Dynamic heterogeneity of cerebral hypoperfusion after prolonged cardiac arrest in dogs measured by the stable xenon/CT technique: a preliminary study

Emergent Management of Hypoxic-Ischemic Brain Injury

OBJECTIVE

This article outlines interventions used to improve outcomes for patients with hypoxic-ischemic brain injury after cardiac arrest.

LATEST DEVELOPMENTS

Emergent management of patients after cardiac arrest requires prevention and treatment of primary and secondary brain injury. Primary brain injury is minimized by excellent initial resuscitative efforts. Secondary brain injury prevention requires the detection and correction of many pathophysiologic processes that may develop in the hours to days after the initial arrest. Key physiologic parameters important to secondary brain injury prevention include optimization of mean arterial pressure, cerebral perfusion, oxygenation and ventilation, intracranial pressure, temperature, and cortical hyperexcitability. This article outlines recent data regarding the treatment and prevention of secondary brain injury. Different patients likely benefit from different treatment strategies, so an individualized approach to treatment and prevention of secondary brain injury is advisable. Clinicians must use multimodal sources of data to prognosticate outcomes after cardiac arrest while recognizing that all prognostic tools have shortcomings.

ESSENTIAL POINTS

Neurologists should be involved in the postarrest care of patients with hypoxic-ischemic brain injury to improve their outcomes. Postarrest care requires nuanced and patient-centered approaches to the prevention and treatment of primary and secondary brain injury and neuroprognostication.

Cervical Vagus Nerve Stimulation Improves Neurologic Outcome After Cardiac Arrest in Mice by Attenuating Oxidative Stress and Excessive Autophagy

BACKGROUND

Cerebral ischemia and reperfusion (I/R) induces oxidative stress and activates autophagy, leading to brain injury and neurologic deficits. Cervical vagus nerve stimulation (VNS) increases cerebral blood flow (CBF). In this study, we investigate the effect of VNS-induced CBF increase on neurologic outcomes after cardiac arrest (CA).

MATERIALS AND METHODS

A total of 40 male C57Bl/6 mice were subjected to ten minutes of asphyxia CA and randomized to vagus nerve isolation (VNI) or VNS treatment group. Eight mice received sham surgery and VNI. Immediately after resuscitation, 20 minutes of electrical stimulation (1 mA, 1 ms, and 10 Hz) was started in the VNS group. Electrocardiogram, blood pressure, and CBF were monitored. Neurologic and histologic outcomes were evaluated at 72 hours. Oxidative stress and autophagy were assessed at 3 hours and 24 hours after CA.

RESULTS

Baseline characteristics were not different among groups. VNS mice had better behavioral performance (ie, open field, rotarod, and neurologic score) and less neuronal death (p < 0.05, vs VNI) in the hippocampus. CBF was significantly increased in VNS-treated mice at 20 minutes after return of spontaneous circulation (ROSC) (p < 0.05). Furthermore, levels of 8-hydroxy-2'-deoxyguanosine in the blood and autophagy-related proteins (ie, LC-3Ⅱ/Ⅰ, Beclin-1, and p62) in the brain were significantly decreased in VNS mice. Aconitase activity was also reduced, and the p-mTOR/mTOR ratio was increased in VNS mice.

CONCLUSIONS

Oxidative stress induced by global brain I/R following CA/ROSC leads to early excessive autophagy and impaired autophagic flux. VNS promoted CBF recovery, ameliorating these changes. Neurologic and histologic outcomes were also improved.

Upregulation of serum and glucocorticoid-regulated kinase 1 exacerbates brain injury and neurological deficits after cardiac arrest

Cardiopulmonary arrest (CA) is the leading cause of death and disability in the United States. CA-induced brain injury is influenced by multifactorial processes, including reduced cerebral blood flow (hypoperfusion) and neuroinflammation, which can lead to neuronal cell death and functional deficits. We have identified serum and glucocorticoid-regulated kinase-1 (SGK1) as a new target in brain ischemia previously described in the heart, liver, and kidneys (i.e., diabetes and hypertension). Our data suggest brain SGK1 mRNA and protein expression (i.e., hippocampus), presented with hypoperfusion (low cerebral blood flow) and neuroinflammation, leading to further studies of the potential role of SGK1 in CA-induced brain injury. We used a 6-min asphyxia cardiac arrest (ACA) rat model to induce global cerebral ischemia. Modulation of SGK1 was implemented via GSK650394, a SGK1-specific inhibitor (1.2 μg/kg icv). Accordingly, treatment with GSK650394 attenuated cortical hypoperfusion and neuroinflammation (via Iba1 expression) after ACA, whereas neuronal survival was enhanced in the CA1 region of the hippocampus. Learning/memory deficits were observed 3 days after ACA but ameliorated with GSK650394. In conclusion, SGK1 is a major contributor to ACA-induced brain injury and neurological deficits, while inhibition of SGK1 with GSK650394 provided neuroprotection against CA-induced hypoperfusion, neuroinflammation, neuronal cell death, and learning/memory deficits. Our studies could lead to a novel, therapeutic target for alleviating brain injury following cerebral ischemia.NEW & NOTEWORTHY Upregulation of SGK1 exacerbates brain injury during cerebral ischemia. Inhibition of SGK1 affords neuroprotection against cardiac arrest-induced hypoperfusion, neuroinflammation, neuronal cell death, and neurological deficits.

