The neuropathological findings in irreversible coma. A critque of the "respirator"

1. Postmortem examinations were made on 240 of the 459 cases succumbing (52 percent of the deaths) in the Collaborative Study on Cerebral Survival; the central nervous system was examined in 226 cases. 2. The autopsy was performed on an average of 15.3 hours after death. 3. The mean weight of the brains was 1450 plus or minus 196 grams; the mean weight of the brains of patients on whom resuscitation was stopped, presumably on the basis of "cerebral death," was greater than that of the patients succumbing to cardiac failure. There was a tendency for the brain to increase in weight about 24 hours after the initiation of resuscitative measures. At that time, swelling, discoloration, softening, congestion, and brain herniations also became more prominent. 4. On the basis of a survey of American neuropathologists and the data from this study, the entity commonly termed "respirator brain" may be confirmed. This is a dynamic process that is complicated by concurrent postmortem changes. The respirator brain requires time (approximately 24 hours) for maturation; many patients die a cardiac death during the metamorphosis. If the patient survives for 3 to 4 days, the percentage dying with typical respirator brains is less, and more patients have electroencephalograms with biological activity. 5. The following clinical factors tend to be associated with an increased number of respirator brains: A. Cerebral trauma B. Subnormal body timperature C. Low systolic blood pressure D. Dilated pupils E. Pupils unresponsive to light F. Absence of cephalic reflexes G. Electrocerebral Silence (ECS) 6. The following factors have no apparent effect on the number of respirator brains or tend to be associated with fewer respirator brains: A. Severe drug intoxications B. Small reacting pupils C. Medications D. Presence of spinal reflexes E. Presence of biological activity (BA) in the electroencephalogram 7. A set of common criteria for a respirator brain was used to test the following: A. The local and consultant neuropathologist's diagnosis of respirator brain B. The significance of critical perfusion pressure and critical oxygen tension in respirator brain C. The role of cardiac output in the production of a respirator brain 8. Since a respirator brain is an imperfectly defined entity, an exact correlation with any combination of clinical and EEG findings could not be expected. The use of a standardized measurement of CBF seems a logical and promising confirmatory test for respirator brain.