Electroencephalographic Biomarkers, Cerebral Oximetry, and Postoperative Cognitive Function in Adult Noncardiac Surgical Patients: A Prospective Cohort Study

Electroencephalographic Measures of Delirium in the Perioperative Setting: A Systematic Review

Postoperative delirium (POD) is frequent in older adults and is associated with adverse cognitive and functional outcomes. In the last several decades, there has been an increased interest in exploring tools that easily allow the early recognition of patients at risk of developing POD. The electroencephalogram (EEG) is a widely available tool used to understand delirium pathophysiology, and its use in the perioperative setting has grown exponentially, particularly to predict and detect POD. We performed a systematic review to investigate the use of EEG in the pre-, intra-, and postoperative settings. We identified 371 studies, and 56 met the inclusion criteria. A range of techniques was used to obtain EEG data, from limited 1-4 channel setups to complex 256-channel systems. Power spectra were often measured preoperatively, yet the outcomes were inconsistent. During surgery, the emphasis was primarily on burst suppression (BS) metrics and power spectra, with a link between the frequency and timing of BS, and POD. The EEG patterns observed in POD aligned with those noted in delirium in different contexts, suggesting a reduction in EEG activity. Further research is required to investigate preoperative EEG indicators that may predict susceptibility to delirium.

Preoperative biomarkers associated with delayed neurocognitive recovery

To identify baseline biomarkers of delayed neurocognitive recovery (dNCR) using monitors commonly used in anesthesia. In this sub-study of observational prospective cohorts, we evaluated adult patients submitted to general anesthesia in a tertiary academic center in the United States. Electroencephalographic (EEG) features and cerebral oximetry were assessed in the perioperative period. The primary outcome was dNCR, defined as a decrease of 2 scores in the global Montreal Cognitive Assessment (MoCA) between the baseline and postoperative period. Forty-six adults (median [IQR] age, 65 [15]; 57% females; 65% American Society of Anesthesiologists (ASA) 3 were analyzed. Thirty-one patients developed dNCR (67%). Baseline higher EEG power in the lower alpha band (AUC = 0.73 (95% CI 0.48-0.93)) and lower alpha peak frequency (AUC = 0.83 (95% CI 0.48-1)), as well as lower cerebral oximetry (68 [5] vs 72 [3], p = 0.011) were associated with dNCR. Higher EEG power in the lower alpha band, lower alpha peak frequency, and lower cerebral oximetry values can be surrogates of baseline brain vulnerability.

Exercise-conditioned plasma ameliorates postoperative cognitive dysfunction by activating hippocampal cholinergic circuit and enhancing BDNF/TrkB signaling

BACKGROUND

Postoperative cognitive dysfunction (POCD) is a prevalent complication following anesthesia and surgery, particularly in the elderly, leading to increased mortality and reduced quality of life. Despite its prevalence, there are no effective clinical treatments. Exercise has shown cognitive benefits in aging and various diseases, which can be transferred to sedentary animals through plasma. However, it is unclear if exercise-conditioned plasma can replicate these benefits in the context of POCD.

METHODS

Sixteen-month-old male C57BL/6J mice underwent 30 days of voluntary running wheel training or received systemic administration of exercise-conditioned plasma, followed by tibial fracture surgery under general anesthesia at 17 months of age. Cognitive performance, hippocampal synaptic deficits, neuroinflammation, BDNF/TrkB signaling, and medial septum (MS)-hippocampal cholinergic activity were evaluated through immunohistochemical staining, transmission electron microscopy, Western blotting, and biochemical assays. To investigate the role of hippocampal BDNF signaling and cholinergic activity in the therapeutic effects, the TrkB antagonist ANA-12 and the cholinergic receptor muscarinic 1 (CHRM1) antagonist trihexyphenidyl (THP) were administered via intraperitoneal injection, and adeno-associated virus (AAV) vectors expressing Chrm1 shRNA were delivered via intrahippocampal stereotaxic microinjection.

RESULTS

Exercise-conditioned plasma mimicked the benefits of exercise, alleviating cognitive decline induced by anesthesia/surgery, restoring hippocampal synapse formation and levels of regulators for synaptic plasticity, inhibiting neuroinflammatory responses to surgery by microglia and astrocytes, augmenting BDNF production and TrkB phosphorylation in hippocampal neurons, astrocytes, and microglia, upregulating MS expression of choline acetyltransferase (CHAT) and hippocampal expression of CHRM1 in neurons and astrocytes, and enhancing hippocampal cholinergic innervation and acetylcholine release. Conversely, ANA-12 administration blocked TrkB activation and reduced the protective effects on cognition, synaptic deficits, and neuroinflammatory reactivity of glial cells post-surgery. Similarly, THP administration or intrahippocampal delivery of AAV-Chrm1 shRNA inhibited the activation of the hippocampal cholinergic circuit by exercise plasma, negating the cognitive and neuropathological benefits and reducing BDNF/TrkB signaling enhancements.

CONCLUSION

Exercise-conditioned plasma can replicate the protective effects of exercise against anesthesia/surgery-induced neuroinflammation, synaptic, and cognitive impairments, at least partly, through CHRM1-dependent regulation of hippocampal cholinergic activity and BDNF/TrkB signaling.

Postoperative Delirium and the Older Adult: Untangling the Confusion

Postoperative delirium is one of the most prevalent postoperative complications, affecting mostly older adults. Its incidence is expected to rise because of surgical advances, shifting demographics, and increased life expectancy. Although an acute alteration in brain function, postoperative delirium is associated with adverse outcomes, including progressive cognitive decline and dementia, that place significant burdens on patients' lives and healthcare systems. This has prompted efforts to understand the mechanisms of postoperative delirium to provide effective prevention and treatment. There are multiple mechanisms involved in the etiology of postoperative delirium that share similarities with the physiological changes associated with the aging brain. In addition, older patients often have multiple comorbidities including increased cognitive impairment that is also implicated in the genesis of delirium. These tangled connections pinpointed a shift toward creation of a holistic model of the pathophysiology of postoperative delirium. Scientific advancements integrating clinical risk factors, possible postoperative delirium biomarkers, genetic features, digital platforms, and other biotechnical and information technological innovations, will become available in the near future. Advances in artificial intelligence, for example, will aggregate cognitive testing platforms with patient-specific postoperative delirium risk stratification studies, panels of serum and cerebrospinal fluid molecules, electroencephalogram signatures, and gut microbiome features, along with the integration of novel polygenetic variants of sleep and cognition. These advances will allow for the enrollment of high-risk patients into prevention programs and help uncover new pharmacologic targets.