重症意識障害における聴性脳幹反応

Auditory evoked brainstem responses (ABRs) in severe brain damaged patients.

はじめに

　聴性脳幹反応（ABR）は一次的あるいは二次的脳幹障害を客観的に把握できるために，重症意識障害の病態解明の一助として応用されている^{5,7,9,14,15,24）}。とくに，neurosurgical intensive care，あるいはcritical careの分野では，ABRは非侵襲的であり，かつbed sideで即座に脳幹障害の有無を判定できるものとして，その意義は周知である。しかし，従来のABRの評価は経時的変化の追跡に乏しく，また体温（BT），血圧（BP），頭蓋内圧（ICP），脳灌流圧（CPP）などの及ぼす影響に対する検討が不十分であった。このような欠点を補いつつ，重症意識障害の病態の客観的かつ視覚的認識を可能とするため，筆者らは自動的かつ経時的ABRモニタリングシステムを開発し^17），ABRならびに各パラメーターを鳥瞰図として表現し，意識障害の病態の統合的解析を行なっている^18,19）。

Short latency auditory evoked brainstem re-sponses (ABRs) reflect the activities of the neuralaxis from the auditory brainstem to investigate if ABRs would be a good index to predict the outcome of patients with severe brain damage following primary or secondary brainstem injury. However, previous investigations have been mainly focused on ABRs alone i.e., changes cf latency and amplitude without considering other crucial parameters such as intracranial pressure (ICP), arterial mean pressure (AMP), cerebral perfusion pressure (CPP), electroencephalogram (EEG) and body temperature (BT). We investigated the re-lationship between ABRs and those parameters in patients by using a newly developed multi-modal serial monitoring system. The particular feature of this system was a real time display of all these parameters as a bird's-eye view. The results obtained were as follows. (1) The magni-tude of increased ICP or of decrease in CPP was apparently correlated with the latency of the fifth wave of ABRs. (2) Hypothermia induced by drug intoxication elongated the latency of ABRs. This was reversed by normalizing the BT and improving consciousness level. It could be con-cluded that although ABRs gave us useful infor-mations as to the judgment of neural activities in patients particularly of brain death, they were so easily influenced by other parameters as we described. The bird's-eye view method here we used was valuable to overcome these problems, and should contribute to early and appropriate management in patients with severe brain damage.