EEG Alone Cannot Diagnose Brain Death


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(Updated 7/18/04)

Horikawa M, Harada H, Yarita M.
Detection limit in low-amplitude EEG measurement.
J Clin Neurophysiol. 2003 Feb;20(1):45-53.
"Electrocerebral inactivity for the determination of cerebral death is defined as no findings of EEG greater than the amplifier's inherent internal noise level when recording at increased sensitivity. A surface biopotential electrode contains two interfaces composed of skin gel (electrolyte) and gel electrode (metal), each forming a noise source. The power spectral density, S(f), of extremely low noise signals was obtained by means of autocorrelation and fast Fourier transformation. Interelectrode resistance, R(f), was measured with synchronous rectification. The formula of equivalent noise resistance R(n) = S(f)/4kT, where k is the Boltzmann constant and T is room temperature in Kelvin, gives a resistance that generates the thermal noise corresponding to the measured S(f). Rn/R is a parameter derived from normalization by R. When Rn/R = 1, measured noise contains thermal noise only. Meanwhile, Rn/R > 1 indicates presence of excess noise, such as 1/f, and tissue noise in addition to the thermal noise. Mean square root (Rn/R) of the scalp noise was 10.8 at 10 Hz, showing existence of excess noise. The study results suggest that it is necessary to take excess noise into consideration in the measurement of low-amplitude EEG for the determination of cerebral death." [Abstract]

Karakatsanis KG, Tsanakas JN.
A critique on the concept of "brain death".
Issues Law Med. 2002 Fall;18(2):127-41.
"Since the concept of "brain death" was introduced in medical terminology, enough evidence has come to light to show that the concept is based on an unclear and incoherent theory. The "brain death" concept suffers by internal inconsistencies in both the tests-criterion and the criterion-definition relationships. It is also evident that there are residual vegetative functions in "brain dead" patients. Since the content of consciousness is inaccessible in these patients who are in a profound coma, the diagnosis of "brain death" is based on an unproved hypothesis. A critical evaluation of the role and the limitations of the confirmatory tests in the diagnosis of "brain death" is attempted. Finally it is pointed out that a holistic approach to the problem of "brain death" in humans should necessarily include the inspection of the content of consciousness." [Abstract]

de Tourtchaninoff, M., Hantson, P., Mahieu, P., Guerit, J.M.
Brain death diagnosis in misleading conditions
QJM 1999 92: 407-414
"The necessity of defining brain death (BD) arose from technological development in medical science. The definition of this concept had practical consequences and opened the way to organ donation from BD patients. Nowadays, the imbalance between the number of organs available for transplantation and the size of the demand is becoming critical. In most laboratories, a BD diagnosis is made according to precise criteria and in a well-defined process. BD diagnosis should be improved, not only to assure the safety and to preserve the human dignity of the patient, but also in order to increase the rate of organ donation. By analysing some epidemiological parameters in BD diagnosis and organ donation, it appears that BD diagnoses can be made more often and more rapidly if one has a reliable, accurate, and safe confirmatory test, especially under misleading conditions (hypothermia, drugs, metabolic disturbances). In our experience, the use of multimodality evoked potentials (MEPs) to confirm a BD diagnosis has many advantages: MEPs can be rapidly performed at the patient's bedside, assess the brain stem as well as the cerebral cortex, and are innocuous for the patient. Moreover, their insensitivity to the aforementioned misleading factors is sufficient to distinguish BD from clinical and EEG states that mimic BD. They give an immediate diagnosis, and no delay is required in BD confirmation if there is sufficient cause to account for BD. MEPs are a safe, accurate, and reliable tool for confirming a BD diagnosis, and their use can improve the organ donation rate while preserving the safety of the patient." [Full Text]

Heckmann JG, Lang CJ, Pfau M, Neundorfer B.
Electrocerebral silence with preserved but reduced cortical brain perfusion.
Eur J Emerg Med. 2003 Sep;10(3):241-3.
"Isoelectric electroencephalogram in conformance with clinical findings is strongly suggestive of brain death. In clinical practice, isoelectric electroencephalogram in not-brain-dead patients is rarely seen. We report on a 53-year-old patient who suffered ischaemic encephalopathy after cardiopulmonary arrest. He had residual brainstem function with sufficient spontaneous breathing and evidence of cerebral blood flow on single photon emission computed tomography scan, but his electroencephalogram was isoelectric. He survived this condition for more than 7 weeks. This case demonstrates that isoelectric electroencephalogram can not be equated with brain death, and that in prognostic assessment both clinical findings and supportive technical methods are mandatory." [Abstract]

