Cerebrovascular reactivity in comatose patients resuscitated from a cardiac arrest

Relationships of Jugular Bulb Parameters with Cerebral Perfusion and Metabolism After Resuscitation from Cardiac Arrest: A Post-Hoc Analysis of Experimental Studies Using a Minipig Model

BACKGROUND

Cerebral blood flow (CBF) decreases in the first few hours or days following resuscitation from cardiac arrest, increasing the risk of secondary cerebral injury. Using data from experimental studies performed in minipigs, we investigated the relationships of parameters derived from arterial and jugular bulb blood gas analyses and lactate levels (jugular bulb parameters), which have been used as indicators of cerebral perfusion and metabolism, with CBF and the cerebral lactate to creatine ratio measured with dynamic susceptibility contrast magnetic resonance imaging and proton magnetic resonance spectroscopy, respectively.

METHODS

We retrospectively analyzed 36 sets of the following data obtained during the initial hours following resuscitation from cardiac arrest: percent of measured CBF relative to that at the prearrest baseline (%CBF), cerebral lactate to creatine ratio, and jugular bulb parameters, including jugular bulb oxygen saturation, jugular bulb lactate, arterial-jugular bulb oxygen content difference, cerebral extraction of oxygen, jugular bulb-arterial lactate content difference, lactate oxygen index, estimated respiratory quotient, and arterial-jugular bulb hydrogen ion content difference. Linear mixed-effects models were constructed to examine the effects of each jugular bulb parameter on the %CBF and cerebral lactate to creatine ratio.

RESULTS

The arterial-jugular bulb oxygen content difference (P = 0.047) and cerebral extraction of oxygen (P = 0.030) had a significant linear relationship with %CBF, but they explained only 12.0% (95% confidence interval [CI] 0.002-0.371) and 14.2% (95% CI 0.005-0.396) of the total %CBF variance, respectively. The arterial-jugular bulb hydrogen ion content difference had a significant linear relationship with cerebral lactate to creatine ratio (P = 0.037) but explained only 13.8% (95% CI 0.003-0.412) of the total variance in the cerebral lactate to creatine ratio. None of the other jugular bulb parameters were related to the %CBF or cerebral lactate to creatine ratio.

CONCLUSIONS

In conclusion, none of the jugular bulb parameters appeared to provide sufficient information on cerebral perfusion and metabolism in this setting.

Complex Heart-Lung Ventilator Emergencies in the CICU

This review aims to enhance the comprehension and management of cardiopulmonary interactions in critically ill patients with cardiovascular disease undergoing mechanical ventilation. Highlighting the significance of maintaining a delicate balance, this article emphasizes the crucial role of adjusting ventilation parameters based on both invasive and noninvasive monitoring. It provides recommendations for the induction and liberation from mechanical ventilation. Special attention is given to the identification of auto-PEEP (positive end-expiratory pressure) and other situations that may impact hemodynamics and patients' outcomes.

Feasibility of Magnetic Resonance-Based Conductivity Imaging as a Tool to Estimate the Severity of Hypoxic-Ischemic Brain Injury in the First Hours After Cardiac Arrest

BACKGROUND

Early identification of the severity of hypoxic-ischemic brain injury (HIBI) after cardiac arrest can be used to help plan appropriate subsequent therapy. We evaluated whether conductivity of cerebral tissue measured using magnetic resonance-based conductivity imaging (MRCI), which provides contrast derived from the concentration and mobility of ions within the imaged tissue, can reflect the severity of HIBI in the early hours after cardiac arrest.

METHODS

Fourteen minipigs were resuscitated after 5 min or 12 min of untreated cardiac arrest. MRCI was performed at baseline and at 1 h and 3.5 h after return of spontaneous circulation (ROSC).

RESULTS

In both groups, the conductivity of cerebral tissue significantly increased at 1 h after ROSC compared with that at baseline (P = 0.031 and 0.016 in the 5-min and 12-min groups, respectively). The increase was greater in the 12-min group, resulting in significantly higher conductivity values in the 12-min group (P = 0.030). At 3.5 h after ROSC, the conductivity of cerebral tissue in the 12-min group remained increased (P = 0.022), whereas that in the 5-min group returned to its baseline level.

CONCLUSIONS

The conductivity of cerebral tissue was increased in the first hours after ROSC, and the increase was more prominent and lasted longer in the 12-min group than in the 5-min group. Our findings suggest the promising potential of MRCI as a tool to estimate the severity of HIBI in the early hours after cardiac arrest.

Canadian Cardiovascular Society/Canadian Cardiovascular Critical Care Society/Canadian Association of Interventional Cardiology Clinical Practice Update on Optimal Post Cardiac Arrest and Refractory Cardiac Arrest Patient Care

Survival to hospital discharge among patients with out-of-hospital cardiac arrest (OHCA) is low and important regional differences in treatment practices and survival have been described. Since the 2017 publication of the Canadian Cardiovascular Society's position statement on OHCA care, multiple randomized controlled trials have helped to better define optimal post cardiac arrest care. This working group provides updated guidance on the timing of cardiac catheterization in patients with ST-elevation and without ST-segment elevation, on a revised temperature control strategy targeting normothermia instead of hypothermia, blood pressure, oxygenation, and ventilation parameters, and on the treatment of rhythmic and periodic electroencephalography patterns in patients with a resuscitated OHCA. In addition, prehospital trials have helped craft new expert opinions on antiarrhythmic strategies (amiodarone or lidocaine) and outline the potential role for double sequential defibrillation in patients with refractory cardiac arrest when equipment and training is available. Finally, we advocate for regionalized OHCA care systems with admissions to a hospital capable of integrating their post OHCA care with comprehensive on-site cardiovascular services and provide guidance on the potential role of extracorporeal cardiopulmonary resuscitation in patients with refractory cardiac arrest. We believe that knowledge translation through national harmonization and adoption of contemporary best practices has the potential to improve survival and functional outcomes in the OHCA population.

Investigating the effects of tilting the postural drainage lithotripsy system on cerebral blood flow, intracranial pressure, heart rate, and blood pressure

PURPOSE

To investigate the effect of the postural drainage lithotripsy system developed by our experimental team on the vital signs of patient with urinary stones during the stone removal process.

METHODS

Four groups of 15 subjects (0°, 10°, 40°, and 70°) were subjected to different angles of head-down tilt to measure middle cerebral artery blood flow velocity (MCAv), cerebrovascular conductance coefficient (CVCi), intracranial pressure (nICP), heart rate (HR), and mean arterial blood pressure (MAP).

