outcomes for all patients with normal or bilaterally absent SEPs. Papers were not considered if subjects were neonates, consisted of abstracts where all necessary details were unavailable, were case reports or duplications of other published studies, or dealt only with brain dead subjects.

DATA SYNTHESIS

For all studies (n = 44), positive likelihood ratio, positive predictive value, and sensitivity were 4.04, 71.2%, and 59.0%, respectively, for normal SEPs (predicting favorable outcome) and 11.41, 98.5%, and 46.2%, respectively, for bilaterally absent SEPs (predicting unfavorable outcome). Summary receiver operating characteristic curve analysis detected a cut-off criterion effect for only blinded studies of bilaterally absent SEPs. Twelve patients (12/777) were identified with bilaterally absent SEPs who had favorable outcomes. These false positives are typically pediatric patients or have suffered traumatic brain injuries. We suggest criteria for the use of bilaterally absent SEPs in the prediction of poor outcome, which include absence of focal lesions, subdural or extradural fluid collections, and no decompressive craniotomy in previous 48 hrs. Using these criteria the data suggest that the false-positive rate is <0.5% for bilaterally absent SEPs.

CONCLUSIONS

SEPs are powerful predictors of outcome, particularly poor outcome, if patients with focal lesions, subdural effusions, and those who have had recent decompressive craniotomies are excluded.

The role of evoked potentials in anoxic-ischemic coma and severe brain trauma

The early recognition of comatose patients with a hopeless prognosis-regardless of how aggressively they are managed-is of utmost importance. Median somatosensory evoked potentials supplement and enhance neurologic examination findings in anoxic-ischemic coma and severe brain trauma, and are useful as an early guide to outcome. The key finding is that bilateral absence of cortical evoked potentials, generated by thalamocortical tracts, reliably predicts unfavorable outcome in comatose patients after cardiac arrest, and correlates strongly with death or persistent vegetative state in severe brain trauma. The author studied 50 comatose patients with preserved brainstem function after cardiac arrest. All 23 patients with bilateral absence of cortical evoked potentials died without awakening. Neuropathologic study in seven patients disclosed widespread ischemic changes or frank cortical laminar necrosis. The remaining 27 patients with normal or delayed central conduction times had an uncertain prognosis because some died without awakening or entered a persistent vegetative state. The majority of patients with normal central conduction times had a good outcome, whereas a delay in central conduction times increased the likelihood of neurologic deficit or death. This report includes a systematic review of the literature concerning adults in anoxic-ischemic coma and severe brain trauma, in which somatosensory evoked potentials were used as an early guide to predict clinical outcome. Greater use of somatosensory evoked potentials in anoxic-ischemic coma and severe brain trauma would identify those patients unlikely to recover and would avoid costly medical care that is to no avail.

Hemicraniectomy for massive cerebral infarction: Evoked potentials as presurgical prognostic factors

In patients with massive hemispheric infarctions, mortality exceeds 80% with medical therapy alone. In certain conditions hemicraniectomy may result in meaningful survival. We studied presurgical clinical and electrophysiological parameters that may serve as prognostic factors to assess efficacy of decompressive surgery. We evaluated 26 consecutive patients with severe focal neurological deficit, deterioration of consciousness, and massive hemispheric infarction by cranial computerized tomography who underwent hemicraniectomy. Clinical examination included pupillary size and reaction, and determination of level of consciousness on an hourly basis. Median nerve somatosensory evoked potentials and brainstem auditory evoked potentials were obtained before and after hemicraniectomy. Outcome was assessed by using the Barthel Index. Clinical and evoked potential data were correlated with the outcome. Fisher's Exact Test was applied to establish statistical significance. With surgery 18 of 26 patients survived on an average intensive care treatment of 29.6 (+/-27.5) days. Barthel Index at discharge was 61.7 (+/-24.4) in survivors. Presurgical pupillary reaction, level of consciousness, and somatosensory evoked potentials were not found to correlate with outcome. In contrast, presurgical brainstem auditory evoked potentials showed a significant correlation with survival (P<.05). All patients with good outcomes (Barthel Index >/=60: n=12, 46.1%) had normal brainstem auditory evoked potentials before surgery. Clinical parameters did not reliably forecast prognosis in patients with massive cerebral infarction treated with hemicraniectomy.

Somatosensory evoked potentials and intracranial pressure in severe head injury

The purpose of this study was to explore the relationship between neurologic function, using a quantitative measurement of continuous somatosensory evoked potentials (SSEPs), and intracranial pressure (ICP) following traumatic brain injury. During a 6 year period, severely head-injured patients with a Glascow Coma Scale < or = 8 who were not moribund were monitored with SSEPs and ICP measurements. SSEPs from each hemisphere and ICP were recorded hourly for each patient. Neurologic outcomes were scored using the Glasgow Outcome Scale at three months post injury. Although initial SSEP amplitude did not correlate well with outcome, final SSEP summed peak to peak amplitude from both hemispheres (p = .0001), the best hemisphere (p = .0004), and the worst hemisphere (p = .0001) correlated well with the Glasgow Outcome Scale groups. Of a total of 72 patients, 40 had deteriorating SSEPs and 32 had stable or improving SSEPs. Peak ICP values were not statistically different in these groups (p = .6). Among patients with deteriorating SSEPs, 52.5% lost the greatest proportion of hemispheric electrical activity prior to ICP elevation. In the remaining patients, the percent reduction of SSEP activity after peak ICP levels was not statistically different from the percent reduction in SSEP activity prior to the peak ICP levels (p = .9). This data suggests that in a select group of patients with severe head injury, ICP does not cause SSEP deterioration, but rather is the consequence of deterioration of brain function.

