Stroke in the postoperative period

Upregulation of GLT-1 via PI3K/Akt Pathway Contributes to Neuroprotection Induced by Dexmedetomidine

Perioperative ischemic stroke usually leads to neurological dysfunction caused by neuron death. During the ischemic condition, excitotoxity due to extracellular glutamate accumulation is a main mechanism of neuron damage. The clearance of glutamate mainly depends on glutamate transporter-1 (GLT-1) which is expressed in astrocytes. Dexmedetomidine, an α2 adrenergic receptor agonist, is proved to induce neuroprotection. This study was set out to investigate the glutamate-related mechanism involved in the neuroprotective effect of dexmedetomidine. Middle cerebral artery occlusion (MCAO) was used as a model of ischemic stroke in our study. We determined Neurological deficit scores (NDS) and Magnetic resonance imaging (MRI) at three points (2, 6, and 24 h) after middle cerebral artery occlusion (MCAO) to evaluate the neuroprotective effect of dexmedetomidine. Besides, we performed western blot (6 and 24 h after MACO) and immunofluorescent staining (24 h after MCAO) to observe the expression of GLT-1. The effect and mechanism of dexmedetomidine on GLT-1 in primary cultured astrocytes were investigated using western blot and RT-PCR. Our results showed that pretreatment with dexmedetomidine improved NDS and reduced infarct volume as well as upregulating GLT-1 expression. Furthermore, using Atipamezole and LY294002, we found that dexmedetomidine significantly increased GLT-1 levels in astrocytes via activating α2 adrenergic receptor and PI3K/AKT pathway both in vitro and in vivo study. Overall, our present study indicated that dexmedetomidine had neuroprotective effects on ischemia stroke and upregulation of GLT-1 levels by PI3K/AKT dependent pathway might be the potential mechanism.

Perioperative stroke - Prediction, Prevention, and Protection

Stroke culminates into 6.2 million deaths annually and is thereby a leading cause of disability and death worldwide. In patients undergoing noncardiac, nonneurological surgery, perioperative stroke can eventuate into a catastropic aftermath with almost eight-fold rise in mortality. In cardiac, neurological, and carotid surgery, stroke rate accounts to be high (2.2%–5.2%) and is a significant instigator of morbidity and mortality as well. These facts kindle interest to review the predictive parameters, preventive measures, and all the possibilities in the management and protection against perioperative stroke.

Low-intensity (400 mW/cm2, 500 kHz) pulsed transcranial ultrasound preconditioning may mitigate focal cerebral ischemia in rats

BACKGROUND

Preconditioning methods, which could increase tolerance of brain to subsequent ischemic injuries with a small dose of non-injury stimuli, have gained attention. Capitalizing on noninvasiveness and safety of ultrasound modality, the pulsed transcranial ultrasound stimulation (pTUS) approach may provide a novel treatment for patients with high risk of stroke.

OBJECTIVE

This study's goal was to investigate whether the risk of stroke could be minimized or eliminated by prior exposure to low-intensity, pulsed transcranial ultrasound stimulation (pTUS).

METHODS

Rats were randomly assigned to control (n = 12) and pTUS preconditioning (pTUS-PC) groups (n = 14). The animals in pTUS-PC group were exposed to transcranial ultrasound stimulation before the induction of photothrombotic stroke, whereas control animals were handled identically but without the ultrasound stimulation. Cerebral blood flow was monitored using laser speckle imaging in both groups during stroke induction, as well as 24 and 48 h after stroke, respectively. Also, infarct volumes and edema were measured at 48 h after stroke.

RESULTS

pTUS-PC rats had smaller ischemic areas during stroke induction, and 24 and 48 h after the stroke, and smaller infarct volume (1.770 ± 0.169%) than the controls (3.215 ± 0.401%) (p < 0.01). Moreover, the pTUS-PC group experienced lower volume of brain edema than the control group (pTUS-PC rats: 6.658 ± 1.183%; control rats: 12.48 ± 1.386%, p < 0.01).

CONCLUSION

These results support the hypothesis that transcranial ultrasound stimulation applied before photothrombosis could provide neuroprotection by increasing the brain's tolerance to subsequently induced focal ischemic injury.

