What does a suppression ratio of 0.8 mean

Animal and human studies confirm that the electroencephalogram (EEG) is a reliable biomarker of the severity of brain injury after resuscitation from cardiac arrest.1, 2 Standard full montage EEG represents a “gold standard”, but requires special training to apply and interpret, and may have limited availability (e.g. nights, weekends, smaller centers).1 Simpler processed EEG monitors can be applied by nurses and physicians, are widely available on a 24/7 basis, and present results as an easily interpretable quantitative biomarker.1

Several processed EEG variables reliably predict outcome after cardiac arrest, including the suppression ratio (SR), which estimates the percent of the EEG epoch with very low voltage, and ranges from 0% to 100%. The SR has been determined from full montage3, 4, 5, 6, 7 and simplified montage devices.8, 9, 10, 11 We previously reported the SR recorded by the Medtronic Vista Bispectral Index monitor to quantify EEG suppression during barbiturate coma12 and after cardiac arrest.13 No prior studies have compared full montage and simplified EEG techniques to determine the SR after cardiac arrest, or validated the SR determined by the Vista monitor among patients resuscitated after cardiac arrest.

Methods

This study sought to establish the validity of the SR measured by the Medtronic Vista monitor (MSR) by blinded comparison to SR measured by a full montage EEG monitor, and to test construct validity by comparing MSR during different “standard” EEG backgrounds,14 and amplitude-integrated EEG (aEEG) patterns.9 After IRB approval with waiver of informed consent, a consecutive sample of adult patients treated with TTM after cardiac arrest and simultaneously monitored with both EEG techniques was

Results

Over a four-month period, 29 adult patients were treated with TTM after cardiac arrest; 23 were included in our study, and 6 treated during weekends when the research team was unavailable were not included. The median age was 58 (46–72) years, most patients were male, with a similar incidence of VT or VF and PEA (Table 1). Most cardiac arrests occurred out-of-hospital (74%), and the time to recovery of spontaneous circulation (ROSC) was 12 (7–18) minutes. At the time of EEG collection, the core

Discussion

This observational study confirms that the SR determined from a simplified EEG montage with the Medtronic Vista monitor agrees well with that derived from full montage recordings using the Natus and Persyst systems. When compared to standardized EEG background categories,14 the MSR varied as expected from 0% during continuous EEG patterns to 64% during Burst Suppression patterns. When compared to established aEEG patterns, the MSR varied from 0% during continuous patterns to 46% during flat

Conclusions

The suppression ratio determined by the Medtronic Vista monitor using a simplified EEG montage is valid, and agrees with full montage EEG technology. The suppression ratio varies as expected with different established EEG backgrounds and aEEG patterns. Additional research to define the appropriate role of simplified EEG montages and processed EEG data to stratify the severity of brain injury and guide therapy after cardiac arrest is needed.

Authors’ contribution

All authors have made substantial contributions to all of the following: (1) the conception and design of the study, or acquisition of data, or analysis and interpretation of data, (2) drafting the article or revising it critically for important intellectual content, (3) final approval of the version to be submitted.

Conflict of interest

None.

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