Central conduction time as an index of ischaemia in subarachnoid haemorrhage.

Central conduction time (CCT) has been measured in 12 healthy volunteers, and in 16 patients admitted to a neurosurgical unit following subarachnoid haemorrhage. Twelve of the patients were subsequently operated upon for the obliteration of an intracranial aneurysm. CCT has been found to have low standard deviation in control cases, and in the normal side following subarachnoid haemorrhage from aneurysms in the Circle of Willis, and to be prolonged during the development of ischaemic complications, either of the haemorrhage or following surgery. Evidence so far suggests that CCT may be useful as a monitor of developing ischaemia in association with surgery for subarachnoid haemorrhage.

Neuro-otologic applications of simultaneous multi-channel auditory evoked response recordings.

Multichannel auditory brain stem response (ABR) recordings were obtained in 75 acute, severely brain injured patients. The purpose of the study was to assess, in patients with varied neuro-otologic pathology, the clinical feasibility and value of measuring the ABR simultaneously with more than one electrode array. The use of alternative electrode arrays, in addition to the conventional (vertex to stimulus ipsilateral ear) array, augmented confident identification of wave components I through VI, and was particularly useful in patients with marked middle ear pathology which confounded ABR interpretation. The ABR recorded with an indifferent (noncephalic) reference electrode, e.g., was characterized by increased Wave V amplitude, and improved definition of Wave IV vs. V. Case studies are presented to illustrate neuro-otologic applications of the multichannel recording technique.

Neuro-otologic evaluation of the patient with acute, severe head injuries: correlations among physical findings, auditory evoked responses, and computerized tomography.

Long-term clinical neurologic and otologic sequelae of traumatic head injury are well recognized. In this article, we describe the relationship among neurophysiologic, neuro-otologic, and neuroradiologic findings in a series of fifty patients with acute, severe head injury. Seventy percent of the patients had one or more otologic abnormalities, of which hemotympanum was most common. Outcome of computerized tomography (CT), auditory brainstem response (ABR), and otologic examination findings were not mutually dependent. For example, otologic disease was found in 50% of the patients with normal ABR. All but one patient in the series showed brain damage by CT; yet only 14% of the series had evidence of temporal bone fracture and, unexpectedly, one third of this group yielded normal otologic findings and a normal ABR. We conclude that combined application of otologic examination, CT scanning, and auditory evoked response assessment provides complementary information on structural and functional neuro-otologic status in persons with acute, severe head injury.

Pediatric applications of serial auditory brainstem and middle-latency evoked response recordings.

Serial auditory brainstem (ABR) and middle-latency (AMR) response recordings were made for 12 children (8 male, 4 female) ranging in age from 2 weeks to 10 years. A total of 40 ABR and 32 AMR assessments were carried out at bedside in varied hospital environments, including a pediatric intensive care unit (ICU), a neonatal ICU and an operating room. Clinical entities were distributed as follows: acute, severe head injury (5), hydrocephalus (2), meningomyelocele (2), hyperbilirubinemia (1), ototoxic drug overdose (1), severe developmental delay (1). Auditory evoked responses were applied in monitoring peripheral and central auditory system status, and contributed to medical, surgical and audiologic management. Abnormalities of the ABR were reversed in some children, such as those with hydrocephalus, with medical or surgical therapy. In other cases, such as a hyperbilirubinemic child, a marked ABR abnormality apparently reversed spontaneously. We present five cases to illustrate diverse applications of serial auditory evoked response measures in children.

Brain stem and somatosensory evoked potentials: application in the operating room and intensive care unit.

Intraoperative monitoring of the brain's electrical function with evoked potentials (EPs) may prove as valuable as cardiac monitoring in detecting abnormalities before permanent damage occurs. To date, evoked potential monitoring has only been employed in select neurological cases, where the significance of electrical changes can be related to postoperative deficits. If EP intraoperative techniques are to be useful in preventing these postoperative deficits, they must be able to predict impending brain dysfunction during surgery. There is strong clinical and experimental data relating EP changes to critical blood flow, brain retraction, and CNS manipulation. However, little is known of the normal fluctuations in electrical activity during routine non-neurological surgery. The data we have collected in control patients (non-neurological) will be a guide to the interpretation of neurological cases (carotid endarterectomy, aneurysm, and cervical spine and cord lesions). We have concentrated on monitoring somatosensory and auditory short-latency EPs since they appear to be the most stable, reproducible and the most applicable to patient monitoring during neurosurgical, vascular and orthopedic procedures.

