A critique on the concept of "brain death".

• Author: Karakatsanis, K.G.

Abstract: 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.

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The clinical findings of "Brain Death" ("BD") were first described by French investigators in 1959, but they did not equate this entity with death itself. (1) The ad hoc Committee of the Harvard University Medical School defined irreversible coma, with no discernible central nervous system activity, as a new criterion for death in 1968. (2) The reasons for this redefinition of death, according to the afore-mentioned Committee, were (1) the need to bring relief to the families of the sick; (2) free up beds in the Intensive Care Units and (3) remove the grounds for objecting to the obtaining of organs for transplantation.

Two criteria were considered for determining "BD": either the irreversible loss of all the functions of the entire brain, including the brain stem, (4) or the irreversible loss of the functions of the brain stem only. (5)

The concept of "BD" has been accepted worldwide but there is no global consensus in diagnostic criteria, especially for the apnea testing using a pC[O.sub.2] target, which is recommended in only 59% of the surveyed countries. (6)

Although "BD" has been accepted by most investigators, opinions to the contrary have been expressed both in the distant past and recently. It has been argued that "BD," either when referring to the entire brain or to the brain stem alone, is a concept without precise clinical or pathological basis and, for this reason, the criteria employed in its diagnosis are arbitrary. (7) It has also been said that "it is difficult or almost impossible to have diagnostic standards for a condition that has never been adequately defined." (8) Likewise, in Europe English anesthetists consider that the current criteria do not suffice to demonstrate that the entire brain stem is invariably dead (9) and that the "BD" organ donors "are not by any definition dead." (10)

Are there vegetative functions in "brain dead" patients?

During the last thirty-four years, since the notion of "BD" was asserted, there has been enough evidence found in "brain dead" patients to determine the following:

1. The existence of hypothalamic-endocrine functions. (11) Some investigators argue that the pituitary gland is supplied through extracerebral circulation, so the maintenance of hypophyseal endocrine activity is not inconsistent with the diagnosis of "BD." Nevertheless, maintaining endocrine activity also includes various integrated neuro-endocrinic functions (e.g. regulation of salt and water balance, as is seen in a high percentage of these patients, (12) temperature control, (13) increase of the levels of growth hormone after IV injection of insulin (14)) in which hypothalamus is also involved in "brain dead" patients. Since the current criteria for the diagnosis of "BD" in the USA, which presuppose the loss of all the functions of the entire brain, are not fulfilled, it is concluded that in these cases the clinical diagnosis of "brain death" is not valid.

2. The maintenance of a stable hemodynamic state usually for a few days--but exceptionally for weeks and even months (15)--in a high percentage of cases (30-78%), (16) depending on the time of examination from the outset of diagnosis. It is worth noting that according to the representative of the American Academy of Neurology the stable hemodynamic state is compatible with the diagnosis of "BD" (17); nevertheless, the same investigator concludes in a recent publication that "one should doubt a clinical diagnosis of brain death in a patient whose condition remains stable." (18)

3. The maintenance of actual electrocerebral activity, (19) even in the absence of demonstrable cerebral blood flow. (20) According to Grigg et al. the EEG activity was present in eleven out of fifty-six patients for a mean of 36.6 hours and a maximum of 168 hours after diagnosis; nine of the eleven patients had low-voltage theta or beta EEG activity throughout the observational period. In two of the eleven patients the EEG activity resembled that of physiologic sleep. (21) Thus, it is clear that the maintenance of EEG activity is evidence of viability of at least a part of the brain. Furthermore, the continuing EEG activity in "BD" patients for many days even in the absence of measurable cerebral blood flow (22) substantiates that there are inconsistencies in the tests-criterion relationships.

4. The uptake of the radiopharmaceutical Tc99m-HMPAO, which is taken up by viable cerebral cells (23) (either by neurons, glial cells or both) in the cerebrum, (24) in the cerebrum and/or the cerebellum (25) or in the basal ganglia and in the brain stem. (26) The afore-mentioned findings--especially the demonstrated posterior fossa perfusion--in "BD" patients (27) underline additional inconsistencies in applying cerebral blood flow patterns to confirm "BD."

5. Some "brain dead" patients show evidence of some environmental responsiveness. Thus, all those who are involved in organ retrieval from "brain dead" donors know that these patients show a clear hemodynamic response to surgical incision. "This suggests that integrated neurological function at a supraspinal level may be present in at least some patients diagnosed as brain dead." (28) Furthermore, an English anesthetist considers that the afore-mentioned hemodynamic responses are mediated by the brain stem and are due to pain caused by surgical incision in "brain dead" patients for the purpose of organ harvesting. (29)

   It has also been noted in "brain dead" patients "reproducible eye opening, but with only a minimal eyelid elevation barely showing the beginning of an iris in response to twisting of a nipple. The reflex pathway is not known." (30)

6. Many "brain dead" patients retain "complex, spinal responses," which were not identified as known reflexes by the investigators of the NINCDS study. (31) Even though in everyday clinical practice a lower percentage is observed, percentages up to 75% are cited. (32) These movements have been observed during the apnea test, at the time of abdominal incision for organ retrieval and also in the morgue. (33) It is worth noting that when these movements are recurrent, paralytic agents are recommended to prevent them during organ retrieval. (34)

   Some of these complex movements, known as "Lazarus sign," (35) have recently been defined as "semipurposeful" and "semidirected." (36) Such movements have also been noticed in the absence of hypoxia (37) or hypotension. (38) In a remarkable "brain dead" case, presented in 1982, these movements--which included hands in a praying position--persisted spontaneously for four days, but were elicited by pain and plantar stimulation for an additional five days. (39)

   Nevertheless, according to the Ad Hoc Committee of the University of Harvard there are neither spontaneous movements nor elicitable reflexes in the "brain dead" patients. (40)

7. It has been shown that some "brain dead" patients retain the jaw jerk and snout reflex (41) while other patients manifest facial myokymia (42) or decerebrate like posturing of the upper limbs. (43) All these reflexes "impli(y) some living neurons in the brain stem and are thus not compatible with `BD' diagnosis." (44)

8. Data concerning the apnea test are inadequate. (45) It is well known that most investigators consider that if spontaneous respiration is not resumed, when the partial pressure of the arterial carbon dioxide reaches the arbitrary (46) value of 60 mm Hg (8 kPa), the apnea test is characterized as positive. (47) Nevertheless, there are recent suggestions to continue the apnea test until the critical value of the pC[O.sub.2] exceeds 90 mmHg (12 kPa) or even 100 (13.3 kPa). The reason for the above suggestions is that spontaneous respiration has been resumed with values of pC[O.sub.2] well above 60 mmHg (8 kPa) (48)--in one instance at 91 mmHg (12.1 kPa). (49)

   Furthermore, the duration of the apnea test was three minutes according to the Ad Hoc Committee of Harvard University, (50) four minutes according to the suggestion of Mohandas and Chou (51) and eight to twenty minutes according to the recent literature. (52)

9. Some "brain dead" patients retain auditory and somatosensory evoked potentials. Thus, in one "brain dead" patient there was preservation of the central auditory pathways for seventy two hours, (53) in an infant there was only delay in brain stem conduction and intact left median nerve somatosensory evoked potential pathways (54) and in seven of eleven clinically "brain dead" patients there were short latency somatosensory evoked potentials in central subcortical afferent pathways. (55)

   The clinical signs of "BD," especially when it is the result of an hypoxic injury, are not adequate for the investigation of all the pathways which run through the brain stem. (56) Some of these pathways can be tested with evoked...