Assessing the impact of cerebral injury after cardiac surgery: will determining the mechanism reduce this injury?

Preoperative neurological dysfunctions: what is their meaning in patients presenting with acute type A aortic dissection?

INTRODUCTION

Type A aortic dissection (AAD) is a life-threatening disease with very high mortality. The gold standard treatment is surgical, as medical treatment has been proven to be ineffective. It is still unclear the role of preoperative neurological dysfunction in the prognosis of the patient. Therefore, the choice of performing surgery in patients with neurological symptoms is still left to the surgeon at the time of the diagnosis. The aim of this study is to make a narrative review of the current literature about the management of patients with neurological symptoms in AAD patients.

EVIDENCE ACQUISITION

A bibliographical research was performed on PubMed, looking for papers containing the words: "((preoperative neurological symptoms in type a aortic dissection) OR brain injury type A aortic dissection) AND ("2010"[Date - Publication]: "3000"[Date - Publication])". A total of 35 papers were found.

EVIDENCE SYNTHESIS

A total of 6 papers were chosen to be reviewed. All of them concluded that even patients with severe neurological symptoms (up to comatose state) had a good chance to recover neurological functions after surgery if treated in the first hours from the onset of symptoms. Interestingly, a hemorrhagic stroke was rarely found.

CONCLUSIONS

Preoperative neurological dysfunction have been long considered a contraindication to surgery. Nevertheless, several authors show neurological and survival good results in patients with preoperative neurological dysfunction. They also stress the importance of surgical timing finding in 5 to 10 hours the surgical time limit to improve neurological dysfunction. A preoperative neurological dysfunction could be considered a strong advice towards surgical intervention. It is time to change and consider prompt surgery not only for survival but also for cerebral protection.

Deep Hypothermia and Circulatory Arrest in Adults

Brain protection during cardiopulmonary bypass has been the subject of intense research. Deep hypothermic circulatory arrest (DHCA) continues to be used for that goal during complex aortic arch and large intracranial aneurysm surgeries. The anesthetic management for adult patients undergoing these types of procedures requires specific knowledge and expertise. Based on our experience and review of the current literature, the authors highlight the key areas of the anesthetic plan, discussing the risk factors associated with adverse neurologic outcome as well as the rationale for decisions regarding specific monitors and medications. In the conclusion an anesthetic protocol for adult patients undergoing DHCA is suggested.

Cerebral injury during paediatric heart surgery: perfusion issues

Suboptimal neurodevelopmental outcome is common in children who have congenital heart disease. Its aetiology is often multifactorial. This review focuses on the role of cardiopulmonary bypass. Hypothermia is the mainstay of cerebral protection. Low flow and regional low flow are preferred to deep hypothermic circulatory arrest in many situations. Cooling and rewarming, aortopulmonary collaterals, pH, air emboli, the systemic inflammatory response, haematocrit, oxygenation, glucose and ultrafiltration can influence neurodevelopmental outcome. Although no pharmacological agents have been shown to have a beneficial effect on neurodevelopmental outcome in clinical practice in children, animal work on the use of steroids several hours before surgery is encouraging.

Changes in metabolism and blood flow in peripheral tissue (skeletal muscle) during cardiac surgery with cardiopulmonary bypass: the biochemical microdialysis study

The aim of this study was to monitor the metabolism and blood flow in the interstitium of the skeletal muscle during cardiac surgery with cardiopulmonary bypass (CPB) and in the early postoperative period by means of microdialysis and to compare metabolic changes during CPB at normothermia (NT) and hypothermia (HT).

Surgical revascularization using CPB was performed in 50 patients, 25 patients (group HT) were operated using hypothermic CPB, 25 (group NT) using normothermic CPB. Interstitial microdialysis was performed by two CMA 60 probes (CMA Microdialysis AB, Solna, Sweden) inserted into the patient’s deltoid muscle. Constituents analysed in the obtained dialysates, collected at intervals, were glucose, urea, glycerol and lactate. Tissue blood flow was monitored by dynamic microdialysis with gentamicin as a marker.

In both groups, NT versus HT, similar dynamics of concentrations were found. Low initial concentrations were followed by gradual increases during CPB and in the following phase of the operation. Concentrations were higher in the NT group. Immediately after the operation, the decrease in values continued, with a gradual increase in the succeeding postoperative period in both groups. Similar dynamic changes in the lactate concentration were found in both groups. The gentamicin concentrations were lower in the NT group (versus the HT group).

