Applying EEG electrodes properly is crucial to obtaining high-quality, accurate recordings of brain activity. Here's a step-by-step guide on how to apply EEG electrodes using the standard 10-20 system:
1. Prepare the Patient
Explain the Procedure: Ensure the patient understands what will happen, the purpose of the test, and that it's non-invasive and painless.
Clean the Scalp: Use an alcohol swab or skin prep gel to clean the scalp where electrodes will be placed. This removes oils and dead skin cells to improve electrode contact and reduce impedance.
2. Measure and Mark Electrode Placement (10-20 System)
Identify Key Landmarks: Find the nasion (bridge of the nose) and inion (the prominent point at the back of the skull). These are key points used for measuring electrode positions.
Measure the Head Circumference: Use a measuring tape to measure the distance between the nasion and inion, and from ear to ear, over the top of the head.
Mark Electrode Locations: Based on the 10-20 system, mark the scalp at 10% and 20% intervals along the head's circumference and midline. Common electrode locations include Fp1, Fp2, F3, F4, C3, C4, P3, P4, O1, O2, etc. (refer to a 10-20 system diagram for exact locations).
3. Apply Electrode Gel or Paste
Conductive Gel/Paste: Apply a small amount of conductive gel or paste to each electrode or directly on the scalp at the marked spots. This helps maintain good electrical contact between the scalp and the electrode.
4. Place the Electrodes
Cup Electrodes: If using cup electrodes, press them gently onto the marked spots on the scalp. Ensure each electrode is securely in place and makes good contact with the skin.
Adhesive or Snap Electrodes: For adhesive electrodes, peel off the backing and stick them on the scalp. For snap electrodes, attach them using a connector system.
5. Secure the Electrodes
Cap or Elastic Netting: Some EEG setups use an elastic cap or net to hold the electrodes in place, especially in high-density EEG setups. Ensure the cap is properly aligned with the marked electrode positions.
Tape/Adhesive: You can also secure electrodes individually with adhesive tape or electrode paste.
6. Check Electrode Impedance
Use an EEG Machine: Connect the electrodes to the EEG machine and check the impedance for each electrode. Impedance should typically be less than 5 kΩ (kilo-ohms) to ensure a good signal.
Adjust if Necessary: If the impedance is too high, re-clean the scalp or add more conductive gel.
7. Attach Reference and Ground Electrodes
Reference Electrodes: Attach the reference electrode(s) to a neutral location, such as the mastoids (behind the ears) or earlobes.
Ground Electrode: Place the ground electrode at a location that won't interfere with brain activity measurements, such as on the forehead or the back of the neck.
8. Connect to the EEG Machine
Plug in the Electrodes: Attach the leads from the electrodes to the EEG amplifier, following the proper channel assignments for each electrode position.
9. Monitor Signal Quality
Check Signal: Start the EEG recording and monitor the signal quality. Ensure there is no significant noise or artifact, and that the EEG waveforms are clear and consistent.
Make Adjustments: If certain electrodes are not showing good signal quality, adjust them, apply more conductive gel, or re-secure them.
10. Begin EEG Recording
Once all electrodes are in place and signal quality is verified, proceed with the EEG recording according to the study protocol or clinical requirement.
Summary
Prepare the patient: Clean the scalp and explain the process.
Mark the electrode positions: Using the 10-20 system.
Apply conductive gel/paste: To ensure good electrode contact.
Place electrodes: Secure them using adhesive, caps, or netting.
Check impedance: Ensure electrodes are well connected.
Monitor signal: Verify the signal is clear before recording.
Correct electrode placement and contact are essential to capturing accurate brain activity during EEG monitoring.