$aL-Pattern EEG during Pediatric Cardiac Operations under Isoflurane Anesthesia

Previous studies of the effects of isoflurane anesthesia on the electroencephalogram (EEG) in humans (1–3) have reported consistent findings of the appearance at sub-MAC concentrations of 12–14 Hertz low-amplitude activity superimposed on 2–6 Hertz high-amplitude waves. At about 1 MAC there is loss of amplitude in the 12–14 Hertz band leaving predominant 2–6 Hertz activity. From 1.5–2 MAC alternate low (6–8 Hertz) and high (2–6 Hertz) amplitude, activity appears in a burst-suppression pattern. We have studied six children who developed unusual EEG changes associated with the introduction of isoflurane during cardiac surgery. We present two typical cases in detail and discuss the implications for this group of patients. The six cases were part of a larger study looking at EEG changes in 48 children during cardiac surgery. Of the other 42 children in the study (all undergoing cardiac surgery), 22 received isoflurane, and none of these 22 children showed the unusual EEG changes associated with the introduction of isoflurane described here. The decision to use (or not to use) isoflurane in any of our patients was based solely on the clinical requirements of each patient (e.g., to aid rewarming, to control hypertension).