INFORMATION-PROCESSING DURING CARDIAC-SURGERY - AN EVENT-RELATED POTENTIAL STUDY

The aim of this study was to investigate whether information processin g persists during general anesthesia, and if so, to determine the rela tionship between the degree of cognitive processing measured during an esthesia and the presence or absence of intraoperative memories measur ed after anesthesia. Subjects were 12 patients, undergoing cardiac sur gery with propofol/alfentanil anesthesia. During several periods of th e operation, event related potentials (ERPs) to frequent and infrequen t tones of different pitch were analyzed. After the operation, a word recognition task with ERP recording was administered to determine whet her intraoperatively presented words would elicit a (covert) recogniti on reaction in the brain. ERP wave forms could be obtained during the intraoperative recording periods but differed substantially from those in the awake state. The presence of ERP components up to 500 msec aft er stimulus presentation suggests that auditory information processing continued during anesthesia up to a certain level of cognition. Intra operative ERPs to frequent and infrequent tones were not different fro m each other implying that differences in pitch could not be detected. The postoperative results demonstrated evidence for intraoperative me mories in 3 patients. For 2 of these 3 patients, low propofol levels a s well as reliable ERPs with large amplitudes were found close to the moment of information presentation. The results emphasize the importan ce of combining intra- and postoperative measurements and suggest that late ERP components might be used as indicators of an increased risk of auditory perception.