Association Between Seizure Periodicity and Responsiveness to Intravenous Antiseizure Medications in Critically Ill Patients

Purpose: Seizures are common in critically ill patients, with a subset exhibiting cyclical organization. This study aimed to determine whether seizure cycle is associated with responsiveness to intravenous antiseizure medications. Methods: We retrospectively reviewed continuous EEG recordings and included those containing repeated seizures. Data were segmented into assessment units (AUs) based on intravenous antiseizure medication bolus timing, which served as the unit of analysis. Circular strength within each AU was quantified using the mean resultant length, with values closer to one indicating stronger alignment. Pharmacologic response was defined as seizure remission within a postbolus assessment window, the duration of which was defined as three times the mean seizure period within the AU. Associations were evaluated using multivariable and population-averaged logistic regression models. Results: We included 88 AUs from 25 critically ill patients (mean AU duration, 1.1 hours; mean number of seizures per AU, seven events). The mean resultant length was 0.71 (range, 0.11–0.99). Strong periodicities were observed across etiologic groups. Seizure remission occurred in 17 of 88 AUs. Higher mean resultant length was associated with lower odds of remission (logistic model: OR = 0.020; 95% CI, 0.001–0.533; p = 0.020; population-averaged model: OR = 0.067; 95% CI, 0.008–0.560; p = 0.013). In some instances, usage of phenobarbital was associated with seizure alleviation even in AUs with strong periodicity. Conclusions: Our preliminary findings suggest that greater seizure cycle was associated with reduced responsiveness to intravenous antiseizure medications.