Brain injury biomarkers in the setting of cardiac surgery: Still a world to explore

Clinical and subclinical acute brain injury caused by invasive cardiovascular procedures

Over the past 50 years, the number and invasiveness of percutaneous cardiovascular procedures globally have increased substantially. However, cardiovascular interventions are inherently associated with a risk of acute brain injury, both periprocedurally and postprocedurally, which impairs medical outcomes and increases health-care costs. Current international clinical guidelines generally do not cover the area of acute brain injury related to cardiovascular invasive procedures. In this international Consensus Statement, we compile the available knowledge (including data on prevalence, pathophysiology, risk factors, clinical presentation and management) to formulate consensus recommendations on the prevention, diagnosis and treatment of acute brain injury caused by cardiovascular interventions. We also identify knowledge gaps and possible future directions in clinical research into acute brain injury related to cardiovascular interventions.

Electrical impedance tomography provides information of brain injury during total aortic arch replacement through its correlation with relative difference of neurological biomarkers

Postoperative neurological dysfunction (PND) is one of the most common complications after a total aortic arch replacement (TAAR). Electrical impedance tomography (EIT) monitoring of cerebral hypoxia injury during TAAR is a promising technique for preventing the occurrence of PND. This study aimed to explore the feasibility of electrical impedance tomography (EIT) for warning of potential brain injury during total aortic arch replacement (TAAR) through building the correlation between EIT extracted parameters and variation of neurological biomarkers in serum. Patients with Stanford type A aortic dissection and requiring TAAR who were admitted between December 2021 to March 2022 were included. A 16-electrode EIT system was adopted to monitor each patient's cerebral impedance intraoperatively. Five parameters of EIT signals regarding to the hypothermic circulatory arrest (HCA) period were extracted. Meanwhile, concentration of four neurological biomarkers in serum were measured regarding to time before and right after surgery, 12 h, 24 h and 48 h after surgery. The correlation between EIT parameters and variation of serum biomarkers were analyzed. A total of 57 TAAR patients were recruited. The correlation between EIT parameters and variation of biomarkers were stronger for patients with postoperative neurological dysfunction (PND(+)) than those without postoperative neurological dysfunction (PND(-)) in general. Particularly, variation of S100B after surgery had significantly moderate correlation with two parameters regarding to the difference of impedance between left and right brain which were MRAIabs and TRAIabs (0.500 and 0.485 with p < 0.05, respectively). In addition, significantly strong correlations were seen between variation of S100B at 24 h and the difference of average resistivity value before and after HCA phase (ΔARVHCA), the slope of electrical impedance during HCA (kHCA) and MRAIabs (0.758, 0.758 and 0.743 with p < 0.05, respectively) for patients with abnormal S100B level before surgery. Strong correlations were seen between variation of TAU after surgery and ΔARVHCA, kHCA and the time integral of electrical impedance for half flow of perfusion (TARVHP) (0.770, 0.794 and 0.818 with p < 0.01, respectively) for patients with abnormal TAU level before surgery. Another two significantly moderate correlations were found between TRAIabs and variation of GFAP at 12 h and 24 h (0.521 and 0.521 with p < 0.05, respectively) for patients with a normal GFAP serum level before surgery. The correlations between EIT parameters and serum level of neurological biomarkers were significant in patients with PND, especially for MRAIabs and TRAIabs, indicating that EIT may become a powerful assistant for providing a real-time warning of brain injury during TAAR from physiological perspective and useful guidance for intensive care units.

Neuromarkers which can predict neurodevelopmental impairment among children with congenital heart defects after cardiac surgery: A systematic literature review

The aim of this systematic literature review was to assess the data regarding neuromarkers used to evaluate the impact of cardiovascular surgery on neurodevelopmental pattern of children with congenital heart defects. A systematic search was performed on PubMed and Google Scholar databases. Out of 713 publications screened, 10 studies (471 patients) met the inclusion criteria. The included studies were coded on several variables: number and heterogeneity of patients (age, congenital heart defects), exclusion of patients with conditions that predispose to neurological impairment, neuroimaging workup pre- and post-surgery, neurodevelopmental assessment, interventions (part of a different study), and follow-up period. Results were reported according to PRISMA guidelines. Findings include: neuron-specific enolase and brain-derived neurotrophic factor are not reliable neuromarkers, for protein S100B different results were reported, for activin A there is lack of evidence, and glial fibrillary acidic protein could represent a reliable neuromarker for acute brain-injury. Directions for future research are discussed.

