Persistent cognitive deficits and neuroinflammation in a rat model of cardiopulmonary bypass

Impact and Implications of Neurocognitive Dysfunction in the Management of Ischemic Heart Failure

Neurocognitive dysfunction is common in heart failure (HF), with 30% to 80% of patients experiencing some degree of deficits in one or more cognitive domains, including memory, attention, learning ability, executive function, and psychomotor speed. Although the mechanism is not fully understood, reduced cardiac output, comorbidities, chronic cerebral hypoperfusion, and cardioembolic brain injury leading to cerebral hypoxia and brain damage seem to trigger the neurocognitive dysfunction in HF. Cognitive impairment is independently associated with worse outcomes including mortality, rehospitalization, and reduced quality of life. Patients with poorer cognitive function are at an increased risk of severe disease as they tend to have greater difficulty complying with treatment requirements. Coronary revascularization in patients with ischemic HF has the potential to improve cardiovascular outcomes but risks worsening neurocognitive dysfunction even further. Revascularization by coronary artery bypass grafting carries inherent risks for delirium, cognitive impairment, neurologic injury, and stroke, which are known to exacerbate the risk of neurocognitive dysfunction. Alternatively, percutaneous coronary intervention, as a less-invasive approach, has the potential to minimize the risk of cognitive impairment but has not yet been evaluated as an alternative to coronary artery bypass grafting in patients with ischemic HF. Therefore, it is paramount to raise awareness of the neurocognitive consequences in ischemic HF and devise strategies for recognition and prevention as an important target of patient management and personalized decision making that contributes to patient outcomes.

Effect of postoperative delirium after cardiovascular surgery on 5-year mortality

INTRODUCTION

Postoperative delirium is a common complication after cardiovascular surgery. A meta-analysis revealed that postoperative delirium was associated with cognitive decline and dementia, which may affect long-term mortality. However, few studies have reported the association between postoperative delirium after cardiovascular surgery and long-term postoperative mortality. Therefore, we investigated the effect of postoperative delirium on 5-year survival rates of patients who underwent cardiovascular surgery.

METHODS

We retrospectively reviewed the records of patients who underwent cardiovascular surgery with cardiopulmonary bypass from January 2016 to December 2019. Postoperative delirium was defined as an Intensive Care Delirium Screening score ≥ 3, which might include subclinical delirium. Cox proportional hazards modeling was performed to assess the association between postoperative delirium and mortality. Postoperative mortality in patients with and without delirium was assessed using the Kaplan-Meier method and compared using the log-rank test.

RESULTS

Postoperative delirium was observed in 562 (31.9%) of 1731 patients. There were more elderly patients, more emergent surgery procedures, longer operative time, and larger transfusion volume in the postoperative delirium group. Cox regression analyses showed that delirium (hazard ratio (HR), 1.501; 95% confidence interval (CI), 1.053-2.140; p = 0.025) and emergent surgery (HR, 3.380; 95% CI, 2.231-5.122; p < 0.001) are significantly associated with 5-year mortality. Among patients who underwent elective surgery, postoperative delirium (HR, 1.987; 95% CI, 1.135-3.481; p = 0.016) is significantly associated with 5-year mortality. Kaplan-Meier survival analysis revealed that patients with postoperative delirium had significantly higher 5-year mortality.

CONCLUSIONS

Patients with postoperative delirium after cardiovascular surgery have significantly higher 5-year mortality.

Associations Between Systemic and Cerebral Inflammation in an Ovine Model of Cardiopulmonary Bypass

BACKGROUND

Intraoperative inflammation may contribute to postoperative neurocognitive disorders after cardiac surgery requiring cardiopulmonary bypass (CPB). However, the relative contributions of general anesthesia (GA), surgical site injury, and CPB are unclear.

METHODS

In adult female sheep, we investigated (1) the temporal profile of proinflammatory and anti-inflammatory cytokines and (2) the extent of microglia activation across major cerebral cortical regions during GA and surgical trauma with and without CPB (N = 5/group). Sheep were studied while conscious, during GA and surgical trauma, with and without CPB.

