A 72-year-old man suffered out-of-hospital cardiac arrest. Following return of spontaneous circulation and endotracheal intubation, point-of-care EEG (Ceribell Inc.) was obtained. EEG resembled burst-suppression. “Bursts” appeared highly epileptiform, had identical morphology and duration, and occurred at regular intervals (Figure 1). 1 A machine artifact was suspected. Bedside examination revealed water condensation within the endotracheal tube. A gurgling sound, time-locked with the “bursts” seen on EEG, was heard with every ventilation.
Figure 1.
EEG resembled burst-suppression. “Bursts” appeared highly epileptiform, with identical morphology. They occurred every ∼2.5 seconds. Each “burst” had a duration of approximately 1 second. Artifact had higher amplitude over the left hemisphere. This may be explained by the position of the ventilator (on the patient’s left side) and/or the ventilator tubing (angled to the left). EEG was recorded using 10 electrodes positioned circumferentially without any parasagittal coverage. Findings are shown using default Ceribell® display settings: sensitivity of ±50 µV, high-pass filter of 1 Hz, and low-pass filter of 30 Hz.
“Water in the tube” or “ventilator liquid movement” artifact is caused by water condensation within the tubing connected to a mechanical ventilator, producing a hydroelectric charge potential.2,3 This artifact can be misinterpreted as epileptiform abnormalities, which may include polysharp/polyspike waves, highly epileptiform bursts, brief potentially ictal rhythmic discharges, paroxysmal fast activity, or generalized periodic discharges with superimposed fast activity.1-4 Clues to artifact identification include its regularity and monomorphic appearance, which often follows a crescendo-and-decrescendo pattern (although crescendo-and-decrescendo morphology was not clearly seen in our patient).2,3 Video/audio recordings may reveal a gurgling sound that is time-locked with the artifact.3,4 This artifact typically improves or disappears after suctioning fluids from the ventilator circuit (Figure 2).3,4
Figure 2.
Immediately after suctioning fluids from the endotracheal tube (arrow), there was a dramatic change in artifact morphology. This supported the contribution of water condensation to the generation of this artifact. Findings are shown using default Ceribell® display settings: sensitivity of ±50 µV, high-pass filter of 1 Hz, and low-pass filter of 30 Hz.
Point-of-care EEG is increasingly being used by neurohospitalists. This technology consists of a limited-montage EEG that can be applied by clinical staff (nurses, physicians, or other providers) after very brief training. Point-of-care EEG has advantages, as EEG can be widely available without delay. 5 However, current absence of video, audio, and/or electrocardiogram recordings, and the availability of a single bipolar montage for EEG review, may hinder recognition of artifacts. If an unexplained artifact is suspected, point-of-care EEG should be read at the patient’s bedside.
Search terms
EEG, clinical neurophysiology, artifact, ICU, neurocritical care
Footnotes
Author contributions: Mauricio F. Villamar, MD: case concept and design, acquisition of data, interpretation of data, manuscript writing, figure editing, literature review, clinical care. Ana C. Albuja, MD: case concept and design, interpretation of data, manuscript editing, literature review.
Declaration of conflicting interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding: The author(s) received no financial support for the research, authorship, and/or publication of this article.
ORCID iD
Mauricio F. Villamar https://orcid.org/0000-0003-4503-8152
References
- 1.Hirsch LJ, Fong MWK, Leitinger M, et al. American clinical neurophysiology society's standardized critical care EEG terminology: 2021 version. J Clin Neurophysiol 2021; 38(1): 1-29. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Tatum WO, Dworetzky BA, Freeman WD, Schomer DL. Artifact: Recording EEG in special care units. J Clin Neurophysiol 2011; 28(3): 264-277. [DOI] [PubMed] [Google Scholar]
- 3.McKay JH, Tatum WO. Artifact mimicking ictal epileptiform activity in EEG. J Clin Neurophysiol 2019; 36(4): 275-288. [DOI] [PubMed] [Google Scholar]
- 4.Yoo JY, Gaspard N, Hirsch LJ, Alkawadri R. Respiratory artifact on EEG independent of the respirator. J Clin Neurophysiol 2014; 31(5): e16-e17. [DOI] [PubMed] [Google Scholar]
- 5.LaMonte MP. Ceribell EEG shortens seizure diagnosis and workforce time and is useful for COVID isolation. Epilepsia Open 2021; 6(2): 331-338. [DOI] [PMC free article] [PubMed] [Google Scholar]