Electroencephalographic depression after abruptly increasing partial pressure of end-tidal carbon dioxide: a case series.

Background: Prolonged electroencephalographic depression during surgery is associated with poor outcomes for patients. However, the published literature on electroencephalographic depression caused by a sudden increase in the partial pressure of end-tidal carbon dioxide (P_ETCO₂) is lacking.

Case presentation: We report four patients who were scheduled for laparoscopic liver surgery under general anesthesia. During the process of EEG monitoring with Sedline, four patients experienced electroencephalographic depression closely after a sudden increase in P_ETCO₂. The four patients showed that electroencephalographic depression mainly manifested as a slow in EEG frequency, a reduction in the amplitude and power of EEG, and a decrease in spectral edge frequency. Patient state index was elevated in three cases.

Conclusions: To summarize, our patients showed EEG depression when P_ETCO₂ suddenly increased, which suggests that clinical doctors should be alert to electroencephalographic depression when the P_ETCO₂ abruptly increases. EEG monitoring devices should be applied in patients with possible hypercapnia. Anesthesiologists must comprehensively interpret the raw EEG, spectral edge frequency, and density spectral array data, in addition to patient sedation index values.