Dexmedetomidine Increases MMP-12 and MBP Concentrations after Coronary Artery Bypass Graft Surgery with Extracorporeal Circulation Anaesthesia without Impacting Cognitive Function: A Randomised Control Trial

Postoperative neurological deficits remain a concern for patients undergoing cardiac surgeries. Even minor injuries can lead to neurocognitive decline (i.e., postoperative cognitive dysfunction). Dexmedetomidine may be beneficial given its reported neuroprotective effect. We aimed to investigate the effects of dexmedetomidine on brain injury during cardiac surgery anaesthesia. This prospective observational study analysed data for 46 patients who underwent coronary artery bypass graft surgery with extracorporeal circulation between August 2018 and March 2019. The patients were divided into two groups: control (CON) with typical anaesthesia and dexmedetomidine (DEX) with dexmedetomidine infusion. Concentrations of the biomarkers matrix metalloproteinase-12 (MMP-12) and myelin basic protein (MBP) were measured preoperatively and at 24 and 72 h postoperatively. Cognitive evaluations were performed preoperatively, at discharge, and 3 months after discharge using Addenbrooke's Cognitive Examination version III (ACE-III). The primary endpoint was the ACE-III score at discharge. Increased MMP-12 and MBP concentrations were observed in the DEX group 24 and 72 h postoperatively. No significant differences in ACE-III scores were observed between the groups at discharge; however, the values were increased when compared with initial values after 3 months (p = 0.000). The current results indicate that the administration of dexmedetomidine as an adjuvant to anaesthesia can increase MMP-12 and MBP levels without effects on neurocognitive outcomes at discharge and 3 months postoperatively.

Serum biomarkers of brain injury after uncomplicated cardiac surgery: Secondary analysis from a randomized trial

Background

Postoperative cognitive dysfunction is common after cardiac surgery. Postoperative measurements of brain injury biomarkers may identify brain damage and predict cognitive dysfunction. We describe the release patterns of five brain injury markers in serum and plasma after uncomplicated cardiac surgery.

Methods

Sixty‐one elective cardiac surgery patients were randomized to undergo surgery with either a dextran‐based prime or a crystalloid prime. Blood samples were taken immediately before surgery, and 2 and 24 h after surgery. Concentrations of the brain injury biomarkers S100B, glial fibrillary acidic protein (GFAP), tau, neurofilament light (NfL) and neuron‐specific enolase (NSE)) and the blood–brain barrier injury marker β‐trace protein were analyzed. Concentrations of brain injury biomarkers were correlated to patients’ age, operation time, and degree of hemolysis.

Results

No significant difference in brain injury biomarkers was observed between the prime groups. All brain injury biomarkers increased significantly after surgery (tau +456% (25th–75th percentile 327%−702%), NfL +57% (28%−87%), S100B +1145% (783%−2158%), GFAP +17% (−3%−43%), NSE +168% (106%−228%), while β‐trace protein was reduced (−11% (−17−3%). Tau, S100B, and NSE peaked at 2h, NfL and GFAP at 24 h. Postoperative concentrations of brain injury markers correlated to age, operation time, and/or hemolysis.

Conclusion

Uncomplicated cardiac surgery with cardiopulmonary bypass is associated with an increase in serum/plasma levels of all the studied injury markers, without signs of blood–brain barrier injury. The biomarkers differ markedly in their levels of release and time course. Further investigations are required to study associations between perioperative release of biomarkers, postoperative cognitive function and clinical outcome.

S100B in cardiac surgery brain monitoring: friend or foe?

