EEG suppression ratio monitoring in successfully resuscitated out-of-hospital cardiac arrest patients: a novel prognostic marker 
S. Bouneb, D. Mesotten, R. Heylen, J. Dens, W. Eertmans, C. De Deyne
Background and Goal of Study
Numerous studies already assessed the role of bispectral index (BIS) monitoring to assist in early neuroprognostication in the post-cardiac arrest (CA) setting. We investigated the prognostic role of the suppression ratio (SR), another parameter calculated by the BIS EEG monitor, in out-of-hospital cardiac arrest (OHCA) patients admitted to the ICU.
Materials and Methods
Between 2011 and 2015, 77 successfully resuscitated OHCA patients were enrolled in this prospective, observational study. Immediately after ICU admission, targeted temperature management (TTM) at 33°C was initiated for 24 hours followed by a rewarming period over 12 hours. Bilateral BIS monitoring was simultaneously initiated using the BIS VISTA™ (Aspect Medical Systems, Inc. Norwood, USA). Suppression ratio values were measured continuously together with BIS values. Mean SR values were then calculated per hour and used for further data analysis. A receiver operator characteristics analysis was performed to determine the optimal SR threshold and optimal time point to predict poor neurological outcome. At 180 days post-CA, neurological outcome was defined using the cerebral performance category where a CPC1-2 and CPC3-5 was defined as good and poor neurological outcome.
Results and Discussion
Thirty-nine (51%) out of the 77 OHCA patients had a poor neurological outcome at 180 days post-CA. In these patients, mean SR was higher during both the hypothermic phase at 33°C (CPC1-2: 6±12 vs CPC3-5: 37±27; p<0.001) and the rewarming period (CPC1-2: 3±12 vs CPC3-5: 22±28; p=0.001). The optimal time point to predict poor neurological outcome was at hour 23 using a mean SR value above 2.5. This corresponded with a positive predictive value of 89.3% (95% CI: 70.6 – 97.2%), a negative predictive value of 71.4% (95% CI: 56.5 – 83%) and a false positive ratio of 10.7% (95% CI: 2.8 – 29.4%). Only three patients with a mean SR value above 2.5 at hour 23 attained a good neurological outcome. The presence of at least a single SR value above 2.5 at hour 23 was associated with a 4.4-fold higher risk of poor neurological outcome (95% CI: 2.09-9.30; p<0.001).
Conclusion
This study demonstrated that EEG suppression ratio, obtained by the BIS monitor, might assist with early poor outcome prognostication in successfully resuscitated OHCA patients.


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