Paradigms and mechanisms of inhalational anesthetics mediated neuroprotection against cerebral ischemic stroke

Cerebral ischemic stroke is a leading cause of serious long-term disability and cognitive dysfunction. The high mortality and disability of cerebral ischemic stroke is urging the health providers, including anesthesiologists and other perioperative professioners, to seek effective protective strategies, which are extremely limited, especially for those perioperative patients. Intriguingly, several commonly used inhalational anesthetics are recently suggested to possess neuroprotective effects against cerebral ischemia. This review introduces multiple paradigms of inhalational anesthetic treatments that have been investigated in the setting of cerebral ischemia, such as preconditioning, proconditioning and postconditioning with a variety of inhalational anesthetics. The pleiotropic mechanisms underlying these inhalational anesthetics-afforded neuroprotection against stroke are also discussed in detail, including the common pathways shared by most of the inhalational anesthetic paradigms, such as anti-excitotoxicity, anti-apoptosis and anti-inflammation. There are also distinct mechanisms involved in specific paradigms, such as preserving blood brain barrier integrity, regulating cerebral blood flow and catecholamine release. The ready availability of these inhalational anesthetics bedside and renders them a potentially translatable stroke therapy attracting great efforts for understanding of the underlying mechanisms.

Perioperative stroke

It is increasingly recognized that one can identify a higher risk patient for perioperative stroke. The risk of stroke around the time of operative procedures is fairly substantial and it is recognized that patients initially at risk for vascular events are those most likely to have this risk heightened by invasive procedures. Higher risk patients include those of advanced age and there is a cumulative risk, over time, of coexistent hypertension, atherosclerosis, diabetes mellitus, cardiac disease and clotting disorders. There are a number of possible mechanisms associated with the procedure (e.g., preoperative hypercoagulability, holding of antithrombic therapy at the time of the procedure and cardiac arrhythmia) that can promote a thrombo-embolic event. Examples of these include: direct mechanical trauma to extracranial vessels related to operations on the head and neck; and vascular injury as a consequence of vascular and innovative endovascular procedures affecting the cerebral circulation (e.g., carotid endarterectomy, extracranial or intracranial angioplasty with stenting, and use of the MERCI clot retrieval device), as well as various endovascular methods that have been developed to obliterate cerebral aneurysms and arteriovenous malformations as an alternative to surgical clipping and surgical resection, respectively.

Cytoprotective effects of the volatile anesthetic sevoflurane are highly dependent on timing and duration of sevoflurane conditioning: findings from a human, in-vitro hypoxia model

Using animal models, volatile anesthetics have been recognized for their neuroprotective effects. Nevertheless, there is still disagreement about the optimal duration and timing of conditioning with the volatile anesthetic sevoflurane in the human system. In the study presented, we employed a human neuronal cell culture model to investigate the effects of hypoxia and to evaluate potential cytoprotective properties of different sevoflurane conditioning strategies. Sevoflurane was applied to human IMR-32 cells in which hypoxic conditions were induced for 2h using our recently described two-enzyme model (Zitta et al., Eur. J. Pharmacol., 2010). Cellular effects of hypoxia and sevoflurane conditioning were evaluated by lactate dehydrogenase (LDH) measurements, brightfield microscopy, ELISAs, cytometric bead arrays, Westernblotting and RT-PCR. Hypoxia increased the release of LDH into the culture medium after 24h (normoxia: 0.15+/-0.02 a.u; hypoxia: 0.69+/-0.08 a.u, P<0.001) and expression of hypoxia associated genes HIF-1alpha, VEGF, catalase. Cytoprotective effects were observed in cultures that received sevoflurane for 30 min before hypoxia (preconditioning: 0.41+/-0.07 a.u., P<0.01) and for 30 min during the hypoxic period (intraconditioning: 0.20+/-0.01 a.u., P<0.001). Application of sevoflurane after the hypoxic insult did not lead to cytoprotection (postconditioning: 0.73+/-0.12a.u., P>0.05). Conditioning with sevoflurane for a total of 3h before, during and after hypoxia, however, resulted in an enhanced release of LDH (periconditioning: 0.97+/-0.10a.u., P<0.01) and additional cell damage. Hypoxia and sevoflurane intraconditioning were associated with changes in erk1/2 phosphorylation (T202/Y204) and HIF-1alpha protein levels, whereas phosphorylation of akt (S473) was not significantly altered. Our results suggest short pre- and intraconditioning with sevoflurane as most potent strategies to reduce hypoxia induced neuronal cell damage.