Recent advances in perioperative management of adult and pediatric patients requiring open heart surgery (OHS) and cardiopulmonary bypass (CPB) for cardiac and/or congenital heart diseases repair allowed a significant reduction in the mortality rate. Conversely morbidity rate pattern has a flat trend. Perioperative period is crucial since OHS and CPB are widely accepted as a deliberate hypoxic-ischemic reperfusion damage representing the cost to pay at a time when standard of care monitoring procedures can be silent or unavailable. In this respect, the measurement of neuro-biomarkers (NB), able to detect at early stage perioperative brain damage could be especially useful. In the last decade, among a series of NB, S100B protein has been investigated. After the first promising results, supporting the usefulness of the protein as predictor of short/long term adverse neurological outcome, the protein has been progressively abandoned due to a series of limitations. In the present review we offer an up-dated overview of the main S100B pros and cons in the peri-operative monitoring of adult and pediatric patients.

Biomarkers of Cerebral Injury for Prediction of Postoperative Cognitive Dysfunction in Patients Undergoing Cardiac Surgery

OBJECTIVES

To assess the ability of the biomarkers neuron-specific enolase (NSE), tau, neurofilament light chain (NFL), and glial fibrillary acidic protein (GFAP) to predict postoperative cognitive dysfunction (POCD) at discharge in patients who underwent cardiac surgery.

DESIGN

Post hoc analyses (with tests being prespecified before data analyses) from a randomized clinical trial.

SETTING

Single-center study from a primary heart center in Denmark.

PARTICIPANTS

Adult patients undergoing elective or subacute on-pump coronary artery bypass grafting and/or aortic valve replacement.

INTERVENTIONS

Blood was collected before induction of anesthesia, after 24 hours, after 48 hours, and at discharge from the surgical ward. The International Study of Postoperative Cognitive Dysfunction test battery was applied to diagnose POCD at discharge and after three months. Linear mixed models of covariance were used to assess whether repeated measurements of biomarker levels were associated with POCD. Receiver operating characteristic (ROC) curves were applied to assess the predictive value of each biomarker measurement for POCD.

MEASUREMENTS AND MAIN RESULTS

A total of 168 patients had biomarkers measured at baseline, and 47 (28%) fulfilled the POCD criteria at discharge. Patients with POCD at discharge had significantly higher levels of tau (p = 0.02) and GFAP (p = 0.01) from baseline to discharge. The biomarker measurements achieving the highest area under the ROC curve for prediction of POCD at discharge were NFL measured at discharge (AUC, 0.64; 95% confidence interval [CI], 0.54-0.73), GFAP measured 48 hours after induction (AUC, 0.64; 95% CI, 0.55-0.73), and GFAP measured at discharge (AUC, 0.64; 95% CI, 0.54-0.74), corresponding to a moderate predictive ability.

CONCLUSIONS

Postoperative serum levels of tau and GFAP were elevated significantly in patients with POCD who underwent cardiac surgery at discharge; however, the biomarkers achieved only modest predictive abilities for POCD at discharge. Postoperative levels of NSE were not associated with POCD at discharge.

Associations between mean arterial pressure during cardiopulmonary bypass and biomarkers of cerebral injury in patients undergoing cardiac surgery: secondary results from a randomized controlled trial

OBJECTIVES

Cardiac surgery is associated with risk of cerebral injury and mean arterial pressure (MAP) during cardiopulmonary bypass (CPB) is suggested to be associated with cerebral injury. The 'Perfusion Pressure Cerebral Infarcts' (PPCI) trial randomized patients undergoing coronary artery bypass grafting (CABG) and/or aortic valve replacement to a MAP of 40-50 or 70-80 mmHg during CPB and found no difference in clinical or imaging outcomes between the groups. We here present PPCI trial predefined secondary end points, consisting of biomarkers of brain injury.

METHODS

Blood was collected from PPCI trial patients at baseline, 24 and 48 h after induction of anaesthesia and at discharge from the surgical ward. Blood was analysed for neuron-specific enolase, tau, neurofilament light and the glial marker glial fibrillary acidic protein. Linear mixed models were used to analyse differences in biomarker value changes from baseline between the 2 MAP allocation groups.