RESULTS

As the angle of HDT changed, MCAv values, nICP values, CVCi values, HR values, and MAP values changed significantly (all P ≤ 0.001), and the difference was statistically significant. During 10°HDT, despite a slight increase in nICP, the other measurements remained stable. During 40°HDT, only the MCAv values did not change significantly, whereas the rest of the measures were significantly altered. During 70°HDT, all indicators changed significantly.

CONCLUSIONS

The significant alterations in cerebral blood flow, intracranial pressure, and hemodynamics induced during the treatment of renal residual fragments with postural drainage should be used with caution in individuals with cerebrovascular accidents.

CHINA CLINICAL TRIALS REGISTRY

ChiCTR2300070671; Registration date: 2023-04-18.

Critical Care Management of Patients After Cardiac Arrest: A Scientific Statement from the American Heart Association and Neurocritical Care Society

The critical care management of patients after cardiac arrest is burdened by a lack of high-quality clinical studies and the resultant lack of high-certainty evidence. This results in limited practice guideline recommendations, which may lead to uncertainty and variability in management. Critical care management is crucial in patients after cardiac arrest and affects outcome. Although guidelines address some relevant topics (including temperature control and neurological prognostication of comatose survivors, 2 topics for which there are more robust clinical studies), many important subject areas have limited or nonexistent clinical studies, leading to the absence of guidelines or low-certainty evidence. The American Heart Association Emergency Cardiovascular Care Committee and the Neurocritical Care Society collaborated to address this gap by organizing an expert consensus panel and conference. Twenty-four experienced practitioners (including physicians, nurses, pharmacists, and a respiratory therapist) from multiple medical specialties, levels, institutions, and countries made up the panel. Topics were identified and prioritized by the panel and arranged by organ system to facilitate discussion, debate, and consensus building. Statements related to postarrest management were generated, and 80% agreement was required to approve a statement. Voting was anonymous and web based. Topics addressed include neurological, cardiac, pulmonary, hematological, infectious, gastrointestinal, endocrine, and general critical care management. Areas of uncertainty, areas for which no consensus was reached, and future research directions are also included. Until high-quality studies that inform practice guidelines in these areas are available, the expert panel consensus statements that are provided can advise clinicians on the critical care management of patients after cardiac arrest.

Neuromonitoring after Pediatric Cardiac Arrest: Cerebral Physiology and Injury Stratification

BACKGROUND

Significant long-term neurologic disability occurs in survivors of pediatric cardiac arrest, primarily due to hypoxic-ischemic brain injury. Postresuscitation care focuses on preventing secondary injury and the pathophysiologic cascade that leads to neuronal cell death. These injury processes include reperfusion injury, perturbations in cerebral blood flow, disturbed oxygen metabolism, impaired autoregulation, cerebral edema, and hyperthermia. Postresuscitation care also focuses on early injury stratification to allow clinicians to identify patients who could benefit from neuroprotective interventions in clinical trials and enable targeted therapeutics.

METHODS

In this review, we provide an overview of postcardiac arrest pathophysiology, explore the role of neuromonitoring in understanding postcardiac arrest cerebral physiology, and summarize the evidence supporting the use of neuromonitoring devices to guide pediatric postcardiac arrest care. We provide an in-depth review of the neuromonitoring modalities that measure cerebral perfusion, oxygenation, and function, as well as neuroimaging, serum biomarkers, and the implications of targeted temperature management.

RESULTS

For each modality, we provide an in-depth review of its impact on treatment, its ability to stratify hypoxic-ischemic brain injury severity, and its role in neuroprognostication.

CONCLUSION

Potential therapeutic targets and future directions are discussed, with the hope that multimodality monitoring can shift postarrest care from a one-size-fits-all model to an individualized model that uses cerebrovascular physiology to reduce secondary brain injury, increase accuracy of neuroprognostication, and improve outcomes.

Critical Care Management of Patients After Cardiac Arrest: A Scientific Statement From the American Heart Association and Neurocritical Care Society

The critical care management of patients after cardiac arrest is burdened by a lack of high-quality clinical studies and the resultant lack of high-certainty evidence. This results in limited practice guideline recommendations, which may lead to uncertainty and variability in management. Critical care management is crucial in patients after cardiac arrest and affects outcome. Although guidelines address some relevant topics (including temperature control and neurological prognostication of comatose survivors, 2 topics for which there are more robust clinical studies), many important subject areas have limited or nonexistent clinical studies, leading to the absence of guidelines or low-certainty evidence. The American Heart Association Emergency Cardiovascular Care Committee and the Neurocritical Care Society collaborated to address this gap by organizing an expert consensus panel and conference. Twenty-four experienced practitioners (including physicians, nurses, pharmacists, and a respiratory therapist) from multiple medical specialties, levels, institutions, and countries made up the panel. Topics were identified and prioritized by the panel and arranged by organ system to facilitate discussion, debate, and consensus building. Statements related to postarrest management were generated, and 80% agreement was required to approve a statement. Voting was anonymous and web based. Topics addressed include neurological, cardiac, pulmonary, hematological, infectious, gastrointestinal, endocrine, and general critical care management. Areas of uncertainty, areas for which no consensus was reached, and future research directions are also included. Until high-quality studies that inform practice guidelines in these areas are available, the expert panel consensus statements that are provided can advise clinicians on the critical care management of patients after cardiac arrest.

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.

Clinical targeting of the cerebral oxygen cascade to improve brain oxygenation in patients with hypoxic-ischaemic brain injury after cardiac arrest

The cerebral oxygen cascade includes three key stages: (a) convective oxygen delivery representing the bulk flow of oxygen to the cerebral vascular bed; (b) diffusion of oxygen from the blood into brain tissue; and (c) cellular utilisation of oxygen for aerobic metabolism. All three stages may become dysfunctional after resuscitation from cardiac arrest and contribute to hypoxic-ischaemic brain injury (HIBI). Improving convective cerebral oxygen delivery by optimising cerebral blood flow has been widely investigated as a strategy to mitigate HIBI. However, clinical trials aimed at optimising convective oxygen delivery have yielded neutral results. Advances in the understanding of HIBI pathophysiology suggest that impairments in the stages of the oxygen cascade pertaining to oxygen diffusion and cellular utilisation of oxygen should also be considered in identifying therapeutic strategies for the clinical management of HIBI patients. Culprit mechanisms for these impairments may include a widening of the diffusion barrier due to peri-vascular oedema and mitochondrial dysfunction. An integrated approach encompassing both intra-parenchymal and non-invasive neuromonitoring techniques may aid in detecting pathophysiologic changes in the oxygen cascade and enable patient-specific management aimed at reducing the severity of HIBI.