Rapid thrombelastography (r-TEG) identifies hypercoagulability and predicts thromboembolic events in surgical patients

BACKGROUND

Despite routine prophylaxis, thromboembolic events (TEs) in surgical patients remain a substantial problem. Furthermore, the timing and incidence of hypercoagulability, which predisposes to these events is unknown, with institutional screening programs serving primarily to establish a diagnosis after an event has occurred. Emerging evidence suggests that point of care (POC) rapid thrombelastography (r-TEG) provides a real-time analysis of comprehensive thrombostatic function, which represents an analysis of both enzymatic and platelet components of thrombus formation. We hypothesized that r-TEG can be used as a screening tool to identify hypercoagulable states in surgical patients and would predict subsequent thromboembolic events.

METHODS

Rapid thrombelastography r-TEG analyses were performed on 152 critically ill patients in the surgical intensive care unit (ICU) during 7 months. Hypercoagulability was defined as clot strength (G)>12.4 dynes/cm(2). Variables of interest for identifying hypercoagulability and thromboembolic events included sex, age, operating hospital service, specific injury patterns, injury severity score (ISS), transfusion within first 24 h, ICU duration of stay, ventilator days, hospital admission days, and thromboprophylaxis. Comparisons between the hypercoagulable and normal groups or between the groups with and without thromboembolic events were performed using Chi-square tests or the Fisher exact test for categorical variables and independent sample t tests or Wilcoxon rank sum tests for continuous variables. Multivariate logistic regression analysis (LR) was performed to identify independent predictors of thromboembolic events. A receiver operating characteristic curve was used to measure the performance of G for predicting the occurrence of a TE event. All tests were 2-sided with significance of P < .05.

RESULTS

In all, 86 patients (67%) were hypercoagulable by r-TEG. More than 85% of patients in the hypercoagulable group and 79% in the normal group received thromboprophylaxis during the study period. The differences between hypercoagulable and normal groups by bivariate analysis included high-risk injuries (52% vs 35%; P = .03), spinal cord injury (27% vs 12%; P = .03), median ICU duration of stay (13 vs 7 days; P < .001), median ventilator days (6 vs 2; P < .001), and median hospital duration of stay (20 vs 13 days; P < .001). A total of 16 patients (19%) of the hypercoagulable group suffered a thromboembolic event, and 10 hypercoagulable patients (12%) had thromboembolic events predicted by prior r-TEG hypercoagulability. No patients with normal coagulability by r-TEG had an event (P < .001). LR analysis showed that the strongest predictor of TE after controlling for the presence of thromboprophylaxis was elevated G value (odds ratio: 1.25, 95% confidence interval [CI]: 1.12-1.39). For every 1 dyne/cm(2) increase in G, the odds of a TE increased by 25%.

CONCLUSION

These results indicate that the presence of hypercoagulability identified by r-TEG is predictive of thromboembolic events in surgical patients. Subsequent study is necessary to define optimal prophylactic treatment strategies for patients with r-TEG proven hypercoagulability.

Thiopental exaggerates ischemic brain damage and neurological deficits after experimental stroke in spontaneously hypertensive rats

Thiopental is an anesthetic used for controlling high intracranial pressure (ICP) caused by brain surgery, brain trauma, and severe stroke. However, it remains controversial whether Thiopental is detrimental or beneficial in ischemic stroke. In this study, we used an animal model of ischemic stroke in spontaneously hypertensive rats to determine whether or not Thiopental is neuroprotective in the setting of brain ischemia. We observed that Thiopental caused a prolonged duration of unconsciousness with a high rate of mortality, that Thiopental created exaggerated neurological deficits that were revealed through limb placement tests at 4 days and 4 weeks after brain ischemia, and that infarct volume was increased in Thiopental-anesthetized rats. These data suggest that Thiopental is detrimental in ischemic stroke. Thus, our findings raise a caution about the use of Thiopental in the setting of ischemic stroke.

Does thromboelastography predict postoperative thromboembolic events? A systematic review of the literature

BACKGROUND

Since thromboelastography (TEG) can detect hypercoagulable states, it is a potentially useful test for predicting postoperative thromboembolic complications. Therefore, we performed a systematic review of the literature to evaluate the accuracy of TEG in predicting postoperative thromboembolic events.

