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

Assessment of the Effects of Sodium Nitroprusside Administered Via Intracranial Subdural Catheters on the Cerebral Blood Flow and Lactate Using Dynamic Susceptibility Contrast Magnetic Resonance Imaging and Proton Magnetic Resonance Spectroscopy in a Pig Cardiac Arrest Model

Background Cerebral blood flow (CBF) is impaired in the early phase after return of spontaneous circulation. Sodium nitroprusside (SNP) administration via intracranial subdural catheters improves cerebral cortical microcirculation. We determined whether the SNP treatment improves CBF in the subcortical tissue and evaluated the effects of this treatment on cerebral lactate. Methods and Results Sixty minutes after return of spontaneous circulation following 14 minutes of untreated cardiac arrest, 14 minipigs randomly received 4 mg SNP or saline via intracranial subdural catheters. CBF was measured in regions of interest within the cerebrum and thalamus using dynamic susceptibility contrast-magnetic resonance imaging. After return of spontaneous circulation, CBF was expressed as a percentage of the baseline value. In the saline group, the %CBF in the regions of interest within the cerebrum remained at approximately 50% until 3.5 hours after return of spontaneous circulation, whereas %CBF in the thalamic regions of interest recovered to approximately 73% at this time point. The percentages of the baseline values in the cortical gray matter and subcortical white matter were higher in the SNP group (group effect P=0.026 and 0.025, respectively) but not in the thalamus. The cerebral lactate/creatine ratio measured using magnetic resonance spectroscopy increased over time in the saline group but not in the SNP group (group-time interaction P=0.035). The thalamic lactate/creatine ratio was similar in the 2 groups. Conclusions SNP administered via intracranial subdural catheters improved CBF not only in the cortical gray matter but also in the subcortical white matter. The CBF improvement by SNP was accompanied by a decrease in cerebral lactate.

Cerebral hemodynamics after cardiac arrest: implications for clinical management

Following resuscitation from cardiac arrest, hypoxic ischemic brain injury (HIBI) ensues, which is the primary determinant of adverse outcome. The pathophysiology of HIBI can be compartmentalized into primary and secondary injury, resulting from cerebral ischemia during cardiac arrest and reperfusion following successful resuscitation, respectively. During the secondary injury phase, increased attention has been directed towards the optimization of cerebral oxygen delivery to prevent additive injury to the brain. During this phase, cerebral hemodynamics are characterized by early hyperemia following resuscitation and then a protracted phase of cerebral hypoperfusion termed "no-reflow" during which additional hypoxic-ischemic injury can occur. As such, identification of therapeutic strategies to optimize cerebral delivery of oxygen is at the forefront of HIBI research. Unfortunately, randomized control trials investigating the manipulation of arterial carbon dioxide tension and mean arterial pressure augmentation as methods to potentially improve cerebral oxygen delivery have shown no impact on clinical outcomes. Emerging literature suggests differential patient-specific phenotypes may exist in patients with HIBI. The potential to personalize therapeutic strategies in the critical care setting based upon patient-specific pathophysiology presents an attractive strategy to improve HIBI outcomes. Herein, we review the cerebral hemodynamic pathophysiology of HIBI, discuss patient phenotypes as it pertains to personalizing care, as well as suggest future directions.

CT perfusion for Assessment of poor Neurological outcome in Comatose Cardiac Arrest Patients (CANCCAP): protocol for a prospective study

INTRODUCTION

Cardiac arrest remains one of the most common causes of death with the majority occurring outside of hospitals (out of hospital cardiac arrest). Despite advancements in resuscitation management, approximately 50% of comatose cardiac arrest patients (CCAP) will suffer a severe unsurvivable brain injury. To assess brain injury, a neurological examination is conducted, however, its reliability in predicting outcomes in the first days following cardiac arrest is limited. Non-contrast CT is the most employed scan to assess hypoxic changes, even though it is not sensitive to early hypoxic-ischaemic changes in the brain. CT perfusion (CTP) has shown high sensitivity and specificity in brain death patients, although its use in predicting poor neurological outcome in CCAP has not yet been explored. The purpose of this study is to validate CTP for predicting poor neurological outcome (modified Rankin scale, mRS≥4) at hospital discharge in CCAP.

METHODS AND ANALYSIS

The CT Perfusion for Assessment of poor Neurological outcome in Comatose Cardiac Arrest Patients study is a prospective cohort study funded by the Manitoba Medical Research Foundation. Newly admitted CCAP receiving standard Targeted Temperature Management are eligible. Patients undergo a CTP at the same time as the admission standard of care head CT. Admission CTP findings will be compared with the reference standard of an accepted bedside clinical assessment at the time of admission. Deferred consent will be used. The primary outcome is a binary outcome of good neurological status, defined as mRs<4 or poor neurological status (mRs≥4) at hospital discharge. A total of 90 patients will be enrolled.

ETHICS AND DISSEMINATION

This study has been approved by the University of Manitoba Health Research Ethics Board. The findings from our study will be disseminated through peer-reviewed journals and presentations at local rounds, national and international conferences. The public will be informed at the end of the study.

TRIAL REGISTRATION NUMBER

NCT04323020.

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.

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.

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.

