Introduction to Compressed Spectral Array (CSA)


The Electroencephalogram (EEG) has many uses in the intensive care unit such as diagnosing seizure activity, encephalopathy and assessing the depth of sedation. The formal EEG involves multiple scalp electrodes and provides a snapshot of brain wave activity over the 20 – 40 minutes of recording. While widely recognised as the gold standard of assessing brain wave activity it has a number of limitations to its widespread use in intensive care. A single recording produces a large amount of data, which is complex to interpret and not normally within the remit of intensive care staff. It also only provides information on what is going on during the recording and the large amount of data produced limits its suitability for continuous monitoring. Also access to the service may be limited outside of normal working hours.

For these reasons there is a need for a system that could be easily set up and interpreted by intensive care staff allowing real time continuous monitoring of brain wave activity. The compressed spectral array (CSA) compresses the raw EEG to provide a 3D graphical display of frequency & power against time, allowing for pattern recognition by the non-specialist. It does however require some basic knowledge of EEG waves.

EEG waves

There are 4 main types of waves measured on the EEG with each corresponding to a different level of consciousness.

Beta Waves

Frequency – 13 to 30 Hz

Behaviour – awake, eyes open or closed

Alpha Waves

Frequency – 8 to 13 Hz

Behaviour – awake, relaxed with eyes closed

Theta Waves

Frequency – 4 to 7 Hz

Behaviour – sleep

Delta Waves

Frequency – <4 Hz

Behaviourdeep sleep

EEG images by Hugo Gamboa, Electroencephalography, Wikipedia, 2005.  CC BY-SA 3.0. Reproduced under GNU Free Documentation License.