RESULTS

Plasma tumor necrosis factor-alpha (mean [95% confidence intervals], 3.7 [2.5-4.9] vs 1.6 [0.8-2.3] ng/mL; P = .0004) and interleukin-6 levels (4.4 [3.0-5.8] vs 1.6 [0.8-2.3] ng/mL; P = .029) were significantly higher at 1.5 hours, with a further increase in interleukin-6 at 3 hours (7.0 [3.7-10.3] vs 1.8 [1.1-2.6] ng/mL; P < .0001) in animals undergoing CPB compared with those that did not. Although cerebral oxygen saturation was preserved throughout CPB, there was pronounced neuroinflammation as characterized by greater microglia circularity within the frontal cortex of sheep that underwent CPB compared with those that did not (0.34 [0.32-0.37] vs 0.30 [0.29-0.32]; P = .029). Moreover, microglia had fewer branches within the parietal (7.7 [6.5-8.9] vs 10.9 [9.4-12.5]; P = .001) and temporal (7.8 [7.2-8.3] vs 9.9 [8.2-11.7]; P = .020) cortices in sheep that underwent CPB compared with those that did not.

CONCLUSIONS

CPB enhanced the release of proinflammatory cytokines beyond that initiated by GA and surgical trauma. This systemic inflammation was associated with microglial activation across 3 major cerebral cortical regions, with a phagocytic microglia phenotype within the frontal cortex, and an inflammatory microglia phenotype within the parietal and temporal cortices. These data provide direct histopathological evidence of CPB-induced neuroinflammation in a large animal model and provide further mechanistic data on how CPB-induced cerebral inflammation might drive postoperative neurocognitive disorders in humans.

Targeting neuroinflammation as a preventive and therapeutic approach for perioperative neurocognitive disorders

Perioperative neurocognitive disorders (PND) is a common postoperative complication associated with regional or general anesthesia and surgery. Growing evidence in both patient and animal models of PND suggested that neuroinflammation plays a critical role in the development and progression of this problem, therefore, mounting efforts have been made to develop novel therapeutic approaches for PND by targeting specific factors or steps alongside the neuroinflammation. Multiple studies have shown that perioperative anti-neuroinflammatory strategies via administering pharmacologic agents or performing nonpharmacologic approaches exert benefits in the prevention and management of PND, although more clinical evidence is urgently needed to testify or confirm these results. Furthermore, long-term effects and outcomes with respect to cognitive functions and side effects are needed to be observed. In this review, we discuss recent preclinical and clinical studies published within a decade as potential preventive and therapeutic approaches targeting neuroinflammation for PND.

Suppression of Neuroinflammation Attenuates Persistent Cognitive and Neurogenic Deficits in a Rat Model of Cardiopulmonary Bypass

Post-operative cognitive dysfunction (POCD) can be a serious surgical complication, and patients undergoing cardiac procedures are at particular risk for POCD. This study examined the effect of blocking neuroinflammation on behavioral and neurogenic deficits produced in a rat model of cardiopulmonary bypass (CPB). Minocycline, a drug with established anti-inflammatory activity, or saline was administered daily for 30 days post-CPB. Treatment with minocycline reduced the number of activated microglia/macrophages observed in the dentate gyrus of the hippocampus at 6 months post-CPB, consistent with an anti-inflammatory action in this CPB model. Behavioral testing was conducted at 6 months post-CPB utilizing a win-shift task on an 8-arm radial maze. Minocycline-treated animals performed significantly better than saline-treated animals on this task after CPB. In addition, the CPB-induced reduction in adult neurogenesis was attenuated in the minocycline-treated animals. Together, these findings indicate that suppressing neuroinflammation during the early post-surgical phase can limit long-term deficits in both behavioral and neurogenic outcomes after CPB.