Placement

  • Full head should be measured according to the 10/20 electrode placement
  • Apply 16, but no fewer than 8 electrodes

Impedance

  • All inter-electrode impedances should be between 500-5000 ohms
  • High electrode impedances or poorly matched impedances can increase line frequency interference

Types

  • Collodion application of scalp electrodes is preferred
  • Sterile subdermal electrodes may be used when the placement of electrodes would impinge on the operative field

Modified Electrode Placement

  • Surgical procedures involving a crani may require modification of the standard 10/20 placement.
  • Alternative placements should be documented
  • Modified placements may also reduce the number of electrodes

HFF

  • 70 Hz is preferable, but lowering this to 35 – 50 Hz may be necessary to reduce electrical noise

LFF

  • 0.3 – 0.5 Hz is best to record the slow EEG activity from anesthetic agents and ischemia

Line-Frequency Filter (Notch Filter)

  • May be necessary due to noise.  Should be used judiciously and only after all other methods of noise reduction have been exhausted

Chart Paper Speed

  • The baseline recording of the EEG should be performed with a standard paper speed of 30 mm/sec
  • The paper can then be slowed to 5-15 mm/sec to emphasize beta asymmetries and slow activity

16 Channel

  • Can detect more localized ischemic events

8 Channel

  • Recordings can give full information for ischemic abnormalities of MCA, ACA, and PCA cerebral regions
  • With 16 channel OR systems it is preferable to run an 8 channel EEG with upper and lower SSEP recordings.  Multi-modality testing gives a better picture of subcortical structures as well as cortical structures

4 Channel

  • EEG gives much less info and must be used with SSEPs.
  • 4 channel EEG should be avoided

 

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