Update on the SedLine® algorithm for calculating the Patient State Index of older individuals during general anesthesia: a randomized controlled trial

Signatures of Thalamocortical Alpha Oscillations and Synchronization With Increased Anesthetic Depths Under Isoflurane

Background: Electroencephalography (EEG) recordings under propofol exhibit an increase in slow and alpha oscillation power and dose-dependent phase–amplitude coupling (PAC), which underlie GABAA potentiation and the central role of thalamocortical entrainment. However, the exact EEG signatures elicited by volatile anesthetics and the possible neurophysiological mechanisms remain unclear.

Methods: Cortical EEG signals and thalamic local field potential (LFP) were recorded in a mouse model to detect EEG signatures induced by 0.9%, 1.5%, and 2.0% isoflurane. Then, the power of the EEG spectrum, thalamocortical coherence, and slow–alpha phase–amplitude coupling were analyzed. A computational model based on the thalamic network was used to determine the primary neurophysiological mechanisms of alpha spiking of thalamocortical neurons under isoflurane anesthesia.

Results: Isoflurane at 0.9% (light anesthesia) increased the power of slow and delta oscillations both in cortical EEG and in thalamic LFP. Isoflurane at 1.5% (surgery anesthesia) increased the power of alpha oscillations both in cortical EEG and in thalamic LFP. Isoflurane at 2% (deep anesthesia) further increased the power of cortical alpha oscillations, while thalamic alpha oscillations were unchanged. Thalamocortical coherence of alpha oscillation only exhibited a significant increase under 1.5% isoflurane. Isoflurane-induced PAC modulation remained unchanged throughout under various concentrations of isoflurane. By adjusting the parameters in the computational model, isoflurane-induced alpha spiking in thalamocortical neurons was simulated, which revealed the potential molecular targets and the thalamic network involved in isoflurane-induced alpha spiking in thalamocortical neurons.

Conclusion: The EEG changes in the cortical alpha oscillation, thalamocortical coherence, and slow–alpha PAC may provide neurophysiological signatures for monitoring isoflurane anesthesia at various depths.

Abnormally high Patient State Index associated with epicardial pacing: a case report

Background

Anesthesiologists monitor electroencephalography (EEG) intraoperatively to maintain adequate depth of anesthesia. However, the EEG signal is affected by noise and interference. The SedLine® is a brain function monitor with which the Patient State Index (PSI) is calculated. In this study, we report abnormally high PSI values associated with epicardial pacing during open heart surgery.

Case presentation

A 50-year-old man was scheduled for total arch replacement. Atrial demand pacing was started before weaning from cardiopulmonary bypass. The PSI increased from 30 to 80 soon after the start of pacing, and the EEG waveform showed spikes synchronized with the pacing. As the pacing output was lowered, the spikes on the EEG attenuated and disappeared, and the PSI decreased to < 40. When the pacing output was increased again, the spikes recurred, and the PSI increased again.

Conclusions

Pacemaker spikes may cause contamination of the EEG, resulting in abnormally high PSI values.