Abstracts

Rationale: Rhythmic and periodic patterns (RPP) are frequently encountered in critically ill patients monitored with continuous EEG. However, whether these discharges are associated with neuronal injury, represent seizures versus an interictal-ictal continuum, and when and how to manage them, remains unclear. In order to clarify the clinical significance of RPP, we compared in-hospital mortality between critically ill patients with continuous RPP (cRPP) and altered consciousness to those with unequivocal electrographic status epilepticus (UESE).Methods: This was a retrospective study of patients diagnosed with and managed for status epilepticus (SE) at a university hospital (1/1/2005-10/31/2012). Status epilepticus was defined based on the 2012 Neurocritical Care Society Guidelines for the Evaluation and Management of Status Epilepticus. Patients with altered consciousness and EEGs demonstrating cRPP were also treated for a presumed diagnosis of status epilepticus. Subjects were classified into two groups: UESE and cRPP. Baseline characteristics included age, gender, APACHE II score, seizure etiology (cardiac arrest; acute/chronic), and seizure classification (nonconvulsive/convulsive; myoclonic; generalized/focal). The primary outcome measure was in-hospital mortality. Secondary outcomes included modified Rankin scale score (mRS) at hospital discharge, days in the ICU, days hospitalized, number of antiepileptic drugs (AEDs) used, and duration of SE. Continuous and categorical data was assessed using 2-tailed t-testing and Pearson’s Chi2, respectively. Logistic regression analysis adjusted for covariates. Significance was set at p<0.05.Results: The final cohort consisted of 141 subjects, 44 (31%) with cRPP and 97 (69%) with UESE. Sixty-five (46%) were male, with a mean age of 60 years, and mean APACHE II score of 17.60. Seizure etiology was acute in 85 (60%), due to cardiac arrest in 45 (32%), nonconvulsive in 54 (38%), and myoclonic in 41 (29%). Subjects with cRPP were more likely to have an acute seizure etiology (73% vs. 55%, p=0.04, Chi2=4.136); otherwise, there were no significant differences in baseline characteristics. Sixty (43%) subjects died; mean mRS=4.40. In unadjusted analysis, cRPP subjects used slightly fewer AEDs (3.43 vs. 4, p=0.04) and were in SE for a longer duration of time (111 vs. 41 minutes, p=0.001); however, there was no difference in mortality, mRS score, and days in the ICU and hospital. After adjusting for significant covariates, SE duration remained significantly longer in the cRPP subjects (p=0.001).Conclusions: Individuals with continuous rhythmic and periodic EEG patterns exhibit poor prognosis equivalent to that of those with unequivocal electrographic status epilepticus in the ICU, suggesting that these patterns demonstrate clinically significant sequelae. As a risk factor associated with high morbidity and mortality, this may have treatment implications regarding the management of patients demonstrating altered consciousness and continuous rhythmic and periodic EEG patterns.