Neuroprotection during cardiac surgery

Contemporary Neuroprotection Strategies during Cardiac Surgery: State of the Art Review

Open-heart surgery is the leading cause of neuronal injury in the perioperative state, with some patients complicating with cerebrovascular accidents and delirium. Neurological fallout places an immense burden on the psychological well-being of the person affected, their family, and the healthcare system. Several randomised control trials (RCTs) have attempted to identify therapeutic and interventional strategies that reduce the morbidity and mortality rate in patients that experience perioperative neurological complications. However, there is still no consensus on the best strategy that yields improved patient outcomes, such that standardised neuroprotection protocols do not exist in a significant number of anaesthesia departments. This review aims to discuss contemporary evidence for preventing and managing risk factors for neuronal injury, mechanisms of injury, and neuroprotection interventions that lead to improved patient outcomes. Furthermore, a summary of existing RCTs and large observational studies are examined to determine which strategies are supported by science and which lack definitive evidence. We have established that the overall evidence for pharmacological neuroprotection is weak. Most neuroprotective strategies are based on animal studies, which cannot be fully extrapolated to the human population, and there is still no consensus on the optimal neuroprotective strategies for patients undergoing cardiac surgery. Large multicenter studies using universal standardised neurological fallout definitions are still required to evaluate the beneficial effects of the existing neuroprotective techniques.

Intraoperative Ischemic Stroke in Elective Spine Surgery: A Retrospective Study of Incidence and Risk

STUDY DESIGN

. Retrospective study.

OBJECTIVE

. To determine incidence, risk factors, complications, and early postoperative outcome in patients with intraoperative ischemic stroke during elective spine surgery.

SUMMARY OF BACKGROUND DATA

. Overall, stroke is the fifth leading cause of death in the United States and the second leading cause of death worldwide. It can be a catastrophic event and the main cause of neurological disability in adults.

METHODS

. A retrospective review of the electronic medical records of patients who underwent elective spine surgery between January 2016 and November 2018 at a larger tertiary referral center was conducted. Patients with infection and neoplastic disease were excluded. Patient demographics, pre- and postoperative neurological status, surgical treatment, surgical time, blood loss, intraoperative abnormalities, risk factors, history of stroke, medical treatment, diagnostics, hospital stay, complications, and mortality were collected.

RESULTS

. Out of 5029 surgically treated patients receiving elective spine surgery, a total of seven patients (0.15%) were identified who developed an ischemic stroke during the surgical procedure. Patients were predominantly females (n = 6). Ischemic pontine stroke occurred in two patients. Further distributions of ischemic stroke were: left caudate nucleus, left posterior inferior cerebellar artery, left external capsule, left middle cerebral artery, and acute ischemic supratentorial spots. The main risk factors identified for intraoperative ischemic stroke include hypertension, diabetes, smoking, dyslipidemia, and possibly major intraoperative CSF leak. Three patients (43%) had neurological deficits which did not improve during hospital stay. Two patients recovered fully and two patients died. Therefore, in-hospital mortality rate of this subset of patients was 29%.

CONCLUSION

. With the increase of spinal procedures, it is important to identify patients at risk for having an ischemic stroke and to optimize their comorbidities preoperatively. Patients with intraoperative ischemic stroke carry a higher risk for morbidity and mortality during the index hospitalization.

LEVEL OF EVIDENCE

4.

Single aortic clamping in coronary artery bypass surgery reduces cerebral embolism and improves neurocognitive outcomes

Aortic manipulation releases embolic material, thereby enhancing the probability of adverse neurologic outcomes following coronary artery bypass grafting (CABG). We prospectively evaluated 59 patients undergoing CABG. Patients in the single (SC, n = 37) and multiple clamp (MC, n = 22) groups were comparable in relation to age and operative risk (p > 0.05). Neurocognitive evaluation consisted of the Auditory Verbal Learning Test (AVLT), Color Trails Test A, the Grooved Pegboard test and the Mini-Mental State Examination. Data acquisition was performed preoperatively, early postoperatively and at the 4-month follow-up. Intraoperative transcranial Doppler (TCD) monitoring was used to quantify the embolic load in relation to different aortic clamping strategies. Preoperative neurocognitive results were similar between the groups (p > 0.05). The incidence of postoperative delirium was greater in the MC group but this failed to reach statistical significance (23% vs 8%, p = 0.14). SC patients had fewer embolization signals (270 ± 181 vs 465 ± 160, p < 0.0001). Early postoperative neurocognitive results were depressed in comparison to preoperative values in both groups (p < 0.05 for multiple comparisons). The magnitude of this cognitive depression was greater in the MC group (p < 0.05 for multiple comparisons). Preoperative levels of neurocognition were restored at follow-up in the SC group in all tests except the AVLT. A trend towards improvements in neurocognitive performances at follow-up was also observed in the MC group. Residual attention, motor skill and memory deficits were, however, documented with multiple tests. In conclusion, the embolic burden was significantly lower in the SC group. This TCD imaging outcome translated into fewer early cognition deficits and superior late restoration of function.

