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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] |
