Mid-Latency Auditory Evoked Potentials During Ketamine Anaesthesia in Humans

Abstract

We studied mid-latency auditory evoked potentials (MLAEP) during induction of general anaesthesia with ketamine 2 mg kg-1. MLAEP were recorded before, during and after induction of general anaesthesia on the vertex (positive) and mastoid (negative) positions. Latencies of the peak V, Na, Pa, Nb, P1 and amplitudes Na/Pa, Pa/Nb and Nb/P1 were measured. Fast-Fourier transformation was used to calculate power spectra of the MLAEP. In the awake state, MLAEP had large peak-to-peak amplitudes and a periodic waveform. Peak latencies remained within the normal range. Power spectra indicated high energy in the 30-40 Hz frequency range. After induction of general anaesthesia with ketamine, there was no change in latency of peaks V, Na, Pa, Nb, P1 and no apparent reduction in amplitudes Na/Pa, Pa/Nb and Nb/P1. In the power spectra, frequencies in the range of 30-40 Hz retained high energy. Amplitudes and latencies of MLAEP did not change during induction of general anaesthesia with ketamine. Primary processing of auditory stimuli in the primary auditory cortex seemed to be preserved under ketamine. Suppression of sensory (auditory) information processing must take place at a higher cortical level in a dissociative manner.

Cortico-centric effects of general anesthetics on cerebrocortical evoked potentials

“…Evoked potential slope is not typically measured in clinical studies; however, an increase in population event amplitude is usually accompanied by an increase in event slope. Clinical studies have shown mixed results for ketamine, with either maintenance [5] or enhancement [20] of N20-P23 amplitude. The effects of etomidate and ketamine contrast with the volatile anesthetics, tending to reduce the amplitude and increase the latency of cortical evoked responses [3,21] .…”

“…However, there are exceptions that call into question the thalamic gate explanation as a unifying mechanism. Most notable is ketamine, which not only preserves sensory transmission to the cortex [5] , but may even enhance cortical responsiveness to incoming sensory information [6] and maintains an activated EEG.…”

Gamma and Delta Neural Oscillations and Association with Clinical Symptoms under Subanesthetic Ketamine

“…We did not find significant ketamine effects on the low range of gamma . One study reported that general anesthetic dose (2 mg/kg) ketamine did not change 30-40 Hz power in response to auditory click in humans (Schwender et al, 1993).…”

Anesthesia and the Electrophysiology of Auditory Consciousness

“…Perhaps one piece of evidence for the latter position is that the anesthetic ketamine affects MLRs and ASSRs differently. Ketamine anesthesia does not have any significant effects on AMLRs (Schwender, Klasing, Madler, Poppel, & Peter, 1993b), but it increases the amplitude of the ASSR (Plourde, Baribeau, & Bonhomme, 1997). The latter authors note this apparent discrepancy and resolve it by using the actual data presented by the former authors to compute a predicted effect of ketamine on the ASSR, assuming that the ASSR is purely a summation of overlapping AMLRs.…”