METHODS

PUBMED and EMBASE electronic databases were searched by two independent investigators to identify prospective studies involving adult patients undergoing operative procedures in which a TEG test was performed perioperatively and outcomes were measured by reference standards. The quality of included studies was assessed and measures of diagnostic test accuracy were estimated for each included study.

RESULTS

Ten studies (with a total of 1056 patients) were included in this analysis; however, only five reported measures of TEG test accuracy. The overall quality of the studies and level of diagnostic evaluation of the studies were highly variable, from poor to good. As there were variations in the definition of hypercoagulability, TEG methodology and patient characteristics, reference standards used and outcomes measured, a meta-analysis was not undertaken. The sensitivity and specificity ranged from 0% to 100% and 62% to 92%, respectively. The diagnostic odds ratio ranged from 1.5 to 27.7; area under the curve ranged from 0.57 to 0.91. Of the TEG variables, maximum amplitude seems to be the best parameter to identify hypercoagulable states and to predict thromboembolic events.

CONCLUSIONS

The predictive accuracy of TEG for postoperative thromboembolic events is highly variable. To determine if the TEG is a clinically useful screening test in high-risk surgical populations, more prospective studies are needed.

Gender-specific response to isoflurane preconditioning in focal cerebral ischemia

Inhalation anesthetics are effective chemical preconditioning agents in experimental cerebral ischemia. However, previous work has been performed exclusively in male animals. We determined if there is a gender difference in ischemic outcome after isoflurane preconditioning (IsoPC), and if this sex-specific response is linked to differences in Akt phosphorylation or expression of neuronal inducible cell-death putative kinase (NIPK), a negative modulator of Akt activation. Young and middle-aged male and female mice were preconditioned for 4 h with air (sham PC) or 1.0% IsoPC and recovered for 24 h. Cortices were subdissected from preconditioned young male and female mice for measurement of Akt phosphorylation (Western blot) and NIPK mRNA (quantitative polymerase chain reaction). Additional cohorts underwent 2 h of reversible middle cerebral artery occlusion. Lastly, male and female Akt1(+/+) and Akt1(-/-) mice were studied to determine if gender differences in ischemic outcome after IsoPC is Akt1-dependent. Infarction volume was determined at 22 h reperfusion (2,3,5-triphenyltetrazolium chloride). As expected, IsoPC decreased ischemic damage as compared with sham PC in young and middle-aged male mice. In contrast, IsoPC markedly increased infarction in young female mice and had no effect in middle-aged female mice. Cortical phospho-Akt was increased by IsoPC versus sham PC only in male mice. No increase was observed in IsoPC female mice. NIPK mRNA was higher in female mice than in male mice regardless of preconditioning status. Male IsoPC neuroprotection was lost in Akt1-deficient male mice. We conclude that IsoPC is beneficial only in ischemic male brain and that sex differences in IsoPC are mediated through Akt activation and basal NIPK expression.

Inhalational anesthetics as neuroprotectants or chemical preconditioning agents in ischemic brain

This review will focus on inhalational anesthetic neuroprotection during cerebral ischemia and inhalational anesthetic preconditioning before ischemic brain injury. The limitations and challenges of past and current research in this area will be addressed before reviewing experimental and clinical studies evaluating the effects of inhalational anesthetics before and during cerebral ischemia. Mechanisms underlying volatile anesthetic neuroprotection and preconditioning will also be examined. Lastly, future directions for inhalational anesthetics and ischemic brain injury will be briefly discussed.

In-hospital onset ischemic stroke may be associated with atrial fibrillation and right-to-left shunt

BACKGROUND AND PURPOSE

Ischemic stroke during hospitalization can occasionally be found, but the mechanisms and causes underlying stroke have not been investigated in detail. The present study aimed to identify differences in stroke etiology between in-hospital and out-of-hospital onset.

METHODS

Subjects comprised 357 consecutive patients (221 men, 136 women) with ischemic stroke prospectively enrolled within 24 h of onset. Contrast saline transcranial Doppler ultrasonography (c-TCD) or transesophageal echocardiography (TEE) was performed in all participants to identify right-to-left shunts (RLS). Patients were divided into 2 groups: in-hospital onset (IHO group, n=49); and out-of-hospital onset (OHO group, n=308). Clinical characteristics were compared between groups.

