[The use of EEG in the diagnosis of brain death in France]

Neurophysiological assessment of brain dysfunction in critically ill patients: an update

The aim of this review was to provide up-to-date information about the usefulness of clinical neurophysiology testing in the management of critically ill patients. Evoked potentials (EPs) and electroencephalogram (EEG) are non-invasive clinical neurophysiology tools that allow an objective assessment of the central nervous system's function at the bedside in intensive care unit (ICU). These tests are quite useful in diagnosing cerebral complications, and establishing the vital and functional prognosis in ICU. EEG keeps a particularly privileged importance in detecting seizures phenomena such as subclinical seizures and non-convulsive status epilepticus. Quantitative EEG (QEEG) analysis techniques commonly called EEG Brain mapping can provide obvious topographic displays of digital EEG signals characteristics, showing the potential distribution over the entire scalp including filtering, frequency, and amplitude analysis and color mapping. Evidences of usefulness of QEEG for seizures detection in ICU are provided by several recent studies. Furthermore, beyond detection of epileptic phenomena, changes of some QEEG panels are early warning indicators of sedation level as well as brain damage or dysfunction in ICU. EPs offer the opportunity for assessing brainstem's functional integrity, as well as subcortical and cortical brain areas. A multimodal use, combining EEG and various modalities of EPs is recommended since this allows a more accurate functional exploration of the brain and helps caregivers to tailor therapeutic measures according to neurological worsening trends and to anticipate the prognosis in ICU.

EEG guidelines in the diagnosis of brain death

In France, for the determination and diagnostic validation of brain death the law requires either two EEG recordings separated by a 4-hour observation period, both showing electrocerebral inactivity; or cerebral angiography examination. Since EEG is available in most hospitals and clinics, it is often used in this indication, at the patient's bedside, especially in the context of organ donation. However, very precise methodology must be followed. The last French guidelines date back to 1989, before the development of digital EEG recording. We present the new guidelines from the Société de Neurophysiologie Clinique de Langue Française. Electrocerebral inactivity may be confirmed when a 30-minute good quality EEG recording shows complete electrocerebral silence, defined as no cerebral activity greater than 2 uV, having first ruled out the possible influence of sedative drugs, metabolic disorders or hypothermia. In the presence of sedative drugs, CT brain angiography will be the gold standard test for this diagnosis. In the newborn, the utmost caution is indicated since electrocerebral inactivity can be observed in the absence of cerebral death. In the infant, the criterion for the observation period to be respected between both EEG recordings needs to be more clearly refined.

[French guidelines on electroencephalogram]

Electroencephalography allows the functional analysis of electrical brain cortical activity and is the gold standard for analyzing electrophysiological processes involved in epilepsy but also in several other dysfunctions of the central nervous system. Morphological imaging yields complementary data, yet it cannot replace the essential functional analysis tool that is EEG. Furthermore, EEG has the great advantage of being non-invasive, easy to perform and allows control tests when follow-up is necessary, even at the patient's bedside. Faced with the advances in knowledge, techniques and indications, the Société de Neurophysiologie Clinique de Langue Française (SNCLF) and the Ligue Française Contre l'Épilepsie (LFCE) found it necessary to provide an update on EEG recommendations. This article will review the methodology applied to this work, refine the various topics detailed in the following chapters. It will go over the summary of recommendations for each of these chapters and underline proposals for writing an EEG report. Some questions could not be answered by the review of the literature; in those cases, an expert advice was given by the working and reading groups in addition to the guidelines.

Emergent EEG in clinical practice

OBJECTIVE

Emergency situations require a rapid and precise diagnostic approach. However, the exact role and value of the electroencephalogram (EEG) in emergent conditions have yet to be clearly defined. Our objective was to determine why clinicians order an emergency EEG, to assess to what extent it helps establish a correct diagnosis and to evaluate the result it has on subsequent patient management.

METHODS

We studied all successive emergency EEGs ordered during a 3-month period in our institution. We analyzed the reasons why each EEG was ordered and interviewed the prescribing clinicians in order to determine the impact the result of the EEG had on the diagnosis and subsequent therapeutic management.

