Background and Goal of Study: Postoperative delirium occurs frequently after cardiac surgery and is associated with an increased morbidity rate as well as a prolonged length of stay at the ICU. Given that delirium displays with cerebral symptoms, we analysed whether it could be detected by bilateral EEG-monitoring prior to its clinical appearance.
Material and Methods: In a prospective observational study, 81 patients undergoing on-pump cardiac surgery were included. Bilateral BIS-monitoring (BIS Vista monitor, Covidien Inc.) was applied during the pre-, intra- and postoperative period, and processed parameters such as EEG-asymmetry (Asym), burst-suppression-ratio (BSR) and Bispectral Index (BIS) were recorded. Delirium was diagnosed according to the CAM-ICU (Confusion Assessment Method for the Intensive Care Unit). Delirious and non-delirious patients were compared by t-test or - in case of a failed normality test - by the Mann-Whitney test. All data are shown as mean ± std dev or as median and interquartile range (IQR).
Results and Discussion: Postoperative delirium was detected in 26 patients (32%). A trend towards a lower EEG-asymmetry was observed in the delirium group on the preoperative day (Asym = 48,2 ± 3,6 %) as well as before induction of anaesthesia (Asym = 49,5 % ; IQR [47,4;51,5]) as compared to the non-delirium group (Asym = 50,0 ± 4,7 %; p = 0,087 respectively Asym = 50,6 %; IQR [49,1;54,2]; p = 0,081). Delirious patients showed a significantly (p = 0,028) higher BSR (1,24; IQR [0,28;3,78]) and remained significantly (p = 0,019) longer in a burst-suppression state (269 minutes; IQR [133;535]) than non-delirious patients (BSR = 0,44; IQR [0,05;2,02]; 136 Minuten; IQR [55;320]). In the pre- and intraoperative period, BIS-values were similar in both groups.
Conclusion: Preoperative monitoring of EEG-asymmetry as well as intraoperative assessment of the burst-suppression-ratio are potential methods to predict a postoperative delirium and should be investigated in further studies. So far it remains unknown, whether there is causal relation or rather an association between preoperative EEG-parameters and the development of a postoperative delirium.