Nau R, Prange HW, Klingelhofer J, Kukowski B, Sander D, Tchorsch R, Rittmeyer K.
Results of four technical investigations in fifty clinically brain dead patients.
Intensive Care Med. 1992;18(2):82-8.
"Fifty consecutive patients (aged 19-77 years, median 56 years) with primary cerebral diseases and the clinical signs of absent cortical and brainstem function were subjected to electroencephalography (EEG), brainstem acoustic evoked potentials (BAEP), extracranial Doppler ultrasonography (ECD) and arterial digital subtraction angiography (DSA). In the majority of cases the results of the technical tests agreed with the clinical signs and were suggestive of brain death. However, in one patient EEG revealed clear bioelectrical activity. In 6 cases, doubts existed about whether the EEG was isoelectric; in 3 of the 6 cases biological activity might have been present. In 31 of 42 patients ECD showed a typical pattern of intracranial circulatory arrest, in 9 of 42 ECD revealed a pattern suggestive of the cessation of cerebral blood flow. In four patients BAEP recordings compatible with brain death were recorded 2-3 days before intracranial circulatory arrest. In 2 patients with isoelectric EEG and absent BAEP arterial DSA demonstrated residual perfusion. The findings are discussed in view of the conceptional differences concerning brain death. It is concluded that the strict application of the concept of death of the whole brain requires angiographic demonstration of absent intracerebral blood flow." [Abstract]

Paolin A, Manuali A, Di Paola F, Boccaletto F, Caputo P, Zanata R, Bardin GP, Simini G.
Reliability in diagnosis of brain death.
Intensive Care Med. 1995 Aug;21(8):657-62.
"OBJECTIVE: To compare some of the confirmatory investigations of brain death with clinical criteria in order to achieve the most sensitive and accurate diagnosis of brain death. DESIGN: All patients with isolated brain lesions and Glasgow Coma Scale (GCS) = 3 were subjected to neurological examination after ruling out hypothermia, metabolic disorders and drug intoxications and diagnosed as clinically brain-dead when the brainstem reflexes were absent and the apnea test positive. PATIENTS: 15 patients with clinical diagnosis of brain death entered this study. MEASUREMENTS AND RESULTS: The patients were submitted to the following investigations: electroencephalogram (EEG), transcranial Doppler (TCD) of the middle cerebral arteries (MCA), cerebral blood flow measurements with the i.v. Xe-133 method (CBF) and selective cerebral angiography (CA). EEG was isoelectric in 8 patients while the remaining 7 patients showed persistence of electrical activity. TCD was compatible with intracranial circulatory arrest in 18 MCA districts, compatible with normal flow in 2 and undetectable in 10 out of 30 districts insonated. In CBF examinations, however, all the patients showed a characteristic "plateau" of the desaturation curves lasting through the whole investigation and suggestive of absent cortical flow. CA showed circulatory arrest in both carotid and vertebral arteries. CONCLUSIONS: Our study suggests that cerebral angiography and CBF studies are the most reliable investigations whereas the role of EEG and TCD remains to be determined because of the presence of false negatives and positives." [Abstract]

Okii Y, Akane A, Kawamoto K, Saito M.
Analysis and classification of nasopharyngeal electroencephalogram in "brain death" patients.
Nippon Hoigaku Zasshi. 1996 Apr;50(2):57-62.
"Nasopharyngeally-derived electroencephalogram (EEG) was recorded and digitized in 12 "brain death" subjects with flat-line scalp EEG and loss of auditory brain stem response. The nasopharyngeal EEGs of these cases were classified into three types: Type Ia with complete flat-line, Type Ib with almost but incomplete flat-line EEG, and Type II with low-amplitude slow fluctuations. Digitization of the nasopharyngeal EEG showed that equivalent electric potentials in low frequency bands (delta and/or theta 1) remained within the values of healthy volunteers in Types Ib and II. These results suggested that the tissue in or around the brain stem still functioned in Type 1b and II "brain death" patients. The origin of nasopharyngeal EEG was also discussed in this paper." [Abstract]

Scher MS, Barabas RE, Barmada MA.
Clinical examination findings in neonates with the absence of electrocerebral activity: an acute or chronic encephalopathic state?
J Perinatol. 1996 Nov-Dec;16(6):455-60.
"Although the presence of an isoelectric electroencephalogram (EEG) in an older patient may reflect brain death caused by an acute brain injury, this electrographic abnormality may appear in more diverse clinical situations in the neonate with encephalopathy. During a 6-year period, 20 neonates were identified with a severe encephalopathy on neurologic examination who had at least one isoelectric EEG during their treatment in a neonatal intensive care unit. Seventy-four EEG recordings were obtained including 36 isoelectric EEG records. Partially preserved clinical brain function was present in 15 (75%) of 20 infants at the time an isoelectric EEG was obtained. The initial EEG was isoelectric in 16 of 20 infants. Although electrographic activity reemerged in nine of these infants, significant clinical improvement was seen in only two patients. Thirteen of 20 neonates also had electrographic or other evidence of clinical seizures. Of the five survivors (25%), three had severe neurologic sequelae. The remaining two had either transient or persistent neurologic deficits. An isoelectric EEG may be obtained in the neonate with partially preserved brain function and, therefore, may not be a reliable confirmatory test of neonatal brain death. In addition, serial EEGs not only can help assess the severity of a neonatal encephalopathy but also may correlate with chronic and acute neurologic insults." [Abstract]

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