RESULTS

Mean age was 71.5+/-12.3 years. Mean National Institute of Health stroke scale score was 6.9+/-7.2. RLS, atrial fibrillation (AF) and malignancy were more frequent in the IHO group than in the OHO group (39% vs. 20%, p=0.006; 45% vs. 16%, p<0.001; 18% vs. 4%, p<0.001, respectively). AF and/or RLS was more frequent in the IHO group (61%) than in the OHO group (30%, p<0.001).

CONCLUSION

Ischemic stroke with in-hospital onset may be associated with AF and RLS.

Ischemic Stroke Following Multiple Traumas in a Child: A Case Report

Stroke is an uncommon disorder in children but an increasingly recognized cause of disability. Acute stroke may be attributable to trauma, but this topic is seldom discussed. In limited reports, most ischemic strokes following trauma were detected after a considerable delay. Early recognition of stroke following trauma might reduce secondary neurologic complications. We report a case of posterior cerebral artery area infarct following multiple traumas in a child. A comprehensive etiologic survey was undertaken and discussed. Although the definite pathogenesis is still unclear, adequate, individualized, and uncomplicated management can significantly affect the outcome.

Thromboelastography maximum amplitude predicts postoperative thrombotic complications including myocardial infarction

Postoperative thrombotic complications increase hospital length of stay and health care costs. Given the potential for thrombotic complications to result from hypercoagulable states, we sought to determine whether postoperative blood analysis using thromboelastography could predict the occurrence of thrombotic complications, including myocardial infarction (MI). We prospectively enrolled 240 patients undergoing a wide variety of surgical procedures. A cardiac risk score was assigned to each patient using the established revised Goldman risk index. Thromboelastography was performed immediately after surgery and maximum amplitude (MA), representing clot strength, was determined. Postoperative thrombotic complications requiring confirmation by a diagnostic test were assessed by a blinded observer. Ten patients (4.2%) suffered a total of 12 postoperative thrombotic complications. The incidence of thrombotic complications with increased MA (8 of 95 = 8.4%) was significantly (P = 0.0157) more frequent than that of patients with MA < or =68 (2 of 145 = 1.4%). Furthermore, the percentage suffering postoperative MI in the increased MA group (6 of 95 = 6.3%) was significantly larger than that in the MA < or =68 group (0 of 145 = 0%) (P = 0.0035). In a multivariate analysis, increased MA (P = 0.013; odds ratio, 1.16; 95% confidence interval, 1.03-1.20) and Goldman risk score (P = 0.046; odds ratio, 2.39; 95% confidence interval, 1.02-5.61) both independently predicted postoperative MI. A postoperative hypercoagulable state as determined by thromboelastography is associated with postoperative thrombotic complications, including MI, in a diverse group of surgical patients.

Prolonged retraction on the normal common carotid artery induced lethal stroke after cervical spine surgery

STUDY DESIGN

Case report.

OBJECTIVE

To report a previously undescribed complication of prolonged retraction on the normal common carotid artery after anterior cervical spine surgery.

SUMMARY OF BACKGROUND DATA

Previous study showed that prolonged retraction could decrease the blood flow of the common carotid artery during anterior cervical spine surgery. A case report revealed that prolonged retraction could induce the formation of thrombosis in the atherosclerotic common carotid artery.

METHODS

Notes review. Computed tomography of the brain was performed on the first and the fourth postoperative day. Carotid Doppler ultrasound and transcranial Doppler ultrasound were performed to evaluate the left common carotid artery and the left intracranial cerebral arteries.

RESULTS

After lengthy anterior cervical spinal surgery, the patient did not regain his consciousness during the stay in the postoperative care unit. Large infarction of left cerebral hemisphere was revealed by computed tomography. The patient died on the seventh postoperative day of perioperative lethal stroke.

CONCLUSION

We suggest that prolonged retraction, even on the normal common carotid artery, could induce lethal stroke after anterior cervical spine surgery. We recommend that retractor should be placed carefully and cerebral perfusion should be maintained adequately.

Perioperative stroke: evaluation, management, and possible preventive measures

Mechanisms of perioperative ischemic stroke include: hypotension, hypercoagulability, arrhythmias with embolism, or direct vascular insult. Mechanisms of perioperative hemorrhagic stroke include: use of antithrombotics, hypertension, or direct vascular insult.