RESULTS

A total of 193 (98%) patients were included. We found no differences in biomarker levels over time from baseline to discharge between the 2 MAP allocation groups (PNSE = 0.14, PTau = 0.46, PNFL = 0.21, PGFAP = 0.13) and the result did not change after adjustment for age, sex and type of surgery.

CONCLUSIONS

We found no significant differences in levels of biomarkers of neurological injury in patients undergoing elective or subacute CABG and/or aortic valve replacement randomized to either a target MAP of 40-50 mmHg or a target MAP of 70-80 mmHg during CBP.

Current Evidence Regarding Biomarkers Used to Aid Postoperative Delirium Diagnosis in the Field of Cardiac Surgery-Review

Postoperative cognitive disorders after cardiac surgery may manifest as postoperative delirium (POD) or later as postoperative cognitive dysfunction (POCD). The incidence of POD after cardiac surgery ranges from 16% to 73%. In contrast to POD, POCD is usually diagnosed after the discharge from hospital, with an incidence of 30 to 70% of cases, very often noticed only by close relative or friends, decreasing after six (20–30%) and twelve (15–25%) months after surgery. Perioperative cognitive disorders are associated with adverse short- and long-term effects, including increased morbidity and mortality. Due to the complexity of delirium pathomechanisms and the difficulties in the diagnosis, researchers have not yet found a clear answer to the question of which patient will be at a higher risk of developing delirium. The risk for POD and POCD in older patients with numerous comorbidities like hypertension, diabetes, and previous ischemic stroke is relatively high, and the predisposing cognitive profile for both conditions is important. The aim of this narrative review was to identify and describe biomarkers used in the diagnosis of delirium after cardiac surgery by presenting a search through studies regarding this subject, which have been published during the last ten years. The authors discussed brain-derived biomarkers, inflammation-related biomarkers, neurotransmitter-based biomarkers, and others. Work based on inflammation-related biomarkers, which are characterized by the low cost of implementation and the effectiveness of delirium diagnosis, seems to be the closest to the goal of discovering an inexpensive and effective marker. Currently, the use of a panel of tests, and not a single biomarker, brings us closer to the discovery of a test, or rather a set of tests ideal for the diagnosis of delirium after cardiac surgery.

Cardiac Surgery and the Blood-Brain Barrier

Neurologic abnormality after cardiac surgery is common, and neurologic complications after cardiac surgery are among the most devastating problems that can occur in the postoperative period. Disruption of the blood-brain barrier (BBB) plays an important role in these complications. Assessment of the BBB integrity relies on cognitive testing, MRI, and measurement of brain biomarkers. In applying these methods, up to 50% of cardiac patients show some degree of BBB disruption and most of these abnormalities are short lived. To date there is no single test or measure that can predict BBB disruption in cardiac surgery.

A case series on the value of tau and neurofilament protein levels to predict and detect delirium in cardiac surgery patients

BACKGROUND

Delirium following cardiac surgery is a relevant complication in the majority of elderly patients but its prediction is challenging. Cardiopulmonary bypass, essential for many interventions in cardiac surgery, is responsible for a severe inflammatory response leading to neuroinflammation and subsequent delirium. Neurofilament light protein (NfL) and tau protein (tau) are specific biomarkers to detect neuroaxonal injury as well as glial fibrillary acidic protein (GFAP), a marker of astrocytic activation.

METHODS

We thought to examine the perioperative course of these markers in a case series of each three cardiac surgery patients under off-pump cardiac arterial bypass without evolving delirium (OPCAB-NDEL), patients with a procedure under cardio-pulmonary bypass (CPB) without delirium (CPB-NDEL) and delirium after a CPB procedure (CPB-DEL). Delirium was diagnosed by the Confusion Assessment Method for the ICU and chart reviews.

RESULTS

We observed increased preoperative levels of tau in patients with later delirium, whereas values of NfL and GFAP did not differ. In the postoperative course, all biomarkers increased multi-fold. NfL levels sharply increased in patients with CPB reaching the highest levels in the CPB-DEL group.

CONCLUSION

Tau and NfL might be of benefit to identify patients in cardiac surgery at risk for delirium and to detect patients with the postoperative emergence of delirium.

