ECG Artifact and BIS in Severe Brain Injury

Electrocardiographic Interference on Bispectral Index Monitor: A Case of Crossed Wires

The Bispectral Index (BIS) has been widely utilized to monitor patients’ levels of consciousness during anesthesia. Despite its practicality and prevalence, BIS monitors have been reported to show erroneous readings due to various factors that interfere with the proper reading of the brain’s electrical activity. We present a case where the BIS monitor misinterpreted the patient’s cardiac activity as her neural activity and resulted in a falsely elevated BIS number despite proper placement and lack of underlying patient medical condition, including neurological injury. It is crucial to remain vigilant about monitoring and understanding BIS readings to assess patients’ awareness and effectiveness of anesthesia properly.

Electroencephalographic signals during anesthesia recorded from surface and depth electrodes

PURPOSE

Anesthesiologists have increasingly started to use EEG-based indexes to estimate the level and type of unconsciousness. However, the physiology and biophysics are poorly understood in anesthesiological literature.

METHODS

EEG was recorded from electrodes on the surface of head, including scalp, as well as DBS (deep brain stimulation) electrodes implanted deep in the brain. Mathematical modeling with a realistic head model was performed to create illustrative images of the sensitivity of electrode montages.

RESULTS

EEG pattern of anesthesia, burst-suppression, is recordable outside of scalp area as well in the depth of brain because the EEG current loops produce recordable voltage gradients in the whole head. The typical electrodes used in anesthesia monitoring are most sensitive to basal surface of frontal lobes as well as frontal and mesial parts of temporal lobes.

CONCLUSIONS

EEG currents create closed-loops, which flow from the surface of the cortex and then return to the inside of the hemispheres. In the case of widespread synchronous activity like physiological sleep or anesthesia, the currents recorded with surface and depth electrodes return through the base of brain and skull.

The bispectral index, a useful adjunct for the timely diagnosis of brain death in the comatose trauma patient

BACKGROUND

The bispectral index (BIS) is a processed electroencephalographic value (awake = 100, isoelectric = 0). The relationship of BIS and brain death (BD) is assessed.

METHODS

BIS was evaluated in GCS 3 head-injured patients with BD (no brain function including apnea) or near BD (no apnea or negative ancillary test [cerebral perfusion and electroencephalogram]).

RESULTS

In 27 patients, there were 37 BD evaluations (apnea assessment or ancillary test). BD was confirmed in 62% (n = 23). However, 38% (n = 14) showed near BD. BD BIS is 3 + or - 5 and near BD BIS is 36 + or - 31 (P = .002). In the 23 BD patients, BIS was <20 for 7 hours + or - 6 hours before a BD evaluation was performed. Of 14 near BD evaluations, 9 (64%) had BIS > or = 20. BIS <20 for predicting BD had a sensitivity of 100% (23/23), a positive predictive value of 84% (23/28), and a negative predictive value of 100% (9/9).

CONCLUSIONS

Distinguishing brain death and near brain death in severely comatose trauma patients is complex. By indicating the likelihood of brain death, BIS is an adjunct for efficient evaluation.