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.     

Predictive value of P300 event-related potentials compared with EEG and somatosensory evoked potentials in non-traumatic coma

Developments in ethical decision making are increasing demand for more accurate predictions of outcome in coma. New neurophysiologic tests are needed to improve the ability to predict awakening as well as poor outcome. We have recently reported that the P300 event-related potential (P300) correlates with awakening and depth of nontraumatic coma. In this companion study, the predictive value of the P300 was compared with median nerve somatosensory evoked potentials (SEP) and EEG in 20 patients in non-traumatic coma. We also evaluated the predictive value of a simplified grading scale for both the EEG and SEP (the USC SEP scale and USC EEG scale). The resence of a P300 was significantly associated with higher Glasgow coma scores (GCS) and awakening. Severe abnormalities of the somatosensory evoked potentials significantly correlated with the absence of awakening and a low GCS. Moderate abnormalities of the SEP were significantly associated with awakening and higher GCS scores. the EEG was significantly associated with GCS score and severe abnormalities of the EEG were predictive of the absence of awakening and very low GCS scores. The data indicates that the P300 and SEP are more effective than the EEG in predicting awakening, and that the SEP and EEG are more effective than the P300 in predicting poor outcome. We conclude that, in addition to EEG and SEP, the P300 should be considered in the prognostic evaluation of patients in nontraumatic coma. Further, simplified scales for the EEG and SEP are predictive of depth of coma and outcome.     

Predicting outcome in hypoxic-ischemic coma. A prospective clinical and electrophysiologic study.

A prospective analysis of 40 patients with hypoxic-ischemic coma lasting at least 6 h following sudden cardiac arrest was undertaken. The patients, all of whom had preserved brain-stem function, were studied electrophysiologically with electroencephalography (EEG), and median nerve somatosensory evoked potentials (SEPs) within 48 h to establish prognostic indices. Our results indicate that preserved brain-stem function does not necessarily predict favorable outcome following cardiac arrest as 26 of 40 (65%) patients died without awakening. The bilateral absence of cortical evoked potentials predicted death without awakening in 19 of 26 patients (73%) while malignant EEG change was similarly predictive in 11 patients (42%). Bilateral absence of cortical evoked potentials and/or malignant EEG change reliably predicted unfavorable outcome in 21/26 patients (81%). Patients with normal or delayed central conduction time (CCT) as well as 'benign' or 'uncertain' EEG findings had an uncertain prognosis as some entered a persistent vegetative state (PVS) or died without awakening. Fourteen patients (35%) awakened of whom 5 (13%) recovered completely while another 9 (23%) had varying degrees of motor or cognitive impairment. SEP and EEG findings did not distinguish between these outcomes.     

The importance of brain stem evoked potentials in the diagnosis of neurosurgical patients]

The technique of Brainstem Electric Response Audiometry (BERA) is a non-invasive electrophysiologic method used in comatose patients for localization of areas of neuronal and synaptic dysfunction not evident in clinical evaluation. This test has a diagnostic and prognostic value in detection of abnormalities and evaluation of comatose head-injured patients at a reversible clinical stage. In contrast to most clinical signs, brainstem auditory evoked potentials are independent of levels of consciousness, analgesics, sedatives. This test is aetiologically non-specific and must be carefully integrated into the clinical situation. Generators of brainstem auditory evoked potentials are located in the auditory nerve (waves I and II) and brainstem (waves III-V). Patients in acute posttraumatic coma are assessed by means of Glasgow Coma Score (GCS), which is reliable in forecasting a favourable outcome. Patients with a score 8 points have an unfavourable outcome in 16%. Brainstem auditory evoked potentials are reliable predictors of unfavourable outcome. Subsequent brainstem auditory evoked potential testing provides relevant prognostic information, since improvement of graded brainstem auditory evoked potentials indicates a favourable outcome. Progressive deterioration of brainstem auditory evoked potentials indicates irreversible damage and is associated with unfavourable outcome, whereas singular abnormal evoked potentials may result from reversible neuronal dysfunction. The absence of waves III-V associated with the end EEG activity is the proof of brain death. Serial BERA monitoring has been used to evaluate progressive clinical syndromes, such as "uncal herniation" and evolving brain death. The use of serial BERA recordings appeared to improve the outcome predictions in comparison with single BERA tests. A combination of brainstem auditory evoked potentials, somatosensory and visual evoked potentials (multimodality evoked potentials-MEP) provides more information for management of a patient than a single evoked potential modality. The main goal to use BERA is early detection of secondary deterioration in comatose patients suffering from intracranial lesions. The results of brainstem auditory evoked potentials and clinical examination of patients obtained within the acute phase after head injury may indicate increased intracranial pressure (ICP) and incipient transtentorial herniation but do not always predict outcome (GOS). The outcome can be better evaluated later, 3-6 days after head injury. In summary, BERA is a non-invasive, safe and objective method of evaluating patients after severe head injury and adds valuable information for assessment of their outcome.     