The results showed dynamic changes in the interstitial concentrations of glucose, urea, glycerol and lactate, which depend on the phase of the surgery in the CPB and early postoperative phase in the both groups of patients. Higher tissue perfusion of the skeletal muscle was noted in those patients operated on in normothermia. The dynamics of the concentration changes of these substances in the interstitium of the skeletal muscle has been proven to be caused by both the metabolic activity of the tissue and by the blood flow through the interstitium of the muscle.

Cannulation and Cardiopulmonary Bypass Produce Selective Brain Lesions in Pigs

Whether cardiopulmonary bypass alone or together with manipulation of the aorta produces neurologic complications remains controversial. Using a pig model, the immediate effects of aortic cannulation and cardiopulmonary bypass on neural injury in different brain regions were investigated in 3 experimental groups: non-operated controls; operated controls with aortic cannulation without cardiopulmonary bypass; and operated animals undergoing cardiopulmonary bypass. Immunohistochemistry using a monoclonal antibody against calretinin was used to show possible ischemic damage in the hippocampal formation which is one of the most vulnerable regions to ischemia. Both cannulation of the aorta alone and cardiopulmonary bypass resulted in numerous argyrophilic neurons in discrete regions of the prefrontal and cerebellar cortex. Decreased calretinin immunoreaction and a reduced number of calretinin-positive neurons were observed following aortic cannulation or cardiopulmonary bypass compared to the non-operated controls. This suggests that both cannulation of the aorta alone and cardiopulmonary bypass affect a selected population of neurons. Therefore, off-pump, aorta no-touch technique may prevent neurologic complications.

Postoperative encephalopathy with choreoathetosis

Since the 1980s, survival of children with CHD has increased significantly with the introduction of new surgical techniques that incorporate cardiorespiratory arrest (CRA), extracorporeal circulation (ECC), and deep hypothermia. However, an increase in survival has been associated with an increase in recognized postoperative neurological complications. Postoperative encephalopathy with choreoathetosis, also known as "postpump chorea", is one of these well-defined neurological complications and was first reported in 1961. Postpump chorea is considered one of the most devastating neurological complications following cardiac surgery. However, the exact etiology and pathophysiology of this complication is unknown. Several factors may contribute to the postoperative development of choreoathetoid movements, including deep hypothermia (core body temperature < 20ºC) with total circulatory arrest, use of cardiopulmonary bypass, and variability in blood pH and PaCO(2) resulting in fluctuations in cerebral blood flow. The length of time children are affected by choreoathetoid movements and long-term neurological outcome in these children varies and largely depends upon the form of postoperative encephalopathy that they develop, described as either mild or severe. Several groups suggest that age at time of surgery plays a role in the risk of developing postpump chorea, with a tendency for older children to develop the severe persistent form.

Hawley H. Seiler Resident Award. Transcriptional profile of brain injury in hypothermic circulatory arrest and cardiopulmonary bypass

BACKGROUND

Little is known about the molecular mechanisms of neurologic complications after hypothermic circulatory arrest (HCA) with cardiopulmonary bypass (CPB). Canine genome sequencing allows profiling of genomic changes after HCA and CPB alone. We hypothesize that gene regulation will increase with increased severity of injury.

METHODS

Dogs underwent 2-hour HCA at 18 degrees C (n = 10), 1-hour HCA (n = 8), or 2-hour CPB at 32 degrees C alone (n = 8). In each group, half were sacrificed at 8 hours and half at 24 hours after treatment. After neurologic scoring, brains were harvested for genomic analysis. Hippocampal RNA isolates were analyzed using canine oligonucleotide expression arrays containing 42,028 probes.

RESULTS

Consistent with prior work, dogs that underwent 2-hour HCA experienced severe neurologic injury. One hour of HCA caused intermediate clinical damage. Cardiopulmonary bypass alone yielded normal clinical scores. Cardiopulmonary bypass, 1-hour HCA, and 2-hour HCA groups historically demonstrated increasing degrees of histopathologic damage (previously published). Exploratory analysis revealed differences in significantly regulated genes (false discovery rate < 10%, absolute fold change > or = 1.2), with increases in differential gene expression with injury severity. At 8 hours and 24 hours after insult, 2-hour HCA dogs had 502 and 1,057 genes regulated, respectively; 1-hour HCA dogs had 179 and 56 genes regulated; and CPB alone dogs had 5 and 0 genes regulated.

CONCLUSIONS

Our genomic profile of canine brains after HCA and CPB revealed 1-hour and 2-hour HCA induced markedly increased gene regulation, in contrast to the minimal effect of CPB alone. This adds to the body of neurologic literature supporting the safety of CPB alone and the minimal effect of CPB on a normal brain, while illuminating genomic results of both.

