Can Intraoperative Processed EEG Predict Postoperative Cognitive Dysfunction in the Elderly?

Postoperative cognitive dysfunction (POCD) is a serious and costly complication of the elderly; even mild impairment has the potential to impact overall well being. Anesthesiologists continue to search for ways to manipulate intraoperative technique to optimize postoperative cognition in the elderly. Depth of anesthesia during surgery is an area that has shown some promise for short-term outcomes, such as delirium. However, excessive depth has both positive and negative associations with longer-term POCD. We hypothesize that this uncertainty is due to the inability of median depth to capture the amount of burst suppression or electrical silence. In this study, our purpose was to identify the intraoperative processed EEG parameters that are most closely correlated with POCD.

To explore the association of several processed EEG parameters with POCD, we performed a retrospective analysis of a cohort of 105 patients aged >68 years scheduled for major surgery under general anesthesia. Intraoperative medications, hemodynamics, processed EEG and cerebral oxygen saturation were recorded. All patients had a cognitive battery before surgery and repeated at 3 months afterward.

One hundred and five patients enrolled and 77 (73.3%) patients completed the 3-month cognitive testing. The incidence of POCD was 27%; the median Bispectral Index value for patients who developed POCD was similar to patients who did not (46 vs 42 minutes). However, patients who developed POCD spent less time with Bispectral Index <45 minutes (82.8 vs 122.5 minutes, P = 0.01) and burst suppression (35 vs 96 minutes, P = 0.04). Hypotension, cerebral desaturation, and use of total intravenous anesthesia were similar between patients with and without POCD.

Patients who developed POCD spent less time in EEG burst suppression and less time in deep states. Burst suppression may be protective for POCD. Further work is needed to definitively identify the role of burst suppression in the context of other patient and intraoperative variables to prevent POCD.