Postarrest Interventions that Save Lives

Patients resuscitated from cardiac arrest require complex management. An organized approach to early postarrest care can improve patient outcomes. Priorities include completing a focused diagnostic work-up to identify and reverse the inciting cause of arrest, stabilizing cardiorespiratory instability to prevent rearrest, minimizing secondary brain injury, evaluating the risk and benefits of transfer to a specialty care center, and avoiding early neurologic prognostication.

The association between long-term glycaemic control, glycaemic gap and neurological outcome of in-hospital cardiac arrest in diabetics: A retrospective cohort study

AIM

Resuscitation guidelines do not recommend a target blood glucose (BG) level specifically tailored for diabetics experiencing an in-hospital cardiac arrest (IHCA). The glycosylated haemoglobin (HbA1c) level may be associated with neurological prognosis and used to identify the optimal BG level for diabetic IHCA patients.

METHODS

This study was a retrospective study in a single medical centre. Patients with an IHCA between 2006 and 2015 were screened. The estimated average glucose (eAG) level was converted from the HbA1c level measured within three months prior to the IHCA. The minimum glycaemic gap was calculated from the post-resuscitation minimum BG level minus the eAG level.

RESULTS

A total of 141 patients were included in this study. The mean HbA1c was 7.2% (corresponding eAG: 160.2 mg/dL [8.9 mmol/L]). Multivariable logistic regression analysis indicated an eAG level of less than 196 mg/dL (10.9 mmol/L; corresponding HbA1c: 8.5%) was positively associated with a favourable neurological outcome at hospital discharge (odds ratio [OR]: 5.12, 95% confidence interval [CI]: 1.11-23.70; p-value = 0.04). An absolute minimum glycaemic gap of less than 70 mg/dL (3.9 mmol/L) was also positively associated with a favourable neurological outcome (OR: 5.41, 95% CI: 1.41-20.78; p-value = 0.01).

CONCLUSION

For diabetic patients, poor long-term glycaemic control correlated with worse neurological recovery following an IHCA. The HbA1c-derived average BG level could be used as a reference point for glycaemic management during the early stage of post-cardiac arrest syndrome. The glycaemic gap could be used to identify the optimal glycaemic range around the reference point.

Effect of neuromonitor-guided titrated care on brain tissue hypoxia after opioid overdose cardiac arrest

INTRODUCTION

Brain tissue hypoxia may contribute to preventable secondary brain injury after cardiac arrest. We developed a porcine model of opioid overdose cardiac arrest and post-arrest care including invasive, multimodal neurological monitoring of regional brain physiology. We hypothesized brain tissue hypoxia is common with usual post-arrest care and can be prevented by modifying mean arterial pressure (MAP) and arterial oxygen concentration (PaO2).

METHODS

We induced opioid overdose and cardiac arrest in sixteen swine, attempted resuscitation after 9 min of apnea, and randomized resuscitated animals to three alternating 6-h blocks of standard or titrated care. We invasively monitored physiological parameters including brain tissue oxygen (PbtO2). During standard care blocks, we maintained MAP > 65 mmHg and oxygen saturation 94-98%. During titrated care, we targeted PbtO2 > 20 mmHg.

RESULTS

Overall, 10 animals (63%) achieved ROSC after a median of 12.4 min (range 10.8-21.5 min). PbtO2 was higher during titrated care than standard care blocks (unadjusted β = 0.60, 95% confidence interval (CI) 0.42-0.78, P < 0.001). In an adjusted model controlling for MAP, vasopressors, sedation, and block sequence, PbtO2 remained higher during titrated care (adjusted β = 0.75, 95%CI 0.43-1.06, P < 0.001). At three predetermined thresholds, brain tissue hypoxia was significantly less common during titrated care blocks (44 vs 2% of the block duration spent below 20 mmHg, P < 0.001; 21 vs 0% below 15 mmHg, P < 0.001; and, 7 vs 0% below 10 mmHg, P = .01).

CONCLUSIONS

In this model of opioid overdose cardiac arrest, brain tissue hypoxia is common and treatable. Further work will elucidate best strategies and impact of titrated care on functional outcomes.

Emergency Neurological Life Support: Resuscitation Following Cardiac Arrest

Cardiac arrest is the most common cause of death in North America. An organized bundle of neurocritical care interventions can improve chances of survival and neurological recovery in patients who are successfully resuscitated from cardiac arrest. Therefore, resuscitation following cardiac arrest was chosen as an Emergency Neurological Life Support protocol. Key aspects of successful early post-arrest management include: prevention of secondary brain injury; identification of treatable causes of arrest in need of emergent intervention; and, delayed neurological prognostication. Secondary brain injury can be attenuated through targeted temperature management (TTM), avoidance of hypoxia and hypotension, avoidance of hyperoxia, hyperventilation or hypoventilation, and treatment of seizures. Most patients remaining comatose after resuscitation from cardiac arrest should undergo TTM. Treatable precipitants of arrest that require emergent intervention include, but are not limited to, acute coronary syndrome, intracranial hemorrhage, pulmonary embolism and major trauma. Accurate neurological prognostication is generally not appropriate for several days after cardiac arrest, so early aggressive care should never be limited based on perceived poor neurological prognosis.