Aging Effect on Post-recovery Hypofusion and Mortality Following Cardiac Arrest and Resuscitation in Rats

In this study we investigated the effect of aging on brain blood flow following transient global ischemia. Male Fisher rats (6 and 24 months old) underwent cardiac arrest (15 min) and resuscitation. Regional brain (cortex, hippocampus, brainstem and cerebellum) blood flow was measured in non-arrested rats and 1-h recovery rats using [14C] iodoantipyrene (IAP) autoradiography; the 4-day survival rate was determined in the two age groups. The pre-arrest baseline blood flows were similar in cortex, brainstem and cerebellum between the 6-month and the 24-month old rats; however, the baseline blood flow in hippocampus was significantly lower in the 24-month old group. At 1 h following cardiac arrest and resuscitation, both 6-month and 24-month groups had significantly lower blood flows in all regions than the pre-arrest baseline values; compared to the 6-month old group, the blood flow was significantly lower (about 40% lower) in all regions in the 24-month old group. The 4-day survival rate for the 6-month old rats was 50% (3/6) whereas none of the 24-month old rats (0/10) survived for 4 days. The data suggest that there is an increased vulnerability to brain ischemic-reperfusion injury in the aged rats; the degree of post-recovery hypoperfusion may contribute to the high mortality in the aged rats following cardiac arrest and resuscitation.

Early Quantitative Gamma-Band EEG Marker is Associated with Outcomes After Cardiac Arrest and Targeted Temperature Management

BACKGROUND

Brain recovery after cardiac arrest (CA) is sensitive to temperature. Yet the effect of temperature management on different EEG frequency bands has not been elucidated. A novel quantitative EEG algorithm, sub-band information quantity (SIQ), was applied to evaluate EEG recovery and outcomes after CA.

METHODS

Twenty-four Wistar rats undergoing 7-min CA were randomly assigned to immediate hypothermia (32-34 °C), normothermia (36.5-37.5 °C), or hyperthermia (38.5-39.5 °C) (n = 8). EEG was recorded continuously for the first 8 h and then for serial 30-min epochs daily. The neurologic deficit score (NDS) at 72-h was the primary functional outcome. Another four rats without brain injury were added as a control.

RESULTS

Better recovery of gamma-band SIQ was found in the hypothermia group (0.60 ± 0.03) compared with the normothermia group (0.40 ± 0.03) (p < 0.01) and in the normothermia group compared with the hyperthermia group (0.34 ± 0.03) (p < 0.05). The NDS was also improved in the lower temperature groups: hypothermia [median (25th, 75th), 74 (61, 74)] versus normothermia [49 (47, 61)] versus hyperthermia [43 (0, 50)] (p < 0.01). Throughout the 72-h experiment, the gamma-band SIQ showed the strongest correlation at every time point (ranging 0.520-0.788 from 30-min to 72-h post-resuscitation, all p < 0.05) whereas the delta-band SIQ had poor correlation with the 72-h NDS. No significant difference of sub-band EEG was found with temperature manipulation alone.

CONCLUSIONS

Recovery of gamma-band SIQ-qEEG was strongly associated with functional outcomes after CA. Induced hypothermia was associated with faster recovery of gamma-band SIQ and improved functional outcomes. Targeted temperature management primarily affected gamma frequency oscillations but not delta rhythm.

Therapeutic hypothermia after cardiopulmonary resuscitation

Full cerebral recovery after cardiopulmonary resuscitation is still a rare event. Unfortunately, up to now, no specific and outcome-improving therapy was available after such events. From several cases it is known that low body and brain temperature during a cardiocirculatory arrest improves the neurological outcome following these events. As it is not possible in acute events to induce hypothermia beforehand, whether cooling after the insult could also be protective was evaluated. After animal studies in the 1990s and first clinical pilot trials of mild therapeutic and induced hypothermia, two randomized trials of hypothermic therapy after successful resuscitation after cardiac arrest were conducted. These studies demonstrated that hypothermia after cardiac arrest could improve neurological outcome as well as overall mortality.

Hyperoxia and hypoxia in children resuscitated from cardiac arrest

BACKGROUND

Ischemia depletes antioxidant reserves and impairs mitochondrial electron transport. Oxygen within blood reperfusing ischemic tissue can form free radicals, worsen oxidative stress, and exacerbate tissue injury (reperfusion injury). One strategy for limiting reperfusion injury is to limit delivery of "luxuriant" oxygen during or after reperfusion. Resuscitation guidelines for children with cardiac arrest recommend early weaning of supplemental oxygen as tolerated. There are currently no studies demonstrating the frequency and outcomes of hyperoxia and hypoxia after pediatric cardiac arrest.

OBJECTIVE

To determine the frequency and outcomes of hyperoxia and hypoxia in patients following resuscitation from pediatric cardiac arrest admitted to a tertiary care center.

DESIGN AND METHODS

This is a retrospective observational cohort study. Charts of children resuscitated from cardiac arrest and admitted to our hospital from 2004 to 2008 were reviewed. Partial pressures of oxygen (PaO2) obtained within the first 24 hours following return of spontaneous circulation and mortality at 6 months was recorded. Children who did not survive the initial 48 hours, patients having undergone extracorporeal oxygenation or had congenital heart disease, and those in whom arterial blood gases were not obtained were excluded.

RESULTS

Seventy-four patients met inclusion criteria. Of these, 38 (51%) had at least one arterial blood gases with a PaO2 > 300 mm Hg and 10 (14%) had a PaO2 < 60 mm Hg in the first 24 hours. Neither hyperoxia nor hypoxia on initial arterial blood gases (p = 0.912 and p = 0.384) nor any arterial blood gases within the first 24 hours after cardiac arrest (p = 0.325 and p = 0.553) was associated with 6-month mortality.

CONCLUSIONS

Hyperoxia occurs commonly within the first 24 hours of management in children resuscitated from cardiac arrest.

Infusion of 4°C normal saline can improve the neurological outcome in a porcine model of cardiac arrest

BACKGROUND

This study sought to investigate induction of therapeutic hypothermia using ice-cold intravenous fluid after cardiopulmonary resuscitation (CPR). The effects on temperature, hemodynamics, cognitive performance and the accompanying neurohistopathological changes, and apoptosis were assessed.

