Understanding the CSA screen

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EEG1 – Raw, real time, uncompressed EEG between electrodes Fp1 and T3 (left sided electrodes)

EEG2 – Raw, real time, uncompressed EEG between electrodes Fp2 and T4 (right sided electrodes)

CSA1 – Compressed graphical representation of the EEG between electrodes Fp1 and T3 (left sided electrodes)

CSA2 – Compressed graphical representation of the EEG between electrodes Fp2 and T4 (right sided electrodes)

Y-axis – Time – current time displayed at bottom of CSA with tracing getting increasingly older as you move towards top of screen (providing a 3D display of changes in frequency and power against time). Each line on the screen represents 2 seconds, so just under one minute of activity is displaced on the screen at a time.

X-axis – Frequency in Hz of the brain waves (number of waves per second) at the time of recording. The higher the frequency of the brain waves recorded the further the peaks will be to the right hand side and the lower the frequency the further they will be to the left.

SEF (90%) – The Spectral Edge Frequency (SEF) is the solid yellow line which represents the highest significant frequency present in the current EEG (frequency below which 90% of that segments power lies). As the SEF increases the solid yellow line will move to the right hand side and the lower the SEF the further the solid yellow line will move to the left (useful in spotting changes in frequency). SEF1 is the left sided spectral edge frequency and SEF2 is the right sided spectral edge frequency.

Total Power (TP) – The power is a reflection of the amplitude or height of the waves measured with the ‘Total Power’ being the sum of the power for all frequencies on that line. The bigger the amplitude of the waves the bigger the total power. This is also associated with taller peaks on the CSA display. TP1 is the left sided total power and TP2 is the right sided total power. Total power in the non-sedated brain is around 2 ohms where as in the deeply sedated patient can be < 0.1 ohms.

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