**2. Historical note**

There is still a scientific debate regarding these EEG features. Until recently, there was no uniformly accepted nomenclature for those frequently encountered ICU EEG abnormalities such as periodic epileptiform discharges, fluctuating rhythmic patterns and combinations.

Based on these questions, the American Clinical Neurophysiology Society (ACNS) recently proposed new terminology for these controversial EEG patterns [6, 7] (**Table 1**); terms such as "triphasic waves," which implies for many clinicians a metabolic encephalopathy was eliminated; in addition, the use of "ictal," "interictal"


*PLEDS: Periodic Lateralized Epileptiform Discharges; LPDs: Lateralized Periodic Discharges; BIPLEDs: Bilateral Independant Periodic Lateralized Epileptiform Discharges; BIPDs: Bilateral Independant Periodic Discharges; GPEDs/PEDs: Generalized Periodic Epileptiform Discharges/Periodic Epileptiform Discharges; FIRDA: Frontal Intermitent Rhytmic Delta Activity; LRDA: Lateralized rhythmic Delta Activity; SIRPIDS: Stimulus-induced rhythmic, periodic or ictal discharges*

#### **Table 1.**

*ICU periodic EEG patterns: Old vs. new terminology [6].*

*Periodic EEG Patterns in the Intensive Care Unit (ICU): Definition, Recognition and Clinical… DOI: http://dx.doi.org/10.5772/intechopen.95503*

and "epileptiform" for the equivocal patterns was ovoided; these EEG features are now termed Periodic Lateralized Discharges (PLDs), (formerly Periodic lateralized Epileptiform Discharges or PLEDs), Bilateral independent Periodic Discharges or BIPLDs, (formerly Bilateral independent Periodic Lateralized Epileptiform Discharges or BIPLEDs), Generalized Periodic Discharges (GPDs), formerly Generalized Periodic Epileptiform Discharges (GPEDs) and continuous GPD 2 / s with triphasic morphology) (formerly Triphasic Waves or TWs). SI-Evolving LRDA, Stimulus-induced Lateralized Rhythmic Delta Activity (formerly stimulus-induced rhythmic, periodic or ictal discharges or SIRPIDs) are also peculiar, recently discovered EEG patterns, and may manifest as periodic discharges [8]. The other periodic and rhythmic patterns are the occasional brief 2 / s GRDA predominantly frontal (formerly Frontal Intermitent Rhythmic Delta Activity or FIRDA), Evolving Lateralized Rhythmic Delta Activity or Evolving LRDA, (formerly Lateralized Rhythmic Delta Activity (LRDA) or Lateralized seizure delta activity, and Short ictal potential rhythmic discharges or B(I)RDs, will also be briefly discussed in this chapter.
