Auditory evoked potentials of the brain stem in brain death

Brainstem auditory evoked responses were recorded in a neurosurgical intensive care unit in 38 patients who had all the clinical criteria for brain death. Of the brain-dead patients, 65.8% never showed a response. 3.42% showed a type I wave, which was unilateral in 26.3% and bilateral in the other 7.9%. Types II to VII waves were never seen. An increase in latency of type I waves (2.25 +/- 0.24 ms) was noted. The interest and the limits of this non invasive electrophysiologic technique for the diagnosis of brain death are discussed.     

Auditory evoked potentials of the brain stem in brain injury. Prognostic value

The study of brain stem auditory way in severe head trauma patients with auditory evoked potentials is very important for giving elements about functional and anatomic situation of analyzed neuronal substratum; ABR will be normal or altered in conformity with the level and/or the gravity of the damage. Authors have examined 20 post-traumatic comatose patients pointing out the existence of a strict relation between auditory brain stem responses and prognosis. Authors, in accordance with the ample literature in existence, agree to point out the auditory brain stem responses such as a very effective instrument for the prognostic valuation of post-traumatic comatose patients.     

Detailed analysis of intraoperative changes monitoring brain stem acoustic evoked potentials

A series of 31 neurosurgical procedures in the posterior fossa monitored intraoperatively with ipsilateral brain stem acoustic evoked potentials (BAEPs) is analyzed for intraoperative potential changes. The evaluation of patients included pre- and postoperative BAEP recordings and pure tone audiometry. The series included 25 tumors, 4 neurovascular decompressions, 1 basilar artery aneurysm, and 1 arteriovenous malformation. Two intraoperative findings correlated significantly with a postoperative decrease in hearing: an amplitude reduction of more than 50% for Waves I to V and the loss of one of the waves, even if it was a wave that first appeared intraoperatively. We could attribute no significance to reversible or irreversible latency increases for all waves. The transient loss of one of the peaks followed by its reappearance was also insignificant with regard to postoperative hearing. A good prognostic sign was the intraoperative appearance of a peak undetectable on the preoperative recordings. These findings suggest that in intraoperative BAEP monitoring the observation of amplitude reduction is more important than that of latency increases. The surgeon should be informed when an amplitude reduction of more than 50% occurs before the peak is lost totally, as it is impossible to predict whether this peak will reappear intraoperatively.     

利多卡因对脑干听觉诱发电位的影响

目的　观察利多卡因对小脑幕下肿瘤患者脑干听觉诱发电位 (BAEPs)的影响。方法小脑幕下肿瘤病人 2 0例 ,随机分为A、B两组 ,每组 10例。A组为观察组 ,在术前以 0 33mg·kg-1·min-1的速度持续输注 2 %利多卡因 ,至总量达 10mg/kg止 ,并持续监测BAEP。B组为对照组 ,不用利多卡因。结果　A组从输注利多卡因后第 6min开始 ,Ⅰ、Ⅲ、Ⅴ波潜伏期及Ⅰ～Ⅲ、Ⅰ～Ⅴ波间潜伏期较注药前显著延长 ;且随着利多卡因输注剂量增加 ,各波潜伏期逐渐延长。其中Ⅰ、Ⅲ、Ⅴ波潜伏期及Ⅰ～Ⅲ、Ⅰ～Ⅴ波间潜伏期的延长值与利多卡因剂量呈线性相关。B组在全监测过程中BAEP无显著改变。结论　静脉注射一定剂量的利多卡因显著延长BAEP的潜伏期及波间潜伏期 ;在 0～ 10mg/kg剂量范围内 ,Ⅰ、Ⅲ、Ⅴ波潜伏期及Ⅰ～Ⅲ、Ⅰ～Ⅴ波间潜伏期的延长值与利多卡因的剂量呈线性相关     

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.     

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.     

Mild hypoglycemia and impairment of brain stem and cortical evoked potentials in healthy subjects

To evaluate the impact of mild hypoglycemia on CNS function in healthy adults, we measured brain stem auditory evoked potentials and P300 potentials (elicited by cognitive processing of auditory stimuli) during hypoglycemic or euglycemic insulin clamps (80 mU.m-2.min-1). In the hypoglycemic clamp study (n = 8), plasma glucose was allowed to fall from 4.6 to 3 mM in hourly approximately 0.5-mM steps and subsequently returned to euglycemic baseline levels. In the euglycemic clamp study (n = 8), plasma glucose was maintained at baseline levels throughout. Neither brain stem nor P300 responses changed during the euglycemic control study; symptoms and counterregulatory hormones were also unaffected. During the hypoglycemia study, epinephrine and growth hormone rose once plasma glucose reached 3.4 +/- 0.1 mM. Brain stem and P300 potentials remained unchanged until the 3-mM glucose step, when neurophysiological changes suddenly developed in conjunction with reported symptoms. At this glucose level, the wave V component of the brain stem potential was selectively altered in 7 of 8 subjects. Furthermore, P300 latency significantly increased, and amplitude diminished. Changes in both brain stem and cortical (P300) responses reversed when euglycemia was restored. We conclude that modest reductions in plasma glucose (to 3 mM) produce marked alterations in both brain stem and cortical responses to auditory stimuli. These changes in neural function appear at the same time as symptoms and follow rather than precede the rise in counterregulatory hormones during hypoglycemia. Our data suggest that the adverse effects of mild hypoglycemia on brain function are not limited to higher centers but also involve the brain stem.     