METHODS

Fourteen piglets had 4 minutes of untreated ventricular fibrillation, followed by CPR. The animals in which spontaneous circulation was restored were randomly assigned to two groups: the hypothermia group (n = 7) was given an infusion of 4°C cold normal saline solution 30 mL/kg at an infusion rate of 1.33 mL/kg/min, followed by 10 mL/kg/h to 4 hours after restoration of spontaneous circulation; the control group (n = 7) was given the same infusion at room temperature. Variables were measured repeatedly until 4 hours after restoration of spontaneous circulation. Neurocognitive performance was evaluated 24 hours after CPR. Then animals were killed and the brains were removed for histopathology at 24 hours after restoration of spontaneous circulation. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling method was used for apoptosis evaluation.

RESULTS

Compared with the control group, the core temperature of the hypothermia group was significantly decreased (p < 0.01). The cerebral performance categories at 24 hours after restoration of spontaneous circulation in the hypothermia group were better than that in the control group (p < 0.05). The percentage of terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling-positive cells in the cortex and dentate gyrus of the hippocampus were significantly reduced in the hypothermia group compared with the control group at 24 hours after restoration of spontaneous circulation. By observation of transmission electron microscopy, the neuron damages were significantly reduced in hypothermia group.

CONCLUSION

4°C normal saline solution is a safe and effective method to reduce brain damages and prevent apoptotic cell death after cardiac arrest.

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.

Mechanisms of action, physiological effects, and complications of hypothermia

BACKGROUND

Mild to moderate hypothermia (32-35 degrees C) is the first treatment with proven efficacy for postischemic neurological injury. In recent years important insights have been gained into the mechanisms underlying hypothermia's protective effects; in addition, physiological and pathophysiological changes associated with cooling have become better understood.

OBJECTIVE

To discuss hypothermia's mechanisms of action, to review (patho)physiological changes associated with cooling, and to discuss potential side effects.

DESIGN

Review article.

INTERVENTIONS

None.

MAIN RESULTS

A myriad of destructive processes unfold in injured tissue following ischemia-reperfusion. These include excitotoxicty, neuroinflammation, apoptosis, free radical production, seizure activity, blood-brain barrier disruption, blood vessel leakage, cerebral thermopooling, and numerous others. The severity of this destructive cascade determines whether injured cells will survive or die. Hypothermia can inhibit or mitigate all of these mechanisms, while stimulating protective systems such as early gene activation. Hypothermia is also effective in mitigating intracranial hypertension and reducing brain edema. Side effects include immunosuppression with increased infection risk, cold diuresis and hypovolemia, electrolyte disorders, insulin resistance, impaired drug clearance, and mild coagulopathy. Targeted interventions are required to effectively manage these side effects. Hypothermia does not decrease myocardial contractility or induce hypotension if hypovolemia is corrected, and preliminary evidence suggests that it can be safely used in patients with cardiac shock. Cardiac output will decrease due to hypothermia-induced bradycardia, but given that metabolic rate also decreases the balance between supply and demand, is usually maintained or improved. In contrast to deep hypothermia (<or=30 degrees C), moderate hypothermia does not induce arrhythmias; indeed, the evidence suggests that arrhythmias can be prevented and/or more easily treated under hypothermic conditions.

CONCLUSIONS

Therapeutic hypothermia is a highly promising treatment, but the potential side effects need to be properly managed particularly if prolonged treatment periods are required. Understanding the underlying mechanisms, awareness of physiological changes associated with cooling, and prevention of potential side effects are all key factors for its effective clinical usage.

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.

Devices for rapid induction of hypothermia

In industrial countries it is estimated that the incidence of out-of-hospital sudden cardiac arrest lies between 36 and 128 per 100,000 inhabitants per year. Almost 80% of patients who initially survive a cardiac arrest present with coma lasting more than 1 h. Current therapy during cardiac arrest concentrates on the external support of circulation and respiration with additional drug and electrical therapy. Therapeutic hypothermia provides a new and very effective therapy for neuroprotection in patients after cardiac arrest. It is critical that mild hypothermia has to be applied very early after the ischaemic insult to be effective, otherwise the beneficial effects would be diminished or even abrogated. There are numerous methods available for cooling patients after ischaemic states. Surface cooling devices are non-invasive and range from simple ice packs to sophisticated machines with automatic feedback control. Other non-invasive methods include drugs and cold liquid ventilation. The newer devices have cooling rates comparable to invasive catheter techniques. Invasive cooling methods include the administration of ice-cold fluids intravenously, the use of intravascular cooling catheters, body cavity lavage, extra-corporeal circuits and selective brain cooling. Most of these methods are quite invasive and are still in an experimental stage. The optimal timing and technique for the induction of hypothermia after cardiac arrest have not yet been defined, and it is currently a major topic of ongoing research. The induction of hypothermia after cardiac arrest needs to be an integral component of the initial evaluation and stabilization of the patient.

Induced hypothermia and fever control for prevention and treatment of neurological injuries

Increasing evidence suggests that induction of mild hypothermia (32-35 degrees C) in the first hours after an ischaemic event can prevent or mitigate permanent injuries. This effect has been shown most clearly for postanoxic brain injury, but could also apply to other organs such as the heart and kidneys. Hypothermia has also been used as a treatment for traumatic brain injury, stroke, hepatic encephalopathy, myocardial infarction, and other indications. Hypothermia is a highly promising treatment in neurocritical care; thus, physicians caring for patients with neurological injuries, both in and outside the intensive care unit, are likely to be confronted with questions about temperature management more frequently. This Review discusses the available evidence for use of controlled hypothermia, and also deals with fever control. Besides discussing the evidence, the aim is to provide information to help guide treatments more effectively with regard to timing, depth, duration, and effective management of side-effects. In particular, the rate of rewarming seems to be an important factor in establishing successful use of hypothermia in the treatment of neurological injuries.