Electrophysiological prognostication and brain injury from cardiac arrest

Anoxic coma after cardiorespiratory arrest warrants precocious investigation to establish probable outcome. Electroencephalogram (EEG) may uncover subclinical seizures; EEG grades have provided accurate prognosis of poor and favorable outcomes, but are weakest in those patients in between. Somatosensory evoked potentials now have proven benefit in accurately establishing a poor outcome (death or persistent vegetative state) when cortical responses (N20) are absent. These studies are particularly helpful when clinical examination of coma, early on, might yield uncertain prognosis (i.e., when brain stem reflexes are present). Combining clinical examination with electrophysiology has increasingly yielded multimodality approaches to early prognostication of coma after cardiorespiratory arrest, with more recent studies using event-related and middle-latency potentials showing promise for distinguishing good outcome (to consciousness), from awake but vegetative states. Further studies are warranted for this multimodality approach which, hopefully, may yield more widespread practical use of these testing modalities.     

Comparison of the prognostic utility of VEPs and SEPs in comatose children

Visual evoked potentials and somatosensory evoked potentials were recorded in 37 children in coma soon after admission and then repeatedly during coma and emergence from coma. Evoked potentials were graded in 4 categories, ranging from normal to absent, and then related to patient outcome. Somatosensory evoked potentials were reliable predictors of outcome, particularly if both the initial and early repeated somatosensory evoked potentials were considered. Visual evoked potentials were not as reliable predictors as somatosensory evoked potentials; however, the presence or absence of both was significantly related to outcome. These data are generally consistent with the adult literature. We suggest that somatosensory evoked potentials be the evoked potential of choice in evaluating the prognosis of comatose children.     

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.     

Persistent vegetative state with high cerebral blood flow following profound hypoglycemia

A persistent vegetative state (severe dementia) developed in a 30-year-old man following hypoglycemic coma. Despite the poor clinical outcome, sensory evoked response recovered between 6 and 34 months after the insult. The cerebral blood flow level at rest after 34 months was slightly above the normal range. This finding contrasts with the low cerebral blood flow regularly reported in patients who are comatose or stuporous following severe brain hypoxia-ischemia.     

Normal somatosensory evoked potentials in a child in persistent coma

Somatosensory evoked potentials have been useful in predicting coma outcome in children. We present a patient who failed to recover consciousness after a near-drowning episode and has remained in a vegetative state. The initial and subsequent somatosensory evoked potentials have been normal, illustrating that normal results do not necessarily portend a favorable outcome.     

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.     

Auditory evoked potentials in coma after closed head injury: a clinical-neurophysiologic coma scale for predicting outcome

We studied auditory evoked potentials in 45 head-injured patients. All but three were comatose or stuporous at the time of study. Preservation of brainstem auditory or long-latency auditory evoked potentials predicted good outcome. The Glasgow coma scale (GCS), the clinical subtotal of the neurophysiologic coma scale (NPCS), and the NPCS had predictive accuracies of 71%, 82%, and 82%. Although there were 22 falsely pessimistic predictions with the GCS and 9% with the clinical subtotal of the NPCS, there were no falsely pessimistic predictions with the NPCS.     

Prognostic value of evoked potentials and sleep recordings in the prolonged comatose state of children. Preliminary data.