Association of antiplatelet therapy with patient outcomes after out-of-hospital cardiac arrest

BACKGROUND

Cessation of blood flow during out-of-hospital cardiac arrest (OHCA) results in microvascular thrombosis, protracted hypoperfusion after return of spontaneous circulation and damage to vital organs. We tested the hypothesis that pre-arrest antiplatelet and anticoagulant medication use would be associated with less post-arrest organ dysfunction and better outcomes.

METHODS

We included OHCA patients treated from January 2005 to October 2014 at a single academic medical center. We combined our prospective OHCA registry of clinical and demographic data with a structured chart review to abstract home antiplatelet and anticoagulant medications. We fit unadjusted and adjusted regression models to test the association of antiplatelet and anticoagulant medication use with early post-arrest illness severity, survival and functionally favorable recovery.

RESULTS

Of 1054 subjects, 295 (28%) were prescribed an antiplatelet agent and 147 (14%) were prescribed an anticoagulant prior to arrest. In adjusted models, antiplatelet agents were associated with lower post-arrest illness severity (adjusted OR 0.50 95% CI 0.33-0.77), greater odds of survival to discharge (adjusted OR 1.74 95% CI 1.08-2.80) and greater odds favorable functional outcome (adjusted OR 2.11 95% CI 1.17-3.79). By contrast, anticoagulation via any agent was not associated with illness severity, survival to discharge or favorable outcome.

CONCLUSION

Preventing intra-arrest and post-arrest microvascular thrombosis via antiplatelet agents could represent a novel therapeutic target to improve outcomes after OHCA.

The Brain after Cardiac Arrest

Cardiac arrest is common and deadly. Most patients who are treated in the hospital after achieving return of spontaneous circulation still go on to die from the sequelae of anoxic brain injury. In this review, the authors provide an overview of the mechanisms and consequences of postarrest brain injury. Special attention is paid to potentially modifiable mechanisms of secondary brain injury including seizures, hyperpyrexia, cerebral hypoxia and hypoperfusion, oxidative injury, and the development of cerebral edema. Finally, the authors discuss the outcomes of cardiac arrest survivors with a focus on commonly observed patterns of injury as well as the scales used to measure patient outcome and their limitations.

Alterations in Cerebral Blood Flow after Resuscitation from Cardiac Arrest

Greater than 50% of patients successfully resuscitated from cardiac arrest have evidence of neurological disability. Numerous studies in children and adults, as well as in animal models have demonstrated that cerebral blood flow (CBF) is impaired after cardiac arrest. Stages of cerebral perfusion post-resuscitation include early hyperemia, followed by hypoperfusion, and finally either resolution of normal blood flow or protracted hyperemia. At the level of the microcirculation the blood flow is heterogeneous, with areas of no flow, low flow, and increased flow. CBF directed therapies in animal models of cardiac arrest improved neurological outcome, and therefore, the alterations in CBF after cardiac arrest likely contribute to the development of hypoxic ischemic encephalopathy. Current intensive care after cardiac arrest is centered upon maintaining systemic oxygenation, normal blood pressure values for age, maintaining general homeostasis, and avoiding hyperthermia. Assessment of CBF and oxygenation is not routinely performed after cardiac arrest. Currently available and underutilized techniques to assess cerebral perfusion include transcranial doppler, near-infrared spectroscopy, and arterial spin labeling magnetic resonance imaging. Limited clinical studies established the role of CBF and oxygenation monitoring in prognostication after cardiac arrest and few studies suggest that guiding critical care post-resuscitation to mean arterial pressures above the minimal autoregulatory range might improve outcome. Important knowledge gaps thus remain in cerebral monitoring and CBF and oxygen goal-directed therapies post-resuscitation from cardiac arrest.

Impact of time to cooling initiation and time to target temperature in patients treated with hypothermia after cardiac arrest

PURPOSE

Little is known about the role of time to initiation of therapeutic hypothermia and time to target temperature (TTT) in the prognosis of patients resuscitated from cardiac arrest.

METHODS

A retrospective analysis was performed in 145 survivors of cardiac arrest who underwent therapeutic hypothermia between January 2003 and January 2013. The objective was to identify predictors of survival free from significant neurological sequelae (Cerebral Performance Categories Scale (CPC): >2) six months after cardiac arrest. We evaluated the effect of faster and earlier cooling.

RESULTS

Overall survival at six months was 42.1% (61 patients); 59 of these were considered to have a good neurological status (CPC ≤ 2), and in whom therapeutic hypothermia was initiated earlier (87 ± 17 min vs. 111 ± 14 min; p=0.042), and the target temperature was reached at an earlier time (TTT: 316 ± 30 min vs. 365 ± 27 min; p=0.017). Multivariate analysis selected longer duration of cardiac arrest (odds ratio (OR) = 1.06 per min), a non-shockable initial rhythm (OR=13.8), severe acidosis (OR=0.009 per 0.01 unit), older age (OR=1.04 per year) and longer TTT (OR=1.005 per min) as associated with poor prognosis.

CONCLUSION

The most important prognostic factors for death or lack of neurological recovery in patients with cardiac arrest treated with therapeutic hypothermia are initial-rhythm, time from cardiac arrest to return of spontaneous circulation and arterial-pH at admission. Although the speed of cooling initiation and the time to reach target temperature may play a role, its influence on prognosis seems to be less important.