Association between rate of change in PaCO2 and functional outcome for patients with hypercapnia after out-of-hospital cardiac arrest: Secondary analysis of a randomized clinical trial

BACKGROUND

Normocapnia is suggested for post resuscitation care. For patients with hypercapnia after cardiac arrest, the relationship between rate of change in partial pressure of carbon dioxide (PaCO₂) and functional outcome was unknown.

METHODS

This was the secondary analysis of Resuscitation Outcomes Consortium (ROC) amiodarone, lidocaine, and placebo (ALPS) trial. Patients with at least 2 PaCO₂ recorded and the first indicating hypercapnia (PaCO₂ > 45 mmHg) after return of spontaneous circulation (ROSC) were included. The rate of change in PaCO₂ was calculated as the ratio of the difference between the second and first PaCO₂ to the time interval. The primary outcome was modified Rankin Score (mRS), dichotomized to good (mRS 0-3) and poor (mRS 4-6) outcomes at hospital discharge. The independent relationship between rate of change in PaCO₂ and outcome was investigated with multivariable logistic regression model.

RESULTS

A total of 746 patients with hypercapnia were included for analysis, of which 264 (35.4%) patients had good functional outcome. The median rate of change in PaCO₂ was 4.7 (interquartile range [IQR] 1.7-12) mmHg per hour. After adjusting for confounders, the rate of change in PaCO₂ (odds ratio [OR] 0.994, confidence interval [CI] 0.985-1.004, p = 0.230) was not associated the functional outcome. However, rate of change in PaCO₂ (OR 1.010, CI 1.001-1.019, p = 0.029) was independently associated with hospital mortality.

CONCLUSIONS

For OHCA patients with hypercapnia on admission, the rate of change in PaCO₂ was not independently associated with functional outcome; however, there was a significant trend that higher decreased rate was associated with increased hospital mortality.

Extracorporeal cardiopulmonary resuscitation (eCPR) and cerebral perfusion: A narrative review

Extracorporeal cardiopulmonary resuscitation (eCPR) is emerging as an effective, lifesaving resuscitation strategy for select patients with prolonged or refractory cardiac arrest. Currently, a paucity of evidence-based recommendations is available to guide clinical management of eCPR patients. Despite promising results from initial clinical trials, neurological injury remains a significant cause of morbidity and mortality. Neuropathology associated with utilization of an extracorporeal circuit may interact significantly with the consequences of a prolonged low-flow state that typically precedes eCPR. In this narrative review, we explore current gaps in knowledge about cerebral perfusion over the course of cardiac arrest and resuscitation with a focus on patients treated with eCPR. We found no studies which investigated regional cerebral blood flow or cerebral autoregulation in human cohorts specific to eCPR. Studies which assessed cerebral perfusion in clinical eCPR were small and limited to near-infrared spectroscopy. Furthermore, no studies prospectively or retrospectively evaluated the relationship between epinephrine and neurological outcomes in eCPR patients. In summary, the field currently lacks a comprehensive understanding of how regional cerebral perfusion and cerebral autoregulation are temporally modified by factors such as pre-eCPR low-flow duration, vasopressors, and circuit flow rate. Elucidating these critical relationships may inform future strategies aimed at improving neurological outcomes in patients treated with lifesaving eCPR.

Updates on the Management of Neurologic Complications of Post-Cardiac Arrest Resuscitation

Sudden cardiac arrest (SCA) is one of the leading causes of mortality and morbidity in the United States, and survivors are frequently left with severe disability. Of the 10% successfully resuscitated from SCA, only around 10% of these live with a favorable neurologic outcome. Survivors of SCA commonly develop post-cardiac arrest syndrome (PCAS). PCAS is composed of neurologic, myocardial, and systemic injury related to inadequate perfusion and ischemia-reperfusion injury with free radical formation and an inflammatory cascade. While targeted temperature management is the cornerstone of therapy, other intensive care unit-based management strategies include monitoring and treatment of seizures, cerebral edema, and increased intracranial pressure, as well as prevention of further neurologic injury. In this review, we discuss the scientific evidence, recent updates, future prospects, and knowledge gaps in the treatment of post-cardiac arrest patients.

European Resuscitation Council and European Society of Intensive Care Medicine guidelines 2021: post-resuscitation care

The European Resuscitation Council (ERC) and the European Society of Intensive Care Medicine (ESICM) have collaborated to produce these post-resuscitation care guidelines for adults, which are based on the 2020 International Consensus on Cardiopulmonary Resuscitation Science with Treatment Recommendations. The topics covered include the post-cardiac arrest syndrome, diagnosis of cause of cardiac arrest, control of oxygenation and ventilation, coronary reperfusion, haemodynamic monitoring and management, control of seizures, temperature control, general intensive care management, prognostication, long-term outcome, rehabilitation and organ donation.

European Resuscitation Council and European Society of Intensive Care Medicine Guidelines 2021: Post-resuscitation care

The European Resuscitation Council (ERC) and the European Society of Intensive Care Medicine (ESICM) have collaborated to produce these post-resuscitation care guidelines for adults, which are based on the 2020 International Consensus on Cardiopulmonary Resuscitation Science with Treatment Recommendations. The topics covered include the post-cardiac arrest syndrome, diagnosis of cause of cardiac arrest, control of oxygenation and ventilation, coronary reperfusion, haemodynamic monitoring and management, control of seizures, temperature control, general intensive care management, prognostication, long-term outcome, rehabilitation, and organ donation.

Altered cerebrovascular reactivity due to respiratory rate and breath holding: a BOLD-fMRI study on healthy adults

Cerebrovascular reactivity (CVR) is of great significance for the treatment and prevention of cerebrovascular diseases. CVR can be mapped using the blood oxygenation level-dependent (BOLD) signal of fMRI. Breath holding (BH) is a reliable method to produce the desired increase in arterial CO₂, while its application in clinical research is limited due to subject's compliance and variability. BH task with variable respiratory rates could allow more flexibility in clinical populations. In this study, 50 healthy volunteers were scanned for end-inspiration BH tasks with three different respiration rates. For the three respiratory rates BH tasks, the CVR was estimated based on the BOLD signal and general linear model (GLM) separately. Specifically, the extra time delay was considered for the hemodynamic response function, and the optimal delay was estimated for each voxel. To measure CVR in grey matter, BOLD signals of end-inspiration BH were used as regressors in general linear models to quantify their impact on CVR. This was performed for regions and voxels. Systematic differences were observed between the three end-inspiratory breathing rates. The greatest increase in activation intensity was found in fast breathing followed by self-paced and slow breathing. We conclude that the BH task of variable respiratory rates allows for CVR measurement, making breath-holding challenges more flexible and appropriate for routine practice.

