ICU EEG-Ictal and BIRDs

ICU—Ictal and Potentially Ictal Patterns

Written by Trent Tollefson, MD and Sarah Durica, MD

One of the hallmarks of ictal patterns in general is that they demonstrate evolution. Evolution can involve changes in underlying frequency, morphology, or spread in spatial distribution. According to The American Clinical Neurophysiology Society’s Standardized Critical Care EEG Terminology: 2021 Version, an electrographic seizure can involve either epileptiform discharges averaging >2.5 Hertz for greater than or equal to 10 seconds or any pattern with definite evolution lasting greater than or equal to 10 seconds. If an electrographic seizure persists for greater than 10 continuous minutes or occurs for greater than or equal to 20% of any 60-minute period of recording, this meets the definition for electrographic status epilepticus. An electroclinical seizure is characterized by an EEG pattern with definite clinical corelate time-locked to an evolving or periodic pattern or demonstration of both clinical and electrographic improvement with a parenteral anti-seizure medication. If an electroclinical seizure lasts for greater than or equal to 10 minutes (5 minutes if the seizure is convulsive) or occurs for greater than or equal to 20% of any 60-minute period of the EEG, this meets criteria for electroclinical status epilepticus.

Figure 1: Electrographic seizure in P8. The frequency transitions from faster to slower frequencies and the morphology transitions from “spikier” to more blunted as the seizure continues. Image Credit: Trent Tollefson, MD

When interpreting ICU EEG, patterns can occur that stand out from the background that do not meet criteria for an electrographic seizure. Brief potentially Ictal Rhythmic Discharges (BIRDs) is a pattern that consists of either focal or generalized rhythmic activity greater than 4 Hertz lasting between 0.5 to less than 10 seconds that either evolves or demonstrates morphology and location similar to that patient’s seizures or interictal epileptiform discharges.

Figure 2: Brief potentially Ictal Rhythmic Discharges (BIRDs). Image Credit: Zulfi Haneef, MD