EEG and evoked potentials in comatose patients with severe brain damage

Exclusive color-coded duplex sonography of extracranial vessels reliably confirms brain death: A prospective study

Background

Transcranial color-coded duplex sonography (TCCD) can be used as an ancillary test for determining irreversible loss of brain function (ILBF) when demonstration of cerebral circulatory arrest (CCA) is required. However, visualization of the intracranial vessels by TCCD is often difficult, or even impossible, in this patient cohort due to elevated intracranial pressure, an insufficient transtemporal bone window, or warped anatomical conditions. Since extracranial color-coded duplex sonography (ECCD) can be performed without restriction in the aforementioned situations, we investigated the feasibility of omitting TCCD altogether, such that the ILBF examination would be simplified, without compromising on its reliability.

Methods

A total of 122 patients were prospectively examined by two experienced neurointensivists for the presence of ILBF from 01/2019-12/2021. Inclusion criteria were (i) the presence of a severe cerebral lesion on cranial CT or MRI, and (ii) brainstem areflexia. Upon standardized clinical examination, 9 patients were excluded due to incomplete brainstem areflexia, and a further 22 due to the presence of factors with a potentially confounding influence on apnea testing, EEG or sonography. A total of 91 patients were enrolled and underwent needle-EEG recording for >30 min (= gold standard), as well as ECCD and TCCD. The sonographer was blinded to the EEG result.

Results

All patients whose ECCD result was consistent with ILBF had this diagnosis confirmed by EEG (n = 77; specificity: 1). Both ECCD and EEG were not consistent with ILBF in a further 12 patients. In the remaining two patients, ECCD detected reperfusion due to long-lasting cerebral hypoxia; however, ILBF was ultimately confirmed by EEG (sensitivity: 0.975). This yielded a positive predictive value (PPV) of one and a negative predictive value of 0.857 for the validity of ECCD in ILBF confirmation. TCCD was not possible/inconclusive in 31 patients (34%).

Conclusions

The use of ECCD for the confirmation of ILBF is associated with high levels of specificity and a high positive predictive value when compared to needle-electrode EEG. This makes ECCD a potential alternative to the ancillary tests currently used in this setting, but confirmation in a multi-center trial is warranted.

Trial registration

https://www.drks.de, DRKS00017803.

[Determination of irreversibility of clinical brain death. Electroencephalography and evoked potentials]

Principally, in the fourth update of the rules for the procedure to finally determine the irreversible cessation of function of the cerebrum, the cerebellum and the brainstem, the importance of an electroencephalogram (EEG), somatosensory evoked potentials (SEP) and brainstem auditory evoked potentials (BAEP) are confirmed. This paper presents the reliability and validity of the electrophysiological diagnosis, discusses the amendments in the fourth version of the guidelines and introduces the practical application, problems and sources of error.An EEG is the best established supplementary diagnostic method for determining the irreversibility of clinical brain death syndrome. It should be noted that residual brain activity can often persist for many hours after the onset of brain death syndrome, particularly in patients with primary brainstem lesions. The derivation and analysis of an EEG requires a high level of expertise to be able to safely distinguish artefacts from primary brain activity. The registration of EEGs to demonstrate the irreversibility of clinical brain death syndrome is extremely time consuming.The BAEPs can only be used to confirm the irreversibility of brain death syndrome in serial examinations or in the rare cases of a sustained wave I or sustained waves I and II. Very often, an investigation cannot be reliably performed because of existing sound conduction disturbances or failure of all potentials even before the onset of clinical brain death syndrome. This explains why BAEPs are only used in exceptional cases.The SEPs of the median nerve can be very reliably derived, are technically simple and with few sources of error. A serial investigation is not required and the time needed for examination is short. For these reasons SEPs are given preference over EEGs and BAEPs for establishing the irreversibility of clinical brain death syndrome.

Electrophysiological assessments of cognition and sensory processing in TBI: applications for diagnosis, prognosis and rehabilitation