[Therapeutic hypothermia in the intensive care unit]

Experimental studies have demonstrated the neuroprotective effects of induced hypothermia in prevention of secondary insults following acute brain injury. Therefore, therapeutic hypothermia could be effective in the clinical setting of intensive care therapy. In this paper pathophysiological aspects of induced hypothermia are discussed and clinically relevant study results of hypothermia therapy are given in respect to evidence-based medicine.

Clinical review: beyond immediate survival from resuscitation-long-term outcome considerations after cardiac arrest

A substantial body of literature concerning resuscitation from cardiac arrest now exists. However, not surprisingly, the greater part concerns the cardiac arrest event itself and optimising survival and outcome at relatively proximal time points. The aim of this review is to present the evidence base for interventions and therapeutic strategies that might be offered to patients surviving the immediate aftermath of a cardiac arrest, excluding components of resuscitation itself that may lead to benefits in long-term survival. In addition, this paper reviews the data on long-term impact, physical and neuropsychological, on patients and their families, revealing a burden that is often underestimated and underappreciated. As greater numbers of patients survive cardiac arrest, outcome measures more sophisticated than simple survival are required.

Brain tissue oxygen pressure and cerebral metabolism in an animal model of cardiac arrest and cardiopulmonary resuscitation

OBJECTIVE

Direct measurement of brain tissue oxygenation (PbtO2) is established during spontaneous circulation, but values of PbtO2 during and after cardiopulmonary resuscitation (CPR) are unknown. The purpose of this study was to investigate: (1) the time-course of PbtO2 in an established model of CPR, and (2) the changes of cerebral venous lactate and S-100B.

METHODS

In 12 pigs (12-16 weeks, 35-45 kg), ventricular fibrillation (VF) was induced electrically during general anaesthesia. After 4 min of untreated VF, all animals were subjected to CPR (chest compression rate 100/min, FiO2 1.0) with vasopressor therapy after 7, 12, and 17 min (vasopressin 0.4, 0.4, and 0.8 U/kg, respectively). Defibrillation was performed after 22 min of cardiac arrest. After return of spontaneous circulation (ROSC), the pigs were observed for 1h.

RESULTS

After initiation of VF, PbtO2 decreased compared to baseline (mean +/- SEM; 22 +/- 6 versus 2 +/- 1 mmHg after 4 min of VF; P < 0.05). During CPR, PbtO2 increased, and reached maximum values 8 min after start of CPR (25 +/- 7 mmHg; P < 0.05 versus no-flow). No further changes were seen until ROSC. Lactate, and S-100B increased during CPR compared to baseline (16 +/- 2 versus 85 +/- 8 mg/dl, and 0.46 +/- 0.05 versus 2.12 +/- 0.40 microg/l after 13 min of CPR, respectively; P < 0.001); lactate remained elevated, while S-100B returned to baseline after ROSC.

CONCLUSIONS

Though PbtO2 returned to pre-arrest values during CPR, PbtO2 and cerebral lactate were lower than during post-arrest reperfusion with 100% oxygen, which reflected the cerebral low-flow state during CPR. The transient increase of S-100B may indicate a disturbance of the blood-brain-barrier.

Outcomes after ventricular fibrillation out-of-hospital cardiac arrest: expanding the chain of survival

Coronary heart disease is the most common cause of death in the United States, with ventricular fibrillation (VF) the most common initial rhythm when cardiac disease causes arrest. Survival after VF out-of-hospital cardiac arrest (OHCA) depends on a sequence of events called the chain of survival, which Includes rapid access to emergency medical services, cardiopulmonary resuscitation, defibrillation, and advanced care. Because of widespread implementation of defibrillation programs, more patients survive VF OHCAs, making subsequent care of these patients important. Early hospitalization must focus on potential neurologic injury and therapy targeted at the underlying cardiac disease and antiarrhythmic therapy for long-term secondary prevention of sudden death. Attention to certain cohorts who are at high risk despite their underlying disease, such as women and elderly patients, is necessary. These cohorts may have the greatest response to short-term and long-term therapies for cardiac rehabilitation. With these approaches, long-term survival and quality of life after VF OHCA are favorable. Broadening the focus of the chain of survival to include in-hospital and long-term care will further improve favorable outcomes achieved in an early defibrillation program.

[Controlled mild-to-moderate hypothermia in the intensive care unit]

Controlled hypothermia is used as a therapeutic intervention to provide neuroprotection and (more recently) cardioprotection. The growing insight into the underlying pathophysiology of apoptosis and destructive processes at the cellular level, and the mechanisms underlying the protective effects of hypothermia, have led to improved application and to a widening of the range of potential indications. In many centres hypothermia has now become part of the standard therapy for post-anoxic coma in certain patients, but for other indications its use still remains controversial. The negative findings of some studies may be partly explained by inadequate protocols for the application of hypothermia and insufficient attention to the prevention of potential side effects. This review deals with some of the concepts underlying hypothermia-associated neuroprotection and cardioprotection, and discusses some potential clinical indications as well as reasons why some clinical trials may have produced conflicting results. Practical aspects such as methods to induce hypothermia, as well as the side effects of cooling are also discussed.