Relationship of common hemodynamic and respiratory target parameters with brain tissue oxygen tension in the absence of hypoxemia or hypotension after cardiac arrest: A post-hoc analysis of an experimental study using a pig model

Brain tissue oxygen tension (PbtO2)-guided care, a therapeutic strategy to treat or prevent cerebral hypoxia through modifying determinants of cerebral oxygen delivery, including arterial oxygen tension (PaO2), end-tidal carbon dioxide (ETCO2), and mean arterial pressure (MAP), has recently been introduced. Studies have reported that cerebral hypoxia occurs after cardiac arrest in the absence of hypoxemia or hypotension. To obtain preliminary information on the degree to which PbtO2 is responsive to changes in the common target variables for PbtO2-guided care in conditions without hypoxemia or hypotension, we investigated the relationships between the common target variables for PbtO2-guided care and PbtO2 using data from an experimental study in which the animals did not experience hypoxemia or hypotension after resuscitation. We retrospectively analyzed 170 sets of MAP, ETCO2, PaO2, PbtO2, and cerebral microcirculation parameters obtained during the 60-min post-resuscitation period in 10 pigs resuscitated from ventricular fibrillation cardiac arrest. PbtO2 and cerebral microcirculation parameters were measured on parietal cortices exposed through burr holes. Multiple linear mixed effect models were used to test the independent effects of each variable on PbtO2. Despite the absence of arterial hypoxemia or hypotension, seven (70%) animals experienced cerebral hypoxia (defined as PbtO2 <20 mmHg). Linear mixed effect models revealed that neither MAP nor ETCO2 were related to PbtO2. PaO2 had a significant linear relationship with PbtO2 after adjusting for significant covariates (P = 0.030), but it could explain only 17.5% of the total PbtO2 variance (semi-partial R2 = 0.175; 95% confidence interval, 0.086-0.282). In conclusion, MAP and ETCO2 were not significantly related to PbtO2 in animals without hypoxemia or hypotension during the early post-resuscitation period. PaO2 had a significant linear association with PbtO2, but its ability to explain PbtO2 variance was small.

Neurologic complications of cardiac arrest

Cardiac arrest is a catastrophic event with high morbidity and mortality. Despite advances over time in cardiac arrest management and postresuscitation care, the neurologic consequences of cardiac arrest are frequently devastating to patients and their families. Targeted temperature management is an intervention aimed at limiting postanoxic injury and improving neurologic outcomes following cardiac arrest. Recovery of neurologic function governs long-term outcome after cardiac arrest and prognosticating on the potential for recovery is a heavy burden for physicians. An early and accurate estimate of the potential for recovery can establish realistic expectations and avoid futile care in those destined for a poor outcome. This chapter reviews the epidemiology, pathophysiology, therapeutic interventions, prognostication, and neurologic sequelae of cardiac arrest.

The Early Change in PaCO2 after Extracorporeal Membrane Oxygenation Initiation Is Associated with Neurological Complications

Rationale: Large decreases in Pa_CO2 that occur when initiating extracorporeal membrane oxygenation (ECMO) in patients with respiratory failure may cause cerebral vasoconstriction and compromise brain tissue perfusion.Objectives: To determine if the magnitude of Pa_CO2 correction upon ECMO initiation is associated with an increased incidence of neurological complications in patients with respiratory failure.Methods: We conducted a multicenter, international, retrospective cohort study using the Extracorporeal Life Support Organization Registry, including adults with respiratory failure receiving ECMO via any mode between 2012 and 2017. The relative change in Pa_CO2 in the first 24 hours was calculated as (24-h post-ECMO Pa_CO2 - pre-ECMO Pa_CO2)/pre-ECMO Pa_CO2. The primary outcome was the occurrence of neurological complications, defined as seizures, ischemic stroke, intracranial hemorrhage, or brain death.Measurements and Main Results: We included 11,972 patients, 88% of whom were supported with venovenous ECMO. The median relative change in Pa_CO2 was -31% (interquartile range, -46% to -12%). Neurological complications were uncommon overall (6.9%), with a low incidence of seizures (1.1%), ischemic stroke (1.9%), intracranial hemorrhage (3.5%), and brain death (1.6%). Patients with a large relative decrease in Pa_CO2 (>50%) had an increased incidence of neurological complications compared with those with a smaller decrease (9.8% vs. 6.4%; P < 0.001). A large relative decrease in Pa_CO2 was independently associated with neurological complications after controlling for previously described risk factors (odds ratio, 1.7; 95% confidence interval, 1.3 to 2.3; P < 0.001).Conclusions: In patients receiving ECMO for respiratory failure, a large relative decrease in Pa_CO2 in the first 24 hours after ECMO initiation is independently associated with an increased incidence of neurological complications.

Effect of ventilation rate on recovery after cardiac arrest in a pediatric animal model

AIMS

To assess the impact of two different respiratory rates in hemodynamic, perfusion and ventilation parameters in a pediatric animal model of cardiac arrest (CA).

METHODS

An experimental randomized controlled trial was carried out in 50 piglets under asphyxial CA. After ROSC, they were randomized into two groups: 20 and 30 respirations per minute (rpm). Hemodynamic, perfusion and ventilation parameters were measured 10 minutes after asphyxia, just before ROSC and at 5, 15, 30 and 60 minutes after ROSC. Independent medians test, Kruskal-Wallis test and χ2 test, were used to compare continuous and categorical variables, respectively. Spearman's Rho was used to assess correlation between continuous variables. A p-value <0.05 was considered significant.

RESULTS

Arterial partial pressure of carbon dioxide (PaCO2) was significantly lower in the 30 rpm group after 15 minutes (41 vs. 54.5 mmHg, p <0.01), 30 minutes (39.5 vs. 51 mmHg, p < 0.01) and 60 minutes (36.5 vs. 48 mmHg, p = 0.02) of ROSC. The percentage of normoventilated subjects (PaCO2 30-50 mmHg) was significantly higher in the 30 rpm group throughout the experiment. pH normalization occurred faster in the 30 rpm group with significant differences at 60 minutes (7.40 vs. 7.34, p = 0.02). Lactic acid levels were high immediately after ROSC in both groups, but were significantly lower in the 20 rpm group at 30 (3.7 vs. 4.7 p = 0.04) and 60 minutes (2.6 vs. 3.6 p = 0.03).

