Midlatency auditory evoked potentials during anesthesia in children: A narrative review

Abstract

The relationship between anesthesia and the electrical activity of the brain has been described as early as in the 1940's. 1 Development in this field has been extended to the investigation of the relationship between the brain activity and depth of anesthesia. 2 Research of the brain activity as a surrogate to monitor the depth of hypnosis during anesthesia has mostly focused on the spontaneous electroencephalogram (EEG). However, the spontaneous EEG does not mature before adult age, which could influence its reliability in children. 3 Although Mid-Latency auditory evoked potentials (MLAEP) are electrical brain activity, they are fundamentally different from the spontaneous EEG. These potentials are electric responses of the brain to an auditive stimulus.They occur at about 8-50 ms after the stimulus, which is after the auditory brainstem response (0-8 ms) and before the late cortical response (>50 ms). Needless to say, an impaired auditory pathway and/or inadequate delivery of the acoustic stimulus (poor fit of the earbuds in children) will make the recording of a MLAEP unreliable or even impossible.A typical MLAEP waveform consists of 3 troughs (labelled with N for negative polarity) and 2 peaks (labelled with P for positive polarity) of a few microvolts (Figure 1). To put in perspective, the EEG is about ten times stronger and the ECG is about 100 times stronger. The weak signal of the MLAEP makes it susceptible to noise and diminishes its signal quality. The peaks and troughs are commonly labeled as N 0 , P 0 , Na, Pa and Nb and occur, in the awake adult, at about 9 ms, 12 ms, 16 ms, 25 ms and 36 ms, respectively, after the application of an auditive stimulus. 4 The MLAEP is believed to be generated from the medial geniculate body and primary auditory cortex. 5 In anesthetized adult patients, the peaks and troughs decrease in amplitude and the interval when they occur, which are called latencies, increases. [5][6][7][8][9] Myelination of the brain in de developing child strongly influences evoked potentials, this makes it difficult to elicit these in infants having an age of less than 1 year and very difficult in infants less than 6 months of age.MLAEP mature after the first decade of life, around 10-12 years. [10][11][12][13] Mid-Latency auditory evoked potentials could be a parameter to measure the depth of hypnosis in anesthetized children. This narrative review summarizes the current literature concerning the use of MLAEP and its implications in anesthetized children. | ME THODSThis study adheres to the Preferred Reporting Items for Systematic Reviews and MetaAnalysis (PRISMA) guidelines, since it was initiated