The impact of severe acidemia on neurologic outcome of cardiac arrest survivors undergoing therapeutic hypothermia

INTRODUCTION

Therapeutic Hypothermia (TH) has become a standard of care in improving neurological outcomes in cardiac arrest (CA) survivors. Previous studies have defined severe acidemia as plasma pH<7.20. We investigated the influence of severe acidemia at the time of initiation of TH on neurological outcome in CA survivors.

METHODS

A retrospective analysis was performed on 196 consecutive CA survivors (out-of-hospital CA and in-hospital CA) who underwent TH with endovascular cooling between January 2007 and October 2012. Arterial blood gas drawn prior to initiation of TH was utilized to measure pH in all patients. Shockable and non-shockable CA patients were divided into two sub-groups based on pH (pH<7.2 and pH≥7.2). The primary end-point was measured using the Pittsburgh Cerebral Performance Category (CPC) scale prior to discharge from the hospital: good (CPC 1 and 2) and poor (CPC 3 to 5) neurologic outcome.

RESULTS

Sixty-two percent of shockable CA patients with pH≥7.20 had good neurological outcome as compared to 34% patients with pH<7.20. Shockable CA patients with pH≥7.20 were 3.3 times more likely to have better neurological outcome when compared to those with pH <7.20 [p=0.013, OR 3.3, 95% CI (1.28-8.45)]. In comparison, non-shockable CA patients with p≥7.20 did not have a significantly different neurological outcome as compared to those with pH<7.20 [p=0.97, OR 1.02, 95% CI (0.31-3.3)].

CONCLUSION

Presence of severe acidemia at initiation of TH in shockable CA survivors is significantly associated with poor neurological outcomes. This effect was not observed in the non-shockable CA survivors.

Management of the post-cardiac arrest syndrome

BACKGROUND

Recent advances in resuscitation science have revolutionized care of the cardiac arrest patient. Dramatic departures from time-honored advanced cardiac life support therapies, such as cardiocerebral resuscitation and bundled post-arrest care, have given rise to a new paradigm of resuscitation practices, which has boosted the rate of neurologically intact survival.

OBJECTIVES

This article reviews the pathophysiology of the post-cardiac arrest syndrome, the collective pathophysiology after return of spontaneous circulation, and presents management pearls specifically for the emergency physician. This growing area of scientific inquiry must be managed appropriately to sustain improved outcomes.

DISCUSSION

The emergency physician must understand this pathophysiology, manage resuscitated patients according to the latest evidence, and coordinate with appropriate inpatient resources.

CONCLUSION

The new approach to cardiac arrest care is predicated on a chain of survival that spans the spectrum of care from the prehospital arena through the emergency, intensive, and inpatient settings. The emergency physician is a crucial link in this chain.

Vasoactive support in the optimization of post-cardiac arrest hemodynamic status: from pharmacology to clinical practice

As a critical component of post-resuscitation care, prompt optimization of hemodynamic status by means of targeted interventions is vital in order to maximize the likelihood of good outcome. Vasoactive agents play an essential role in the supportive care of post cardiac arrest patients. The administration of these agents is associated with serious side-effects and therefore they should be used in the minimal dose necessary to achieve low-normal mean arterial pressure and adequate systematic perfusion. Careful and frequent serial evaluation of the patient is important primarily to assess volume status and adequacy of circulatory support. Continuous monitoring of blood pressure and laboratory parameters is essential both to accurately titrate therapy and because inotropes and vasopressors have the potential to induce life-threatening side-effects. The clinical efficacy of inotropes and vasopressors has been largely investigated through examination of their impact on hemodynamic end points, and clinical practice has been driven in part by expert opinion, extrapolation from animal studies, and physician preference. Clearly these agents should all be considered as supportive measures to stabilize the patient prior to some form of definitive therapy.

[Transcranial Doppler ultrasonography usefulness in cardiac arrest resuscitation]

An effective tissue perfusion has decisive influence on the final prognosis both during cardiopulmonary resuscitation (CPR) and after recovery of spontaneous circulation (ROSC). The transcranial Doppler ultranosography (TCD) examines the velocity and pulsatility of cerebral blood flow, making it possible to perform "beat to beat" hemodynamic analysis. During CPR, TCD peak systolic velocity reflects cerebral perfusion of the chest compressions. Beyond 2 hours after ROSC, persistence in the cerebral arteries of a hemodynamic TCD pattern (low velocities with high pulsatilities) predicts poor neurological prognosis. Early or delayed presence of a hyperemic TCD pattern (high velocities with low pulsatilities) is associated conclusively with evolution to intracranial hypertension and its appearance during the rewarming process should lead to immediate return to therapeutic hypothermia. The coincidence of hypodynamic cerebral arteries and others with normal or hyperemic TCD patterns may indicate the presence of focal hypoperfusion that could predict stroke after ROSC.

Post-cardiac arrest syndrome: Epidemiology, pathophysiology, treatment, and prognostication: A scientific statement from the International Liaison Committee on Resuscitation; the American Heart Association Emergency Cardiovascular Care Committee; the Council on Cardiovascular Surgery and Anesthesia; the Council on Cardiopulmonary, Perioperative, and Critical Care; the Council on Clinical Cardiology; the Council on Stroke (Part 1)

AIM OF THE REVIEW

To review the epidemiology, pathophysiology, treatment and prognostication in relation to the post-cardiac arrest syndrome.