Central conduction time in primate brain ischemia -- a study in baboons.

The relationship between central conduction time (CCT) and levels of regional blood flow were studied in 9 primates. Flows were recorded in both hemispheres using the method of hydrogen (2 min) clearance. The somatosensory evoked potentials were recorded over the contralateral cortex and the dorsal columns, following median nerve stimulation. The CCT, a measure of the brain's electrical conduction, was determined by the difference in latencies between N10, (the arrival of the afferent volley at the sensory cortex) and N7 (its arrival at the dorsal column). Ischemia was produced by transorbital occlusion of the right middle cerebral artery. In the acute ischemic phase within 5 minute of occlusion, there was a significant correlation between the change in CCT and the decrease in flow. In the later occlusive phase, the CCT was unaltered with flows above 15 ml/100g/min. Below that level smaller decreases in flow resulted in progressively larger changes in CCT until a flow was reached where the N10 disappeared or the entire cortex was electrically silent. Focal ischemia had no effect on the first positive deflection recorded from the cortex (P8) or the first negative peak response from the cervical region (N7). However, the latency of P8 was increased or it was absent with the introduction of hypotension, while N8 was unaltered. From our measurements, it appears that prolongation of CCT can be related to developing ischemia, and that the thresholds for change are not dissimilar to those already recorded for somatosensory evoked responses to the basis of amplitude alterations in the cortex. Below these levels, prolongation of CCT appears to bear a parametric relationship to alteration in blood flow. While the measurement displays only one of the many alterations which are induced by ischemia in the brain, its attraction lies in its simplicity and in the fact that it may be applied with relative ease in the clinical situation. Under these circumstances, it appears to be an adequately sensitive monitor of developing brain ischemia, and deserves further study.

Sensory evoked responses in head injury.

Head trauma is a significant source of morbidity in the United States each year. Approximately 700 patients were admitted to our surgical intensive care unit with some degree of head trauma in a 24-month period. Glasgow Coma Score (GCS) was 8 or less in 90% of this group, and 3 or 4 in 43%. Sensory evoked responses were recorded in over 500 patients. This study is reported to demonstrate that optimum care of the injured brain depends on titration of care aimed at maintaining normal neuronal function. In our series, 25% of the patients with GCS of 3 or 4 returned home or to a rehabilitation unit, a significant decrease in morbidity over other reported series. Chemical paralysis and barbiturate coma were a factor in the decision to monitor in 50-60% of the series. In these patients, the auditory brainstem evoked response (ABR), a monitor of brainstem neuroelectrical function, and the somatosensory evoked response, a monitor of brainstem and cortical function, were used to follow the effectiveness of medical and surgical management in these patients, since neurologic examination was of limited value. Case reports are presented to demonstrate that even at high barbiturate levels, access to the integrity of the central nervous system is still possible. Relations among GCS, computerized tomography (CT), intracranial pressure (ICP), ABR, pupillary response, and outcome were studied for a subgroup of 114 patients. All of these clinical parameters, except CT findings, were significantly correlated with outcome using Chi-square analysis. When the data were further analyzed with linear regression analysis, however, the only parameters that significantly correlated with outcome were pupil reactivity and ABR. The principal conclusion of this report is that the main application of serial monitoring of the sensory central pathway in the head-injured patient is not in the prediction of outcome but in the titration of care of the patient for the preservation of neuronal function.

Auditory brain-stem response in determination of brain death.

A diagnosis of brain death requires evidence of irreversible destruction (or dysfunction) of neurons in the brain stem and cerebrum. The physical examination is not a valid index of brain integrity in patients who are drug-intoxicated or receiving therapeutic paralyzing agents or high-dose barbiturates. We evaluated the use of the auditory brain-stem response (ABR) as an ancillary test in the determination of brain death. A total of 100 combined ABR and nuclear cerebral blood flow studies were completed at bedside with 81 acute, severely brain-injured adults. The ABR and cerebral blood flow outcomes were significantly correlated. We conclude that the ABR is a clinically feasible and useful procedure in the determination of brain death, especially in patients whose medical therapy compromises the neurologic examination.