CONCLUSIONS

This animal model of asphyxial CA shows that a respiratory rate of 30 rpm is more effective to reach normoventilation than 20 rpm in piglets after ROSC. This ventilation strategy seems to be safe, as it does not cause hyperventilation and does not affect hemodynamics or cerebral tissue perfusion.

Cerebral Blood Flow-Guided Manipulation of Arterial Blood Pressure Attenuates Hippocampal Apoptosis After Asphyxia-Induced Cardiac Arrest in Rats

Background In most post-cardiac arrest patients, the autoregulation mechanism of cerebral blood flow (CBF) is dysregulated. We examined whether recovery of CBF by adjusting mean arterial pressure mitigates post-cardiac arrest neuronal damage. Methods and Results Wistar rats that underwent 8-minute asphyxia-induced cardiac arrest and resuscitation were computer-randomized to norepinephrine or control groups. The CBF was measured at the dorsal hippocampal CA1 region of the left hemisphere. In the norepinephrine group, the mean arterial pressure was adjusted to recover CBF to 80% to 100% of baseline. Twenty-four hours following resuscitation, neurological outcomes were assessed, and brain tissues and blood samples were harvested for neuronal apoptosis and injury assessment. Thirty resuscitated rats were randomized into 2 groups, each containing 12 rats that completed the experiments. Norepinephrine infusion effectively prevented posthyperemia hypoperfusion and recovered CBF to pre-arrest baseline levels; a moderate positive linear correlation between mean arterial pressure and CBF during this period was also observed (P<0.001). There were no significant between-group differences in neurological recovery. In the norepinephrine group compared with the control group, upregulated cleaved caspase-3 protein expression in brain tissue determined by Western blot was reduced (P=0.02) and the densities of apoptotic cells in hippocampal CA1 and CA3 regions determined by terminal deoxynucleotidyl transferase-mediated dUTP biotin nick-end labeling were decreased (P<0.001). No significant differences in serum neuron-specific enolase or S100β levels were detected between the 2 groups. Conclusions CBF recovery demonstrated neuroprotective effects by reducing activation of cerebral apoptosis and number of apoptotic neurons. However, these effects did not significantly improve clinical neurological function, necessitating further investigation.

Resuscitating the Globally Ischemic Brain: TTM and Beyond

Cardiac arrest (CA) afflicts ~ 550,000 people each year in the USA. A small fraction of CA sufferers survive with a majority of these survivors emerging in a comatose state. Many CA survivors suffer devastating global brain injury with some remaining indefinitely in a comatose state. The pathogenesis of global brain injury secondary to CA is complex. Mechanisms of CA-induced brain injury include ischemia, hypoxia, cytotoxicity, inflammation, and ultimately, irreversible neuronal damage. Due to this complexity, it is critical for clinicians to have access as early as possible to quantitative metrics for diagnosing injury severity, accurately predicting outcome, and informing patient care. Current recommendations involve using multiple modalities including clinical exam, electrophysiology, brain imaging, and molecular biomarkers. This multi-faceted approach is designed to improve prognostication to avoid "self-fulfilling" prophecy and early withdrawal of life-sustaining treatments. Incorporation of emerging dynamic monitoring tools such as diffuse optical technologies may provide improved diagnosis and early prognostication to better inform treatment. Currently, targeted temperature management (TTM) is the leading treatment, with the number of patients needed to treat being ~ 6 in order to improve outcome for one patient. Future avenues of treatment, which may potentially be combined with TTM, include pharmacotherapy, perfusion/oxygenation targets, and pre/postconditioning. In this review, we provide a bench to bedside approach to delineate the pathophysiology, prognostication methods, current targeted therapies, and future directions of research surrounding hypoxic-ischemic brain injury (HIBI) secondary to CA.

State-of-the-art considerations in post-arrest care

Cardiac arrest has a high rate of morbidity and mortality. Several advances in post-cardiac arrest management can improve outcome, but are time-dependent, placing the emergency physician in a critical role to both recognize the need for and initiate therapy. We present a novel perspective of both the workup and therapeutic interventions geared toward the emergency physician during the first few hours of care. We describe how the immediate care of a post-cardiac arrest patient is resource intensive and requires simultaneous evaluation for the underlying cause and intensive management to prevent further end organ damage, particularly of the central nervous system. The goal of the initial focused assessment is to rapidly determine if any reversible causes of cardiac arrest are present and to intervene when possible. Interventions performed in this acute period are aimed at preventing additional brain injury through optimizing hemodynamics, providing ventilatory support, and by using therapeutic hypothermia when indicated. After the initial phase of care, disposition is guided by available resources and the clinician's judgment. Transfer to a specialized cardiac arrest center is prudent in centers that do not have significant support or experience in the care of these patients.

Parameters Influencing Brain Oxygen Measurement by Regional Oxygen Saturation in Postcardiac Arrest Patients with Targeted Temperature Management

In several studies, regional cerebral oxygen saturation (rSO₂) has been measured in patients with postcardiac arrest syndrome (PCAS) to analyze the brain's metabolic status. However, the significance of rSO₂ in PCAS patients remains unclear. In the present study, we investigated the relationship between rSO₂ and physiological parameters. Comatose survivors of out-of-hospital PCAS with targeted temperature management (TTM) at 34°C for 24 hours were included. All patients were monitored for their rSO₂ and additional parameters (arterial oxygen saturation [SaO₂], hemoglobin [Hb], mean arterial pressure [MAP], arterial carbon dioxide pressure [PaCO₂], and body temperature]) measured at the start of monitoring and 24 and 48 hours after return of spontaneous circulation (ROSC). Patients were divided into favorable and unfavorable groups, and the correlation between rSO₂ and these physiological parameters was evaluated by multiple regression analysis. Forty-nine patients were included in the study, with 15 in the favorable group and 34 in the unfavorable group. There was no significant difference in the rSO₂ value between the two groups at any time point. The multiple regression analysis of the favorable group revealed a moderate correlation between rSO₂ and SaO₂, Hb, and PaCO₂ only at 24 hours (coefficients: 0.482, 0.422, and 0.531, respectively), whereas that of the unfavorable group revealed moderate correlations between rSO₂ and Hb values at all time points, PaCO₂ at 24 hours and MAP at 24 and 48 hours. rSO₂ was moderately correlated to MAP in unfavorable patients. To optimize brain oxygen metabolic balance for PCAS patients with TTM measuring rSO₂, we suggest total evaluation of each parameters of SaO₂, Hb, MAP, and PaCO₂.

Hemodynamic, Biochemical, and Ventilatory Parameters are Independently Associated with Outcome after Cardiac Arrest

BACKGROUND

Hypotension, hyperglycemia, dysoxia, and dyscarbia may contribute to reperfusion injury, and each is independently associated with poor outcome (PO) after cardiac arrest. We investigated whether the combined effects of these physiological derangements are associated with cardiac arrest outcomes.