Translational neuroprotection research in glaucoma: a review of definitions and principles

The maintenance of vision, through prevention and attenuation of neuronal injury in glaucoma, forms the basis of current clinical practice. Currently, the reduction of intraocular pressure is the only proven method to achieve these goals. Although this strategy enjoys considerable success, some patients progress to blindness; hence, additional management options are highly desirable. Several terms describing treatment modalities of neuronal diseases with potential applicability to glaucoma are used in the literature, including neuroprotection, neurorecovery, neurorescue and neuroregeneration. These phenomena have not been defined within a coherent framework. Here, we suggest a set of definitions, postulates and principles to form a foundation for the successful translation of novel glaucoma therapies from the laboratory to the clinic.

Effect of mild and moderate hypothermia on hypoxic injury in nearly pure neuronal culture

PURPOSE

The effects of mild and moderate hypothermic therapy on cerebral injury are still controversial. Our hypothesis is that mild and moderate hypothermia should have some effects on neurons themselves if they really have protective effects. By using a nearly pure neuronal culture, we evaluated the effects and mechanism of hypothermia against hypoxic insult.

METHODS

A nearly pure neuronal culture from cortices of 18-day-old Wister rats was used. The neurons were exposed to below 1% oxygen at 3 different temperatures (30, 33 and 37°C). First, cell viability was measured by assessing viable neurons with trypan blue. Second, to evaluate the mechanism, the extracellular glutamate concentration was measured by high-performance liquid chromatography after hypoxia; cell viability after exposure to extrinsic glutamate was also evaluated. Next, mitochondrial membrane potential was estimated, by monitoring aggregation of MitoCapture™, and the percentage of apoptotic cells was evaluated by staining with Hoechst 33342 and propidium iodide.

RESULTS

After 24-h hypoxic insult, cell viability at 30 and 33°C was significantly higher than at 37°C. There was no significant difference between extracellular concentrations of glutamate after hypoxia or cell viability after glutamate exposure among the 3 temperature groups. In moderate hypothermia, the number of neurons with mitochondrial injury and the percentage of apoptotic cells were significantly reduced.

CONCLUSION

Mild and moderate hypothermia inhibited hypoxic neuronal cell death. The mechanism of this effect may be related to protection of mitochondrial function, presumably followed by inhibition of apoptosis, at least in moderate hypothermia.

Reduction of microembolic signals with a single-clamp strategy in coronary artery bypass surgery: a pilot study

BACKGROUND

Neurologic deficits are perhaps the most feared form of adverse outcome following cardiac surgery. Aortic trauma generates emboli and hence harbors the potential for neurocognitive injury. The single aortic clamp strategy of coronary artery bypass grafting (CABG) aims at reducing aortic manipulation. We hypothesized that this strategy will lead to a reduction in the number microembolic signals (MES) evaluated by transcranial Doppler (TCD), a surrogate measure of cerebral embolism.

METHODS

This pilot study was based on a prospective analysis of 22 patients in whom CABG was performed either with a single aortic clamp (SC group) or with a conventional multiple aortic side-clamp technique (MC group). The 2 groups did not differ with respect to mean age (60 + or - 6 years versus 65 + or - 8 years, not statistically significant [NS]) or EuroSCORE (2.1 + or - 1.5 versus 2.9 + or - 2, P = NS). The neurocognitive evaluation was based on the mini-mental state examination (MMSE). The preoperative MMSE values for the SC and MC groups were similar (29.5 + or - 0.5 and 29.2 + or - 1, respectively; P = NS).

RESULTS

The total number of solid-particle embolization signals secondary to aortic manipulation was lower in the SC group than in the MC group (72 + or - 28 versus 127 + or - 69, P = .02). Neurocognitive performance was moderately reduced in both groups compared with preoperative values. This reduction was more pronounced in the MC group than in the SC group (22.2 + or - 4.1 versus 25.3 + or - 1.6, P = .02). One patient in the MC group had a reversible ischemic neurologic deficit (P = NS). There were no deaths or perioperative myocardial infarctions in either group.

CONCLUSIONS

The single-clamp CABG strategy led to a reduction in MES, indicating a less pronounced embolic burden than with the conventional side-clamp CABG strategy. This strategy translated into a better performance in postoperative neurocognitive testing in the SC group of patients.

Hypothermia as a cytoprotective strategy in ischemic tissue injury

Hypothermia is a well established cytoprotectant, with remarkable and consistent effects demonstrated across multiple laboratories. At the clinical level, it has recently been shown to improve neurological outcome following cardiac arrest and neonatal hypoxia-ischemia. It is increasingly being embraced by the medical community, and could be considered an effective neuroprotectant. Conditions such as brain injury, hepatic encephalopathy and cardiopulmonary bypass seem to benefit from this intervention. It's role in direct myocardial protection is also being explored. A review of the literature has demonstrated that in order to appreciate the maximum benefits of hypothermia, cooling needs to begin soon after the insult, and maintained for relatively long period periods of time. In the case of ischemic stroke, cooling should ideally be applied in conjunction with the re-establishment of cerebral perfusion. Translating this to the clinical arena can be challenging, given the technical challenges of rapidly and stably cooling patients. This review will discuss the application of hypothermia especially as it pertains to its effects neurological outcome, cooling methods, and important parameters in optimizing hypothermic protection.