Traumatic brain injuries are often associated with damage to sensory and cognitive processing pathways. Because evoked potentials (EPs) and event-related potentials (ERPs) are generated by neuronal activity, they are useful for assessing the integrity of neural processing capabilities in patients with traumatic brain injury (TBI). This review of somatosensory, auditory and visual ERPs in assessments of TBI patients is provided with the hope that it will be of interest to clinicians and researchers who conduct or interpret electrophysiological evaluations of this population. Because this article reviews ERP studies conducted in three different sensory modalities, involving patients with a wide range of TBI severity ratings and circumstances, it is difficult to provide a coherent summary of findings. However, some general trends emerge that give rise to the following observations and recommendations: 1) bilateral absence of somatosensory evoked potentials (SEPs) is often associated with poor clinical prognosis and outcome; 2) the presence of normal ERPs does not guarantee favorable outcome; 3) ERPs evoked by a variety of sensory stimuli should be used to evaluate TBI patients, especially those with severe injuries; 4) time since onset of injury should be taken into account when conducting ERP evaluations of TBI patients or interpreting results; 5) because sensory deficits (e.g., vision impairment or hearing loss) affect ERP results, tests of peripheral sensory integrity should be conducted in conjunction with ERP recordings; and 6) patients' state of consciousness, physical and cognitive abilities to respond and follow directions should be considered when conducting or interpreting ERP evaluations.

Prognostic value of somatosensory evoked potentials in comatose children: a systematic literature review

PURPOSE

To review the predictive powers of SEPs in comatose children after acute brain injury.

METHODS

MEDLINE, EMBASE, OVID, ISI Web of Knowledge, BIOMED Central and the Cochrane Library (1981-2007) were searched. First, predictive values were calculated for each primary study. Second, we analysed effects of different factors on the SEP diagnostic odds ratio by meta-regression. Third, we compared SEP predictive values in children and in adults.

RESULTS

We selected 14 studies covering 732 patients; analysis was conducted in 11, while the other 3 were used for simple qualitative examination. In individual papers, the presence of SEP predicted favourable outcomes as shown by the area under both sROC curves being 0.958. The same value was shown by SEP absence for predicting unfavourable outcomes. All covariates showed no significant effects on diagnostic accuracy, but only a slight non-significant trend. For SEP grading, a simple sub-group analysis showed a high predictive value for non-awakening for absence of SEPs (PPV 97.0%) and a high prognostic power to predict awakening for normal SEPs (PPV 92.2%). Pathological SEPs did not show reliable predictivity. In children, the presence of SEPs showed a high prognostic power similar to that in adults.

CONCLUSION

This study supports the use of SEPs in the integrated process of outcome prediction after acute brain injury in children. Caution is recommended in predicting unfavourable outcomes in patients with an absence of SEPs in both TBI and HIE comas. Future studies are needed to resolve the issue of the effect of aetiology and age on SEP's predictive power.

Diagnostic value of neurophysiological tests in the diagnosis of brain death--do we need changes in national guidelines?

For a final diagnosis of brain death one needs particular proof that the brain has fully stopped functioning. In this respect, diagnostic tests need to be used to confirm the clinical findings. Since in different countries there are various national guidelines for the determination of brain death, the aim of this study is to point to the diagnostic value of electroencephalography (EEG) and evoked potentials (EP) in verifying brain death. The need is emphasized for the two methods to be used in combination, and, accordingly, for the current national guidelines to be changed in our country and also in other countries round the world.

Fundamental principles of somatosensory evoked potentials

Studies of SSEP provide unique opportunities for investigating physioanatomic substrates of sensory pathway and cognitive functions of the sensory system. Progress of clinical investigation and application of SSEP have been stalled in more recent years, although SSEP still remain a useful tool for diagnosis of various neurologic disorders and for the monitoring of spinal cord function during surgery. Reflecting complex sensory system in human, scalp-recorded SSEP consists of multiple waves, having different distribution, amplitude, and latencies among different electrodes. The physioanatomic significance of these multiple waves, especially the late components, is largely unknown. These should be explored further, especially in relation to cognitive function.

The prognostic value of evoked responses from primary somatosensory and auditory cortex in comatose patients

OBJECTIVE

To evaluate somatosensory and auditory primary cortices using somatosensory evoked potentials (SEPs) and middle latency auditory evoked potentials (MLAEPs) in the prognosis of return to consciousness in comatose patients.

METHODS

SEPs and MLAEPs were recorded in 131 severe comatose patients. Latencies and amplitudes were measured. Coma had been caused by transient cardiac arrest (n=49), traumatic brain injury (n=22), stroke (n=45), complications of neurosurgery (n=12) and encephalitis (n=3). One month after the onset of coma patients were classified as awake, still comatose or dead. Three months after (M3), they were classified into one of the 5 categories of the Glasgow outcome scale (GOS).

RESULTS

At M3, 41.2% were dead, 47.3% were conscious (GOS 3-5) and 11.5% had not recovered consciousness. None of the patients in whom somatosensory N20 and auditory Pa were absent did return to consciousness and in the post-anoxic group, reduced cortical amplitude too was always associated with bad outcome. Conversely, N20 and Pa were present, respectively, in 33/69 and 34/69 patients who did not recover.

