Background
Brain cell viability was not measured directly during cardiopulmonary resuscitation (CPR) in out-of-hospital cardiac arrest (OHCA). We developed the EEG-based brain resuscitation index (EBRI) which is an expected value of end-tidal CO2 calculated from single-cannel EEG signals measured from forehead during CPR. We compared the observed ETCO2 and EBRI during CPR.
Methods
OHCA patients who received CPR at a tertiary emergency department were enrolled for this study. All CPR procedures were provided without any change, but the single channel EEG electrode was attached on the forehead of OHCA patients. The EEG signals were transmitted via a designed wireless Bluetooth technology to an independent mobile computer. We developed the computation formula to calculate the expected ETCO2 using multiple EEG signal values in previous animal study
EBRI (Expected ETCO2)=a+b_1*BSR+b_2*BetaR+ b_3*SynchFastSlow+b_4*DeltaR
Data collection was conducted till return of spontaneous circulation or termination of CPR. Each data was continuously collected by 0.5 second intervals and extremely deviated values such as observed ETO2 level lower than 5 or higher than 60 were excluded. After 1-minute averaging, Pearson correlation analysis and Bland-Altman agreement plot between observed ETCO2 and EBRI were performed. We tested the repeated measure ANOVA for change of trend.
Results
Total 5 patients with EEG signals during CPR of eligible 13 OHCA patients were enrolled and analyzed from November 2017 to April 2018. Total 4989 observed and EBRI (expected ETCO2) values from five patients were collected. After averaging by 1-minute for all values, Average ETCO2 value per min. were used for correlation and agreement analysis. Positive correlation was found with statistical significance (Pearson correlation coefficient 0.53, p-value <0.01). The agreement by the Bland-Altman plot showed only 4/48 (8.3%) observations were not within agreement range (Figure 1). In repeated measure ANOVA, there was no significant difference in trend according to CPR duration between observed ETCO2 and EBRI (p-value=0.91) (Figure 2)
Conclusions
We found positive correlation and higher agreement between observed ETCO2 and expected ETCO2 from EEG signals during CPR in OHCA patients. Further study on observational and interventional study on the use of non-invasive EEG signal for measuring CPR quality are needed.

5 - correlation and agreement between observed etco2 and predicted etco2 calculated from electroencephalography signals: a pilot trial