METHODS

Relevant articles were identified using PubMed, EMBASE and an American Heart Association EndNote master resuscitation reference library, supplemented by hand searches of key papers. Writing groups comprising international experts were assigned to each section. Drafts of the document were circulated to all authors for comment and amendment.

RESULTS

The 4 key components of post-cardiac arrest syndrome were identified as (1) post-cardiac arrest brain injury, (2) post-cardiac arrest myocardial dysfunction, (3) systemic ischaemia/reperfusion response, and (4) persistent precipitating pathology.

CONCLUSIONS

A growing body of knowledge suggests that the individual components of the postcardiac arrest syndrome are potentially treatable.

Post-cardiac arrest syndrome: epidemiology, pathophysiology, treatment, and prognostication. A Scientific Statement from the International Liaison Committee on Resuscitation; the American Heart Association Emergency Cardiovascular Care Committee; the Council on Cardiovascular Surgery and Anesthesia; the Council on Cardiopulmonary, Perioperative, and Critical Care; the Council on Clinical Cardiology; the Council on Stroke

AIM OF THE REVIEW

To review the epidemiology, pathophysiology, treatment and prognostication in relation to the post-cardiac arrest syndrome.

METHODS

Relevant articles were identified using PubMed, EMBASE and an American Heart Association EndNote master resuscitation reference library, supplemented by hand searches of key papers. Writing groups comprising international experts were assigned to each section. Drafts of the document were circulated to all authors for comment and amendment.

RESULTS

The 4 key components of post-cardiac arrest syndrome were identified as (1) post-cardiac arrest brain injury, (2) post-cardiac arrest myocardial dysfunction, (3) systemic ischaemia/reperfusion response, and (4) persistent precipitating pathology.

CONCLUSIONS

A growing body of knowledge suggests that the individual components of the post-cardiac arrest syndrome are potentially treatable.

Bench to bedside: resuscitation from prolonged ventricular fibrillation

Ventricular fibrillation (VF) remains the most common cardiac arrest heart rhythm. Defibrillation is the primary treatment and is very effective if delivered early within a few minutes of onset of VF. However, successful treatment of VF becomes increasingly more difficult when the duration of VF exceeds 4 minutes. Classically, successful cardiac arrest resuscitation has been thought of as simply achieving restoration of spontaneous circulation (ROSC). However, this traditional approach fails to consider the high early post-cardiac arrest mortality and morbidity and ignores the reperfusion injuries, which are manifest in the heart and brain. More recently, resuscitation from cardiac arrest has been divided into two phases; phase I, achieving ROSC, and phase II, treatment of reperfusion injury. The focus in both phases of resuscitation remains the heart and brain, as prolonged VF remains primarily a two-organ disease. These two organs are most sensitive to oxygen and substrate deprivation and account for the vast majority of early post-resuscitation mortality and morbidity. This review focuses first on the initial resuscitation (achieving ROSC) and then on the reperfusion issues affecting the heart and brain.

Cerebral resuscitation after global brain ischemia: linking research to practice

Despite significant advances in resuscitation medicine, neurologic recovery continues to be the major limiting factor in achieving successful resuscitation outcomes. Clinicians must recognize that successful resuscitation outcomes are not limited to the restoration of normal cardiac rhythm and hemodynamics, but rather the restoration of human mentation. It is well recognized that a cascade of injurious events begins within minutes of ischemia and that ischemic and postischemic events cause significant neuronal damage. An increased understanding of the pathophysiology of global brain ischemia provides evidence of a therapeutic window of opportunity during which interventions hold the potential to improve neurologic outcome. The research basis for understanding global brain ischemia, its clinical prognosis, and potential intervention strategies are examined.

Thrombolysis using plasminogen activator and heparin reduces cerebral no-reflow after resuscitation from cardiac arrest: an experimental study in the cat

OBJECTIVE

Successful resuscitation of the brain requires complete microcirculatory reperfusion, which, however, may be impaired by activation of blood coagulation after cardiac arrest. The study addresses the question of whether postischemic thrombolysis is effective in reducing cerebral no-reflow phenomenon.

DESIGN

14 adult normothermic cats were submitted to 15-min cardiac arrest, followed by cardiopulmonary resuscitation (CPR) and 30 min of spontaneous recirculation. The CPR protocol included closed-chest cardiac massage, administration of epinephrine 0.2 mg/kg, bicarbonate 2 mEq/kg per 30 min, and electrical defibrillation shocks.

INTERVENTIONS

During CPR, animals in the treatment group (n = 6) received intravenous bolus injections of 100 U/kg heparin and 1 mg/kg recombinant tissue type plasminogen activator (rt-PA), followed by an infusion of rt-PA 1 mg/kg per 30 min.

