Abstracts

Rationale: Burst-suppression is present on electroencephalography (EEG) in almost half of comatose patients within the first 48 hours after cardiac arrest. Burst-suppression with extreme similarity of burstshape is a particular subtype of burst-suppression that has been underemphasized and considered a rarity. Through standard use of continuous EEG, we have learned that this pattern occurs relatively frequent within the first days after acute diffuse cerebral ischemia. We studied the incidence and prognostic significance of ``burst-suppression with identical bursts in comatose patients after cardiac arrest, assessed its EEG characteristics en discuss probable underlying mechanismsMethods: Patients with burst-suppression with and without identical bursts were visually identified from our prospective cohort study on continuous EEG in comatose patients after cardiac arrest by two independent reviewers. Outcome was assessed at three months and dichotomized as good (cerebral performance category 1 or 2) or poor (cerebral performance category 3, 4, or 5). Identical burst-suppression was compared with other burst-suppression patterns with regard to EEG characteristics, including cross-correlation of burstshapes, and clinical outcome, including predictive values for poor outcome.Results: Of 101 patients, 48 (48%) had burst-suppression patterns. Twenty (20%) had burst-suppression with identical bursts, which was observed between a median of 12 and 36 hours after cardiac arrest. Identical burst patterns were immediately recognizable: inter-observer agreement was 0.8 and disagreement always resulted from sampling error. An axample is shown in Figure 1.Burst-suppression with identical bursts was more often bilateral synchronous than burst-suppression without identical bursts (100% vs 64%, p<0.03), amplitudes were higher (128 vs 25 V, p=0.0001), and the mean correlation coefficient of burstshapes was almost invariably higher than 0.75 (95% vs. 0%, p<0.0001). All patients with identical bursts had a poor outcome versus 10 (36%) without identical bursts, indicating a specificity and positive predicting value for poor outcome of 100% (Table 1).Conclusions: Our results indicate that burst-suppression with identical bursts is a distinct EEG pattern in approximately twenty percent of comatose patients after cardiac arrest and invariably associated with poor outcome. We discuss possible underlying mechanisms, stating that burst-suppression with identical bursts is an expression of a very low dimensional network state of the brain, probably caused by irreversible selective synaptic failure.