Introduction to EEG Rachel Garvin, MD Neurocritical Care UTHSCSA.

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Presentation transcript:

Introduction to EEG Rachel Garvin, MD Neurocritical Care UTHSCSA

Neuronal Arrangement in Cortex

How does EEG work? EEG sets up a circuit: lead is an electrode and plasma membrane acts a capacitor Negative charges line up on inside of cell membrane and positive on outside  completed circuit

How does EEG work? Neurons in a column in the brain behave as a group EPSP correlate with surface negative EEG waves IPSP correlate with surface positive EEG waves Electrical activity of the brain ranges from microvolts

What areas of the brain does EEG detect Cortex best – more superficial areas better Does not detect deep structures such as BG, thalamus, brainstem Also does not detect well in sulci, sylvian fissure, interhemispheric fissure or skull base area

Electrode Application Electrodes must make good contact with skin Electroconductive gel is used for low impedence of current Max impedence of 5 Kohms – checked before EEG recording Increased impedence = increased noise

Electrode Placement Left sided leadsRight sided leads

Bipolar vs Unipolar

EEG waveforms Frequency = number of complete waveforms/second (Hz) Amplitude: size of wave measured in microvolts

EEG Waveforms cont’d

EEG frequency Ranges Delta: focal or diffuse Theta: central or diffuse Beta: frontal, central Alpha: occipital (alpha rhythm different from alpha frequency)

What is normal

Normal EEG

Normal Background Frequency changes with age

What are we looking for on the tracing? Location Symmetry – Are waveforms the same on L & R (amplitude, frequency) Synchrony – Is there simultaneous occurrence of similar waveforms (epi on one side) Reactivity Morphology – How would you describe the waveform Rhythmicity – Continuous repetition of waveforms that are similar

Abnormal EEG findings Generalized or focal slowing Lack of reactivity Epileptiform discharges Ictal patterns

What are these sharp waves?

Pattern Recognition

FIRDA

PLEDs

Burst Suppression

Diffuse Slowing

Focal Slowing

Breach Artifact

2 Types of Artifact

Looks like seizure…..

Status Epilepticus

Pattern Recognition