The Prognostic Value of Simplified EEG in Out-of-Hospital Cardiac Arrest Patients

Background We previously validated simplified electroencephalogram (EEG) tracings obtained by a bispectral index (BIS) device against standard EEG. This retrospective study now investigated whether BIS EEG tracings can predict neurological outcome after cardiac arrest (CA). Methods Bilateral BIS monitoring (BIS VISTA™, Aspect Medical Systems, Inc. Norwood, USA) was started following intensive care unit admission. Six, 12, 18, 24, 36 and 48 h after targeted temperature management (TTM) at 33 °C was started, BIS EEG tracings were extracted and reviewed by two neurophysiologists for the presence of slow diffuse rhythm, burst suppression, cerebral inactivity and epileptic activity (defined as continuous, monomorphic, > 2 Hz generalized sharp activity or continuous, monomorphic, < 2 Hz generalized blunt activity). At 180 days post-CA, neurological outcome was determined using cerebral performance category (CPC) classification (CPC1-2: good and CPC3-5: poor neurological outcome). Results Sixty-three out-of-hospital cardiac arrest patients were enrolled for data analysis of whom 32 had a good and 31 a poor neurological outcome. Epileptic activity within 6–12 h predicted CPC3-5 with a positive predictive value (PPV) of 100%. Epileptic activity within time frames 18–24 and 36–48 h showed a PPV for CPC3-5 of 90 and 93%, respectively. Cerebral inactivity within 6–12 h predicted CPC3-5 with a PPV of 57%. In contrast, cerebral inactivity between 36 and 48 h predicted CPC3-5 with a PPV of 100%. The pattern with the worst predictive power at any time point was burst suppression with PPV of 44, 57 and 40% at 6–12 h, at 18–24 h and at 36–48 h, respectively. Slow diffuse rhythms at 6–12 h, at 18–24 h and at 36–48 h predicted CPC1-2 with PPV of 74, 76 and 80%, respectively. Conclusion Based on simplified BIS EEG, the presence of epileptic activity at any time and cerebral inactivity after the end of TTM may assist poor outcome prognostication in successfully resuscitated CA patients. A slow diffuse rhythm at any time after CA was indicative for a good neurological outcome.