Brain stem auditory evoked potentials (BAEP) monitoring in brain death

In our intensive care unit, brain stem auditory evoked potentials (BAEP) are measured continuously in comatose patients.For this study we examined 15 patients who fulfilled the criteria of brain death (2). Loss of BAEP in these patients inevitably means loss of brain stem function and consecutive death.     

Diagnosis of brain death]

From the medical, the juridical as well as the theological point of view brain death represents the death of an individual. According to the German Chamber of Physicians, acute brain damage with coma, absence of all brainstem reflexes and apnoe allows the diagnosis of cerebral death, if repetition of the physical examination after distinct time intervals documents the irreversibility of this state. Additional investigations such as EEG, evoked potentials (BAEP), transcranial doppler sonography, brain scintigraphy or cerebral angiography allow to shorten this period if electrocortical silence, absence of waves 3-5 of BAEP or the cessation of cerebral perfusion has been proven. Strict observation of these criteria is mandatory for the diagnosis of brain death.     

Is cerebral panangiography unnecessary in determining brain death?

The diagnosis of brain death, i.e. death of cortex and brainstem, can be established by neurologic examination only if there is no intoxication, sedative therapy, or hypothermia. In the latter cases, until now only cerebral panangiography can establish the diagnosis. We investigated, whether in these cases cerebral perfusion scintigraphy (CPS) in combination with brainstem auditory evoked potential (BAEP) can replace CPA for establishing the diagnosis. METHODS: 40 patients, treated in our interdisciplinary ICU because of primary or secondary brain lesions and in whom determination of brain death by neurological examination was contraindicated, were subjected to the following procedure: When coma was diagnosed, brainstem reflexes were examined. If negative, an atropine-test was done and this being negative, apnea-testing was performed. If apnea was positive, BAEP, CPS and CPA were performed. The results of BAEP and CPS were compared with the results of CPA. RESULTS: In 38 patients with suspected brain death the first examination showed complete correspondence between BAEP and CPS on one hand and CPA on the other hand (Table 3). In patient No. 39, CPS as well as CPA showed minimal supratentorial circulation, whereas BAEP were negative as was circulation in the fossa posterior. In patient No. 40 as well CPS and CPA showed minimal supratentorial circulation. Brainstem testing with BAEP was negative although CPA showed minimal brainstem perfusion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prognostic value of evoked potentials and clinical grading in primary subarachnoid haemorrhage

Summary In a retrospective study of 64 patients suffering from primary subarachnoid haemorrhage (SAH), the clinical grading according to Hunt and Hess as well as the initial findings of brainstem auditory evoked potentials (BAEP) and median-nerve somatosensory potentials (SEP) were correlated with each other and with disease outcome to determine the prognostic value of evoked potential testing in comparison to the initial clinical grading according to Hunt and Hess.All patients were treated in a neurological intensive care unit. Normal evoked potentials usually indicate a favourable course. Alterations of SEP and BAEP increase in parallel with the severity of clinical findings. Unilateral or bilateral loss of SEP or BAEP indicates a poor prognosis. Clinical and electrophysiological findings show a close correlation, but only BAEP provide prognostic information beyond Hunt/Hess grading.In SAH patients, clinical grading was well as evoked potentials correlate significantly with outcome. Use of both clinical and EP rating improves prognostic accuracy.     

Evoked potentials in the follow-up and prognosis of patients with craniocerebral trauma

