The loss of hypoxic ventilatory responses following resuscitation after cardiac arrest in rats is associated with failure of long-term survival

Improving Outcomes After Post-Cardiac Arrest Brain Injury: A Scientific Statement From the International Liaison Committee on Resuscitation

This scientific statement presents a conceptual framework for the pathophysiology of post-cardiac arrest brain injury, explores reasons for previous failure to translate preclinical data to clinical practice, and outlines potential paths forward. Post-cardiac arrest brain injury is characterized by 4 distinct but overlapping phases: ischemic depolarization, reperfusion repolarization, dysregulation, and recovery and repair. Previous research has been challenging because of the limitations of laboratory models; heterogeneity in the patient populations enrolled; overoptimistic estimation of treatment effects leading to suboptimal sample sizes; timing and route of intervention delivery; limited or absent evidence that the intervention has engaged the mechanistic target; and heterogeneity in postresuscitation care, prognostication, and withdrawal of life-sustaining treatments. Future trials must tailor their interventions to the subset of patients most likely to benefit and deliver this intervention at the appropriate time, through the appropriate route, and at the appropriate dose. The complexity of post-cardiac arrest brain injury suggests that monotherapies are unlikely to be as successful as multimodal neuroprotective therapies. Biomarkers should be developed to identify patients with the targeted mechanism of injury, to quantify its severity, and to measure the response to therapy. Studies need to be adequately powered to detect effect sizes that are realistic and meaningful to patients, their families, and clinicians. Study designs should be optimized to accelerate the evaluation of the most promising interventions. Multidisciplinary and international collaboration will be essential to realize the goal of developing effective therapies for post-cardiac arrest brain injury.

Brainstem Damage Underlies Changes in Hypoxic Ventilatory Response Following Cardiac Arrest and Resuscitation in Rats

People resuscitated after sudden cardiac arrest remain at high risk for mortality, with treatment for survivors varying from monitoring to life support. With respect to assessing survivability post cardiac arrest and resuscitation (CAR), we previously demonstrated the potential of the hypoxic ventilatory response (HVR) as a reliable indicator for discerning between survivors and non-survivors in the early stages of recovery following CAR in rats. Since HVR describes the increase in ventilation in response to hypoxia, we hypothesize that damage to cardiorespiratory regulatory centers in the brainstem underlie the loss of HVR observed post resuscitation in nonsurvivors. Wistar rats underwent cardiac arrest (12-min) and resuscitation. At 1 day post-resuscitation, rats were perfused transcardially and the brains were harvested and processed for immunohistostaining of caspase-3, a marker of apoptosis. Positive caspase-3 staining was observed in brainstem regions such as the rostral ventral lateral medulla (RVLM); Co-localization of caspase-3 and NeuN was observed in the RVLM as well, suggesting that apoptosis most likely occurs in neurons. Our results showed positive markers for neuronal apoptosis present in pathways of the brainstem involved in respiratory and cerebrovascular regulation, suggesting brain stem damage underlies changes in HVR following CAR.

Post-resuscitation Arterial Blood Pressure on Survival and Change of Capillary Density Following Cardiac Arrest and Resuscitation in Rats

Transient global brain ischemia, induced by cardiac arrest and resuscitation, results in reperfusion injury leading to delayed selective neuronal cell loss and post-resuscitation mortality. This study determined the effects of post-resuscitation hypotension and hypothermia on long-term survival following cardiac arrest and resuscitation. The capillary density was also determined. Based on the mean arterial blood pressure (MABP) at 1 h of recovery, the normotension group (MABP 80-120 mmHg) and hypotension group (MABP <80 mmHg) were defined. The overall survival was determined at 4 days of recovery. Brain microvascular density was assessed using immunohistochemistry of the glucose transporter, GLUT-1. The pre-arrest MABP was similar in each group; at 1 h after resuscitation, the MABP in the normotension groups was about 80% of their pre-arrest values; the hypotension group had a significantly lower MABP compared to the normotension group. The overall survival rate was lower in the hypotension group compared to the normotension group (36%, 4/11 vs. 67%, 14/21) under the normothermic condition. Brain blood flow in the hypotension group was lower (33% decrease) compared to the normotension group at 1-h post-resuscitation. Compared to the pre-arrest baseline, the capillary density was significantly increased at 14 days of recovery (355 ± 42 vs. 469 ± 50, number/mm²) in the cortex. The capillary density in hippocampus was also increased at 4-30 days following cardiac arrest and resuscitation. Our results suggest that rats able to maintain their post-resuscitation blood pressure at normotension, had higher brain blood flow during the early recovery phase, and improved survival outcome following cardiac arrest and resuscitation. In addition, cardiac arrest and resuscitation induced angiogenesis in brain in the first month of recovery.