Glutamate excitotoxicity mediates neuronal apoptosis after hypothermic circulatory arrest

BACKGROUND

Prolonged hypothermic circulatory arrest results in neuronal cell death and neurologic injury. We have previously shown that hypothermic circulatory arrest causes both neuronal apoptosis and necrosis in a canine model. Inhibition of neuronal nitric oxide synthase reduced neuronal apoptosis, while glutamate receptor antagonism reduced necrosis in our model. This study was undertaken to determine whether glutamate receptor antagonism reduces nitric oxide formation and neuronal apoptosis after hypothermic circulatory arrest.

METHODS

Sixteen hound dogs underwent 2 hours of circulatory arrest at 18 degrees C and were sacrificed after 8 hours. Group 1 (n = 8) was treated with MK-801, 0.75 mg/kg intravenously prior to arrest followed by 75 microg/kg/hour infusion. Group 2 dogs (n = 8) received vehicle only. Intracerebral levels of excitatory amino acids and citrulline, an equal coproduct of nitric oxide, were measured. Apoptosis, identified by hematoxylin and eosin staining and confirmed by electron microscopy, was blindly scored from 0 (normal) to 100 (severe injury), while nick-end labeling demonstrated DNA fragmentation.

RESULTS

Dogs in groups 1 and 2 had similar intracerebral levels of glutamate. However, MK-801 significantly reduced intracerebral glycine and citrulline levels compared with hypothermic circulatory arrest controls. The MK-801 significantly inhibited apoptosis (7.92 +/- 7.85 vs 62.08 +/- 6.28, group 1 vs group 2, p < 0.001).

CONCLUSIONS

Our results showed that glutamate receptor antagonism significantly reduced nitric oxide formation and neuronal apoptosis. We provide evidence that glutamate excitotoxicity mediates neuronal apoptosis in addition to necrosis after hypothermic circulatory arrest. Clinical glutamate receptor antagonists may have therapeutic benefits in ameliorating both types of neurologic injury after hypothermic circulatory arrest.

Cognitive dysfunction in intensive care survivors

Cognitive dysfunction is increasingly recognized as a common, often prolonged and potentially disabling complication of critical illness. While demonstrable in patients who have survived a variety of both medical and surgical conditions, its causes remain unclear. Screening of patients in intensive care units and at follow up may help identify those who could benefit from cognitive rehabilitation.

Influence of hypothermia on right atrial cardiomyocyte apoptosis in patients undergoing aortic valve replacement

BACKGROUND

There is increasing evidence that programmed cell death can be triggered during cardiopulmonary bypass (CPB) and may be involved in postoperative complications. The purpose of this study was to investigate whether apoptosis occurs during aortic valve surgery and whether modifying temperature during CPB has any influence on cardiomyocyte apoptotic death rate.

METHODS

20 patients undergoing elective aortic valve replacement for aortic stenosis were randomly assigned to either moderate hypothermic (ModHT group, n = 10, 28 degrees C) or mild hypothermic (MiHT group, n = 10, 34 degrees C) CPB. Myocardial samples were obtained from the right atrium before and after weaning from CPB. Specimens were examined for apoptosis by flow cytometry analysis of annexin V-propidium iodide (PI) and Fas death receptor staining.

RESULTS

In the ModHT group, non apoptotic non necrotic cells (annexin negative, PI negative) decreased after CPB, while early apoptotic (annexin positive, PI negative) and late apoptotic or necrotic (PI positive) cells increased. In contrast, no change in the different cell populations was observed over time in the MiHT group. Fas expression rose after reperfusion in the ModHT group but not in MiHT patients, in which there was even a trend for a lower Fas staining after CPB (p = 0.08). In ModHT patients, a prolonged ischemic time tended to induce a higher increase of Fas (p = 0.061).

CONCLUSION

Our data suggest that apoptosis signal cascade is activated at early stages during aortic valve replacement under ModHT CPB. This apoptosis induction can effectively be attenuated by a more normothermic procedure.

Noninvasive assessment of brain injury in a canine model of hypothermic circulatory arrest using magnetic resonance spectroscopy

BACKGROUND

Studies have confirmed the neuroprotective effect of diazoxide in canines undergoing hypothermic circulatory arrest (HCA). A decreased N-acetyl-asparate:choline (NAA:Cho) ratio is believed to reflect the severity of neurologic injury. We demonstrated that noninvasive measurement of NAA:Cho with magnetic resonance spectroscopy facilitates assessment of neuronal injury after HCA and allows for evaluation of neuroprotective strategies.