MEASUREMENTS AND RESULTS

Microcirculatory reperfusion of the brain was visualized by labeling the circulating blood with 300 mg/kg of 15% fluorescein isothiocyanate albumin at the end of the recirculation period. Areas of cerebral no-reflow--defined as the absence of microvascular filling--were identified by fluorescence microscopy at eight standard coronal levels of forebrain, and expressed as the percentage of total sectional area. One animal in the treatment group was excluded from further analysis because of intracerebral hemorrhage due to brain injury during trepanation. Autopsy revealed the absence of intracranial, intrathoracic, or intra-abdominal bleeding in all the other animals. In untreated animals (n = 8), no-reflow affected 28 +/- 13% of total forebrain sectional areas, and only 1 out of 8 animals showed homogenous reperfusion (i.e., no-reflow < 15% of total forebrain sectional areas). Thrombolytic therapy (n = 5) significantly reduced no-reflow to 7 +/- 5% of total forebrain sectional areas and all treated animals showed homogenous reperfusion at the microcirculatory level.

CONCLUSIONS

The present data demonstrate that thrombolytic therapy improves microcirculatory reperfusion of the cat brain when administered during reperfusion after cardiac arrest.

Adrenaline, cardiac arrest, and evidence based medicine

In this article we review the evidence supporting the clinical application of adrenaline in cardiopulmonary arrest, and summarize the receptor effects of catecholamines and the basic principles producing perfusion during CPR. Animal and human studies show that in cardiac arrest, adrenaline has positive haemodynamic effects, increasing systemic pressures, myocardial perfusion, and cerebrally directed flow. The problems extrapolating from animal to human data are highlighted. Studies showing improvements in short term survival outcomes with high dose regimens have not been confirmed by other large prospective randomised trials. There is no evidence that high doses of adrenaline improve survival to hospital discharge. Most studies comparing adrenaline with placebo have been non-randomised and uncontrolled, with major methodological problems. Conclusions are difficult, but if anything adrenaline is associated with poorer outcomes.

Resuscitation from cardiac arrest in cats: influence of epinephrine dosage on brain recovery

The quality of brain recovery after cardiac arrest depends crucially on the speed of cardiac resuscitation because the low cerebral perfusion pressure during the resuscitation procedure facilitates the development of no-reflow. To accelerate return of spontaneous circulation, high dose epinephrine has been recommended but the effect on the dynamics of early brain recovery is still unknown. We, therefore, studied the dynamics of brain resuscitation after cardiopulmonary resuscitation (CPR) with standard and high dose epinephrine using non-invasive NMR techniques. Fifteen min cardiac arrest was induced in normothermic cats by ventricular fibrillation. CPR was performed using an inflatable pneumatic vest for cyclic chest compression. With the beginning of CPR the standard dose group received 0.02 mg/kg epinephrine (n = 6) and the high dose group received 0.2 mg/kg (n = 8). Brain recovery was monitored by magnetic resonance imaging of the apparent diffusion coefficient (ADC) of water for 3 h. Although high dose epinephrine treatment led to a significantly higher blood pressure during early reperfusion, rapidly changing heterogeneities of early brain recovery were observed in both groups. High dose epinephrine thus does not improve the quality of post-cardiac arrest brain recovery during the first 3 h of reperfusion.

No-reflow after cardiac arrest

OBJECTIVE

Successful resuscitation of the brain requires unimpaired blood recirculation. The study addresses the question of the severity and reversibility of no-reflow after cardiac arrest.

DESIGN

Adult normothermic cats were submitted to 5, 15 and 30 min cardiac arrest by ventricular fibrillation. The extent of no-reflow was assessed in each cardiac arrest group after 5 min closed chest cardiac massage in combination with 0.2 mg/kg epinephrine or after successful resuscitation followed by 30 min recirculation.

MEASUREMENTS AND RESULTS

Reperfusion of the brain was visualized by labelling the circulating blood with FITC-Albumin. Areas of no-reflow, defined as absence of microvascular filling, were identified by fluorescence microscopy at 8 standard coronal levels of forebrain, and expressed as percent of total sectional area. During cardiac massage, no-reflow affected 21 +/- 5%, 42 +/- 38% and 70 +/- 27% of forebrain after 5, 15 and 30 min cardiac arrest, respectively. After 30 min spontaneous recirculation following successful resuscitation of the heart, no-reflow significantly declined to 7 +/- 11% after 5 min cardiac arrest (p < 0.05) but persisted in 30 +/- 11% and 65 +/- 21% of forebrain after 15 and 30 min cardiac arrest, respectively (n.s.).

CONCLUSION

Our observations demonstrate that resuscitation of the heart by closed chest massage causes severe (and after prolonged cardiac arrest irreversible) no-reflow of the brain. This suggests that no-reflow is an important cause of post-resuscitation brain pathology.

Organ blood flow following cardiac arrest in a swine low-flow cardiopulmonary bypass model

STUDY OBJECTIVE

To determine organ blood flow changes, relative to baseline, following cardiac arrest and resuscitation in a closed-chest cardiac arrest swine model using cardiopulmonary bypass to achieve reproducible return of spontaneous circulation (ROSC).

INTERVENTIONS

Following 10 min of ventricular fibrillation (VF), animals (n = 10) received low-flow cardiopulmonary bypass at 10 ml/kg/min from 10-15 min. At 15 min of VF, norepinephrine (0.12 mg/kg) was given and bypass flow increased to 50 ml/kg/min, followed by countershocks at 16 min. Following ROSC, cardiopulmonary bypass was immediately weaned off with norepinephrine support. Organ blood flows were determined during normal sinus rhythm, during reperfusion of VF and during the early post-ROSC period while off cardiopulmonary bypass support. Organ blood flows during the early ROSC period were compared with organ blood flow at baseline and during VF.

