Methods for monitoring

Electroencephalogram (EEG) is a signal that reflects the electrical activity of neurons in the cerebral cortex (1). Intraoperative EEG monitoring is most commonly performed in daily practice as a monitor of awareness or, more accurately, the depth of anesthesia or depth of hypnosis. The EEG is used also in congenital heart surgery to monitor brain activity during cardiopulmonary bypass and deep hypothermic circulatory arrest. Use of EEG in congenital heart surgery is usually part of a multimodal neuromonitoring protocol in most institutions. However, no studies have clearly shown a correlation between intraoperative EEG findings and neurologic outcomes (2). The effect of anesthetics on EEGs above the age of one year is comparable to that seen in adults. However, the concentration of the anesthetic agent required to produce a given effect may be correlated with age (1). The EEG in the awake state varies along with cerebral maturation and neuronal myelination from birth to adolescence. The newborn EEG has a predominance of slow oscillations. In the first year of life there is a rapidly progressive increase in the dominant frequency along with a decrease in amplitude of oscillations of the EEG. These changes continue with increasing age, but at a more gradual pace (1). The pharmacodynamics of anesthetics on the EEG in infants is not well understood and therefore EEG monitors may not be indicative of depth of anesthesia in this age group (1).