CONCLUSIONS

The prognostic value of SEPs and MLAEPs in comatose patients depends on the cause of coma. Measurement of response amplitudes is informative. Abolition of cortical SEPs and/or cortical MLAEPs precludes post-anoxic comatose patients from returning to consciousness (100% specificity). In any case, the presence of short latency cortical somatosensory or auditory components is not a guarantee for return to consciousness. Late components should then be recorded.

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.

Role of short latency evoked potentials in the diagnosis of brain death

OBJECTIVE

The aim of this study is to confirm the effectiveness of auditory brain-stem responses (ABRs) and somatosensory evoked potentials (SEPs) in the diagnosis of brain death (BD).

METHODS

ABRs and SEPs were recorded at the same session in 130 BD patients (age range 8-77 years, 81 male and 49 female). Twenty-four cases were submitted to serial recordings from preterminal conditions through BD.

RESULTS

ABRs were absent in 92 cases (70.8%), only waves I or I-II were present in 32 cases (24.6%), while in the remaining 6 patients (4.6%) waves V and/or III were still present, excluding the death of the brain-stem. In 4 cases (3.1%) SEPs showed the absence of all components following the cervical N9, preventing the diagnosis of BD. Among 126 cases (96.9%) with preserved cervical N9-N13 SEPs confirmed the absence of brain-stem activity in 122 cases (93.7%), in whom no waves following P11 or P13 were recordable. SEPs excluded the diagnosis of BD in the remaining 4 cases (3.2%) showing preserved P14 and/or N18. In all pre terminal patients the far-field P14-N18 were present, and their disappearance was closely related to the onset of BD.

CONCLUSIONS

The combined us of ABRs and SEPs was able to confirm BD in almost all patients, providing an objective confirmation of the diagnosis, and to exclude it in 7 cases, thus improving the reliability of diagnosis.

Improving the prediction of outcome in severe acute closed head injury by using discriminant function analysis of normal auditory brainstem response latencies and amplitudes

OBJECT

The auditory brainstem response (ABR) is a useful addition to standard medical measures for predicting outcome in patients with severe acute closed head injury (ACHI). Limiting this success, however, is the poor predictive value of a so-called "normal" ABR. In this study the authors used discriminant function analysis (DFA) of ABR Wave I, III, and V latencies and amplitudes to improve the predictive accuracy of the normal ABR, both as a single measure and in combination with other standard medical measures.

METHODS

The DFAs were conducted using the ABR and medical results in 68 patients with severe ACHI (30 who died [ACHI-died], and 38 who survived [ACHI-lived]) who presented with normal ABR responses in the neurosurgical intensive care unit of the authors' hospital in Johannesburg. All patients had undergone surgery to remove an intracranial hematoma. Correct predictions of outcome by ABR DFA measures were 83% for the ACHI-died group (48% at > or = 90% confidence level) and 87% for the ACHI-lived group (71% at > or = 90% confidence level); by medical DFA measures the correct predictions were 83% for the ACHI-died group (96% at >; or = 90% confidence level) and 95% for the ACHI-lived group (94% at > or = 90% confidence level); and by combined ABR and medical DFA measures correct predictions were 100% for the ACHI-died group (100% at > or = 90% confidence level) and 97% for the ACHI-lived group (100% at > or = 90% confidence level).

CONCLUSIONS

The DFA of ABR Wave I, III, and V latencies and amplitudes improved the predictive ability of normal ABR results to rates similar to those obtained using DFA for the medical measures, although at lower confidence levels. The DFA of the combined ABR and medical measures improved correct predictions to rates significantly higher than for either of the measures on its own.

Neurological outcome prediction in a cardiorespiratory arrest survivor

Outcome prediction of neurological recovery in an unconscious survivor of cardiorespiratory arrest is difficult and uncertain. We describe the case of a 25-yr-old post-arrest survivor who made a remarkable neurological improvement despite a seemingly hopeless prognosis. Conventional clinical and neurophysiological assessments need to be interpreted with care in the presence of uncontrolled seizure activity and sedative medications. The measurement of biochemical markers in the serum and cerebrospinal fluid may be useful in helping the clinician to arrive at a more accurate neurological outcome prediction.

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

OBJECTIVE

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).

DESIGN

Prospective cohort study.

SETTING

Neurologic intensive care unit (ICU) of a university hospital.

PATIENTS

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.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

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).

CONCLUSIONS

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.

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.

Favorable recovery from bilateral loss of somatosensory evoked potentials

OBJECTIVES

Bilateral loss of the cortical somatosensory evoked potentials (SEP) is usually regarded as a strong predictor for a very poor clinical outcome. We present four patients with a favorable recovery from bilaterally absent cortical SEP.