Principles of pressure transducer function and sources of error in clinical use

The invasive measurement of physiological pressures is a common requirement in anaesthesia and intensive care medicine. From arterial blood pressure to intracranial pressure, these calculated variables give a swift graphical and numerical representation of a patient's current physiological status. This allows us to respond rapidly to conditions outside our preferred parameters and to carefully titrate treatment to target effects. These systems are, however, not infallible. An understanding of the principles of their function will promote appropriate use and an ability to recognize and react to sources of error. This article aims to furnish the reader with this level of understanding in order to inform their academic and clinical practice.     

Principles of pressure transducer function and sources of error in clinical use

The invasive measurement of physiological pressures is a common requirement in anaesthesia and intensive care medicine. From arterial blood pressure to intracranial pressure, these calculated variables give a swift graphical and numerical representation of a patient's current physiological status. This allows us to respond rapidly to conditions outside our preferred parameters and to carefully titrate treatments to target effects. These systems are, however, not infallible. An understanding of the principles of their function will promote appropriate use and an ability to recognize and react to sources of error. This article aims to furnish the reader with this level of understanding in order to inform their academic and clinical practice.     

Retrolabyrinthine vestibular neurectomy with simultaneous monitoring of eighth nerve and brain stem auditory evoked potentials

We have used retrolabyrinthine vestibular neurectomy in 36 of 49 cases as the primary surgical procedure to relieve vertigo. Most of the patients (46 of 49) had Meniere's disease. Results indicate that 71% (35 of 49) of the patients had no vertigo after the operation, while 22% (11 of 49) had much improvement. Hearing was maintained within 20 dB of the preoperative level in 78% (38 of 49) of the patients. During surgery in the last 23 patients, direct nerve potentials were recorded from the middle ear promontory and the intracranial cochlear nerve. Brain stem auditory evoked responses were simultaneously recorded in the last 10 patients. It appears that the intraoperative direct cochlear nerve potentials can be used as a sensitive monitor of trauma to the cochlear nerve during and after vestibular neurectomy. If the latency of the eighth nerve action potential changes less than 0.3 msec and the waveform does not change after vestibular neurectomy, there is an excellent chance that hearing at 1 month after surgery will be within 15 dB of the level before surgery. The retrolabyrinthine vestibular neurectomy has replaced the middle fossa vestibular neurectomy and the endolymphatic subarachnoid shunt procedure in our clinic.     

Use of the Cavitron ultrasonic surgical aspirator and evoked potentials for the treatment of thalamic and brain stem tumors in children

We subtotally removed nine pediatric central gliomas (five brain stem and four thalamic) with the Cavitron ultrasonic surgical aspirator (CUSA). Greater than 70% of the tumor was removed in eight of the nine cases. Evoked potentials were monitored during six of the operations. Of the six children who were operated on with monitoring, four had no deficit and two had single cranial nerve palsies. Of the three children who were operated on without evoked potential monitoring, one had no deficit, one was in a permanent state of obtundation, and one died of a pulmonary embolus 6 weeks postoperatively. Because the prognosis of children with malignant astrocytomas correlates with the extent of tumor removal, extensive tumor removal with the CUSA is probably indicated for some children with relatively discrete, enhancing central gliomas. Evoked potential monitoring may be useful during such operations.     

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.     

Relationship of nuclear magnetic resonance examinations to clinical data,cerebrospinal fluid findings and visual evoked potentials in multiple sclerosis

We examined 150 patients with a 0.5 Tesla MR system. Fourteen patients were excluded from the study, because, in addition to the clinical signs of multiple sclerosis, they showed other abnormalities (spinal canal narrowing, embolic disease, Vitamin B12 deficiency, etc.). The results of the 136 examinations were related to the duration of disease, index of impairment on Kurtkze's disability scale, the clinical course, and the CSF and VEP results. The MR studies were evaluated in a semiquantitative manner. Patients with a long duration of disease demonstrated more changes than did cases with a short course. We found more periventricular confluences and more white matter plaques in the centrum semiovale. In addition, more lesions were seen in patients with a severe course of disease. All patients with negative CSF results (n = 13) showed positive MR examinations, and vice versa, patients with positive CSF findings showed negative MR results (n = 5). First results of a follow-up study demonstrate that most abnormalities in MR are not related to the clinical course or therapeutical procedure.     

Considerations for safety in the use of extracranial stimulation for motor evoked potentials

The possibility of neural damage during extracranial brain stimulation for motor evoked potentials (MEPs) is discussed from the perspective of animal studies in which the stimulating electrodes were in direct contact with the brain. These data indicate that the charge per phase used in most of the extracranial MEP protocols is sufficient to induce neural damage if the stimulation is applied continuously for several hours. However, in most cases dispersion of the stimulus current in the extracranial tissue and skull is probably adequate to attenuate the stimulus charge density at the brain surface to a safe level (less than approximately 40 microC/cm2 X ph). However, the possibility exists that low resistance paths between the stimulating electrode and the brain may give rise to foci of high charge density. The possibility of such focusing may be less with magnetic field than with direct electrical field stimulation. We stress the need for additional animal studies designed to delineate a range of safe stimulus parameters for this particular technique.