Article
Brainstem evoked potentials (BAEP) – an alternative method of acquisition reveals additional information
Akkustische Hirnstammpotentiale (BAEP) – eine alternative Ableitungsmethode ermöglicht zusätzliche Information
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Authors
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M. Lorenz
- Neurochirurgische Klinik, Medizinische Hochschule Hannover
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J. Köppen
- Neurochirurgische Klinik, Medizinische Hochschule Hannover
| Published: | May 30, 2008 |
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Outline
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Objective: The auditory pathway runs in its first part vertically from the cochlea to the brainstem and then turns up in a caudal-cranial direction in an angle of almost 90 degree. The standard recording of BAEPs collects the field potentials between the ends of a virtual triangle. Using an additional recording electrode in the posterior pharyngeal wall adjacent to the upper brainstem and a 2-channel registration the recorded volleys would lie approximately parallel to the auditory pathway.
Methods: A pharyngeal electrode should only be acceptable under general anaesthesia. Therefore, we investigated 37 anesthetized patients with pathologies of the posterior cranial fossa or severe cranial injuries. We registered the clinical patterns and the latencies and amplitudes of the peaks I to V of the BAEPs in standard- and the modified recording technique in comparison to a normal standard-collective.
Results: In 5 patients no reliable result could be obtained and in 25% of all recordings failed to show sufficient comparability in at least one modality due to technical, mainly electromagnetic disturbances or as a result of damage to the investigated structures. In these patients, mydriasis was also common of at least one side. In 25% of the patients the 2-channel recording revealed an improved identification of different peaks compared to the standard procedure.
Conclusions: In patients with brainstem lesions the prognosis frequently influences the extent of therapy. The validity of clinical examinations is limited in anesthetized patients. BAEPs offer a reliable tool for a bedside assessment which are relatively stable to the uppermost narcotics or hypnotics. Normal 1-channel BAEP registrations are the gold standard. However, in selected cases the modified 2-channel recording technique, which can be done without major efforts within the routine investigations at the ICU or the OP, may offer additional information, which may lead to a better understanding of the functionality of the auditory pathway in the brainstem, and can be of considerable value for example in braindeath investigations or intraoperative monitoring.
