Pre-oxygenation and Measures of Gas Exchanges During Seizures in the Epilepsy Monitoring Unit

The primary goal of the study is to assess the effect of pre-oxygenation on oxygen and
carbon dioxide levels during seizures in patients admitted at the Epilepsy Monitoring Unit
(EMU). The investigators hypothesize that providing oxygen prior to seizures will help
eliminate the drops in changes seen during seizures, such as the drop in oxygen saturation
and increase in carbon dioxide levels.

Research will be done on patients that are admitted to the EMU specifically to have seizures
occur and to be recorded on video electroencephalography (vEEG), and the only research
intervention will be the use of oxygen prior to some of the seizures.

The importance of this research relates to the phenomenon of sudden unexplained death in
epilepsy patients (SUDEP). SUDEP cases are typically patients with epilepsy who are found
dead by their families in the morning, without a clear cause for death. The risk of SUDEP is
as high as 9.3 per 1000 person-years (Shorvon and Tomson 2011). There may be multiple
mechanisms for SUDEP to occur, however a leading hypothesis is a decrease in ventilation
during the seizure leading to hypoxia. Blood oxygen saturation levels have been found to
decrease significantly in 25-50% of patients during or shortly after a seizure while being
monitored in hospitals. In rare situations, a significantly lowered oxygen level may trigger
a cascade of events from which the body may not be able to recover, leading to SUDEP. In
animal models, providing oxygen prior to seizures occurring has been shown to eliminate
oxygen desaturation, but more importantly eliminate mortality in animals prone to death due
to seizures.

Pre-oxygenation is a standard procedure during rapid-sequence induction anesthesia as it
reduces the risk of oxygen desaturation during the apneic period of the procedure. On room
air, the estimated duration of safe apnea is 1 minute, but this can increase to 8 minutes
following pre-treatment with high FiO2 (Weingart and Levitan 2012). This is primarily due to
oxygen replacing nitrogen within alveoli, creating a reservoir of oxygen within the lungs
from which transfer to the bloodstream can continue despite the lack of ventilation. The
apneic episode during seizures should benefit from the same principle.

The main purpose of the Epilepsy Monitoring Unit (EMU) is to evaluate patients to better
characterize seizures, to identify the main seizure focus. In addition to standard EEG with
electrodes on the scalp, some patients require invasive localization of the epileptic focus
by surgically placing electrodes within the skull (often referred to as GRID patients) on or
within the brain, with the goal of being able to resect the area that is causing seizures.
To identify where seizure originate electrically, it requires that seizures occur during the
vEEG procedure. To provoke seizures, medications are typically lowered, and both partial
seizures and those with secondary generalization to full tonic-clonic (GTC) seizures will
occur. Prior research has shows that oxygen desaturation below 90% occurs with some complex
partial seizures, but hypoxia is more common and more profound with GTCs. Some centers use
oxygen saturation and CO2 monitors as their standard of care, and at NYULMC the
investigators also have the capability for both for clinical usage.

Oxygen is not currently a mandated standard-of-care, but is often provided by nasal prongs
following seizures as part of the post-ictal nursing care, though there is no outcome data
to support its use. It is unknown whether pre-treatment with oxygen will reduce the rate of
oxygen desaturations clinically, as seen in animal models, and this is the goal of this
research project.