OBJECTIVES: Sleep recordings and evoked potentials (EPs) were used in five comatose children to evaluate their predictive value for outcome following a severe comatose state. METHODS AND SUBJECTS: The protocol included EEG, Brainstem Evoked Responses (BERs), Somatosensory Evoked Potentials (SEPs) and polysomnography. From 10 to 15 days post-coma (D10 to D15), EEG and clinical examinations were carried out every second day, then one day in four from 15 to 30 days post-coma (D15 to D30), and one day in seven from D30 to six months (M6). Evoked potentials and Polysomnography were recorded on D10-D15 or D30 in the second month (M2) and in M6. Of the five children, three were in anoxic coma and two in traumatic coma. All had extensive lesions and a Glasgow Coma Scale (GCS) score of less than five. The results of the EEG, polysomnographic and EP recordings were compared to the clinical outcome. RESULTS AND CONCLUSION: In the three anoxic comas we observed BER abnormalities and the absence of SEP N20 associated with wide cortical lesions with brainstem extension. Sleep recordings showed major alterations of the wake-sleep cycle without any improvement in M6. Abnormalities included loss of the normal REM-sleep pattern associated with alteration of NREM sleep and periods of increase in motor activity without EEG arousal. This sleep pattern appeared to be associated with involvement of the brainstem. In the two traumatic comas, alterations of the early cortical SEP responses were less severe and the BERs were normal. Some sleep spindles were observed as well as the persistence of sleep cycles in the first weeks post-coma. The combined use of EEG, EPs and polysomnography improved the outcome prediction in comparison with the use of just one modality. EPs and sleep recordings were far superior to clinical evaluation and to GCS in the appreciation of the functional status of comatose children. The reappearance of sleep patterns is considered to be of favorable prognosis for outcome of the coma state, as is the presence of sleep spindles in post-trauma coma. This study showed that EPs and sleep recordings help to further distinguish between patients with good or bad outcomes.     

Proving cortical death after vascular coma: Evoked potentials,EEG and neuroimaging

Objectives

Several studies have shown that bilateral abolition of somatosensory evoked potentials after a nontraumatic coma has 100% specificity for nonawakening with ethical consequences for active care withdrawal. We propose to evaluate the prognostic value of bilateral abolished cortical components of SEPs in severe vascular coma.

Prognostic determination in anoxic-ischemic and traumatic encephalopathies.

Clinical assessment of the unresponsive patient is limited to examination of brainstem reflexes and simple motor responses to stimulation. It is thus difficult, especially if brainstem functions are intact, to give early, accurate prognostic information on comatose patients. Neurochemical tests and imaging have not been validated and have significant limitations. Electrophysiologic investigations provide a window into cerebral function and are tested, clinically useful, safe, available, and inexpensive. Persistent abnormalities of brainstem auditory evoked potentials and short-latency somatosensory evoked potentials reliably indicate the likelihood permanent vegetative state or death. Conversely, the presence of "cognitive" event-related brain potentials (e.g., P300 and mismatch negativity) reflects the functional integrity of higher-level information processing and, therefore, the likelihood of capacity for cognition. A combined clinical and electrophysiologic approach provides optimal prediction of outcome and level of disability.     

N18 in median somatosensory evoked potentials: a new indicator of medullary function useful for the diagnosis of brain death