Application of therapeutic hypothermia in the ICU: opportunities and pitfalls of a promising treatment modality. Part 1: Indications and evidence

OBJECTIVE

Hypothermia has been used for medicinal purposes since ancient times. This paper reviews the current potential clinical applications for mild hypothermia (32-35 degrees C).

DESIGN AND SETTING

Induced hypothermia is used mostly to prevent or attenuate neurological injury, and has been used to provide neuroprotection in traumatic brain injury, cardiopulmonary resuscitation, stroke, and various other disorders. The evidence for each of these applications is discussed, and the mechanisms underlying potential neuroprotective effects are reviewed. Some of this evidence comes from animal models, and a brief overview of these models and their limitations is included in this review.

RESULTS

The duration of cooling and speed of re-warming appear to be key factors in determining whether hypothermia will be effective in preventing or mitigating neurological injury. Some other potential usages of hypothermia, such as its use in the peri-operative setting and its application to mitigate cardiac injury following ischemia and reperfusion, are also discussed.

CONCLUSIONS

Although induced hypothermia appears to be a highly promising treatment, it should be emphasized that it is associated with a number of potentially serious side effects, which may negate some or all of its potential benefits. Prevention and/or early treatment of these complications are the key to successful use of hypothermia in clinical practice. These side effects, as well as various physiological changes induced by cooling, are discussed in a separate review.

Hyperbaric oxygen reduces neuronal death and improves neurological outcome after canine cardiac arrest

BACKGROUND AND PURPOSE

Studies suggest that hyperbaric oxygen (HBO) is neuroprotective after experimental cerebral ischemia, but the mechanism is unknown. This study tested the hypotheses that postischemic HBO affords clinical and histopathological neuroprotection after experimental cardiac arrest and resuscitation (A/R) and that this neuroprotection results from improved cerebral oxygen metabolism after A/R.

METHODS

Anesthetized adult female beagles underwent A/R and randomization to HBO (2.7-atm absolute [ATA] for 60 minutes, 1 hour after A/R) or control (Po2=80 to 100 mm Hg; 1 ATA). Animals underwent neurological deficit scoring (NDS) 23 hours after A/R. After euthanasia at 24 hours, neuronal death (necrotic and apoptotic) in representative animals was determined stereologically in hippocampus and cerebral neocortex. In experiment 2, arterial and sagittal sinus oxygenation and cerebral blood flow (CBF) were measured. Cerebral oxygen extraction ratio (ERc), oxygen delivery (Do2c), and metabolic rate for oxygen (CMRo2) were calculated (baseline and 2, 30, 60, 120, 180, 240, 300, and 360 minutes after restoration of spontaneous circulation).

RESULTS

NDS improved after A/R in HBO animals (HBO, 35+/-14; controls, 54+/-15; P=0.028). Histopathological examination revealed significantly fewer dying neurons in HBO animals; the magnitude of neuronal injury correlated well with NDS. HBO corrected elevations in ERc (peak, 60+/-14% for controls, 26+/-4% for HBO) but did not increase Do2c or CMRo2, which decreased approximately 50% after A/R in both groups.

CONCLUSIONS

HBO inhibits neuronal death and improves neurological outcome after A/R; the mechanism of HBO neuroprotection is not due to stimulation of oxidative cerebral energy metabolism.

Treatment of comatose survivors of out-of-hospital cardiac arrest with induced hypothermia

BACKGROUND

Cardiac arrest outside the hospital is common and has a poor outcome. Studies in laboratory animals suggest that hypothermia induced shortly after the restoration of spontaneous circulation may improve neurologic outcome, but there have been no conclusive studies in humans. In a randomized, controlled trial, we compared the effects of moderate hypothermia and normothermia in patients who remained unconscious after resuscitation from out-of-hospital cardiac arrest.

METHODS

The study subjects were 77 patients who were randomly assigned to treatment with hypothermia (with the core body temperature reduced to 33 degrees C within 2 hours after the return of spontaneous circulation and maintained at that temperature for 12 hours) or normothermia. The primary outcome measure was survival to hospital discharge with sufficiently good neurologic function to be discharged to home or to a rehabilitation facility.

RESULTS

The demographic characteristics of the patients were similar in the hypothermia and normothermia groups. Twenty-one of the 43 patients treated with hypothermia (49 percent) survived and had a good outcome--that is, they were discharged home or to a rehabilitation facility--as compared with 9 of the 34 treated with normothermia (26 percent, P=0.046). After adjustment for base-line differences in age and time from collapse to the return of spontaneous circulation, the odds ratio for a good outcome with hypothermia as compared with normothermia was 5.25 (95 percent confidence interval, 1.47 to 18.76; P=0.011). Hypothermia was associated with a lower cardiac index, higher systemic vascular resistance, and hyperglycemia. There was no difference in the frequency of adverse events.

CONCLUSIONS

Our preliminary observations suggest that treatment with moderate hypothermia appears to improve outcomes in patients with coma after resuscitation from out-of-hospital cardiac arrest.

The effect of mild hypothermia and induced hypertension on long term survival rate and neurological outcome after asphyxial cardiac arrest in rats

STUDY OBJECTIVE

we studied the long-term effect of a combined treatment with resuscitative mild hypothermia and induced hypertension on survival rate and neurological outcome after asphyxial cardiac arrest (CA) in rats.