DESIGN

Case series.

SETTING

Neurocritical care unit at the University of Heidelberg.

PATIENTS

Four patients with viral encephalitis, carbamazepine intoxication, head trauma, and left-side, space-occupying hemispheric infarction, respectively.

INTERVENTIONS

Serial recording of somatosensory and auditory evoked potentials, therapy of increased intracranial pressure, including decompressive surgery, hypothermia, and barbiturate coma.

MEASUREMENTS AND MAIN RESULTS

Three patients had an excellent outcome (Glasgow Outcome Scale 4 and 5). In those three patients, the SEP became completely normal during the clinical course. In one patient who remained severely disabled, the SEP became detectable again over the contralateral hemisphere, but remained abnormal. Possible influencing factors were sedative and analgetic drugs in all patients, and hypothermia and barbiturate coma in one of the patients.

CONCLUSIONS

The absence of cortical SEP does not invariably imply an unfavorable prognosis. Absent cortical SEP indicates a severe neuronal dysfunction, which may be completely reversible if the underlying disease does not lead to permanent structural damage.

[[Emergency pediatric EEG in mental confusion, behavioral disorders and vigilance disorders: a retrospective study]

Recording of electroencephalogram (EEG) is of value to estimate vigilance states in children as in adults. In order to determine the diagnostic and prognostic value of emergency EEG in case of mental confusion, behavioral disorders and vigilance disorders in childhood, we conducted a retrospective study in 397 children (aged 2 months to 16 years). EEG was recorded less than 24 hours after an emergency consultation for acute confusion or acute behavioral disorder (n = 106) or after admission to the intensive care unit for comatose stage (n = 291). EEG gave diagnostic indications mainly in case of convulsive pathology or hepatic encephalopathy. In comatose children, we established a 4-stage EEG scale of increasing severity. This classification was compared to EEG scales already published in the literature and appeared very similar to that from Pampiglione and Harden, established in 150 children after cardiac arrest. A highly poor prognostic value was associated with burst-suppression post-anoxic patterns and with isoelectric records signaling brain death. Our classification of emergency EEG patterns is mainly helpful in these two situations, but does not exclude strict and repeated clinical and EEG follow-up in other cases, as a relatively preserved initial EEG may later deteriorate.

Auditory and somatosensory evoked potentials in coma following spontaneous cerebral hemorrhage: early prognosis and outcome

The aim of this study was to check the prognostic power of auditory brain-stem responses (ABRs) and somatosensory evoked potentials (SEPs) in coma following spontaneous cerebral hemorrhage. Seventy patients comatose following subarachnoidal or hypertensive hemorrhage were submitted to ABR and SEP recordings during the acute phase of clinical course. Twenty-one patients survived (30%), two remained vegetative (2.9%) and 47 died (68.1%). The Glasgow Coma Score (GCS) was significantly related to the outcome (P < 0.001), but showed a low sensitivity, since about 50% of patients with GCS = 5-8 died or remained vegetative. ABRs and SEPs showed a much closer correlation with outcome (P < 0.001): their combined use allowed there to be a sensitivity of 96%, a specificity of 90% and a predictive power of 96%; the relative risk of poor outcome in patients with at least one abnormal modality was equal to 223 times the one for patients with normal evoked potentials. Moreover, in surviving patients a significant relationship appeared to exist between abnormalities of SEPs during the acute phase and the severity of disability. Our results confirm the prognostic effectiveness of short latency evoked potentials in cerebral hemorrhage: they are far superior to clinical data, being able to yield a marked decrease of falsely optimistic predictions.

Prognosis in anoxic and traumatic coma

This article presents a systematic review of the prognostic factors in coma caused by hypoxia and anoxia, and traumatic head injury. In the case of anoxic coma, poor prognosis can be determined very accurately at the bedside by the lack of brainstem reflexes assessed at day three post-insult. Electroencephalogram (EEG) and evoked potentials (i.e., auditory and somatosensory) detect additional patients with poor prognosis. Clinical examination is not as helpful in the case of traumatic coma. Evoked potentials performed within the first week detect approximately half of patients with a poor prognosis. EEG adds only a small amount of prognostic information.