OBJECTIVES: To record N18 in median somatosensory evoked potentials (SEPs) for deeply comatose or brain dead patients and to demonstrate the usefulness of N18 for the diagnosis of brain death in comparison with auditory brain stem responses (ABRs) and P13/14 in median SEPs, which have been conventionally used as complementary tests for the diagnosis of brain death. METHODS: Subjects were 19 deeply comatose or brain dead patients. Thirteen recordings were performed in deeply comatose but not brain dead conditions, and 12 recordings were performed in brain death. N18 was evaluated in the CPi-C2S lead (or other scalp-C2S leads) to obtain a flat baseline. RESULTS: N18 was preserved in 12 of 13 non-brain dead comatose recordings whereas it was completely lost for all of the 12 brain death recordings. P13/14 in median SEPs was preserved for all the comatose recordings, whereas apparent P13/14-like potentials, usually of low amplitude, were seen in nine of 12 brain death recordings-that is, frequent false positives. The ABRs already showed features which were characteristic for brain death (loss of components other than wave 1 or small wave 2) for four comatose recordings, in three of which N18 was preserved. The last result not only corresponds with the fact that ABRs can evaluate pontine and midbrain functions and not medullary function, but further supports the medullary origin of N18. In the four patients followed up for the course of progression from coma to brain death, N18s preserved in normal size during the comatose state were completely lost after brain death was established. CONCLUSIONS: The N18 potential is generated by the cuneate nucleus in the medulla oblongata in the preceding studies. N18 is suggested to be a promising tool for the diagnosis of brain death because there were no false positives and rare false negatives in the present series for detecting the remaining brain stem function.     

Early prognosis in coma after cardiac arrest: a prospective clinical, electrophysiological, and biochemical study of 60 patients.

BACKGROUND: The univariate study of clinical, electrophysiological, or biochemical variables has been shown to predict the outcome in postanoxic coma in about 50% of patients for each type of variable. Previous studies did not, however, consider the prognostic accuracy of a multivariate approach. METHODS: Sixty patients in coma for more than six hours after cardiac arrest were prospectively examined by means of repeated clinical examinations (including Glasgow coma score (GCS)), EEG, and medianus nerve somatosensory evoked potentials (SEPs). In 16 patients, the early concentrations of serum neuron specific enolase and ionised calcium were also measured. RESULTS: Within the first year after cardiac arrest, 20% of patients made a good neurological recovery; 80% remained in a vegetative state or died. Clinical examination correctly predicted outcome in 58% of patients, SEP in 59%, and EEG in 41%. The combination of clinical examination, SEP, and EEG raised the percentage of correct predictions to 82%, without false pessimistic predictions. Concentrations of serum neuron specific enolase and ionised calcium were of no additional prognostic help. Multivariate regression analysis identified the association of GCS < 8 at 48 hours with abnormal or absent early cortical SEPs as highly predictive of a bad outcome (risk = 97%, 95% confidence interval = 86-99%). CONCLUSION: The combination of GCS at 48 hours, SEP, and if these are non-conclusive, EEG, permits a more reliable prediction of outcome in postanoxic coma than clinical examination alone.     

Prognostic value of dynamic electroencephalogram in comatose patients with different diseased regions

BACKGROUND: It has proved that dynamic electroencephalogram (EEG) is definite in judging the outcome of ischemic hypoxic comatose patients, EEG is more sensitive to the cortical affection, but not sensitive to the subcortical and brainstem affections, thus it is necessary to clarify the indications of this technique in the clinical application. OBJECTIVE: To observe and compare the prognostic value of dynamic EEG and Glasgow coma score in comatose patients with different diseased region. DESIGN: A clinical case-controlled observation. SETTING: Union Hospital of Fujian Medical University. PARTICIPANTS: Sixty-eight comatose patients were selected from the Union Hospital affiliated to Fujian Medical University from June 1998 to January 2005. The diseased regions were identified using cranial CT (n =43) or MR (n =25). According to different primarily diseased regions, the comatose patients were divided into two groups: ① brainstem affection group (n =23): 13 males and 10 females, 14–62 years of age; ② diffuse cortical affection group (n =45): 28 males and 17 females, 23–75 years of age. METHODS: The dynamic EEG and Glasgow coma score were examined in the 45 comatose patients with primarily cortical affection and 22 comatose patients with primarily brainstem affection at acute phase. The patients were followed-up for 3 months to observe the outcome, The termination of outcome judgment was 3 months after attack or the death. The clinical outcome was classified as complete rehabilitation, survived with disability, death or vegetative state. Correlations of dynamic EEG and Glasgow coma score with the outcome of patients were analyzed. The correlations of dynamic EEG grades and Glasgow coma scores with the outcome were analyzed, and the prognostic value of dynamic EEG grades was compared between the two groups. MAIN OUTCOME MEASURES: ① Correlations of dynamic EEG and Glasgow coma score with the outcome of patients; ② Comparison of the prognostic value of dynamic EEG grades between the two groups. RESULTS: All the 68 patients were involved in the analysis of results. ① Correlations of dynamic EEG grades and Glasgow scores and their correlation analysis: EEG grades had significant negative correlation with Glasgow coma scores in both the cortical affection group and brainstem affection group (r =–0.743, –0.564, P < 0.01, 0.05). In the cortical affection group, the Glasgow coma scores and dynamic EEG grades in the patients with the outcome of death or vegetative state were significantly different from those with the outcome of rehabilitation (P < 0.05–0.01). In the brainstem affection group, the Glasgow coma scores were only significantly different between the patients with outcome of rehabilitation and death (P < 0.05), and there was no significant difference in dynamic EEG grades among the three prognostic states (P > 0.05). ② Comparison of the prognostic value of dynamic EEG grades between comatose patients with cortical affection and brainstem affection: The sensitivity, specificity and accuracy were all higher (P < 0.05), while the error rate was lower (P < 0.05) in the cortical affection group than in the brainstem affection group. CONCLUSION: Dynamic EEG was valuable in predicting the outcome of comatose patients with primarily cortical affection, but it was not certainly valuable in those with primarily brainstem affection.     