METHODS

36 male Wistar rats, were randomised into three groups: Group I (n=10): anaesthetised with halothane and N(2)O/O(2) (70/30%) had vessel cannulation but no asphyxial CA; mechanical ventilation was continued to 1 h. Group II (n=13): under the same anaesthetic conditions and vessel cannulation, was subjected to asphyxial CA of 8 min, reversed by brief external heart massage and followed by mechanical ventilation to 1 h post restoration of spontaneous circulation (ROSC). Group III (n=13): received the same insult and resuscitation as described in group II, but in contrast to the previous group, a combination treatment of hypothermia (34 degrees C) and induced hypertension was started immediately after ROSC and maintained for 60 min ROSC. Survival rate and neurological deficit (ND) scores were determined before arrest, at 2 and 24 h, and each 24-h up to 4 weeks after ROSC.

RESULTS

Baseline variables were the same in the three groups. Comparison of the asphyxial CA groups (groups II and III), showed an increased, although not statistically significant, survival rate at 72 h after ROSC in group III, and it became highly significant at 4 weeks after ROSC. The ND scores were the same in both asphyxial CA groups (groups II and III).

CONCLUSIONS

Resuscitative mild hypothermia and induced hypertension after asphyxial CA in rats is associated with a better survival rate. This beneficial effect persisted for 4 weeks after ROSC.

Maximisation of cerebral blood flow during experimental cardiopulmonary resuscitation does not ameliorate post-resuscitation hypoperfusion

Continuous intra-aortic balloon occlusion has been reported to improve cerebral blood flow during cardiopulmonary resuscitation (CPR) but not to ameliorate the impaired blood recirculation occurring after restoration of spontaneous circulation (ROSC). Volume expansion with hypertonic solutions may improve recovery of brain function by enhancing post-resuscitation cerebral blood flow. We hypothesised that the combination of these treatments with open-chest CPR would improve cerebral blood flow during CPR, and attenuate post-resuscitation flow disturbances. In 32 anaesthetised piglets, catheters were placed for haemodynamic and blood gas monitoring. Open-chest CPR was initiated after 9 min of ventricular fibrillation. The piglets were treated either with 3 ml kg(-1) hypertonic saline and dextran (HSD) (n = 10), HSD and balloon occlusion (n = 10) or with normal saline (n = 12). After 7 min of CPR, internal defibrillatory shocks were administered to restore spontaneous circulation. Haemodynamic variables, continuous cerebral cortical blood flow, cerebral tissue pH and pCO2 and blood gas parameters were measured during CPR and up to 210 min after ROSC. Higher cerebral perfusion pressure was found in the balloon-HSD group during CPR. This group exhibited less arterial hypertension immediately after ROSC compared with the other groups. Thereafter, a fairly rapid decrease of the perfusion pressures was observed in all groups reaching a minimum level approximately 30 min after ROSC. Cerebral cortical blood flow was significantly higher and cerebral oxygen extraction ratio significantly lower in the balloon-HSD group during CPR, but not after ROSC. In conclusion, a combination of intra-aortic balloon occlusion and HSD administration improves cerebral blood flow and brain oxygen supply during experimental open-chest CPR. In contrast, cerebral blood flow after ROSC was not shown to be influenced by this treatment.

Preliminary clinical outcome study of mild resuscitative hypothermia after out-of-hospital cardiopulmonary arrest

The effects of mild hypothermia (MH) were investigated. From 1995 to 1996, 28 adult patients with out-of-hospital cardiopulmonary arrest (CPA) had return of spontaneous circulation and survived for more than two days. Thirteen patients were in the MH group. In the MH group, core temperature was maintained between 33 and 34 degrees C for 48 h, and then re-warmed to a temperature of 37 degrees C, at a rate of no greater than 1 degrees C per day. Fifteen patients, admitted before the MH protocol was instituted, were in the control group. Despite the fact that the number of witnessed arrests in the control group were greater than in the MH group, there were both more survivors (7/13 vs. 5/15) and more fully recovered patients (3/13 vs. 1/15) in the MH vs Control groups. Eleven of 13 MH patients, as compared to 6/15 controls developed pneumonia. Our study, although preliminary, suggests that MH might confer improved outcome, as has been shown in animal models, after CPA. This treatment is associated with an increase in pneumonic complications.

The influence of chronic prearrest health conditions on mortality and functional neurological recovery in cardiac arrest survivors

PURPOSE

To study the impact of chronic prearrest health conditions on mortality and neurological recovery in patients after witnessed cardiac arrest and primary successful resuscitation.

PATIENTS AND METHODS

The study was set in the community of Vienna, Austria. Data concerning cardiopulmonary resuscitation of adult patients who survived a witnessed cardiac arrest were collected according to an internationally recommended protocol (Utstein-Style). Chronic prearrest health conditions and New York Heart Association (NYHA) functional classes were evaluated. All patients were followed up for 6 months after the event or death. Adverse outcome was defined as death or severe neurological impairment. A forward stepwise logistic regression model was applied to assess the impact of pre-arrest morbidity on unfavorable outcome, expressed as odds ratio (OR) with 95% confidence intervals (CI).

RESULTS

Of 411 patients, 269 (66%) had one or more of the following pre-arrest diseases: coronary heart disease (45%), hypertension (26%), congestive heart failure (20%), diabetes mellitus (14%), chronic pulmonary disease (6%), and cerebrovascular disease (5%). In 22% a NYHA class of III or IV was present before cardiac arrest. At 6-month follow-up, 161 (40%) of the patients were alive with favorable neurological recovery; overall mortality was 57% (n = 233). Increasing NYHA classes (OR 1.4 per NYHA class increase; CI 1.1 to 1.7) and increasing age were independent predictors of adverse outcome (OR 1.03 per 10-year increase; CI 1.01 to 1.05), as were durations of cardiac arrest (OR 1.10 per 5-minute increase; CI 1.07 to 1.12) and the presence of ventricular fibrillation or tachycardia (OR 0.3; CI 0.2 to 0.5). The remaining health conditions, as listed above, were not independently associated with outcome.

