1. Sweat Artifact

Sweat artifact occurs when sweat accumulates on the skin, particularly under electrodes, and the sodium chloride (NaCl) in sweat generates a small electrical charge that is detected by the EEG electrodes. The resulting artifact is typically slow in frequency, often less than 0.5 Hz, and exhibits low amplitude. It does not resemble normal brain activity patterns and can appear as a continuous, low-frequency signal overlaying the actual cerebral rhythms.

These artifacts can be challenging to localize and may appear bilaterally, unilaterally, or in a very focal area depending on the distribution of sweat. Sweat artifacts may vary based on the patient's level of perspiration, body position, and environmental factors. For example, if a patient is feverish or in a warm room, sweat accumulation is more likely, leading to potential interference in EEG recordings. To manage this, clinicians should monitor electrode placement and clean the skin to prevent excessive buildup of sweat, which could distort results.

Identifying Sweat Artifact

The slow frequency of sweat artifacts (often less than 0.5 Hz) helps differentiate it from more typical brainwave activity. If the artifact is widespread across multiple electrodes, the source may be sweat buildup under electrodes. The artifact will not follow a specific cerebral pattern and can be minimized by adjusting electrode placement, repositioning, or using filters during the analysis.

2. Chest Physiotherapy Artifact

Chest physiotherapy (Chest PT) artifact is often encountered in critically ill or sedated patients who require respiratory therapy. Chest PT is a medical procedure aimed at clearing the lungs and facilitating breathing, which involves rhythmic movements or vibrations applied to the chest. These movements can produce rhythmic artifacts that resemble seizure activity in EEG recordings. While Chest PT-induced artifacts can mimic seizures, they differ in key ways:

  • Rhythm: Chest PT artifact is rhythmic, while seizures typically exhibit more complex, evolving patterns.
  • Lack of Field or Evolution: Unlike seizures, Chest PT artifacts do not evolve over time or have a significant spread across the scalp.
  • Video Confirmation: Video monitoring of the patient can often confirm that the rhythmic movements are due to Chest PT, not a seizure.

These artifacts typically appear in the posterior regions of the EEG, but their location can vary depending on the patient's position and where the therapy is being applied. For example, if the patient is lying on their back or side, the artifact may be more prominent in the lower parts of the EEG signal.

Identifying Chest PT Artifact

Clinicians can identify Chest PT artifact by looking for rhythmic patterns that lack the progression typical of seizures. Additionally, checking the patient's video feed for chest physiotherapy movements will aid in confirming the source of the artifact. In cases of suspected artifact, confirming the absence of evolving or spreading brain activity can help rule out seizures.

3. Movement Artifact

Movement artifact occurs when the patient moves their body in a way that affects the electrode placement or introduces noise into the EEG system. Movement can be caused by involuntary muscle contractions, shifts in body position, or intentional movement. This type of artifact appears as high-amplitude, irregular patterns that do not correspond to normal brain activity. Movement artifacts often disrupt the signal and can result in significant baseline shifts.

Head Shaking Artifact

Head shaking artifact occurs when the patient moves their head rapidly, often while lying down or resting. This can be more apparent when the patient is in a relaxed position, such as on a pillow, and typically appears as slow, low-amplitude activity, often localized to the posterior (back) part of the scalp. Head shaking artifact can resemble roving eye movements in drowsiness, but it typically affects the posterior electrodes (occipital region), while eye movements are seen in the anterior (frontal) leads.

This type of artifact can mimic certain types of cerebral activity, but it can usually be distinguished by its relatively low frequency and lack of coherent brainwave patterns. Ensuring the patient remains still during the EEG recording or adjusting the setup can help reduce this type of interference.

Identifying Movement Artifact

Movement artifacts are generally easy to identify because they tend to be high amplitude and appear in chaotic or irregular patterns. If the patient moves their body or changes position during the EEG, it is important to check the data for unusual spikes or baseline shifts. Head shaking artifact can be recognized by its slow frequency and posterior localization. If movement artifact is suspected, reviewing the video feed for patient motion can help confirm the cause.

4. Other Types of EEG Artifacts

Bubble Artifact

A bubble artifact is seen in patients who are intubated and may develop a small air bubble on the tip of the nose or mouth. The presence of a bubble that moves with each breath can generate periodic bursts of activity in the EEG, which will appear rhythmic. However, this artifact is unrelated to brain activity and should be considered carefully when analyzing the EEG. To confirm, one should observe the pattern and check the patient for any visible bubbles or other potential sources of mechanical interference.

Electrode Artifact

Electrode artifact is one of the most common types of artifact and occurs when the electrodes become loose or improperly attached to the scalp. This leads to interference that appears as a sharp, irregular peak in the signal. If this artifact is present at a specific electrode, the clinician should check the placement of the electrode to ensure it is securely attached. The presence of electrode artifact can be confirmed by ensuring that no movement in the patient corresponds to the artifact in the EEG.

5. Conclusion

Understanding the different types of EEG artifacts is crucial for accurate interpretation of EEG recordings. Sweat artifact, chest physiotherapy artifact, and movement artifacts each have unique characteristics that can help differentiate them from true brain activity. Recognizing these artifacts and distinguishing them from actual cerebral events ensures that EEG results are reliable and not influenced by external or physiological factors. Clinicians should be vigilant when interpreting EEG data, and where necessary, confirm potential artifacts with video feeds, patient status, and electrode adjustments.