METHODS

This institutional review board-approved retrospective cohort study included consecutive resuscitated cardiac arrest patients that received targeted temperature management at Maine Medical Center from 2013 to 2015. We abstracted demographics, intra-arrest factors, and physiological parameters. The primary outcome was dichotomized cerebral performance category (CPC 1-2 vs 3-5) at hospital discharge. After comparing demographics, clinical factors, and persistent post-arrest physiological derangements in patients with good and PO, we constructed a logistic regression model comprised of clinical and demographic factors separately associated with severity, and physiology variables, attempting to evaluate the independent effects of persistent physiological derangements on outcome.

RESULTS

Sixty-eight of 222 (31%) patients had CPC 1-2 (good outcome [GO]) at discharge. In bivariate analysis, factors associated with PO included increased time from collapse to resuscitation, non-shockable rhythm, and age-combined Charlson comorbidity index. In multivariate analysis, each persistent physiological derangement incrementally decreased the likelihood of GO [OR GO per derangement 0.71 (interquartile range [IQR] 0.51-0.99), p = 0.042, area under the curve (AUC) for final model 0.769].

CONCLUSIONS

Uncorrected physiological derangements in the first 24 h after cardiac arrest are independently associated with PO. Although causality cannot be established, these findings support preclinical models suggesting that aggressive normalization of physiology after resuscitation may be a reasonable strategy to decrease reperfusion injury.

Novel Quantitative Contrast-Enhanced Ultrasound Detection of Hypoxic Ischemic Injury in Neonates and Infants: Pilot Study 1

OBJECTIVES

To investigate whether quantitative contrast-enhanced ultrasound (CEUS) can accurately identify neonates and infants with hypoxic ischemic brain injury.

METHODS

In this prospective cohort study, 8 neonates and infants with a suspicion of hypoxic ischemic injury were evaluated with CEUS.

RESULTS

An interesting trend was observed in the central gray nuclei-to-cortex perfusion ratios. The ratios at the peak enhancement, wash-in area under the curve, perfusion index, and maximum wash-in slopes were lower in all of the affected cases compared to the normal group but not statistically significant given the small sample size (P = .0571). Additionally, when the central gray nuclei-to-cortex perfusion ratio was plotted for all time points along the time-intensity curve, it was observed that the affected cases showed a trend that was qualitatively different from that of the normal cases. In the affected cases, the ratio time-intensity curves either stayed below 1.0 for the entire enhancement period or reached 1.0 close to peak wash-in before falling just below 1.0 for the remaining period of enhancement. However, in the unaffected patients, there was a steep wash-in that crossed the 1.0 threshold and remained above 1.0 for most of the enhancement period.

CONCLUSIONS

Bedside CEUS is an easily obtainable brain-imaging modality that has the potential to effectively identify infants and neonates with evolving brain injury. A larger prospective study evaluating the correlation between CEUS findings and the reference standard of diffusion- and perfusion-weighted magnetic resonance imaging is needed to establish it as a diagnostic tool.

Near-infrared spectroscopy after out-of-hospital cardiac arrest

Background

Cerebral hypoperfusion may aggravate neurological damage after cardiac arrest. Near-infrared spectroscopy (NIRS) provides information on cerebral oxygenation but its relevance during post-resuscitation care is undefined. We investigated whether cerebral oxygen saturation (rSO₂) measured with NIRS correlates with the serum concentration of neuron-specific enolase (NSE), a marker of neurological injury, and with clinical outcome in out-of-hospital cardiac arrest (OHCA) patients.

Methods

We performed a post hoc analysis of a randomised clinical trial (COMACARE, NCT02698917) comparing two different levels of carbon dioxide, oxygen and arterial pressure after resuscitation from OHCA with ventricular fibrillation as the initial rhythm. We measured rSO₂ in 118 OHCA patients with NIRS during the first 36 h of intensive care. We determined the NSE concentrations from serum samples at 48 h after cardiac arrest and assessed neurological outcome with the Cerebral Performance Category (CPC) scale at 6 months. We evaluated the association between rSO₂ and serum NSE concentrations and the association between rSO₂ and good (CPC 1–2) and poor (CPC 3–5) neurological outcome.

Results

The median (inter-quartile range (IQR)) NSE concentration at 48 h was 17.5 (13.4–25.0) μg/l in patients with good neurological outcome and 35.2 (22.6–95.8) μg/l in those with poor outcome, p < 0.001. We found no significant correlation between median rSO₂ and NSE at 48 h, r_s = − 0.08, p = 0.392. The median (IQR) rSO₂ during the first 36 h of intensive care was 70.0% (63.5–77.0%) in patients with good outcome and 71.8% (63.3–74.0%) in patients with poor outcome, p = 0.943. There was no significant association between rSO₂ over time and neurological outcome. In a binary logistic regression model, rSO₂ was not a statistically significant predictor of good neurological outcome (odds ratio 0.99, 95% confidence interval 0.94–1.04, p = 0.635).

Conclusions

We found no association between cerebral oxygenation measured with NIRS and NSE concentrations or outcome in patients resuscitated from OHCA.

Trial registration

ClinicalTrials.gov, NCT02698917. Registered on 26 January 2016.

Electronic supplementary material

The online version of this article (10.1186/s13054-019-2428-3) contains supplementary material, which is available to authorized users.

Partial pressure of arterial carbon dioxide after resuscitation from cardiac arrest and neurological outcome: A prospective multi-center protocol-directed cohort study

AIMS

Partial pressure of arterial carbon dioxide (PaCO₂) is a regulator of cerebral blood flow after brain injury. We sought to test the association between PaCO₂ after resuscitation from cardiac arrest and neurological outcome.

METHODS

A prospective protocol-directed cohort study across six hospitals.

INCLUSION CRITERIA

age ≥18, non-traumatic cardiac arrest, mechanically ventilated after return of spontaneous circulation (ROSC), and receipt of targeted temperature management. Per protocol, PaCO₂ was measured by arterial blood gas analyses at one and six hours after ROSC. We determined the mean PaCO₂ over this initial six hours after ROSC. The primary outcome was good neurological function at hospital discharge, defined a priori as a modified Rankin Scale ≤3. Multivariable Poisson regression analysis was used to test the association between PaCO₂ and neurological outcome.