CONCLUSIONS

A large proportion of patients with cardiac arrest had chronic diseases before the event. The presence of impaired functional performance in patients with structural heart disease increased unfavorable outcome within 6 months in primary cardiac arrest survivors. However, the impact of chronic prearrest conditions on outcome seems to be very small, and should not influence decisions whether to withhold or withdraw therapy.

Brain temperature exceeds systemic temperature in head-injured patients

OBJECTIVE

To identify the temperature differences in readings taken from the brain, jugular bulb, and core body in head-injured patients.

DESIGN

Prospective, observational study.

SETTING

Neurosurgical intensive care unit of a university-affiliated county hospital.

PATIENTS

Thirty patients with severe head injuries had measurements of brain and core body temperatures. Fourteen patients also had measurements of jugular venous blood at the level of the jugular bulb.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Brain temperature was increased an average of 2.0 degrees F (1.1 degrees C) over the core body temperature. In individual patients, the average brain temperature increase over the core body temperature ranged from -0.5 degrees to 3.8 degrees F (-0.30 degrees to 2.1 degrees C). Jugular vein and core body temperatures were similar. The difference in the brain and body temperatures increased when cerebral perfusion pressure decreased to between 20 and 50 mm Hg. The difference in the brain and body temperatures decreased in those patients treated with barbiturate coma.

CONCLUSIONS

Direct measurement of temperature in head-injured patients is a safe procedure. Temperatures in the brain are typically increased over the core body temperature and the jugular bulb temperatures. Jugular vein temperature measurement is not a good measurement of brain temperature since it reflects body, not brain temperature. These findings support the potential importance of monitoring brain temperature and the importance of controlling fever in severely head-injured patients since brain temperature may be higher than expected.

The association between blood lactate concentration on admission, duration of cardiac arrest, and functional neurological recovery in patients resuscitated from ventricular fibrillation

OBJECTIVE

To assess the association between arterial lactate concentration on admission and the duration of human ventricular fibrillation cardiac arrest, and to what degree the arterial lactate concentration on admission is an early predictor of functional neurological recovery in human cardiac arrest survivors.

DESIGN

Cohort study. Arterial lactate concentrations and out-of-hospital data concerning cardiac arrest and cardiopulmonary resuscitation were collected retrospectively according to a standardized protocol. Functional neurological recovery was assessed prospectively at regular intervals for 6 months.

SETTING

Emergency department of an urban tertiary care hospital.

PATIENTS

A total of 167 primary survivors of witnessed out-of-hospital ventricular fibrillation cardiac arrest.

MEASUREMENTS

The association between arterial lactate concentration on admission, the duration of cardiac arrest, and functional neurological recovery was assessed. Further, we assessed whether admission concentrations of arterial lactate and duration of cardiac arrest can predict unfavorable functional neurological recovery. Functional neurological recovery was measured in cerebral performance categories (CPC). No or minimal functional impairment (CPC 1 and 2) was defined as favorable outcome; the remaining categories (CPC 3, 4 and 5) were defined as unfavorable functional neurological recovery.

RESULTS

In 167 patients, a weak association between total duration of cardiac arrest and admission levels of lactate (r = 0.49, P < 0.001) could be shown. With increasing admission concentrations of arterial lactate functional neurological recovery was more likely to be unfavorable (OR 1.15 per mmol/l increase, 95% CI 1.04-1.27). Nevertheless, only at very high levels of lactate (16.3 mmol/l) could unfavorable neurological recovery be detected with 100% specificity, yielding a very low sensitivity of 16%.

CONCLUSIONS

The arterial admission lactate concentration after out-of-hospital ventricular fibrillation cardiac arrest is a weak measure of the duration of ischemia. High admission lactate levels are associated with severe neurological impairment. However, this parameter has poor prognostic value for individual estimation of the severity of subsequent functional neurological impairment.

Clinical trial of induced hypothermia in comatose survivors of out-of-hospital cardiac arrest

STUDY OBJECTIVE

To examine the effects of moderate hypothermia (33 degrees C), induced by surface cooling in the ED and maintained for 12 hours in the ICU, on patients with anoxic brain injury after out-of-hospital cardiac arrest.

METHODS

We conducted the study in a teaching hospital in Melbourne, Victoria, Australia. Participants were 22 adults who remained unconscious after return of spontaneous circulation following out-of-hospital cardiac arrest. This treatment group was studied prospectively, and a control group of 22 similar patients was studied by retrospective chart review. Moderate hypothermia (33 degrees C) was induced in the ED by means of surface cooling and maintained for 12 hours in the ICU with rewarming to normothermia over 6 hours; control patients were maintained at normothermia.

RESULTS

There were no significant adverse effects of induced hypothermia. Cardiovascular changes included decreased pulse rate, but there were no significant differences in mean arterial blood pressure between the two groups. Small increases in serum potassium and decreases in pH at 18 hours in the hypothermic patients compared with normothermic controls were of no clinical significance. There were no septic complications. There was a significant increase in the number of patients with good outcome (Glasgow Outcome Coma Scale category 1 or 2) with induced hypothermia (11 of 22, versus 3 of 22 for normothermic controls; P<.05), and the mortality rate was significantly lower (10 of 22 versus 17 of 22; P<.05).

CONCLUSION

Compared with historical normothermic controls, outcome was significantly improved and there was no increase in complications when moderate hypothermia was induced in comatose survivors of out-of-hospital cardiac arrest and maintained for 12 hours. Larger, prospective, randomized, controlled studies of induced moderate hypothermia in comatose survivors of out-of-hospital cardiac arrest are warranted.