RESULTS

During early reperfusion of VF prior to any drug therapy, myocardial, cerebral and abdominal organ blood flows were all low. All animals achieved ROSC at 16.9 +/- 0.7 min and were weaned from bypass in < 5 min following ROSC. During the early post-ROSC period, blood flow to the myocardial, cerebral and adrenal vascular beds was significantly elevated relative to baseline. Simultaneously, blood flow to the kidneys, liver, spleen and lungs was reduced relative to baseline.

CONCLUSIONS

This low-flow bypass model produces reproducible high resuscitation rates and ROSC times. Early post-resuscitation organ blood flow is characterized by a selective hyperemia involving the cerebral, myocardial and adrenal vascular beds, in contrast to hypoperfusion of the pulmonary and mesenteric vascular beds.

Mild hypothermia after cardiac arrest in dogs does not affect postarrest cerebral oxygen uptake/delivery mismatching

PURPOSE

To compare measurements of cerebral arteriovenous oxygen content differences (oxygen extraction ratios, oxygen utilization coefficients) in dogs after cardiac arrest, resuscitated under normothermia vs. mild hypothermia for 1-2 h or 12 h.

METHODS

In 20 dogs, we used our model of ventricular fibrillation (no blood flow) of 12.5 min, reperfusion with brief cardiopulmonary bypass, and controlled ventilation, normotension, normoxemia, and mild hypocapnia to 24 h. We compared a normothermic control Group I (37.5 degrees C) (n = 8); with brief mild hypothermia in Group II (core and tympanic membrane temperature about 34 degrees C during the first hour after arrest) (n = 6); and with prolonged mild hypothermia in Group III (34 degrees C during the first 12 h after arrest) (n = 6).

RESULTS

In Group I, the cerebral arteriovenous O2 content difference was 5.6 +/- 1.6 ml/dl before arrest; was low during reperfusion (transient hyperemia) and increased (worsened) significantly to 8.8 +/- 2.8 ml/dl at 1 h, remained increased until 18 h, and returned to baseline levels at 24 h after reperfusion. These values were not significantly different in hypothermic Groups II and III. The cerebral venous (saggital sinus) PO2 (PssO2) was about 40 mmHg (range 29-53) in all three groups before arrest and decreased significantly below baseline values, between 1 h and 18 h after arrest; the lowest mean values were 19 +/- 19 mmHg in Group I, 15 +/- 8 in Group II (NS), and 21 +/- 3 in Group III (NS). Postarrest PssO2 values of < or = 20 mmHg were found in 6/8 dogs in Group I, 5/6 in Group II and 4/6 in Group III. Among the 120 values of PssO2 measured between 1 h and 18 h after arrest, 32 were below the critical value of 20 mmHg.

CONCLUSIONS

After prolonged cardiac arrest, critically low cerebral venous O2 values suggest inadequate cerebral O2 delivery. Brief or prolonged mild hypothermia after arrest does not mitigate the postarrest cerebral O2 uptake/delivery mismatching.

Cerebral and systemic arteriovenous oxygen monitoring after cardiac arrest. Inadequate cerebral oxygen delivery

BACKGROUND

After prolonged cardiac arrest, under controlled normotension, cardiac output and cerebral blood flow are reduced for several hours. This dog study documents for the first time the postarrest reduction in oxygen (O2) delivery in relation to O2 uptake for brain and entire organism.

METHODS

In eight dogs we used our model of ventricular fibrillation (VF) cardiac arrest of 12.5 min, reperfusion with brief cardiopulmonary bypass, and controlled normotension, normoxemia, and mild hypocapnia to 24 h.

RESULTS

Between 4 and 24 h after cardiac arrest, cardiac output decreased by about 25% and the systemic arteriovenous O2 content difference doubled, while the calculated systemic O2 utilization coefficient (O2 UC) increased and the systemic venous PO2 decreased, both not to critical levels. The cerebral arteriovenous O2 content difference however, which was 5.6 +/- 1.7 ml/dl before arrest, increased between 1 and 18 h, to 10.8 +/- 3.2 ml/dl at 4 h. The cerebral O2 UC increased and the cerebral venous PO2 decreased, both to critical levels.

CONCLUSIONS

After prolonged cardiac arrest in dogs with previously fit hearts, the reduction of O2 transport to the brain is worse than its reduction to the whole organism. Monitoring these values might help in titrating life-support therapies.

Mild hypothermia after cardiac arrest in dogs does not affect postarrest multifocal cerebral hypoperfusion

BACKGROUND AND PURPOSE

Although mild resuscitative hypothermia (34 degrees C) immediately after cardiac arrest improves neurological outcome in dogs, its effects on cerebral blood flow and metabolism are unknown.

METHODS

We used stable xenon-enhanced computed tomography to study local, regional, and global cerebral blood flow patterns up to 4 hours after cardiac arrest in dogs. We compared a normothermic (37.5 degrees C) control group (group I, n = 5) with a postarrest mild hypothermic group (group II, n = 5). After ventricular fibrillation of 12.5 minutes and reperfusion with brief cardiopulmonary bypass, the ventilation, normotension, normoxia, and mild hypocapnia were controlled to 4 hours after cardiac arrest. Group II received (minimal) head cooling during cardiac arrest, followed by systemic bypass cooling (to 34 degrees C) during the first hour of reperfusion after cardiac arrest.