RESULTS

Of the 280 patients included, the median (interquartile range) PaCO₂ was 44 (37-52) mmHg and 30% had good neurological function. We found mean PaCO₂ had a quadratic (inverted "U" shaped) association with good neurological outcome, with a mean PaCO₂ of 68 mmHg having the highest predictive probability of good neurological outcome, and worse neurological outcome at higher and lower PaCO₂. Presence of metabolic acidosis attenuated the association between PaCO₂ and good neurological outcome, with a PaCO₂ of 51 mmHg having the highest predictive probability of good neurological outcome among patients with metabolic acidosis.

CONCLUSION

PaCO₂ has a "U" shaped association with neurological outcome, with mild to moderate hypercapnia having the highest probability of good neurological outcome.

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.

Targeting low- or high-normal Carbon dioxide, Oxygen, and Mean arterial pressure After Cardiac Arrest and REsuscitation: study protocol for a randomized pilot trial

Background

Arterial carbon dioxide tension (PaCO₂), oxygen tension (PaO₂), and mean arterial pressure (MAP) are modifiable factors that affect cerebral blood flow (CBF), cerebral oxygen delivery, and potentially the course of brain injury after cardiac arrest. No evidence regarding optimal treatment targets exists.

Methods

The Carbon dioxide, Oxygen, and Mean arterial pressure After Cardiac Arrest and REsuscitation (COMACARE) trial is a pilot multi-center randomized controlled trial (RCT) assessing the feasibility of targeting low- or high-normal PaCO₂, PaO₂, and MAP in comatose, mechanically ventilated patients after out-of-hospital cardiac arrest (OHCA), as well as its effect on brain injury markers. Using a 2³ factorial design, participants are randomized upon admission to an intensive care unit into one of eight groups with various combinations of PaCO₂, PaO₂, and MAP target levels for 36 h after admission.

The primary outcome is neuron-specific enolase (NSE) serum concentration at 48 h after cardiac arrest. The main feasibility outcome is the between-group differences in PaCO2, PaO2, and MAP during the 36 h after ICU admission. Secondary outcomes include serum concentrations of NSE, S100 protein, and cardiac troponin at 24, 48, and 72 h after cardiac arrest; cerebral oxygenation, measured with near-infrared spectroscopy (NIRS); potential differences in epileptic activity, monitored via continuous electroencephalogram (EEG); and neurological outcomes at six months after cardiac arrest.

Discussion

The trial began in March 2016 and participant recruitment has begun in all seven study sites as of March 2017. Currently, 115 of the total of 120 patients have been included. When completed, the results of this trial will provide preliminary clinical evidence regarding the feasibility of targeting low- or high-normal PaCO₂, PaO₂, and MAP values and its effect on developing brain injury, brain oxygenation, and epileptic seizures after cardiac arrest. The results of this trial will be used to evaluate whether a larger RCT on this subject is justified.

Trial registration

ClinicalTrials.gov, NCT02698917. Registered on 26 January 2016.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-2257-0) contains supplementary material, which is available to authorized users.

Critical Care Management Focused on Optimizing Brain Function After Cardiac Arrest

The discussion of neurocritical care management in post-cardiac arrest syndrome (PCAS) has generally focused on target values used for targeted temperature management (TTM). There has been less attention paid to target values for systemic and cerebral parameters to minimize secondary brain damage in PCAS. And the neurologic indications for TTM to produce a favorable neurologic outcome remain to be determined. Critical care management of PCAS patients is fundamental and essential for both cardiologists and general intensivists to improve neurologic outcome, because definitive therapy of PCAS includes both special management of the cause of cardiac arrest, such as coronary intervention to ischemic heart disease, and intensive management of the results of cardiac arrest, such as ventilation strategies to avoid brain ischemia. We reviewed the literature and the latest research about the following issues and propose practical care recommendations. Issues are (1) prediction of TTM candidate on admission, (2) cerebral blood flow and metabolism and target value of them, (3) seizure management using continuous electroencephalography, (4) target value of hemodynamic stabilization and its method, (5) management and analysis of respiration, (6) sedation and its monitoring, (7) shivering control and its monitoring, and (8) glucose management. We hope to establish standards of neurocritical care to optimize brain function and produce a favorable neurologic outcome.

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.

What is the value of regional cerebral saturation in post-cardiac arrest patients? A prospective observational study

Background

The aim of this study was to elucidate the possible role of cerebral saturation monitoring in the post-cardiac arrest setting.

Methods

Cerebral tissue saturation (SctO₂) was measured in 107 successfully resuscitated out-of-hospital cardiac arrest patients for 48 hours between 2011 and 2015. All patients were treated with targeted temperature management, 24 hours at 33 °C and rewarming at 0.3 °C per hour. A threshold analysis was performed as well as a linear mixed models analysis for continuous SctO₂ data to compare the relation between SctO₂ and favorable (cerebral performance category (CPC) 1–2) and unfavorable outcome (CPC 3–4–5) at 180 days post-cardiac arrest in OHCA patients.

Results

Of the 107 patients, 50 (47 %) had a favorable neurological outcome at 180 days post-cardiac arrest. Mean SctO₂ over 48 hours was 68 % ± 4 in patients with a favorable outcome compared to 66 % ± 5 for patients with an unfavorable outcome (p = 0.035). No reliable SctO₂ threshold was able to predict favorable neurological outcome. A significant different course of SctO₂ was observed, represented by a logarithmic and linear course of SctO₂ in patients with favorable outcome and unfavorable outcome, respectively (p < 0.001). During the rewarming phase, significant higher SctO₂ values were observed in patients with a favorable neurological outcome (p = 0.046).

Conclusions

This study represents the largest post-resuscitation cohort evaluated using NIRS technology, including a sizeable cohort of balloon-assisted patients. Although a significant difference was observed in the overall course of SctO₂ between OHCA patients with a favorable and unfavorable outcome, the margin was too small to likely represent functional outcome differentiation based on SctO₂ alone. As such, these results given such methodology as performed in this study suggest that NIRS is insufficient by itself to serve in outcome prognostication, but there may remain benefit when incorporated into a multi-neuromonitoring bedside assessment algorithm.

A systematic review and meta-analysis of the association between arterial carbon dioxide tension and outcomes after cardiac arrest

INTRODUCTION

Arterial carbon dioxide tension (PaCO₂) abnormalities are common after cardiac arrest (CA). Maintaining a normal PaCO₂ makes physiological sense and is recommended as a therapeutic target after CA, but few studies have examined the association between PaCO₂ and patient outcomes. This systematic review and meta-analysis aimed to assess the effect of a low or high PaCO₂ on patient outcomes after CA.