The aims of this study were to find a reliable way of establishing the prognosis for the final outcome in the first week after head injury, to show the correlation between abnormalities in evoked potentials (EP) and clinical coma score, and finally, to document EP results in patients with the clinical diagnosis of brain death. We examined 46 patients, 23 in different states of coma and 23 with bulbar syndrome (complete absence of cortical and brain stem function). In the group of comatose patients brain stem auditory EP (BAEP) and somatosensory EP (SEP) were recorded in the first 48 h, 3-5 days, 1 week and 4 weeks after the head injury. The depth of coma was scaled with a scoring system devised by the authors and with the Innsbruck coma scale. Outcome was evaluated with the Glasgow outcome scale after 3, 6, and 9 months. BAEP were recorded bilaterally after stimulation with clicks; SEP were recorded from the neck (C2) and the contralateral cortex (C3', C4') after electrical stimulation of the median nerve. Evoked potentials were scored according to a four-point scale from grade 1 (normal) to grade 4 (only component I present in BAEP or absence of cortical responses on both sides in SEP). We found a significant correlation between the mean SEP score of the first week and the Glasgow outcome of the 3rd month, but no significant correlation between the BAEP score of the first week and the Glasgow outcome. There was a significant correlation between SEP (BAEP) scores and the corresponding clinical score.(ABSTRACT TRUNCATED AT 250 WORDS)     

从神经电生理角度探讨亚低温对特重型颅脑伤的疗效

目的　通过诱发电位(EP)监测,探讨亚低温对特重型颅脑伤的疗效。　方法　选择受伤后10h内入院的特重型颅脑伤患者(GCS≤5)24例,患者随机分为亚低温组和常温组。亚低温组体温降至32～34℃,于降温前、降温过程中及复温后监测正中神经短潜伏期体感诱发电位(SLSEP)和脑干听觉诱发电位(BAEP);常温组在同样的时间段监测上述指标。统计分析亚低温组与常温组诱发电位的变化情况。　结果　亚低温组在治疗前后SLSEP的N20波幅变化值为(0.67±0.41)μV,常温组为(0.61±0.39)μV,两者差异无显著性意义(P＞0.05);BAEP的V/I波幅比值,差异也无显著性意义（P＞0.05）。　结论　从神经电生理角度来看,亚低温对GCS为3～5分的特重型颅脑伤无明显疗效。     

Brain death: Determination with brain stem evoked potentials and radionuclide isotope studies

Summary Thirty-three patients fulfilling the clinical criteria for brain death were tested by Brainstem Auditory Evoked Potentials (BAEP) and Radionuclide Cerebral Angiography and Brain Perfusion Studies. There was a significant correlation between the BAEP and radionuclide study outcomes. All patients with absence of BAEP showed no cerebral perfusion. These findings, added to the clinical findings, resulted in a final diagnosis of brain death in all patients. It is concluded that BAEP and Radionuclide Cerebral Perfusion studies are useful adjuncts for proving that brain death has really occurred.     

Transtentorial brain herniation in the monkey: analysis of brain stem auditory and somatosensory evoked potentials

A monkey model of transtentorial brain herniation (TBH) was created to simulate the clinically encountered situation of a gradually expanding intracranial lesion. TBH was produced by extradural balloon inflation over a 4-hour period and documented by the appearance of the pupils as dilated or fixed at midposition. Intracranial pressure (ICP), brain stem auditory evoked potentials (BAEP), and short-latency somatosensory evoked potentials (SSEP) were recorded before, during, and after TBH. Statistical significance from baseline values to TBH was found for diminution of the BAEP amplitude, rise of the ICP, and diminution of the SSEP amplitude. An ICP rise to twice the baseline value and a 25% decrease in Wave V amplitude was found 1 hour before TBH. Changes in BAEP and SSEP took several minutes after deflation to return to baseline values. Analysis of Wave V of the BAEP was as sensitive as ICP in warning of TBH. Discussion centers upon previous animal studies of brain herniation and ICP elevation, and findings reported in humans deteriorating as a result of intracranial mass lesions. BAEP and SSEP monitoring may be used as noninvasive tests for brain stem compression in the setting of primate TBH, and in the future may be used to guide the effectiveness of therapy.     