METHODS

Canines underwent 2 hours of HCA at 18 degrees C and were observed for 24 hours. Animals were divided into three groups (n = 15 in each group): normal (unoperated), HCA (HCA only), and HCA+diazoxide (pharmacologic treatment before HCA). The NAA:Cho ratios were obtained 24 hours after HCA by spectroscopy. Brains were immediately harvested for fresh tissue NAA quantification by mass spectrometry. Separate cohorts of HCA (n = 16) and HCA+diazoxide (n = 23) animals were kept alive for 72 hours for daily neurologic assessment.

RESULTS

Cortical NAA:Cho ratios were significantly decreased in HCA versus normal animals (1.01 +/- 0.29 versus 1.31 +/- 0.23; p = 0.004), consistent with severe neurologic injury. Diazoxide pretreatment limited neurologic injury versus HCA alone, reflected in a preserved NAA:Cho ratio (1.21 +/- 0.27 versus 1.01 +/- 0.29; p = 0.05). Data were substantiated with fresh tissue NAA extraction. A significant decrease in cortical NAA was observed in HCA versus normal (7.07 +/- 1.9 versus 8.54 +/- 2.1 micromol/g; p = 0.05), with maintenance of normal NAA levels after diazoxide pretreatment (9.49 +/- 1.1 versus 7.07 +/- 1.9 micromol/g; p = 0.0002). Clinical neurologic scores were significantly improved in the HCA+diazoxide group versus HCA at all time points.

CONCLUSIONS

Neurologic injury remains a significant complication of cardiac surgery and is most severe after HCA. Magnetic resonance spectroscopy assessment of NAA:Cho ratios offers an early, noninvasive means of potentially evaluating neurologic injury and the effect of neuroprotective agents.

Methods of cerebral protection in surgery of the thoracic aorta

During the last decade, a considerable increase in the number of operations on the thoracic aorta has been observed. Although patient's outcomes have improved considerably, this surgery is still associated with significant morbidity and mortality due to neurological complications. Various methods have been proposed and widely used as means to protect the brain from ischemic damage. This review summarizes the principal methods of cerebral protection, describes the advantages and disadvantages of each method and their impact on patient outcomes, and discusses the different surgical techniques proposed to minimize the risk of cerebral injuries.

Neonatal Brain Protection and Deep Hypothermic Circulatory Arrest: Pathophysiology of Ischemic Neuronal Injury and Protective Strategies

Deep hypothermic circulatory arrest (DHCA) has been used for the past 50 years in the surgical repair of complex congenital cardiac malformations and operations involving the aortic arch; it enables the surgeon to achieve precise anatomical reconstructions by creating a bloodless operative field. Nevertheless, DHCA has been associated with immediate and late neurodevelopmental morbidities. This review provides an overview of the pathophysiology of neonatal hypoxic brain injury after DHCA, focusing on cellular mechanisms of necrosis, apoptosis, and glutamate excitotoxicity. Techniques and strategies in neonatal brain protection include hypothermia, acid base blood gas management during cooling, and pharmacologic interventions such as the use of volatile anesthetics. Surgical techniques consist of intermittent cerebral perfusion during periods of circulatory arrest and continuous regional brain perfusion.

Apoptosis: pathophysiology and therapeutic implications for the cardiac surgeon

Cardiomyocyte apoptosis has been associated with the pathogenesis of heart failure as well as ischemic and inflammatory myocardial conditions. The aim of this study is to give a critical synopsis of cardiomyocyte apoptosis and identify methods to prevent or attenuate apoptosis in patients undergoing cardiac surgery. Clinical conditions and agents associated with decreased apoptotic index are early repair or replacement of valvular pathology before deterioration of ventricular function, afterload reduction with medication or intraaortic balloon pulsation in patients with acute increase in afterload or in hemodynamically compromised patients, decreasing catecholamine-induced cardiotoxicity by using beta-blockers, phosphodiesterase inhibitors, or early insertion of intraaortic balloon pulsation or ventricular assist device. Prompt coronary revascularization, which reduces myocardial ischemia time, is the most effective antiapoptotic therapy. Reduction of myocardial apoptosis associated with cardiopulmonary bypass and aortic cross-clamping are other therapeutic targets. Some investigational therapies include ischemic preconditioning and use of antiapoptotic medication such as the caspase inhibitors, antioxidants, calcium-channel blockers, the insulin-like growth factor-1, and the poly-adenosine diphosphate-ribose-synthetase inhibitors. Most of the therapeutic implications in reducing cardiomyocyte apoptosis are still in the experimental phase. Some options are already incorporated in the clinical practice of the cardiovascular surgeon. New therapeutic considerations include avoiding sustained and long-term use of catecholamines and reducing or avoiding cardiopulmonary bypass-when clinically feasible. Noncatecholamine inotropes should be preferred for patients undergoing heart failure surgery and for patients with low output syndrome after open-heart surgery. The lessons learned from apoptosis research reinforce more liberal and early insertion of intraaortic balloon pulsation or ventricular assist device in clinical low output states.

