How Critical Illness Affects the Brain…and Vice Versa

Delirium in Cardiac and Cardiovascular Surgical Intensive Care Units

Delirium is a common occurrence in cardiac and cardiovascular surgical intensive care units. Due to multiple confounding factors, this diagnosis remains challenging for medical professionals. Multiple theories exist regarding the pathophysiology of delirium, which include disruption of neurotransmitters as well as inflammation. Delirium has been associated with prolonged hospitalizations and an increase in mortality. Although there are widely used screening tools for delirium, none have been validated in this particular patient population. Limited treatments exist for delirium, so: both pharmacologic and nonpharmacologic preventative measures should be employed in this patient population.

Thromboelastography Parameters as Predictors for Long-Term Survival in Critically Ill Patients

Thromboelastography (TEG) is used for monitoring abnormal blood coagulation in critically ill patients. However, the correlation between TEG parameters and long-term survival in these patients is unknown. We aimed to quantify the effect of TEG on long-term survival of critically ill patients. Critically ill patients undergoing TEG were retrospectively examined. Baseline patient characteristics and coagulation function indexes were compared. Cox regression, receiver–operating characteristic curve analysis, and Kaplan-Meier survival estimate curve were performed. We included 167 critically ill patients. Clot formation speed (K) and reaction time (R) were higher, whereas maximum amplitude (MA) and angle were lower in the mortality group than in the survival group (P < .01). All TEG parameters were risk factors for 2-year survival in critically ill patients (P < .01). The area under the curve of MA for predicting 2-year survival was 0.756 (95% confidence interval: 0.670-0.841). The Kaplan-Meier survival estimate curve analysis showed that MA predicted 2-year survival of critically ill patients(P < .01). Maximum amplitude can effectively predict 2-year survival of critically ill patients, indicating the influence of the coagulation system on these patients.

Non-convulsive seizures in the encephalopathic critically ill cancer patient does not necessarily portend a poor prognosis

Background

Non-convulsive status epilepticus (NCSE) is present in 10–30% of ICU patients with altered mental status (AMS) and is associated to poor outcomes. To our knowledge, there is no data describing the prevalence and outcomes of critically ill cancer patients with AMS associated to non-convulsive seizures (NCS) or NCSE. We aim to describe the outcomes and risk factors of critically ill cancer patients with encephalopathy associated with non-convulsive seizures (NCS).

Methods

This is a 3-year prospective observational study in a mixed oncological ICU at MD Anderson Cancer Center. Data of ICU patients with moderate to severe encephalopathy (Glasgow Coma Score < 13) that underwent EEG monitoring to rule out NCS were collected. Multivariate logistic regression was performed to identify risk factors and outcomes.

Results

Of the 317 patients with encephalopathy who underwent EEG monitoring, 14.5% had NCS. Known risk factors such as sepsis, CNS infection, antibiotics, and cardiac arrest were not associated with increased risk of NCS. Patients with NCS were more likely to have received recent chemotherapy (41.3% vs 21.4%; p = 0.0036), have a CNS disease (39% vs 24.4%; p = 0.035), and abnormal brain imaging (60.9% vs 44.6%; p = 0.041). Patients with lower SOFA scores, normal renal function, and absence of shock were likely to have NCS as the cause of their encephalopathy (p < 0.03). After multivariate analysis, only abnormal brain imaging and absence of renal failure were associated with NCS. Mortality was significantly lower in patients with non-convulsive seizures when compared to those without seizures (45.7% vs 64%; p = 0.022); however, there was no significant association of seizures and mortality on a multivariable logistic regression analysis.

Conclusions

NCS in critically ill cancer patients is associated with abnormalities on brain imaging and lower prevalence of organ failure. Diagnosis and treatment of NCS should be a priority in encephalopathic cancer patients, as they can have lower mortality than non-seizing patients. Opposite to other populations, NCS should not be considered a poor prognostic factor in critically ill encephalopathic cancer patients as they reflect a reversible cause for altered mentation.

NMDA receptor modulation of glutamate release in activated neutrophils

Background

Neutrophil depletion improves neurologic outcomes in experimental sepsis/brain injury. We hypothesized that neutrophils may exacerbate neuronal injury through the release of neurotoxic quantities of the neurotransmitter glutamate.

Methods

Real-time glutamate release by primary human neutrophils was determined using enzymatic biosensors. Bacterial and direct protein-kinase C (Phorbol 12-myristate 13-acetate; PMA) activation of neutrophils in human whole blood, isolated neutrophils or human cell lines were compared in the presence/absence of N-Methyl-d-aspartic acid receptor (NMDAR) antagonists. Bacterial and direct activation of neutrophils from wild-type and transgenic murine neutrophils deficient in NMDAR-scaffolding proteins were compared using flow cytometry (phagocytosis, reactive oxygen species (ROS) generation) and real-time respirometry (oxygen consumption).

Findings

Both glutamate and the NMDAR co-agonist d-serine are rapidly released by neutrophils in response to bacterial and PMA-induced activation. Pharmacological NMDAR blockade reduced both the autocrine release of glutamate, d-serine and the respiratory burst by activated primary human neutrophils. A highly specific small-molecule inhibitor ZL006 that limits NMDAR-mediated neuronal injury also reduced ROS by activated neutrophils in a murine model of peritonitis, via uncoupling of the NMDAR GluN2B subunit from its' scaffolding protein, postsynaptic density protein-95 (PSD-95). Genetic ablation of PSD-95 reduced ROS production by activated murine neutrophils. Pharmacological blockade of the NMDAR GluN2B subunit reduced primary human neutrophil activation induced by Pseudomonas fluorescens, a glutamate-secreting Gram-negative bacillus closely related to pathogens that cause hospital-acquired infections.

Interpretation

These data suggest that release of glutamate by activated neutrophils augments ROS production in an autocrine manner via actions on NMDAR expressed by these cells.

Fund

GLA: Academy Medical Sciences/Health Foundation Clinician Scientist. AVG is a Wellcome Trust Senior Research Fellow.

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Neutrophil depletion improves neurologic outcome after injury and infection.

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Pharmacologic NMDAR blockade reduces rapid autocrine release of glutamate/d-serine from activated neutrophils.

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Genetic ablation/small-molecule inhibition of PSD-95 reduces neutrophil ROS.

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NMDAR blockade reduces human neutrophil activated by glutamate-secreting bacteria.

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Activated neutrophils may exacerbate neuronal injury in various forms of critical illness through the release of glutamate.