Effect of Etomidate on the Auditory Evoked Response in Man

Abstract

The effect of etomidate on the auditory evoked response was examined in a double-blind study carried out before the start of surgery. Fourteen patients were anaesthetized with 70% nitrous oxide and oxygen after induction with thiopentone. Ventilation was controlled. Seven of the patients received a continuous infusion of etomidate, increasing in five equal steps from 0.01 mg kg-1 min-1 to 0.05 mg kg-1 min-1 over a period of 50 min. The other seven received similarly an equivalent volume of saline. The patients given etomidate were easily distinguishable from those given saline, solely on the basis of changes in the early cortical peaks Pa and Nb. In the etomidate group the latencies of these peaks increased and their amplitudes decreased. These changes were linearly related to serum etomidate concentration. There was no effect of etomidate on the brainstem response.

Motor signs of wakefulness during general anaesthesia with propofol, isoflurane and flunitrazepam/fentanyl and midlatency auditory evoked potentials

“…A similar increase of latencies and decrease of amplitudes has been found for halothane [8], enflurane [8,23], isoflurane [7,11,241, etomidate [9,25], propofol [14] and Althesin [13]. There is also a dose dependent linear prolongation of peak latencies and a decrease of amplitudes with rising end-expiratory concentrations of isoflurane [7j.…”

“…In contrast, midlatency peaks of the AEP do not differ within and between individuals. Under general anaesthesia with a range of anaesthetic agents MLAEP are suppressed dose-dependently [7][8][9][11][12][13][14], and have been used recently to monitor depth of anaesthesia and to indicate intraoperative wakefulness and awareness [15-171. During combined general and local anaesthesia it is difficult to use autonomic signs to assess whether wakefulness is suppressed adequately [18]. Furthermore, it is not known whether under these conditions, and using different anaesthetic regimens, different incidences of motor signs of wakefulness can be observed.…”

Evoked potential monitoring in anaesthesia and analgesia

“…7) and desflurane reduce the amplitude and increase the latency of Pa and Nb waves of early cortical AEP in a dose-related manner [113][114][115][116]. In a recent study, Sharpe et al [116] concluded that AEP may be a more sensitive indicator of anaesthetic depth at low desflurane doses and the EEG more sensitive at higher concentrations.…”

Midlatency auditory evoked potentials and purposeful movements after thiopentone bolus injection

“…The late latency auditory evoked potentials (LLAEP) reflect neural activity of association areas 100 to 1000 ms after stimulus. These potentials are strongly influenced by subjective factors like stimulus evaluation and cognitive analysis [7-111. The early evoked potentials, generated in the brainstem, remain nearly stable under anaesthetic medication [12][13][14]. The late cortical components show a great variation of latencies and amplitudes in the awake state [I, 7, while midlatency peaks do not differ between and within individuals.…”