Serial proton magnetic resonance spectroscopy of the brain in children undergoing cardiac surgery

We used proton magnetic resonance spectroscopy to study 11 children (age < 8 years) with congenital heart disease undergoing cardiopulmonary bypass to determine whether low (10 +/- 4; n = 6) vs high (20 +/- 4; n = 5) perfusate hematocrits during bypass resulted in changes in brain metabolites which correlate with neurologic injury. Long and short echo time single voxel magnetic resonance spectroscopy in occipital gray matter and neurologic assessment were performed preoperatively and 2 and 5 days postoperatively. We also determined whether prolonged periods at low flow rates during bypass affected spectroscopy variables. We found no significant differences in metabolite ratios between the low vs high hematocrit groups or the lower vs higher flow rate groups (repeated measures analysis of variance of observation ranks converted to normal scores). However, our study was limited by statistical power due to the small sample size, therefore no conclusions could be made. Additional studies involving a greater number of patients are necessary. In all 11 children, magnetic resonance spectroscopy detected a significant decrease in brain N-acetyl-aspartate, and increases in myoinositol and glutamate/glutamine after surgery (Quade test) demonstrating that magnetic resonance spectroscopy is sensitive in detecting subtle postoperative changes in brain metabolites.

Poly(ADP-ribose) polymerase inhibition improves postischemic myocardial function after cardioplegia-cardiopulmonary bypass

BACKGROUND

Poly(ADP-ribose) polymerase activation has been shown to contribute to the pathogenesis of myocardial ischemia-reperfusion injury. We hypothesized that a novel poly(ADP-ribose) polymerase inhibitor, INO-1001, provides myocardial protection and improves cardiac function after regional ischemia and cardioplegia-cardiopulmonary bypass (CPB).

STUDY DESIGN

Pigs were subjected to 30 minutes of regional ischemia by distal left anterior descending coronary artery ligation followed by CPB (60 minutes) with hyperkalemic cardioplegia (45 minutes). The myocardium then was reperfused post-CPB for 90 minutes. After 15 minutes of ischemia, the treatment group (n = 6) received an INO-1001 bolus (1mg/kg) before a continuous infusion (1mg/kg/hour). Control pigs (n = 6) received vehicle solution. Left ventricular pressure was monitored, from which the maximum, positive first derivative of left ventricular pressure over time (+dP/dt) was calculated. Regional myocardial function in the ischemic area was determined by sonomicrometric analysis. Infarct size was measured as the percent of the ischemic area by tetrazolium staining. Myocardial sections were immunohistochemically stained for poly(ADP-ribose) as a measure of poly(ADP-ribose) polymerase activity and inhibition.

RESULTS

Pigs treated with INO-1001 showed improvements in the +dP/dt at 60 and 90 minutes of post-CPB reperfusion (both p = 0.03) and percent segmental shortening at 30, 60, and 90 minutes of post-CPB reperfusion (p = 0.03, 0.009, and 0.03, respectively). Infarct size was decreased in the treatment group (18.5 +/- 5.7% versus 52.0 +/- 7.7%, INO-1001 versus control, p = 0.03). Poly(ADP-ribose) was reduced in myocardial sections from INO-1001-treated animals compared with controls.

CONCLUSIONS

These results suggest that INO-1001 provides myocardial protection by reducing the extent of infarction and improves cardiac function after regional ischemia and cardioplegia-CPB.

Brain injury in children with congenital heart disease

The incidence of neurodevelopmental impairment in children with congenital heart disease is high. Its aetiology is multiple and complex. Prevention and treatment must start during the preoperative period and continue through the intra- and postoperative periods. Research has resulted in a clearer understanding of the relationship between congenital heart disease and the brain, and of the effects of cardiopulmonary bypass, hypothermia and circulatory arrest. This has led to modifications in management which may improve neurological outcome in the future.