The usefulness of EEG, exogenous evoked potentials, and cognitive evoked potentials in the acute stage of post-anoxic and post-traumatic coma

Three-modality evoked potentials (TMEPs) have been used for several years in association with the EEG as a diagnostic and prognostic tool in acute anoxic or traumatic coma. Cognitive EPs have been recently introduced. EEG and cognitive EPs provide functional assessment of the cerebral cortex. TMEP parameters can be described by two indices: the index of global cortical function (IGCF) and the index of brainstem conduction (IBSC). Although it remains a unique tool for epilepsy assessment, the value of EEG is largely limited by its high sensitivity to the electrical environmental noise, its dependence on sedative drugs, and its inability to test the brainstem. Major TMEP alterations (absence of cortical activities more than 24 hours after the onset of post-anoxic coma, major pontine involvement in head trauma) are associated in all cases with an ominous prognosis (death or vegetative state). However, even if mild TMEP changes are associated with a good prognosis in 65% (post-anoxic coma) to 90% (head trauma) of cases, some patients never recover despite exogenous TMEPs that are only mildly altered in the acute stage. Thus, cognitive EPs can usefully complement exogenous EPs as a prognostic tool in coma. Indeed, even if the absence of cognitive EPs in comatose patients does not have any prognostic value, their presence implies a very high (more than 90%) probability of consciousness recovery. The major technical challenge for the future will be the development of reliable tools for continuous EEG and TMEP monitoring.     

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.     

Heart rate variability in brain death

The sensitivity and specificity of heart rate variability (HRV) in the corroboration of brain death diagnosis in patients with acute traumatic intracranial lesions was evaluated in 20 patients with clinical criteria of brain death, nine patients in deep coma (Glasgow scale <7) and 18 normal controls, all age matched. The electrocardiogram was sampled at 650 Hz and several parameters of HRV were calculated, in both time and frequency domains. The HRV parameters were significantly lower in the brain death group compared with the deep coma group. Linear discriminant analysis between brain death and deep coma patients was performed on a data set made of nine randomly selected patients with clinical criteria of brain death and nine patients in deep coma. Cross-validation was performed on the remaining 11 patients with clinical criteria of brain death. All patients in the data set were correctly classified (sensitivity and specificity of 100%). All patients in the cross-validation set were correctly classified (sensitivity of 100%). Further studies are necessary to evaluate the specificity of the method in the independent set of deep coma patients and in the follow-up of comatose and vegetative patients to identify irreversibility of HRV. Nevertheless, these results suggest that HRV analysis constitutes a fully sensitive and specific method for assessing brain death in potential organ donors with acute traumatic lesions of the brain. This fast, quantitative and bedside method seems very promising for the early confirmation of brain death, which is an important factor for the success of transplantation procedures and could have a high predictive value of brain death in comatose patients with brain injuries without fully diagnostic criteria.