METHODS

We searched MEDLINE, EMBASE, CINAHL and Cochrane CENTRAL, for studies that evaluated the association between PaCO₂ and outcomes after CA. The primary outcome was hospital survival. Secondary outcomes included neurological status at the end of each study's follow up period, hospital discharge destination and 30-day survival. Meta-analysis was conducted if statistical heterogeneity was low.

RESULTS

The systematic review included nine studies; eight provided sufficient quantitative data for meta-analysis. Using PaCO₂ cut-points of <35mmHg and >45mmHg to define hypo- and hypercarbia, normocarbia was associated with increased hospital survival (odds ratio [OR] 1.30, 95% confidence interval [CI] 1.23, 1.38). Normocarbia was also associated with a good neurological outcome (cerebral performance category score 1 or 2) compared to hypercarbia (OR 1.69, 95% CI 1.13, 2.51) when the analysis also included an additional study with a slightly different definition for normocarbia (PaCO₂ 30-50mmHg).

CONCLUSIONS

From the limited data it appears PaCO₂ has an important U-shape association with survival and outcomes after CA, consistent with international resuscitation guidelines' recommendation that normocarbia be targeted during post-resuscitation care.

Emergency Neurological Life Support: Resuscitation Following Cardiac Arrest

Cardiac arrest is the most common cause of death in North America. Neurocritical care interventions, including targeted temperature management (TTM), have significantly improved neurological outcomes in patients successfully resuscitated from cardiac arrest. Therefore, resuscitation following cardiac arrest was chosen as an emergency neurological life support protocol. Patients remaining comatose following resuscitation from cardiac arrest should be considered for TTM. This protocol will review induction, maintenance, and re-warming phases of TTM, along with management of TTM side effects. Aggressive shivering suppression is necessary with this treatment to ensure the maintenance of a target temperature. Ancillary testing, including electrocardiography, computed tomography and/or magnetic resonance imaging of the brain, continuous electroencephalography monitoring, and correction of electrolyte, blood gas, and hematocrit changes, are also necessary to optimize outcomes.

Minimum oxygen flow needed for vital support during simulated post-cardiorespiratory arrest resuscitation

According to the ERC and the AHA guidelines, FiO2 should be titrated to achieve an O2Sat ≥ 94%. The aim of this study was to determine the minimum oxygen flow and time needed to reach an FiO2 of 0.32 and 0.80 during post-cardiac arrest care. An experimental analysis was performed that consisted of a simulated post-cardiac arrest situation. Different resuscitators were tested and connected to an artificial lung: Mark IV, SPUR II, Revivator Res-Q, O-TWO. The oxygen flow levels tested were 2, 5, 10 and 15 lpm. Bonferroni and Mann-Whitney U tests were used. An FiO2 of 0.32 or more was obtained using any of the oxygen flow and resuscitators. Only the Mark IV achieved an FiO2 of 0.80 after a minimum of 75s ventilating with 2 or 5 lpm. Clinical and statistical differences (P<.05) were found: at 15 lpm it took 35s to reach an FiO2 of 0.80 or more for Mark IV (85.6 [0.3]) and Revivator (84.3 [1.5]) compared to 50s for SPUR II (87.1 [6.4]); at 2 lpm, all of the devices reached an FiO2 of ≥ 0.32 at 30s(Mark IV (34.8 [1.3]), Revivator (35.7 [1.5]) and SPUR II (34.4 [2.1]), except for O-TWO, which took 35s (36.3 [4.3]). Patients could be ventilated with any of the resuscitators using 2 lpm to obtain an FiO2 of 0.32, although possibly O-TWO would be the last option during the first 60s. In order to reach an FiO2 of 0.80, ventilating with 10 lpm should be sufficient, and preferably using Mark IV or Revivator Res-Q. In conclusion, on observing the results of our study, in any possible scenario, it would be advisable to use Revivator Res-Q or Mark IV rather than O-TWO or SPUR II.

Influence of α-stat and pH-stat blood gas management strategies on cerebral blood flow and oxygenation in patients treated with therapeutic hypothermia after out-of-hospital cardiac arrest: a crossover study

OBJECTIVES

In patients treated with therapeutic hypothermia after out-of-hospital cardiac arrest, two blood gas management strategies are used regarding the PaCO2 target: α-stat or pH-stat. We aimed to compare the effects of these strategies on cerebral blood flow and oxygenation.

DESIGN

Prospective observational single-center crossover study.

SETTING

ICU of University hospital.

PATIENTS

Twenty-one therapeutic hypothermia-treated patients after out-of-hospital cardiac arrest more than 18 years old without history of cerebrovascular disease were included.

INTERVENTIONS

Cerebral perfusion and oxygenation variables were compared in α-stat (PaCO2 measured at 37 °C) versus pH-stat (PaCO2 measured at 32-34 °C), both strategies maintaining physiological PaCO2 values: 4.8-5.6 kPa (36-42 torr).

MEASUREMENTS AND MAIN RESULTS

Bilateral transcranial middle cerebral artery flow velocities using Doppler and jugular vein oxygen saturation were measured in both strategies 18 hours (14-23 hr) after the return of spontaneous circulation. Pulsatility and resistance indexes and cerebral oxygen extraction were calculated. Data are expressed as median (interquartile range 25-75) in α-stat versus pH-stat. No differences were found in temperature, arterial blood pressure, and oxygenation between α-stat and pH-stat. Significant differences were found in minute ventilation (p = 0.006), temperature-corrected PaCO2 (4.4 kPa [4.1-4.6 kPa] vs. 5.1 kPa [5.0-5.3 kPa], p = 0.0001), and temperature-uncorrected PaCO2 (p = 0.0001). No differences were found in cerebral blood velocities and pulsatility and resistance indexes in the overall population. Significant differences were found in jugular vein oxygen saturation (83.2% [79.2-87.6%] vs. 86.7% [83.2-88.2%], p = 0.009) and cerebral oxygen extraction (15% [11-20%] vs. 12% [10-16%], p = 0.01), respectively. In survivors, diastolic blood velocities were 25 cm/s (19-30 cm/s) versus 29 cm/s (23-35 cm/s) (p = 0.004), pulsatility index was 1.10 (0.97-1.18) versus 0.94 (0.89-1.05) (p = 0.027), jugular vein oxygen saturation was 79.2 (71.1-81.8) versus 83.3% (76.6-87.8) (p = 0.033), respectively. However, similar results were not found in nonsurvivors.

CONCLUSIONS

In therapeutic hypothermia-treated patients after out-of-hospital cardiac arrest at physiological PaCO2, α-stat strategy increases jugular vein blood desaturation and cerebral oxygen extraction compared with pH-stat strategy and decreases cerebral blood flow velocities in survivors.