Delayed hyperemia causing intracranial hypertension after cardiopulmonary resuscitation

OBJECTIVE

To clarify whether early or delayed failure of cerebral perfusion after cardiopulmonary resuscitation (CPR) occurs in humans and contributes to secondary brain damage.

DESIGN

Prospective, repeated-measures study.

SETTING

Intensive care unit of Hiroshima University School of Medicine.

PATIENTS

Eight comatose patients who had undergone successful resuscitation from cardiac arrest.

INTERVENTIONS

All patients underwent transcranial Doppler sonography examination. The intracranial cerebral pressure (ICP) and jugular venous oxygen saturation (SO2) also were continuously monitored in five patients and three patients, respectively.

MEASUREMENTS AND MAIN RESULTS

In each patient, we measured the mean flow velocity of the middle cerebral artery transcranially and the mean flow velocity of the internal carotid artery, high in the neck, using transcranial Doppler sonography. The pulsatility index for each measurement was also calculated. The first examinations were performed within 4 to 12 hrs of CPR, and repeat examinations were performed approximately every 12 hrs. The initial mean flow velocities of the middle cerebral artery and the initial mean flow velocities of the internal carotid artery were relatively low, with relatively high pulsatility indices. The mean flow velocities of the middle cerebral artery began to increase at 12 to 24 hrs after CPR and peaked 24 to 120 hrs after CPR. A simultaneous increase in mean flow velocities of the internal carotid artery was observed during this period. The pulsatility index in both arteries dropped significantly during peak mean flow velocity of the middle cerebral artery. In six of seven patients with an abnormal increase (> 100 cm/ sec) in peak mean flow velocity of the middle cerebral artery, the ratio of mean flow velocity of the middle cerebral artery to mean flow velocity of the internal carotid artery was < 3. This value tended to be lower in patients with poor outcomes. An increased mean flow velocity of the middle cerebral artery, with a ratio of < 3 for mean flow velocity of the middle cerebral artery to mean flow velocity of the internal carotid artery, was defined as hyperemia. Although the mean flow velocity of the internal carotid artery was not measured, another patient with an abnormal increase in mean flow velocity of the middle cerebral artery revealed a high jugular venous SO2 value of 83.5%, also representing hyperemia. All ICP values were within the normal range 4 to 12 hrs after CPR and tended to increase before peak mean flow velocity of the middle cerebral artery. The two patients with the lowest ratios of mean flow velocity of the middle cerebral artery to mean flow velocity of the internal carotid artery showed significant increases in ICP after the peak mean flow velocity of the middle cerebral artery. These two patients subsequently developed brain death.

CONCLUSIONS

Delayed hyperemia occurs in humans after resuscitation from cardiac arrest. Our data suggest that this delayed hyperemia can lead to intracranial hypertension and occasionally acute brain swelling, contributing to a poor outcome. A high mean flow velocity of the middle cerebral artery with a low ratio of mean flow velocity of the middle cerebral artery to mean flow velocity of the internal carotid artery may be predictive of critical hyperemia. As an indirect method of measuring cerebral blood flow transcranial Doppler sonography can be used to adjust treatment for failure of cerebral perfusion after resuscitation.

Effect of an endothelin-1 antagonist, BQ-485, on cerebral oxygen metabolism after complete global cerebral ischemia in dogs

Endothelin-1 (ET-1) plays an important role in the physiologic or pathophysiologic regulation of cerebral circulation. To evaluate the effects of the newly synthesized ETA receptor-selective antagonist, BQ-485 (N-perhydroazepin-l-ylcarbonyl-Leu-D-Trp-D-Trp-OH), on the cerebral metabolism of oxygen during the delayed cerebral hypoperfusion that follows global cerebral ischemia, we occluded the ascending aorta and caval veins of 10 beagle dogs for 12.5 min. The animals were randomized into two groups. BQ-485 was given directly into the carotid artery at 0.03 mg/kg per min for 30 min, starting 15 min after reperfusion in the treatment group (n = 5). Isotonic saline was infused in the control group (n = 5). A fiberoptic catheter was inserted into the superior sagittal sinus to monitor its oxygen saturation (SssO2) continuously. Arterial O2 content (CaO2), and sagittal sinus O2 content (CssO2) were monitored before and at 0.5, 1, 2, 4, 6 and 8 h after the ischemic insult. BQ-485 significantly prevented the expected decrease in SssO2 and increase in the cerebral O2 utilization coefficient at 4, 6 and 8 h after the ischemic insult (P < 0.05). Thus, BQ-485 ameliorated the mismatch between O2 supply and demand in the delayed hypoperfusion phase. We conclude that ET may be involved in the pathogenesis of delayed cerebral hypoperfusion after cardiac arrest.

Induced hypothermia in intensive care medicine

Induced hypothermia as adjunctive therapy has been the subject of considerable research interest and debate for over fifty years. Recently the first prospective randomized controlled trials were undertaken in humans with severe traumatic brain injury, with supportive results. Another prospective controlled study of induced hypothermia in severe septic adult respiratory distress syndrome also suggested improved outcome. Other studies in patients with anoxic brain injury have been suggested following promising findings in animal models. There have been anecdotal reports of the use of induced hypothermia in a wide range of other neurological injuries. There are significant physiological changes during induced hypothermia, particularly affecting the cardiovascular system. In addition, hypokalaemia, prolonged clotting times and neutropenia may occur. The evidence that induced hypothermia may be hazardous is mostly drawn from the literature on accidental hypothermia occurring in trauma, or patients with sepsis. It is likely that further trials will be conducted and if benefit is confirmed, induced hypothermia may become more widely used in selected patients in the intensive care unit.