Changes of evoked potentials and evaluation of mild hypothermia for treatment of severe brain injury

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Brainstem auditory evoked potentials and blink reflexes in patients with pontocerebellar angle tumors

Brainstem auditory evoked potentials (BAEP) and blink reflexes (BR) were obtained from 13 patients with pontocerebellar angle (PCA) tumors whose pathological diagnosis was as follows: 7 acoustic neurinoma, 3 meningioma, 1 neurinoma, 1 brain stem epidermoid tumor, 1 arteriovenous malformation. The most prominent abnormality was noted in BAEP generated by stimulating the ear ipsilateral to the lesion and ipsilateral R₁ reflexes obtained from ipsilateral stimulation of the supraorbital nerve.     

Multimodality electroneurophysiological findings in intra-axial and extra-axial lesions of the brain stem

Summary In 330 patients with a space occupying lesion of the posterior cranial fossa, the blink (BR) and masseter (MR) reflexes and brain stem auditory (BAEP) and somatosensory evoked potentials (SEP) were registered. The aim of our study was to look for electrophysiological criteria of differentiating between lesions within or outside the brain stem. The ipsilateral loss of BAEP in cerebellopontine angle tumours and the altered SEP in tumours within the brain stem turned out as frequent, almost specific findings. Prolonged ipsi- and contralateral late BR responses and prolonged MR responses, a long somatosensory central conduction time of the SEP and a prolonged wave III latency as well as a prolonged interpeak latency of the BAEP are not indicative but highly suspicious for a lesion within the brain stem. Prolonged early responses of the BR together with prolonged interpeak latencies of the BAEP are characteristic findings in cerebello-pontine angle tumours.     

Microsurgical vascular decompression for hemifacial spasm. Follow-up over one year, clinical results and prognostic factors. Study of a series of 100 cases

BACKGROUND AND PURPOSE: The results of a series of 100 patients operated on for hemifacial spasm (HFS), using microsurgical vascular decompression (MVD), are reported. METHOD: MVD was performed through a retromastoid keyhole approach, under monitoring of brainstem auditory evoked potentials (BAEP) and facial EMG, and consisted in dissection of VII nerve from conflicting vessel(s), and interposition of Teflon fibers and/or screen(s). RESULTS: The offending vessels found were: the antero-inferior cerebellar artery in 57 cases, the postero-inferior cerebellar artery in 56 cases, the vertebrobasilar artery in 22 cases. A multiple conflict was found in 32 cases (32%). The result was considered excellent if there was no residual spasm, good if only "minimal twitching" remained with relief>80%, poor for spasm relief 20 to 80%, and as a failure if relief<20%. The effect of MVD was satisfying (excellent or good) in 75 patients (75%) at discharge (10th day) and in 85 (85%) after 1 to 18 years follow-up (mean: 5 years). Amongst the latter patients, 29 (34%) experienced a delayed (up to 3(1/2) years in one) cure. Spasm recurrence was noted in 9 cases after satisfying effect on discharge. We encountered following permanent neurological complications: 1 facial palsy, 7 cases of hearing deficit (5 of them complete), and 1 case of IX-X deficit. Neither death nor ischaemic complication at brainstem or cerebellum. Most of our hearing complications occurred before using intraoperative BAEP monitoring (3 cases of cophosis among our first 7 patients vs 2 out of our last 93). Local complications were: 1 meningitis, 8 cases of CSF leakage requiring either a series of lumbar punctures or a lumbar external drain, and 3 cases of wound infection and/or delayed woundhealing requiring surgical treatment. CONCLUSIONS: Our data are consistent with those of the literature, especially concerning high rate of long-term success and low complication rate of MVD for HFS. We do not recommend early re-operation in case of initial poor result. Again, the necessity of intraoperative BAEP monitoring to prevent hearing morbidity is highlighted.     

Delayed hearing loss after surgery for acoustic neurinomas: clinical and electrophysiological observations.