The basic biology of apoptosis and its implications for cardiac function and viability

Apoptosis or programed cell death is a continuous process of destruction of nonfunctional cells. It is a physiologic process whereby the body disposes of unwanted cells by self-destruction and is our utmost defense against damaged cells. There are several pathways leading to programed cell death. Apoptosis is seen in failing, infarcted, and hibernating human hearts, and during open heart surgery. Apoptosis appears to be induced by myocardial ischemia-reperfusion injury and this is reduced by ischemic preconditioning. Antiapoptotic interventions may be a future target for myocardial protection.

Cerebral metabolism of nitric oxide during retrograde cerebral perfusion

The aim of this study was to determine whether alpha- or pH-stat protects the brain during deep hypothermic retrograde cerebral perfusion. Fifteen anesthetized dogs on cardiopulmonary bypass were cooled to 18 degrees C under alpha-stat and underwent retrograde cerebral perfusion for 90 minutes under alpha-stat or pH-stat, or underwent antegrade cardiopulmonary bypass under alpha-stat as the control. Cerebral blood flow of the cortex was monitored and serial analyses of blood gases and total nitric oxide oxidation products made. Cerebral blood flow and cerebral metabolic rate for oxygen were significantly higher and plasma levels of nitric oxide oxidation products in the outflow from the brain were significantly lower in retrograde cerebral perfusion under pH-stat than under alpha-stat. This study shows that reduced levels of nitric oxide oxidation products may protect against neuronal damage induced by nitric oxide and that increased cerebral blood flow under pH-stat may lead to a reduction of nitric oxide oxidation products. Under retrograde cerebral perfusion, pH-stat is thus better than alpha-stat for protecting the brain.

Temporal and segmental distribution of constitutive and inducible nitric oxide synthases after traumatic spinal cord injury: effect of aminoguanidine treatment

Nitric oxide (NO) has been shown to play an important role in the pathophysiology of traumatic brain injury (TBI) and cerebral ischemia. However, its contribution to the pathogenesis of traumatic spinal cord injury (SCI) remains to be clarified. This study determined the time course of constitutive and inducible nitric oxide synthases (cNOS and iNOS, respectively) after SCI. Rats underwent moderate SCI at T10 using the NYU impactor device and were allowed to survive for 3, 6, or 24 h and 3 days after SCI (n = 5 in each group). For the determination of enzymatic activities, spinal cords were dissected into five segments, including levels rostral and caudal (remote) to the injury site. Other rats were perfusion fixed for the immunohistochemical localization of iNOS protein levels. cNOS activity was significantly decreased at 3 and 6 h within the traumatized T10 segment and at 3, 6, and 24 h at the rostral (T9) level (p < 0.05). Rostral (T8) and caudal (T11, T12) to the injury site cNOS activity was also decreased at 3 h after injury (p < 0.05). However, cNOS activity returned to control levels within 6 h at T8, T11 and T12 and at one day at T10 and T9 segments. iNOS enzymatic activity was elevated at all time points tested (p < 0.05), with the most robust increase observed at 24 h. Immunostaining for iNOS at 24 h revealed that a significant cellular source of iNOS protein appeared to be invading polymorphonuclear leukocytes (PMNLs). To assess the functional consequences of iNOS inhibition, aminoguanidine treatment was initiated 5 min after SCI and rats tested using the BBB open field locomotor score. Treated rats demonstrated significantly improved hindlimb function up to 7 weeks after SCI. Histopathological analysis of contusion volume showed that aminoguanidine treatment decreased lesion volume by 37% (p < 0.05). In conclusion, these results indicate that (1) cNOS and iNOS activities are regionally and temporally affected after moderate SCI, (2) the early accumulation of PMNLs are a potentially significant source of NO-induced cytotoxic products, and (3) acute aminoguanidine treatment significantly improves functional and histopathological outcome after SCI.

