Auditory evoked potentials

Auditory evoked potentials (AEPs) are an electrical m a n i fe s t ation of the brain response to an auditory stimu l u s. M i d - l at e n cy auditory evo ked potentials (MLAEPs) and the coherent frequency of the AEP a re the most promising for monitoring depth of a n a es t h e s i a . MLAEPs show graded ch a n ges with incre asing anaesthetic concentration over the clinical conc e n t ration ra n ge. The latencies of Pa and Nb lengthen and their amplitudes reduce. These changes in fe at u res of wave fo rm are similar with both inhaled and intravenous anaesthetics. C h a n ges in latency of Pa and Nb waves are highly correlated to a transition from awa ke to loss of c o n s c i o u s n e s s. MLAEPs re c o rding may also provide info rm at i o n about cereb ral processing of the auditory input, p rob ably because it re flects activity in the tempora l l o b e / p r i m a ry cort ex , sites invo l ved in sounds elab oration and in a complex mechanism of implicit (non declarative) memory processing. The coherent freq u e n cy has found to be disrupted by the anaesthetics as well as to be implicated in attentional mech a n i s m . These results support the concept that the A E P s re flects the balance between the arousal effects of s u rgical stimu l ation and the dep ressant effects of a n a e s t h e t i c s.H oweve r, AEPs are n’t a perfect measure o f anaesthesia dep t h . Th ey can’t predict pat i e n t s m ovements during surge ry and the signal may be a ffected by mu s cle art e fa c t s, d i at h e rmy and other electrical operating theat re interfe re n c e s. In concl us i o n , once re l i ability of the AEPs re c o rding became p roved and the signal acquisition improved it is like ly to became a routine feature of clinical anaesthetic practice