RESULTS

The postarrest homogeneous transient hyperemia was followed by global hypoperfusion from 1 to 4 hours after arrest, with increased "no-flow" and "trickle-flow" voxels (compared with baseline), without group differences. At 1 to 4 hours, mean global cerebral blood flow in computed tomographic slices was 55% of baseline in group I and 64% in group II (NS). No flow (local cerebral blood flow < 5 mL/100 cm3 per minute) occurred in 5 +/- 2% of the voxels in group I versus 9 +/- 5% in group II (NS). Trickle flow (5 to 10 mL/100 cm3 per minute) occurred in 10 +/- 3% voxels in group I versus 16 +/- 4% in group II (NS). Cerebral blood flow values in eight brain regions followed the same hyperemia-hypoperfusion sequence as global cerebral blood flow, with no significant difference in regional values between groups. The global cerebral metabolic rate of oxygen, which ranged between 2.7 and 4.5 mL/100 cm3 per minute before arrest in both groups, was at 1 hour after arrest 1.8 +/- 0.3 mL in normothermic group I (n = 3) and 1.9 +/- 0.4 mL is still-hypothermic group II (n = 5); at 2 and 4 hours after arrest, it ranged between 1.2 and 4.2 mL in group I and between 1.2 and 2.6 mL in group II.

CONCLUSIONS

After cardiac arrest, mild resuscitative hypothermia lasting 1 hour does not significantly affect patterns of cerebral blood flow and oxygen uptake. This suggests that different mechanisms may explain its mitigating effect on brain damage.

Magnetic resonance imaging findings associated with cardiac arrest

BACKGROUND AND PURPOSE

The frequency and prognostic significance of neuroradiological findings after cardiac arrest are unknown. Using healthy volunteers as control subjects, we studied the magnetic resonance imaging (MRI) findings associated with cardiac arrest, adjusted for confounding factors.

METHODS

The presence of cerebral infarcts, leukoaraiosis, atrophy, and edema on ultra-low-field MRI was assessed in 88 community volunteers and 52 cardiac arrest survivors enrolled in a placebo-controlled, randomized, double-blind trial of nimodipine in out-of-hospital ventricular fibrillation.

RESULTS

Cardiac arrest was an independent risk factor for the presence of infarcts in a logistic regression model adjusted for age, sex, and history of myocardial infarction, stroke, coronary heart disease, cardiac failure, and hypertension (odds ratio, 3.6; 95% confidence interval, 1.3 to 9.9; P = .01). Leukoaraiosis was associated with increasing age but not with cardiac arrest. Adjusted for age, the delay of advanced life support had an inverse correlation with the degree of atrophy in placebo-treated patients (r = -.62, P < .0001) but not in patients treated with nimodipine (r = -.10, P = .43). Lack of age-related atrophy, possibly implicating the presence of brain edema, predicted poor outcome after cardiac arrest (odds ratio, 4.6; 95% confidence interval, 1.4 to 15.8; P = .01).

CONCLUSIONS

Cardiac arrest was associated with deep cerebral infarcts but not with leukoaraiosis. MRI findings did not predict the functional outcome at 1 year. Nimodipine treatment had no significant effect on the MRI findings, but delayed resuscitation was associated with probable brain edema only in placebo-treated patients.

Multifocal cerebral blood flow by Xe-CT and global cerebral metabolism after prolonged cardiac arrest in dogs. Reperfusion with open-chest CPR or cardiopulmonary bypass

Using the stable xenon-enhanced computed tomography (Xe-CT) method in dogs, we studied local, regional and global cerebral blood flow (LCBF, rCBF and gCBF) in two sham experiments and nine cardiac arrest experiments. Within the same experiments without arrest, gCBF and rCBF values were reproducible and stable. LCBF values varied over time. In group I (n = 4), ventricular fibrillation cardiac arrest (no blood flow) of 10 min was reversed by open-chest cardiopulmonary resuscitation (CPR). In group II (n = 5), ventricular fibrillation cardiac arrest of 12.5 min was reversed by brief closed-chest cardiopulmonary bypass. This was followed by controlled ventilation, normotension, normoxia, normocarbia and normothermia to 4 h (n = 7) or 20 h (n = 2) postarrest. The postarrest CBF patterns were similar in both groups. Open-chest CPR during ventricular fibrillation generated near-baseline gCBF and lower LCBF ranges. During postarrest spontaneous circulation, transient diffuse hyperemia was without low-flow regions, longer in brain stem and basal ganglia than in neocortex. During delayed hypoperfusion at 1-4 h postarrest (n = 9), mean gCBF was 44-60% baseline, rCBF in primarily gray matter regions was 15-49 ml/100 cm3 per min and LCBF voxels with trickle-flow and low-flow values, in percent of CT cut area, were increased over baseline. Global CMRO2 (n = 3 of group II) recovered to near baseline values between 1 and 4 h postarrest, while gCBF and O2 delivery were about 50% baseline (mismatching of O2 uptake and O2 delivery).