RESULTS

We prospectively studied a total of 111 consecutive recordings. The main reasons for ordering an emergent EEG were: suspected cerebral death (21%), non-convulsive status epilepticus (19.7%), subtle status epilepticus (14%) and follow-up of convulsive status epilepticus (11.2%). In 77.5% of the cases the clinicians considered that the EEG contributed to making the diagnosis and that it helped confirm a clinically-suspected diagnosis in 36% of the cases. When subtle status epilepticus (SSE) or non-convulsive status epilepticus (NCSE) was suspected, the diagnosis was confirmed in 45% and 43.3% of the cases, respectively. In 22.2% of the requests involving follow-up of convulsive status epilepticus after initial treatment, the EEG demonstrated persistent status epilepticus. It resulted in a change in patient treatment in 37.8% of all the cases. When the EEG helped establish the diagnosis, patient treatment was subsequently modified in 46.6% of the cases.

CONCLUSIONS

This prospective study confirms the value of an emergent EEG in certain specific clinical contexts: the management of convulsive status epilepticus following initial treatment or to rule out subtle status epilepticus. An emergent EEG can also be ordered if one suspects the existence of non-convulsive status epilepticus when a patient presents with mental confusion or altered wakefulness after first looking for the specific signs suggesting this diagnostic hypothesis.

SIGNIFICANCE

After 50 years of development and use in daily practice, the EEG remains a dependable, inexpensive and useful diagnostic tool in a number of clearly-defined emergency situations.

[The electroencephalogram is not an adequate test to confirm the diagnosis of brain death]

PURPOSE

In France, legislation mandates that the clinical diagnosis of brain death be confirmed by one paraclinical test before organ donation is allowed. That test may be either the electroencephalogram (EEG) or cerebral angiography. We report a case in which the clinical diagnosis of brain death was first confirmed by two EEGs performed according to the French guidelines, but ruled out by cerebral angiography. Considering that the EEG is no longer recommended to establish the diagnosis of brain death, we discuss the relevance of maintaining the EEG for brain death diagnosis in France.

CLINICAL FINDINGS

A 58 yr-old man was admitted to the intensive care unit because of coma secondary to a massive subarachnoid hemorrhage with herniation below the falx shown by computed tomography. Clinical criteria of brain death were rapidly present. Two EEGs first confirmed the diagnosis but a four-vessel cerebral angiography was finally performed because the patient moved spontaneously. This cerebral angiography showed flow in the right internal carotid artery. A computed tomography performed the next day definitely confirmed the absence of brain death and organ donation did not occur.

CONCLUSIONS

This case demonstrates the limitations of the EEG for this indication and suggests that angiography should be preferred. French legislation is probably maladjusted and would benefit by incorporating guidelines of other countries like Canada. International harmonization of criteria for brain death diagnosis would also be welcome.

Place de l’EEG dans le diagnostic de mort encéphalique

Brain death diagnosis is based upon several clinical and paraclinical criteria that have been legally defined. There is a medico-legal protocol when brain death diagnosis is made in order to allow organ removal for a possible transplantation. In France, EEG or cerebral arteriography must legally be used to confirm a clinical brain death suspicion. There is a specific procedure to perform an EEG to confirm the diagnosis of brain death. However all the criteria have been made using conventional paper EEG, while numerized is now used. The comparison of EEG recording using both analogical and numerised acquisition allow us to report several recommendations to use EEG for brain death diagnosis.

[Emergency EEG: actual indications and results]

PURPOSE

The indications of emergency electroencephalogram (eEEG) were defined by a French consensus conference in May 1996. We retrospectively confronted the recommendations with the actual requests for emergency EEG in our University hospital, in order to determine the contribution of the eEEG in the most frequent clinical situations encountered.

MATERIAL AND METHOD

Three hundred and twenty nine consecutive eEEGs over a 6-months period were retrospectively analyzed.

RESULTS AND CONCLUSION

The most frequent indications were presumption of brain death (13%), convulsive status epilepticus after treatment (12.1%), and suspicion of nonconvulsive epilepticus status (10.6%). More than one third of the requests (38.6%) were not in conformity with the recommendations of the consensus conference. The contribution of the EEG is much improved by the application of the consensual criteria. Thus, the EEG remains essential for the management of convulsive status epilepticus after treatment, to seek a subtle epilepticus status or a nonconvulsive epilepticus status. Conversely, the EEG did not prove useful in emergency after a transient loss or alteration of consciousness or a focal, non-febrile, neurological transient or permanent deficit.