Hypoxic brain injury: evaluation by single photon emission computed tomography

Single photon emission computed tomography (SPECT) with 99mTc-labeled hexamethylpropylene-amine oxime (HMPAO) was used to evaluate cerebral blood flow in 6 patients with hypoxic brain injury (HBI). The SPECT scans were compared with electroencephalograms (EEGs), magnetic resonance imaging (MRI) scans, or computer tomography (CT) scans. The findings on SPECT scans in all 6 patients supported the clinical impression of HBI. SPECT showed decreased perfusion in regions of the brain including the hippocampus, cerebellum white matter, rostral brain stem, the cortex, and occiput. MRI, CT, and EEG provided information that was often not representative of HBI. It was believed that SPECT provided more useful information in the identification of HBI. SPECT imaging with 99mTc HMPAO appears to be a valuable adjunct for evaluation and clinical diagnosis of HBI patients.

Prediction of outcome in patients with anoxic coma: a clinical and electrophysiologic study

OBJECTIVE

To evaluate and compare the predictive powers of clinical examination, electroencephalography (EEG), and studies of short-latency somatosensory evoked potentials in determining the prognosis in anoxic coma.

DESIGN

Prospective case series of patients in anoxic coma, whose prognoses were uncertain based on previously established clinical criteria. The clinical features, EEG, and somatosensory evoked potentials results were correlated with outcome.

SETTING

A 40-bed intensive care unit in a university teaching hospital.

PATIENTS

Thirty-four consecutive patients admitted over a 2-yr period with anoxic coma as the principal diagnosis.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Twenty-seven (79%) patients never recovered consciousness and seven (21%) patients made a good recovery. One of six patients whose pupillary reflexes were present but whose other cranial nerve reflexes were absent on day 1 recovered, but none of the seven patients with these features still present on day 3 survived. None of the patients with motor responses of extension to painful stimuli or worse on days 1 or 3 recovered. The EEGs were classified into benign, uncertain, and malignant categories. The results of both EEG and somatosensory evoked potentials studies were strongly associated with outcome. With malignant EEG, the sensitivity was 74%, the specificity was 71%, and the positive predictive value was 90% [corrected] for the prediction of no recovery (death or persistent vegetative state). However, two patients with an initially malignant EEG eventually made a good recovery. The sensitivity for low amplitude or absent somatosensory evoked potentials for prediction of no recovery was 66%. There were no falsely pessimistic predictions with somatosensory evoked potentials, as all 18 patients with absent or low-amplitude responses had no recovery (specificity and positive predictive value were 100%). EEG and somatosensory evoked potentials studies were complementary to clinical examination in the determination of prognosis. Using a combined clinical and electrophysiologic approach, 63% of patients who had no recovery could be identified by day 3. Repeat EEG and somatosensory evoked potentials studies were of value in patients whose prognoses were uncertain, as their evolution invariably correlated with outcome.

CONCLUSIONS

Based on the present data and a literature review, we propose that clinical examination combined with the results of EEG and somatosensory evoked potentials can be used to establish an early, definitive prognosis in a significant proportion of patients in anoxic coma. On day 3 or thereafter, patients with motor response of extension to pain or worse and malignant EEG, or those patients with flexor posturing or worse and bilaterally absent cortical somatosensory evoked potentials invariably have poor outcome. However, some patients with initially malignant EEG and normal somatosensory evoked potentials may recover and should be supported until their prognoses become more definitive.

Alpha, theta and alpha-theta coma: a clinical outcome study utilizing serial recordings

Alpha coma (AC), theta coma (TC) and alpha-theta coma (ATC) are transient clinical-electroencephalographic phenomena which do not differ from each other in etiology or outcome and are indicative of a severe disturbance in thalamo-cortical physiology. Although most patients do poorly, these patterns are not reliably predictive of outcome, regardless of etiology. We found that AC, TC or ATC usually change to a more definitive pattern by 5 days from coma onset. EEG reactivity in subsequent patterns is relatively favorable, while a burst-suppression pattern without reactivity is unfavorable in anoxic-ischemic encephalopathy.

Follow-up studies of somatosensory evoked potentials and auditory brainstem evoked potentials in patients with post-coma unawareness (PCU) of traumatic brain injury

Some patients who suffer severe traumatic brain injury (TBI) fail to recover higher brain functions in spite of giving the appearance of sleep-wake cycles. Such a state is called post-coma unawareness (PCU) and varies in type and degree. Patients may remain in this state for months or even years. This study focused on the follow-up of upper-limb somatosensory evoked potential (USEP) measurements and auditory brainstem responses (ABR), with an emphasis on dynamic changes, in 10 patients with PCU resulting from TBI. The prognostic value of USEP and ABR was evaluated. Results showed that the presence of ABR in PCU patients had no prognostic value, because ABRs were found both in patients who recovered and those who did not, even a year after the trauma. The presence of normal ABR in PCU patients may suggest that the brainstem has been spared in the pathoanatomy of the PCU condition, with the significant damage occurring above this level, in cortical and subcortical (that is, hemispheral) areas. USEP was graded using the new system of Houlden [1] for 'acute' comatose patients. It was found that USEP measurements had some prognostic value in PCU patients. Most of the patients who remained in the PCU state had grade 2 or less initially, whereas most of the patients who later recovered or achieved at least a 'reduced life' state were grade 4 or more. On initial testing (when all patients were still in the PCU state), defined cortical potential (mainly in the slope of the building NI potential) was seen in only some of the patients who later recovered.(ABSTRACT TRUNCATED AT 250 WORDS)

