Neurocognitive Function after Cardiac Surgery: From Phenotypes to Mechanisms

Abstract

For half a century, it has been known that some patients experience neurocognitive dysfunction after cardiac surgery; however, defining its incidence, course, and causes remains challenging and controversial. Various terms have been used to describe neurocognitive dysfunction at different times after cardiac surgery, ranging from "postoperative delirium" to "postoperative cognitive dysfunction or decline." Delirium is a clinical diagnosis included in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5). Postoperative cognitive dysfunction is not included in the DSM-5 and has been heterogeneously defined, though a recent international nomenclature effort has proposed standardized definitions for it. Here, the authors discuss pathophysiologic mechanisms that may underlie these complications, review the literature on methods to prevent them, and discuss novel approaches to understand their etiology that may lead to novel treatment strategies. Future studies should measure both delirium and postoperative cognitive dysfunction to help clarify the relationship between these important postoperative complications.

Figure 1

One of the principal distinctions between postoperative (Post-Op) delirium and postoperative cognitive dysfunction (POCD) is the time frame in which they are found. Emergence delirium occurs in the operating room (OR) or immediately after in the post-anesthesia care unit (PACU). Postoperative delirium occurs 24–72 h after surgery. POCD is measured at weeks to months after surgery and anesthesia. Pre-Op= preoperative. Reproduced from Silverstein J et al.

Figure 2

Pathophysiologic Mechanisms That May Play a Role in Postoperative Cognitive Dysfunction and/or Delirium. Starting from the top, in clockwise order the pullout boxes represent cellular/molecular and synaptic mechanisms (such as AD-related pathology), cerebral oximetry monitoring, anesthetic dosage, resolution of inflammation, vascular mechanisms (such as emboli), and blood brain barrier dysfunction, which may be involved in POCD and delirium. Additional physiologic variables that may be involved in POCD and delirium are listed in free text.

Figure 3

Functionally Connected Networks in the Human Brain. These functional brain network region of interest (ROI) maps were derived from independent components analysis (ICA) of low-frequency BOLD fMRI data from the Human Connectome Project dataset (n = 497). A) default mode network ROIs (blue), salience network ROIs (red); B) Dorsal attention network ROIs (black), frontoparietal network ROIs (light green); C) Language network ROIs (purple), visual network ROIs (pink); and D) Cerebellar network ROIs (yellow), sensorimotor network ROIs (green). Abbreviations: ROIs = Regions of Interest, BOLD = Blood Oxygen Dependent Signal, fMRI = functional magnetic resonance imaging.