In a series of 26 patients with medium-sized and large acoustic neurinomas and documented hearing before surgery, 7 patients had preservation of hearing initially after the procedure but then developed delayed hearing loss. The most prominent intraoperative electrophysiological finding in these cases was a gradual deterioration of brain stem auditory evoked potentials (BAEP), especially of Wave V. Four additional patients with a similar gradual intraoperative loss of BAEP and severe postoperative hearing deterioration received vasoactive treatment after surgery (low-molecular weight dextran). In all 4 patients, including 1 patient with documented total deafness after surgery, hearing was preserved. Initial preservation of cochlear nerve function after the removal of an acoustic neurinoma does not guarantee postoperative hearing. Intraoperative BAEP help to identify patients at risk for delayed postoperative hearing loss. The pathophysiological mechanism can be attributed to disturbances of the microcirculation in endoneurial vasa nervorum caused by the mechanical manipulation of the cochlear nerve.     

Limitations of brain stem auditory evoked potentials for intraoperative monitoring during a posterior fossa operation: case report and technical note

We have encountered an example of the insensitivity of brain stem auditory evoked potentials (BAEPs) for monitoring the brain stem during a posterior fossa operation. The addition of somatosensory evoked potential recording to conventional BAEP protocols is readily accomplished and is likely to improve the sensitivity of intraoperative electrophysiological assessment of brain stem function.     

Evoked potentials and post-traumatic evolution

Visual, somatosensory, and brainstem auditory evoked potentials provide functional quantitative assessment of the cerebral cortex and brainstem. Their contribution at the acute stage of coma concerns diagnosis, prognosis, and follow-up. Four patterns are observed in traumatic coma: pattern 1=dysfunction of the cerebral cortex, brainstem integrity: good prognosis in more than 80% of cases; pattern 2=midbrain dysfunction: prognosis depends on both the reversibility of midbrain dysfunction and the extent of associated axonal lesions in the hemispheric white matter; pattern 3=pontine dysfunction due to transtentorial herniation: ominous prognosis, this pattern must be early detected by continuous monitoring; pattern 4=brain death: we currently use evoked potentials at the only brain-death confirmatory test, even in sedated patients. The contribution of evoked potentials in vegetative or minimally responsive states concerns the identification of these patients whose state is determined by midbrain dysfunction and the evaluation of persisting cognitive abilities in individual cases.     

The definition and determination of brain death

In most countries, brain death is defined as the irreversible and complete loss of (clinically ascertainable) function of the entire brain, including the brain stem. It is characterized by an irreversible loss of the capacity for consciousness, combined with loss of motor responses to painful stimuli, irreversible loss of brain stem reflexes and loss of the capacity to breathe. The diagnosis can be made clinically based on at least two examinations separated by a time interval, which depends on the cause of the underlying brain damage, the patient’s age and national conventions. Ancillary tests can confirm and speed the diagnosis of irreversible loss of brain function. Conventional angiography is the most sensitive technique, but relatively expensive, and because of potential side-effects not allowed for diagnosis in all countries. Electroencephalography and transcranial Doppler ultrasonography are alternative methods. Other techniques, for example evoked potentials, radionuclide techniques and magnetic resonance studies, are less valuable or need to be validated.     

Experimental study of evoked potentials in predicting the reversibility of brain function following tentorial herniation

Brainstem auditory evoked potentials (BAEP), somatosensory evoked potentials (SEP) and EEG were recorded sequentially in cat with mass-induced intracranial hypertension in correlation with mass volume, intracranial pressure (ICP), systemic blood pressure (BP) and size of the pupils. 1) As the intracranial pressure was raised by expansion of a supratentorial epidural balloon, suppression of cortical SEP (CSEP) and pupillary abnormality appeared first, EEG, waves IV and III of BAEP and wave III of short latency SEP (SSEP) were suppressed in this order. 2) As far as wave IV of BAEP remained and decompression was started within 30 minutes after peaks of CSEP completely suppressed, changes in P1 and N1 of CSEP were reversible. 3) Further raising of ICP was followed by loss of waves IV and III of BAEP and wave III of SSEP in this order. Simultaneously with loss of wave III in SSEP, systemic blood pressure dropped rapidly. By immediate balloon deflation after disappearance of wave III of SSEP, animals recovered from hypotension, but hardly from suppression in EEG, CSEP and BAEP. 4) Preservation of wave IV of BAEP indicated good improvement of pupillary abnormality even after removal of compression. These results suggest that for the patient with disturbed consciousness caused by supratentorial mass lesion, decompressive procedure should be started before wave V of BAEP and brainstem components of SEP disappear. EP monitor seems to be useful clinical method for preventing irreversible change of the brain in patients with coma caused by supratentorial mass lesions.     