The combined monitoring of brain stem auditory evoked potentials and intracranial pressure in coma. A study of 57 patients

Continuous monitoring of brainstem auditory evoked potentials (BAEPs) was carried out in 57 comatose patients for periods ranging from 5 hours to 13 days. In 53 cases intracranial pressure (ICP) was also simultaneously monitored. The study of relative changes of evoked potentials over time proved more relevant to prognosis than the mere consideration of "statistical normality" of waveforms; thus progressive degradation of the BAEPs was associated with a bad outcome even if the responses remained within normal limits. Contrary to previous reports, a normal BAEP obtained during the second week of coma did not necessarily indicate a good vital outcome; it could, however, do so in cases with a low probability of secondary insults. The simultaneous study of BAEPs and ICP showed that apparently significant (greater than 40 mm Hg) acute rises in ICP were not always followed by BAEP changes. The stability of BAEP's despite "significant" ICP rises was associated in our patients with a high probability of survival, while prolongation of central latency of BAEPs in response to ICP modifications was almost invariably followed by brain death. Continuous monitoring of brainstem responses provided a useful physiological counterpart to physical parameters such as ICP. Serial recording of cortical EPs should be added to BAEP monitoring to permit the early detection of rostrocaudal deterioration.

A comparison between electroencephalography and somatosensory evoked potentials for outcome prediction following severe head injury

The value of somatosensory evoked potentials (SEPs) for the prediction of outcome following severe head injury (HI) is established. The role of the electroencephalogram (EEG) in this setting is uncertain. In this comparative study, SEPs and EEGs were recorded within 3 days of severe HI in 90 patients, and the results related to outcome at 6 months. Patients with an isoelectric EEG or an EEG with repeated isoelectric intervals died. Reactivity of the EEG to external stimulation tended to be associated with favorable outcome. Grading of the EEGs on the basis of frequency composition otherwise provided no prognostic information. The presence of SEP scalp potentials bilaterally predicted favorable outcome, particularly if the central conduction times were normal. Conversely, the absence of one of both scalp potentials was associated with unfavorable outcome. EEGs thus provided useful prognostic information in only a minority of patients. By comparison, SEPs allowed prediction of both favorable and unfavorable outcomes in a much larger number of patients, and were therefore prognostically superior.

Brain-stem monitoring. II. Preterminal BAEP changes observed until brain death in deeply comatose patients

Preterminal BAEP changes were studied until brain death in 8 head-injured patients out of a series of 38 comas monitored by means of a system allowing high-rate sequential recording. Two different modalities of BAEP degradation were disclosed: (1) simultaneous latency increase of all components associated with a decrease of cerebral perfusion pressure (CPP), consistent with ongoing ischaemia of the posterior fossa; (2) deterioration of brain-stem components (waves III-V) with preserved or even enhanced wave I. The latter pattern was not consistently associated with any haemodynamic change and might be related to mechanical factors causing rostro-caudal deterioration of brain-stem function. The time course of BAEP degradation ranged from a few minutes to more than 10 h. In the case of slow preterminal evolution definitely pathological trends were identified even when individual BAEPs were still within normal limits. Such trends would have remained unnoticed in single BAEP records. Hypothermia and anaesthetic drugs were found to induce falsely alarming BAEP changes very similar to those seen during preterminal evolution. Our results suggest that continuous brain-stem monitoring could be helpful for management of comatose head-injured patients.

Brainstem auditory evoked response and vestibulo-ocular reflex in severe head injury patients. A prospective study of 60 cases

Brainstem auditory evoked response (BAER) performed in 60 serious head injury patients, over the last two year period at All India Institute of Medical Sciences, New Delhi have been analysed, to correlate the findings with ultimate outcome. All patients included in this study were unconscious, not following any command at the time of initial evaluation, mostly within 48 hours of injury. Repeat studies were performed in surviving patients. Computerized cranial tomography was performed to establish the nature of the intracranial pathology. The clinical status and cold caloric responses were recorded in all. The patients were followed up for 1 to 24 months. Three patients had extradural haematoma, 2 patients had subdural haematoma and 30 patients had intracerebral contusion/haematoma. Brain oedema was recorded in 14 cases. BAER was normal in 32 patients and 26 of them had good recovery (81%). Three patients with normal BAER died. Abnormal BAER was recorded in 21 patients and only 50% of them had good recovery and 25% of them died. In 7 patients BAER was absent and only 2 (29%) had a good recovery. Thus 48 out of 60 patients (66%) had a good recovery and 11 (18%) died. When compared to cold caloric response, 87% patients with normal caloric response had a good recovery and 5 out of 6 patients with absent caloric response died and remaining 1 left in a vegetative state. Thus the caloric response is at least as good a prognostic factor as BAER.