Protective effects of the free radical scavenger edaravone against glutamate neurotoxicity in nearly pure neuronal culture

PURPOSE

Edaravone, a free radical scavenger, has shown neuroprotection in both animals and humans. To evaluate the mechanism of this protection, we examined the effect of edaravone on neurons themselves against glutamate neurotoxicity.

METHODS

Neurons were collected from 18-day fetal rat brains and a culture of almost pure neurons was obtained after 14-day culture. The neurons were exposed to 50 muM glutamate for 10 min, followed by normal culture for 24 h. Edaravone was added to the medium during the glutamate insult (prophylactic effect) or after the insult (treatment effect). First, the cell survival rate was measured by staining with trypan blue. Second, the cells were stained with 6-carboxy-2', 7'-dichlorodihydrofluorescein diacetate, di-(acetoxymethyl ester) (C-DCDHF-DA) and the relative amount of reactive oxygen species (ROS) was measured by flow cytometry. Third, the cells were stained with Hoechst 33342 and propidium iodide and the numbers of apoptotic and necrotic cells were counted.

RESULTS

A dose-dependent prophylactic effect was observed and the cell survival rate in 500 muM edaravone was significantly higher than that without it. However, there was no treatment effect beyond 2 h after the insult. The amount of ROS under 500 muM edaravone at 4 h after the glutamate insult was significantly lower than the control amount. Necrosis, but not apoptosis, was significantly inhibited by edaravone.

CONCLUSION

Edaravone mainly showed a prophylactic effect on neurons against glutamate neurotoxicity, possibly through the inhibition of necrosis via the suppression of ROS production. However, for a protective effect, a higher, supraclinical concentration was required, compared to the concentrations producing a protective effect in glial and endothelial cells in previous studies.

[Neuromonitoring and neuroprotection in cardiac anaesthesia. Nationwide survey conducted by the Cardiac Anaesthesia Working Group of the German Society of Anaesthesiology and Intensive Care Medicine]

OBJECTIVE

The primary objective of this nationwide survey carried out in department of cardiac anesthesia in Germany was to identify current practice with regard to neuromonitoring und neuroprotection.

METHODOLOGY

The data are based on a questionnaire sent out to all departments of cardiac anesthesia in Germany between October 2007 und January 2008. The anonymized questionnaire contained 26 questions about the practice of preoperative evaluation of cerebral vessels, intra-operative use of neuromonitoring, the nature und application of cerebral protective measures, perfusion management during cardiopulmonary bypass, postoperative evaluation of neurological status, and training in the field of cerebral monitoring.

RESULTS

Of the 80 mailed questionnaires 55% were returned and 90% of department evaluated cerebral vessels preoperatively with duplex ultrasound. The methods used for intra-operative neuromonitoring are electroencephalography (EEG, 60%) for type A dissections (38.1%), for elective surgery on the thoracic and thoraco-abdominal aorta (34.1% and 31.6%, respectively) and in carotid surgery (43.2%) near infrared spectroscopy (40%), evoked potentials (30%) and transcranial Doppler sonography (17.5%), with some centers using combined methods. In most departments the central nervous system is not subjected to monitoring during bypass surgery, heart valve surgery, or minimally invasive surgery. Cerebral protective measures used comprise patient cooling on cardio-pulmonary bypass (CPB 100%), extracorporeal cooling of the head (65%) and the administration of corticosteroids (58%), barbiturates (50%) and antiepileptic drugs (10%). Neuroprotective anesthesia consists of administering inhalation anesthetics (32.5%; sevoflurane 76.5%) and intravenous anesthesia (20%; propofol and barbiturates each accounting for 46.2%). Of the departments 72.5% cool patients as a standard procedure for surgery involving cardiovascular arrest and 37.5% during all surgery using CPB. In 84.6% of department CPB flow equals calculated cardiac output (CO) under normothermia, while the desired mean arterial pressure (MAP) varies between 60 and 70 mmHg (43.9%) and between 50 and 60 mmHg (41.5%), respectively. At body temperatures less than 18 degrees C CPB flow is reduced below the calculated CO (70%) while 27% of departments use normothermic flow rates. The preferred MAP under hypothermia is between 50 and 60 mmHg (59%). The results of intra-operative neuromonitoring are documented on the anesthesia record (77%). In 42.5% of the departments postoperative neurological function is estimated by the anesthesiologist. Continuing education sessions pertaining to neuromonitoring are organized on a regular basis in 32.5% of the departments and in 37.5% individual physicians are responsible for their own neuromonitoring education.

CONCLUSION

The present survey data indicate that neuromonitoring and neuroprotective therapy during CPB is not standardized in cardiac anesthesiology departments in Germany. The systemic use of available methods to implement multimodal neuromonitoring would be desirable.