Strain specific differences in a cardio-pulmonary resuscitation rat model

An asphyxial cardiac arrest rat model, originally developed for Sprague-Dawley rats, was transferred to a Wistar rat model. Several strain specific life support adjustments, i.e. ventilator settings, anaesthesia, and drug requirements, were necessary to stabilize the model for Wistar rats. Despite these arrangements numerous resuscitation related variables appeared different. Three groups were evaluated and compared: a temperature monitored Wistar group 1 (n=34), a temperature controlled Wistar group 2 (n=26) and a temperature controlled Sprague-Dawley group 3 (n=7). Overall, Wistar rats seem to have more sensitive cardio-circulatory system evidenced by a more rapid development of cardiac arrest (164 vs. 201 s), requiring higher adrenaline/epinephrine doses (10 vs. 5 microg/kg) and requiring more time for recovery after resuscitation (i.e. for return of blood pressure and blood gases). Without strict temperature control (as in groups 2+3 rats) group 1 rats went into spontaneous mild to moderate hypothermia during the first 24 h after restoration of spontaneous circulation (ROSC). Spontaneous hypothermia delayed the development of overall visible CA1 neuronal damage 24-48 h, but did not prevent it; therefore the model seemed to be suitable for future studies. Neuronal damages in the CA1 region in Wistar rats appeared to be more as shrunken cell bodies and pyknotic nuclei before resorption took place, whereas in Sprague-Dawley rats appeared in the same region.

Involvement of apoptosis in neurological injury after hypothermic circulatory arrest: a new target for therapeutic intervention?

BACKGROUND

This study was undertaken to evaluate the role of apoptosis in neurological injury after hypothermic circulatory arrest (HCA).

METHODS

Twenty-one pigs (27 to 31 kg) underwent 90 minutes of HCA at 20 degrees C and were electively sacrificed at 6, 24, 48, and 72 hours, and at 7, 10, and 12 days after HCA, and compared with unoperated controls. In addition, 3 animals that had HCA at 10 degrees C, and 3 treated with cyclosporine A (CsA) in conjunction with HCA at 20 degrees C, were examined 72 hours after HCA. After selective perfusion and cryopreservation, all brains were examined to visualize apoptotic DNA fragmentation and chromatin condensation on the same cryosection of the hippocampus: fluorescent in situ end labeling (ISEL) was combined with staining with a nucleic acid-binding cyanine dye (YOYO).

RESULTS

In addition to apoptosis, which was seen at a significantly higher level (p = 0.05) after HCA than in controls, two other characteristic degenerative morphological cell types (not seen in controls) were characterized after HCA. Cell death began 6 hours after HCA and reached its peak at 72 hours, but continued for at least 7 days. Compared with the standard protocol at 20 degrees C, HCA at 10 degrees C and CsA treatment both significantly reduced overall cell death after HCA, but not apoptosis.

CONCLUSIONS

The data establish that significant neuronal apoptosis occurs as a consequence of HCA, but at 20 degrees C, other pathways of cell death, probably including necrosis, predominate. Although preliminary results suggest that the neuroprotective effects of lower temperature and of CsA are not a consequence of blockade of apoptotic pathways, inhibition of apoptosis nevertheless seems promising as a strategy to protect the brain from the subtle neurological injury that is associated with prolonged HCA at clinically relevant temperatures.

Cyclosporine A as a potential neuroprotective agent: a study of prolonged hypothermic circulatory arrest in a chronic porcine model

OBJECTIVE

To assess whether Cyclosporine A (CsA) or cycloheximide (CHX) can reduce ischemia-induced neurological damage by blocking apoptotic pathways, we assessed their effects on cerebral recovery in a chronic animal model of hypothermic circulatory arrest (HCA).

METHODS

Twenty-eight pigs (28-33 kg) underwent 90 min of HCA at 20 degrees C. In this blinded study, animals were randomized to placebo (n=12), 5 mg/kg CsA (n=8), given intravenously before and subcutaneously for 7 days after HCA, or a single dose of 1 mg/kg CHX (n=8), given after weaning from cardiopulmonary bypass. Hemodynamics, intracranial pressure (ICP) and neurophysiological data (EEG, SSEP) were assessed for 3 h after HCA; early behavioral recovery was scored, and neurological/behavioral evaluation (9=normal) was carried out daily until elective sacrifice on postoperative day (POD) 7. Brains were selectively perfused and evaluated histopathologically for apoptosis.

RESULTS

Basic hemodynamic data revealed no differences between CsA or CHX and control groups. ICP was significantly lower throughout rewarming (P=0.009) and reperfusion (P=0.05) in the CsA group. EEG recovery 3 h after HCA was observed in four of eight CsA animals but in only 1 of 12 controls (P=0.11) and one of eight CHX animals; cortical SSEP recovery also seemed faster in CsA animals, but failed to reach significance. Some early recovery scores were significantly better in the CsA group, and daily behavioral scores were consistently and significantly higher in the CsA-treated animals from POD1 through POD4.