Effects of Isolated Impaired Fasting Glucose on Brain Injury During Cardiac Surgery Under Cardiopulmonary Bypass

Objective: To evaluate the effects of isolated impaired fasting glucose (IIFG) on brain injury in patients undergoing cardiopulmonary bypass (CPB) surgery. Methods: Patients with rheumatic heart valve disease who underwent elective mitral valve replacement were included and divided into control and IIFG groups. Pre-, intra-, and postoperative blood glucose levels, serum insulin levels, insulin resistance index (HOMA-IR), lactic acid levels, and neuron-specific enolase (NSE) and S100B levels were measured. The cerebral oxygen extraction ratio (OER) was calculated. Cognitive function was assessed via the Mini-Mental State Examination (MMSE). Results: HOMA-IR levels were higher in the IIFG group than the control group 30 min after the beginning of CPB, at the termination of CPB, and 2 h after the termination of CPB. Cerebral OER and lactic acid increased intraoperatively in both groups, especially in the IIFG group. NSE and S100B levels were higher in the IIFG group than in the control group at the termination of CPB, 2 h after the termination of CPB, and at 24 h postoperatively. The MMSE scores did not significantly differ between the two groups. Delirium occurred in two patients in the IIFG group, and one in the control group. No other signs and symptoms of brain injuries were detected in either group. Conclusions: The increased postoperative NSE and S100B levels in the IIFG group compared with controls may be associated with severe insulin resistance and stress hyperglycemia. However, the IIFG group did not have clinical manifestations of brain injuries, including cognitive impairment.

The neurologic protection of unilateral versus bilateral antegrade cerebral perfusion in aortic arch surgery with deep hypothermic circulatory arrest: A study of 77 cases

BACKGROUD

Unilateral and bilateral antegrade cerebral perfusions (ACP) are recognized methods of cerebral protection in aortic arch surgery. However, the adequacy of cerebral protection in aortic arch surgery with deep hypothermic circulatory arrest is controversial. In this study, we compared unilateral and bilateral ACP of cerebral protection in aortic arch surgery by assessing the patient's intraoperative and postoperative brain function.

METHODS

A total of 77 patients undergoing aortic arch surgery were included in this study. Unilateral ACP was performed using a cannula in the innominate artery (n = 40), whereas bilateral ACP was conducted using an additional cannula in the left carotid artery (n = 37). Levels of S-100β and neuron specific enolase (NSE) were assayed at the beginning of cardiopulmonary bypass (T1), the beginning of circulatory arrest (T2), and post ACP at T = 25 min (T3), the end of ACP (T4), the end of cardiopulmonary bypass (T5), and at T = 1 h (T6), T = 6 h (T7), and T = 24 h (T8). Transcranial Doppler ultrasonography was used both preoperatively and intraoperatively to detect the blood flow of bilateral middle cerebral artery (MCA), and neurologic deficit incidence and mortality rates were obtained.

RESULTS

At time points T1, T2, and T3, plasma levels of S-100β and NSE were not statistically different between groups. However, S-100β and NSE levels for each time point ranging from T = T4 to T = T8 did show statistically significant differences between groups. Patients who with one side of the middle cerebral artery stenosis, used bilateral antegrade cerebral perfusions method, intraoperative Transcranial Doppler ultrasonography examination showed narrow side blood flow weaker than the normal side during the deep hypothermic circulatory arrest (DHCA), however no significant differences could be observed between the two sides (P > 0.05). The incidence of neurological dysfunction was higher in the unilateral ACP group compared to the bilateral ACP group (25% vs. 8.11%, respectively, P = 0.028). Moreover, no marked differences were observed in mortality (2.5% vs. 5.41%, respectively, P = 1.000).

CONCLUSIONS

When the duration of DHCA was 25 min or less, no significant differences were observed between unilateral and bilateral ACP. However, when DHCA exceeded 25 min, bilateral ACP was more effective compared to unilateral ACP. Due to the high variations in circle of Willis as well as increased safety, simplicity, and efficiency, the bilateral ACP approach is preferred over the unilateral technique.