A physiological coma scale: grading of coma by combined use of brain-stem trigeminal and auditory evoked potentials and the Glasgow Coma Scale

Forty-five comatose patients were prospectively studied by means of clinical examination and evoked potentials. In each patient, clinical data included Glasgow Coma Scale (GCS) score, age, pupillary response to light, corneal reflex, and eye movements. Neurophysiological evaluation was based on brain-stem trigeminal evoked potentials (BTEPs) and brain-stem auditory evoked potentials (BAEPs). For each physiological test, a progressive grading system was designed. This system was based on the evaluation of central conduction times along the trigeminal and the auditory pathways within the brain-stem. The accuracy of the clinical and the neurophysiological indicants in predicting "favorable" or "unfavorable" outcome was assessed singly and in combination. Of the clinical indicants, the GCS provided the most accurate prognosis (80%). Similar results were provided by the BAEP and the BTEP, with significant improvement in the confidence of outcome prediction. No significant difference in the accuracy of outcome predictions could be found between combined clinical data and neurophysiological data. However, the combination of clinical and neurophysiological data markedly increased both the accuracy and the confidence of outcome prediction, reaching 86% correct predictions at the over 90% confidence level with only 2% false pessimistic errors. According to these findings, a clinical-physiological coma scale, the trigeminal-auditory Glasgow (Coma Scale) score (TAG score) was designed. The TAG score demonstrated the highest accuracy at each confidence level as compared to other single indicants. We concluded that the TAG score may improve the evaluation of deep comatose patients and assist the physician in the management of such patients.

Density spectral array, evoked potentials, and temperature rhythms in the evaluation and prognosis of the comatose patient

Glasgow Coma Scale (GCS), density spectral array (DSA), EEG, BAEP and circadian temperature rhythm were studied in comatose patients in order to determine level of arousal and appraise the prognostic capability of these combined measures. Subjects were 29 comatose patients in the neurosurgical ICU at the Rambam Medical Center suffering from head trauma, vascular disorders or metastatic growth. Results show that best prognostic capabilities were for DSA, GCS and BAEP, in that order. As a single parameter physiological response to a sound stimulus (increase in EMG, change in EEG frequency and appearance of sharp waves or k-complex) was the single best predictor for outcome, with significant response rates for the good, deficit, vegetative and death outcomes at 83%, 57%, 37% and 18%, respectively. Rectal temperature was analysed for 24 h circadian periodicity. Daily acrophases were found to shift forward or backward on the level of about 2-7 h a day with fluctuations about a stable or unstable mean. The absence of 'free-running rhythms' associated with environmental isolation studies might reflect an ability to respond to environmental Zeitgerbers while unconscious. Temperature oscillations as well as 24 h rhythms were found even in the most severely brain-damaged patients, reflecting the resilience of the circadian oscillators in the brain to trauma.

Multimodality evoked potentials (auditory, somatosensory and motor) in coma

Auditory brainstem responses (ABRs) have proved to be significantly related to outcome, both in severe head injury and brain hemorrhage. Nevertheless, the usefulness of ABR is limited by the anatomic extent of the investigated pathways. The combined use of ABRs and somatosensory evoked potentials (SEPs) improves the outcome prediction in comparison to the use of only one modality. It mainly decreases the rate of false negatives, since patients with severe hemispheric damage sparing the brain stem may have a poor outcome despite normal ABRs. The use of motor evoked potentials (MEPs) from magnetic transcranial stimulation is also significantly related to outcome: it appears to be far superior to the clinical evaluation of motor responses, while the combined use of MEPs and SEPs gives a new opportunity of checking sensorimotor dysfunction. ABRs and SEPs may also be useful tools in the confirmation of brain death, the kernel of which is the assessment of brainstem death: they allow to check lemniscal pathways, which cannot be properly evaluated by clinical examination, and provide an objective confirmation of absence of brain stem activity.