CONCLUSIONS

The data indicate that treatment with Cyclosporine A but not cycloheximide has a positive effect on cerebral recovery following HCA. Whether CsA results in inhibition of neuronal apoptosis, and/or inhibits release of cytokines and thereby reduces postischemic cerebral edema remains to be elucidated. The neuroprotective effect of CsA, if confirmed in further studies, would make its clinical application conceivable.

Cerebral effects of cold reperfusion after hypothermic circulatory arrest

OBJECTIVES

This study was undertaken to explore whether an interval of cold reperfusion can improve cerebral outcome after prolonged hypothermic circulatory arrest.

METHODS

Sixteen pigs (27-30 kg) underwent 90 minutes of circulatory arrest at a brain temperature of 20 degrees C. Eight animals were rewarmed immediately after hypothermic circulatory arrest (controls), and 8 were reperfused for 20 minutes at 20 degrees C and then rewarmed (cold reperfusion). Electrophysiologic recordings, fluorescent microsphere determinations of cerebral blood flow, calculations of cerebral oxygen consumption, and direct measurements of intracranial pressure (millimeters of mercury) were obtained at baseline (37 degrees C), before hypothermic circulatory arrest, after discontinuing circulatory arrest at 37 degrees C deep brain temperature, and at 2, 4, and 6 hours thereafter. Histopathologic features and percent brain water were determined after the animals were sacrificed.

RESULTS

Cerebral blood flow and oxygen consumption decreased during cooling: cerebral oxygen consumption returned to baseline levels after 4 hours, but cerebral blood flow remained depressed until 6 hours in both groups. Cold reperfusion failed to improve electrophysiologic recovery or to reduce brain weight, but median intracranial pressure increased significantly less after cold reperfusion than in controls (P =.02). Although no significant difference in the incidence of histopathologic abnormalities between groups was found, all 3 animals with an intracranial pressure of more than 15 mm Hg after immediate rewarming had histopathologic lesions, and high intracranial pressure was more prevalent among all animals with subsequent histopathologic lesions (P =.03).

CONCLUSIONS

Cold reperfusion significantly inhibited the rise in intracranial pressure seen in control pigs after 90 minutes of circulatory arrest at 20 degrees C, suggesting that cold reperfusion may decrease cerebral edema and thereby improve outcome after prolonged hypothermic circulatory arrest.

Lamotrigine improves cerebral outcome after hypothermic circulatory arrest: a study in a chronic porcine model

BACKGROUND

Glutamate excitotoxicity has an important role in the development of brain injury after prolonged hypothermic circulatory arrest. The goal of the present studies was to determine the potential efficacy of lamotrigine, an Na(+) channel blocker, to mitigate cerebral injury after hypothermic circulatory arrest.

METHODS

Sixteen pigs (21-27 kg) were randomly assigned to receive lamotrigine (20 mg/kg) or placebo in a blinded fashion before a 75-minute period of hypothermic circulatory arrest (20 degrees C). Hemodynamic, electroencephalographic, and metabolic monitoring were carried out. S-100beta protein was determined up to the first postoperative morning. Daily behavioral assessment was performed until the animal died or was put to death on day 7. Histologic analysis of the brain was carried out in all animals.

RESULTS

Complete behavioral recovery was seen in 5 of 8 (63%) animals after lamotrigine administration, compared with 1 of 8 (13%) in the placebo group (P =.02). Among the animals that survived for 7 days, the median behavioral score was higher in the lamotrigine group (8 vs 7, P =.02). The medians of recovered electroencephalographic bursts in the lamotrigine group were higher than those in the placebo group 4 1/2 hours after the start of rewarming (P =.01). The median S-100beta level was lower in the lamotrigine group (0.01 microg/L) than in placebo controls (0.1 microg/L) 20 hours after the start of rewarming (P =.01). The median of total histopathologic score was 5.5 in the lamotrigine group and 7.5 in the placebo group (P =.06).

CONCLUSIONS

The present data suggest that lamotrigine improves neurologic outcome after a prolonged period of hypothermic circulatory arrest.

Surgical techniques. Aortic arch and deep hypothermic circulatory arrest: real-life suspended animation

Surgical reconstruction of the aortic arch is a complex procedure requiring careful preoperative analysis of the pathology and forethought toward surgical approach. Development of surgical techniques has brought dramatic improvement survival and reduction of neurological events associated with these procedures, yet significant morbidity is still encountered. New approaches to the patient with these pathologies include antegrade and retrograde perfusions to the brain. Continued research into physiology of hypothermic circulatory arrest offers the promise of pharmacological protection of the brain during aortic reconstruction and potentially development of therapeutic modalities to treat and limit ischemic brain damage.