Abstracts

Rationale: Electroencephalogram (EEG) can monitor brain activity continuously in post cardiac arrest patients undergoing therapeutic hypothermia (TH), where obtaining neurological exam and brain imaging can be difficult. This now standard practice can be a vehicle to understand the effects of temperature on the brain. The aim of this project was to determine changes in certain EEG characteristics from cooling to rewarming phases to aid with prognostication.Methods: We retrospectively characterized EEG patterns in a blinded fashion during the cooling and rewarming phases of 20 patients who had undergone TH. These patients were from a larger database collected at our institution (2010-2013). For each patient, we analyzed six 30-minute EEG segments at designated time periods (3 cooled and 3 rewarmed). We characterized and systematically classified the segments on the following criteria: continuity, background frequency, inter-ictal epileptiform discharges (IEDs), and discrete seizures. We also reviewed mortality at discharge and confounding factors, such as metabolic dysfunction, infections, and treatment with anti-epileptic drugs (AEDs) or anesthetics.Results: Of the 20 patients, 40% (n=8) survived to hospital discharge. The majority of all subjects demonstrated no significant change in the background EEG from the cooled to rewarmed phases in continuity, frequency, and presence of seizures. Continuity and frequency were stable in 11/20 and 13/20 patients, respectively. Records were nearly continuous or continuous in 12/20 patients in the cooled and in 13/20 patients in the rewarmed phases. Delta/theta background was found in 18/20 patients in the cooled and in 19/20 patients in the rewarmed phases. Seizure activity was only detected in the cooled phase in 2 patients who were later placed on AEDs. The absolute presence of IEDs in the survivor group was 12.5% (n=1/8) in the cooled phase, which increased to 50% (n=4/8) in the rewarmed phase; whereas in the non-survivor group, IEDs were seen in 25% (n = 3/12) in the cooled phase, increasing to 50% (n = 6/12) in the rewarmed phase. The change in IEDs from the cooled to rewarmed phases, either newly detected or worsened, was 37.5% (n=3/8) in the survivor group and 50% (n=6/12) in the non-survivor group. The change in IEDs was not affected by the number of AEDs/anesthetics or other major toxic/metabolic factors.Conclusions: Many characteristics of continuous EEG in post cardiac arrest patients undergoing TH did not exhibit significant change between cooled and rewarmed phases, including continuity, frequency, and presence of seizure activity. However, there could be a trend toward a greater change in IEDs (i.e. either newly detected or worsening) in the non-survivor group compared to the survivor group as patients were rewarmed; however, both groups seemed to show similar trend and our finding is limited by sample size. Treatment with AEDs and anesthetic agents did not appear to affect IEDs in either group; however, reactivity and amplitude were not evaluated and may be useful markers in future prospective studies to better elucidate prognosis in this population.