Visual evoked potentials and electroretinography in brain-dead patients

Visual evoked potentials and electroretinograms were elicited by light-emitting diode stimulation and recorded simultaneously, with cephalic and noncephalic references, in 30 normal subjects and in 30 brain-dead patients. A characteristic pattern was found in the group of patients: when a cephalic reference was used for both visual evoked potentials and the electroretinogram, the a- and b-waves of the electroretinogram were recognized in all patients, and visual evoked responses consisted of waves with inverse polarity, similar morphologic characteristics, the same latency, and less amplitude than those of the electroretinogram. When a noncephalic derivation was chosen for the electroretinogram and visual evoked potentials, electroretinogram did not change in either morphologic features or latency, whereas the visual evoked potential channel showed no response. Only in two cases was it possible to record waves in the visual evoked potential lead with a noncephalic reference, showing a spread of the electroretinogram to the occipital area, with a considerably reduced amplitude. These results suggest that, although contamination of visual evoked potential records by the spread of the electroretinogram to the occipital area could occur, it is easy to confirm the absence of a true cortical visual response in brain-dead patients by means of a noncephalic reference. This pattern clearly confirms that in the visual pathways of brain-dead patients, electrical activity is confined to the retina.

The effectiveness of directed multisensory stimulation versus non-directed stimulation in comatose CHI patients: pilot study of a single subject design

In view of the difficulties in finding control groups in sensory stimulation research, a single case methodology was explored. A pilot study was conducted on six comatose CHI patients in a neurosurgical intensive care unit. Each patient was given alternating weeks of directed multisensory stimulation (SDS) and non-directed stimulation (NDS) for half an hour a day in an ABAB single subject design. Eye movement, motor and vocal response to stimulation were recorded using the Sensory Stimulation Assessment Measure (Rader Scale). Comparisons of eye movement and motor responses on the Rader Scale appeared to indicate a greater degree of responsiveness to the SDS as compared with the NDS treatment. Overall improvement levels on the GCS, Rancho Scale and Western Neurosensory Stimulation Profile are discussed. The results are interpreted as indicative of the potential value of using single case methodology in this population, and future research directions are also discussed.

[Importance of evoked potentials in the evolutive prognosis of coma during cerebral anoxia in adults]

Ten cases of postanoxic coma have been studied. A clinical neurological examination with study of brainstem reflexes and the EEG recording were made on the first day (J1), the third day (J3) and the tenth day (J10) after the start of the coma. A recording of the visual evoked potentials, the brainstem evoked potentials and the somatosensory potentials combined was made at the same time. A clinical examination is carried out one month after the coma when the patient survives. According to the initial clinical examination, we distinguished 3 groups of subjects. The results show that in group III the visual evoked potentials such as EEG have a slightly significant prognostic value; frequently the near outcome lead to death whereas EEG activity persists and the visual evoked potentials disappear later. On the other hand, the association of brainstem evoked potentials and somatosensory potentials clearly has a higher prognostic value in this group. The disappearance of the shortest brainstem responses and the cortical somatosensory responses is clearly an unfavourable prognosis. This disappearance associated with the end EEG activity is the absolute proof of brain death. On the other hand, the persistence of these responses is of a better prognosis at least on the survival level, but their degradation during evolution is unfavourable.

Evaluation of the central nervous function in resuscitated comatose patients by multilevel evoked potentials

Multilevel evoked potentials were examined in 17 patients who became comatose after cardiac arrest and resuscitation. In 4 patients, the P1 through N3 components of the somatosensory evoked cerebral potential (SECP) were present altogether within 100 ms after the ischemic insults. They all subsequently regained consciousness, though three of them developed intelligence and motor disturbances to some extent. In 11 patients who regained consciousness, or remained in a vegetative state, the evoked potentials which reflect brainstem functions, such as the auditory evoked brainstem potential, the R1 wave of the orbicularis oculi reflex and the slow positive wave of the somatosensory evoked brainstem potential, were recognized. The somatosensory evoked spinal potential and spinal monosynaptic reflex showed normal appearances in the state of vegetation and even after the determination of brain death. The measures of SECP could be useful in predicting restoration of consciousness.