Neurophysiologic monitoring in posterior fossa surgery

Summary In 135 cases of posterior fossa surgery almost exclusively in the cerebellopontine angle (CPA) intraoperative monitoring of brainstem acoustic evoked potentials (BAEP) and partly somatosensory evoked potentials (SEP) was performed. The series consisted of 20 microvascular decompressions, 63 acoustic neurinomas, 7 vascular lesions and 45 other space occupying lesions, mostly in the CPA. BAEP monitoring alone was employed in 76 cases, combined BAEP und SEP monitoring less frequently. The technique of anaesthesia and intraoperative monitoring is presented in detail including an analysis of technical problems (17 in 135=13% of cases) and technical failures (11 of 135=8%). The results of monitoring brainstem pathways contralateral to the lesion are detailed. It is concluded that the technical principles of evoked potential monitoring in posterior fossa surgery are well established. The applications and limits of this technique including its modifications are described.     

Auditory evoked potentials during isoflurane anaesthesia

Brainstem auditory evoked potentials (BAEP) were determined in 12 volunteers. The effect of isoflurane anaesthesia on BAEP was determined in six patients. Body temperature and end-tidal CO2% were controlled. Increasing end-tidal isoflurane concentration from 0.6-2.4% increased BAEP wave I, III and V latencies. The amplitude of wave V decreased with increasing isoflurane concentration. Thus a dose-related change was demonstrated between end-tidal concentration of isoflurane and BAEP latencies.     

Deterioration of auditory evoked potentials during cerebellopontine angle manipulations. An interpretation based on an experimental model in dogs

Evoked action potentials from the internal auditory meatus portion of the cochlear nerve (IAM-EAP's) and brain-stem auditory evoked potentials (BAEP's) from the vertex were simultaneously recorded during cerebellopontine angle (CPA) manipulations (retractions of the cerebellar hemisphere and the cochlear nerve) in dogs. The BAEP changes noted in these dogs were the same as those seen in patients. The IAM-EAP's showed graded deterioration related to BAEP changes. The results are as follows: Prolongation of the I-V interpeak latency of BAEP's, the most common finding during CPA manipulations, is the reflection of prolongation of the I-II interpeak latency, which is caused by conduction impairment or block of the nerve impulses between the extracranial portion of the cochlear nerve and the brain stem. The operative manipulations representing stretch or compression injury to the cochlear nerve in the CPA leads to an acute traumatic cranial nerve root lesion--a retrocochlear lesion. The obliteration of all BAEP components including wave I cannot be caused by conduction block. This is caused by occlusion of the internal auditory artery. Wave I of the BAEP's and the P1-N1 complex of the IAM-EAP's are important indicators of cochlear blood flow during surgical intervention. As possible causes of internal auditory artery obstruction, mechanical distortion of the relationship between the anterior inferior cerebellar artery (AICA) and the internal auditory artery at the junctional portion, mechanical vasospasm of the AICA-internal auditory artery complex, and ensuing no-reflow phenomena are discussed. Evoked action potentials are expected to be a useful intraoperative real-time monitor during CPA surgery that can detect rapid changes derived from cochlear artery insufficency. The real-time aspects can overcome some of the disadvantages of BAEP monitoring.