Evozierte Potentiale in der neurologischen Intensivmedizin - eine Standortbestimmung

Prediction of secondary deterioration in comatose neurosurgical patients by serial recording of multimodality evoked potentials

In 75 comatose neurosurgical patients suffering from various types of intracranial lesions, multimodality evoked potentials (auditory, somatosensory, visual) were serially recorded at short intervals in order to evaluate their usefulness for early detection of secondary deterioration in the clinical course. The best parameter for prediction of secondary deterioration (as estimated by pupillary status) was a diminution in amplitude or disappearance of the primary cortical SEP peak. Considering these parameters, sensitivity of the prediction of pupillary behaviour was 71%, specificity 84%. Additional consideration of SEP latencies or BAEP or VEP parameters did not further increase the efficacy of prediction. In cases of correct positive prediction, deterioration of SEP occurred 4 to 144 hours before the deterioration of pupillary physiology.

Continuous multivariable monitoring in neurological intensive care patients--preliminary reports on four cases

Evoked potential monitoring is a standard examination method in neurological intensive therapy units. Previously, multimodality observation was only possible in follow-up examinations. First experience with a new bed-side system continuously monitoring 12 neurophysiological and clinical parameters is reported. It consists of a personal computer and various stimulation units. EEG activity, median nerve somatosensory evoked potentials (SEPs) and brainstem auditory evoked potential (BAEPs) are recorded. Additionally, EEG spectral band power, heart rate, heart rate variability, intracranial pressure, body temperature, expiratory PCO2, blood pressure and transcutaneously measured oxygenation can be monitored. This paper reports on 4 exemplary cases of the 33 patients we have monitored to date, illustrating the principles and main advantages of the system. The system was developed to support the observation of ICU patients as well as to aid therapeutic decisions. It supports the clinical determination of brain death by specifying the deterioration of various neurological systems.

Evoked potentials in basilar artery thrombosis: correlation with clinical and angiographic findings

In 28 patients with vertebro-basilar or basilar artery thrombosis brain-stem auditory evoked potentials (BAEPs) and somatosensory evoked potentials (SEPs) have been recorded. Visual evoked potentials (VEPs) were recorded in 7 of these 28 patients. In 24 patients the diagnosis was angiographically proven and in 4 patients Doppler sonography and computerized tomography suggested this diagnosis. The BAEP and SEP findings were correlated to clinical and angiographical signs. BAEPs could be classified into 6 different patterns. In more than half of the patients different BAEP patterns from the two ears could be found. A pathological IV/V complex was most often found in comatose patients and in patients with a basilar artery occlusion distal to the anterior inferior cerebellar artery. Prolonged interpeak latency of I-III was mainly found in alert or drowsy patients with caudal occlusions. The frequent occurrence of a BAEP with only wave I preserved, or with no waves preserved, in patients with brain-stem functions suggests that BAEPs are not useful in the diagnosis of brain death when basilar artery thrombosis is suspected. SEPs were either absent bilaterally or else severely altered on one side in all comatose patients. In alert patients, including those with 'locked-in' syndrome, SEPs were never absent bilaterally. Increased N13-N20 interpeak latency was an uncommon finding in this series. There was no correlation between the SEP and the angiographically proven location of the occlusion. In the 'locked-in' syndrome both SEP and BAEP findings were non-uniform. Normal SEPs were sometimes found in combination with severely altered BAEPs, suggesting partial deafferentation. Since basilar artery thrombosis is now a treatable condition, early diagnosis and documentation of functional deficits moves into a more important clinical area than heretofore.

Serial recording of median nerve stimulated subcortical somatosensory evoked potentials (SEPs) in developing brain death

Subcortical somatosensory evoked potentials (SEPs) to median nerve stimulation were recorded serially in 35 patients during the evolution towards brain death and in brain death. Neuropathological alterations of the central nervous system down to the C1/C2 spinal cord segment in brain death are well known. SEP components supposed to be generated above this level should be lost in brain death, while components generated below should not be altered. Erb's point, scalp and neck potentials were recorded at C3/4, or over the spinous process C7, using an Fz reference. In 10 patients additional montages, including spinous process C2-Fz, a non-cephalic reference (Fz-contralateral shoulder) and a posterior to anterior neck montage (spinous process C7-jugulum) were used. The cephalic referenced N9 and N11 peaks remained unchanged until brain death. N9 and N11 decreased in parallel in amplitude and increased in latency after systemic effects like hypoxia or hypothermia occurred. The cephalic referenced 'N14' decreased in amplitude and increased in latency after the clinical brain death syndrome was observed, while N13 in the posterior to anterior neck montage remained unchanged. The alteration of 'N14' went parallel to the decrease of the P14 amplitude. The subcortical SEPs in the cephalic referenced lead are supposed to be a peak composed by a horizontally orientated dorsal horn generated N13 and a rostrally orientated P14 arising at the level of the foramen magnum. The deterioration of the non-cephalic referenced P14 and of its cephalic referenced reflection 'N14' seems to provide an additional objective criterion for the diagnosis of brain death.

Short-latency somatosensory evoked potentials in brain death

Simultaneous recording of somatosensory evoked potentials to median nerve stimulation above the upper and lower neck in brain-dead patients revealed that all cervical responses were preserved in 10%, whereas a marked reduction in amplitude or even loss of N 13b at the level of the C2 spinous process was observed in 90%. Of the patients, 55% revealed an additional loss of N 13a, recorded at the level of the C7 spinous process; in 15% all cortical and spinal evoked potentials were missing, but Erb's point waves were still normal. These results suggest two different origins of the main negative waves (N 13a and N 13b), recorded above the upper and lower cervical spinal cord. N 13a (C7) is supposed to arise in the dorsal horn at the C6/7 level, N 13b (C2) in the cervicomedullary junction.