SEP testing in deeply comatose and brain dead patients: the role of nasopharyngeal, scalp and earlobe derivations in recording the P14 potential

Median nerve somatosensory evoked potentials (SEPs) were tested in 50 patients (20 brain dead, 18 comatose and in 12 progressing from coma to brain death, i.e., 32 cases with brain death and 30 cases with coma were recorded). Derivations were taken from nasopharynx, earlobes, scalp, and neck using cephalic and non-cephalic references. Cortical and subcortical SEP components were evaluated, focussing on the P14 potential. There is evidence that rostral and caudal parts of the P14 generator (lemniscus medialis) are differently affected in brain death, resulting in an abolition of the rostral part, while occasionally leaving intact for some time the caudal part. Non-cephalic referenced scalp records pick up the whole P14 dipole, whereas nasopharyngeal and earlobe derivations pick up different parts of P14, depending on the reference used. Scalp-to-nasopharynx records derive the most rostral part of P14; this "rostral P14" was bilaterally lost in all brain dead patients, but preserved in all deeply comatose patients with diffuse brain-stem injuries. Scalp-to-earlobe records, in contrast, picked up a P14 dipole segment reaching more caudally, resulting in a P14 potential also in brain dead patients. It is concluded that midfrontal scalp-to-nasopharynx derivations give the most valuable contribution to the electrophysiological assessment of brain death versus deep coma.

Brain-stem auditory evoked potentials and brain death

BAEP records were obtained from 30 brain-dead patients. Three BAEP patterns were observed: (1) no identifiable waves (73.34%), (2) an isolated bilateral wave I (16.66%), and (3) an isolated unilateral wave I (10%). When wave I was present, it was always significantly delayed. Significant augmentation of wave I amplitude was present bilaterally in one case and unilaterally in another. On the other hand, in serial records from 3 cases wave I latency tended to increase progressively until this component disappeared. During the same period, wave I amplitude fluctuations were observed. A significant negative correlation was found for wave I latency with heart rate and body temperature in 1 case. Two facts might explain the progressive delay and disappearance of wave I in brain-dead patients: a progressive hypoxic-ischaemic dysfunction of the cochlea and the eighth nerve plus hypothermia, often present in brain-dead patients. Then the incidence of wave I preservation reported by different authors in single BAEP records from brain-dead patients might depend on the moment at which the evoked potential study was done in relation to the onset of the clinical state. It is suggested that, although BAEPs provide an objective electrophysiological assessment of brain-stem function, essential for BD diagnosis, this technique could be of no value for this purpose when used in isolation.

Somatosensory evoked potentials in prolonged postcomatose unawareness state following traumatic brain injury

Somatosensory evoked potentials (SEPs) were found by several authors to have a prognostic value in traumatically brain-injured (TBI) patients and can serve for monitoring changes in the state of TBI patients. Most of the studies were performed in the acute phase of trauma and most of reports have dealt with the short-latency components. The present study reports on seven patients (mean age 26.2 years) who suffered severe blunt TBI and were in prolonged post-comatose unawareness (PCU) state, in whom early and late SEP components were recorded at least 5 weeks after sustaining trauma. The SEPs studied could not reveal a uniform pattern apart from prolonged central conduction time (CCT), which was common to all patients. This may be due to individual non-homogeneous patterns of brain damage in our severe TBI patients. Meaningful late recovery of consciousness occurred in one patient and correlated with shortening of CCT. We suggest that the prolonged CCT found in our patients is related to diffuse subcortical axonal injury and that the shortened CCT found during the second examination in this patient actually reflects late partial recovery--either structural or functional--of affected brain regions. This patient is also an example of the possible relationship between reduction of CCT and recovery of consciousness a long time after injury.

Spatial mapping of SEP in comatose patients: improved outcome prediction by combined parietal N20 and frontal N30 analysis

The aim of this study is to evaluate whether SEP spatial mapping can improve outcome prediction in comparison to the conventional SEP recordings. Twenty patients comatose as a result of head injury or cerebral vascular disorders were submitted to 19-channel SEP mapping from median nerve stimulation. SEP recording were performed within the 4th hospital day in 18 cases and over one month from the insult in the remaining two. Nine patients (45%) showed a good recovery or a mild disability, 3 (15%) a severe disability and the rest (40%) died or remained in a vegetative state. Five patients (28%) had bilaterally normal SEP, 5 (28%) the absence of both parietal N20 and frontal N30, while the others (44%) had a dissociation N20/N30 (namely, preserved N20 with absent N30). The SEP mapping was significantly related to the outcome (P = 0.0087) and improved the outcome prediction in comparison to the conventional SEP recordings, allowing to check the presence of frontal N30: in patients with bilaterally present N20 the outcome appeared to depend upon the N30. SEP mapping proved to be a far superior prognostic indicator than the Glasgow Coma Scale. In 3 patients with midline shift on CT scan an abnormal spatial distribution of N20 was disclosed by SEP mapping. Our preliminary results suggest that SEP mapping may improve the assessment of comatose patients in comparison to the use of parietal derivations only.

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.