Abstracts

Rationale: It is hypothesized that peri-ictal hypoxemia may contribute to sudden unexpected death in epilepsy (SUDEP). Currently, no direct measure of cerebral oxygenation is routinely utilized in epilepsy monitoring units (EMUs). However, such technology is available. Non-invasive cerebral tissue oximetry using near-infrared spectroscopy (NIRS) has demonstrated cerebral hypoxemia in the peri-ictal period in small proof-of-concept studies. We aimed to determine whether peri-ictal cerebral hypoxemia was associated with seizures in a larger cohort of patients. We also aimed to determine if such hypoxemia was associated with higher SUDEP risk and postictal memory dysfunction. Methods: Patients with histories of generalized tonic clonic seizures (GTCS) were recruited between March 2015 and July 2017. All subjects were evaluated in our EMU with continuous 30-channel scalp EEG and 2 transcutaneous regional cerebral oxygen saturation (rSO2) sensors placed on each side of the forehead. Data from the rSO2 sensors were recorded by a SenSmart Model X-100 Universal Oximetry System (Nonin, Plymouth, MN, U.S.A.). Minimum rSO2 values in the 5 minutes preceding EEG seizure onset, during the seizure, and in the 5 minutes following seizure offset were recorded. SUDEP risk was assessed using the SUDEP-7 Inventory. Potential postictal cognitive, memory, and thinking impairments were measured by comparing scores obtained on the Self-Administered Gerocognitive Exam (SAGE) at baseline (non-seizure state) and within 3 hours of recorded seizures with impaired awareness. Results: Data was obtained from 22 patients and 75 seizures. Of the 71 seizures with usable rSO2 data throughout the peri-ictal period, 42% (n=30) had an rSO2 decrease of <10% and 38% (n=27) showed a =10% decline in rSO2. The difference in rSO2 values in the preictal versus peri-ictal periods was statistically significant (p<0.0001), including when focal impaired awareness seizures and GTCS were analyzed separately. There was a difference in the mean peri-ictal rSO2 declines when comparing patients with SUDEP-7 scores <4 to =4 (Mean: -8.0 vs -16.0); however, this did not reach statistical significance (p = 0.08). Baseline SAGE scores were available for 21 patients and 35/75 seizures. The median decline in SAGE score from baseline to the postictal period was -1 (range -12 to +8).  There was no significant association between changes in SAGE scores and rSO2 measurements, including when seizure type (focal impaired awareness seizures versus GTCS) were taken into account. Conclusions: Our results suggest that seizures, including focal seizures without progression to bilateral tonic-clonic seizures, can be associated with peri-ictal cerebral hypoxemia. Although patients with more historical risk factors for SUDEP tended to have greater cerebral oxygenation desaturations, this did not reach statistical significance. These findings suggest that peri-ictal cerebral hypoxemia commonly occurs in focal seizures; further exploration of this phenomenon may provide additional insights into SUDEP pathophysiology. Funding: Funding was provided by the University of Cincinnati Department of Neurology. The SenSmart Model X-100 Universal Oximetry System was provided free of charge by Nonin Medical Inc.