Protective Effect of Dl-3-n-Butylphthalide on Recovery from Cardiac Arrest and Resuscitation in Rats

In this study we investigated the effect of Dl-3-n-butylphthalide (NBP), a clinically used drug for stroke patients in China, on the recovery following cardiac arrest and resuscitation in rats. Male Wistar rats (3-month old) underwent cardiac arrest (12 min) and resuscitation. Rats were randomly assigned to the following groups: sham non-arrested group, vehicle group (vehicle-treated, 7 days before cardiac arrest and 4 days post-resuscitation), NBP pre-treated group (NBP-treated, 7 days before cardiac arrest), and NBP post-treated group (NBP-treated, 4 days post-resuscitation). Overall survival rates and hippocampal neuronal counts were determined in each group at 4 days post-resuscitation. Results showed that NBP pre-treated group (80 %) and NBP post-treated group (86 %) had significantly higher survival rates compared to that of the vehicle group (50 %). At 4 days of recovery, only about 20 % of hippocampal neurons were preserved in the vehicle group compared to the sham non-arrested group. The hippocampal CA1 cell counts in the NBP pre-treated group and NBP post-treated group were significantly higher than the counts in the vehicle group, about 50-60 % of the counts of non-arrested rats. The data suggest that NBP has both preventive and therapeutic effect on improving outcome following cardiac arrest and resuscitation, and NBP might be a potential early phase treatment for patients recovered from cardiac arrest and resuscitation.

Emulsified isoflurane combined with therapeutic hypothermia improves survival and neurological outcomes in a rat model of cardiac arrest

Emulsified isoflurane (EIso), when introduced following cardiopulmonary resuscitation (CPR), significantly improves survival and neurological outcomes in a rat model of cardiac arrest (CA). The present study aimed to examine whether EIso combined with therapeutic hypothermia (TH) confers an additive neuroprotective effect. Adult male Sprague-Dawley rats that were subjected to return of spontaneous circulation (ROSC) after a 6-min asphyxia-induced CA were randomized to five groups: Sham group, control group under normothermic conditions, EIso group (4 ml/kg for 30 min under normothermic conditions), TH group (33°C for 2 h), and EIso plus TH group. Survival conditions and neurological outcomes were evaluated at 1 day and 7 days after ROSC. Animal survival rate at 7 days after ROSC was 30.7% in the CPR group, 60% in the EIso group, 63.6% in the TH group and 72.7% in the EIso plus TH group. EIso, TH and EIso plus TH yielded significant improvements in survival rates, neural deficit score and cognitive function, and ameliorated hippocampal CA1 region cell injury and apoptosis at 1 day and 7 days after ROSC compared with the CPR group. Combined therapy of EIso and TH was superior to EIso or TH alone, suggesting that combined EIso and TH treatment results in significant improvements in survival and neurological outcomes, and was more effective than independent EIso or TH treatment.

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.

An improved simple rat model for global cerebral ischaemia by induced cardiac arrest

OBJECTIVES

Cerebral hypoxic-ischaemic injury following cardiac arrest is a devastating disease affecting thousands of patients each year. There is a complex interaction between post-resuscitation injury after whole-body ischaemia-reperfusion and cerebral damage which cannot be explored in in vitro systems only; there is a need for animal models. In this study, we describe and evaluate the feasibility and efficiency of our simple rodent cardiac arrest model. >

METHODS

Ten wistar rats were subjected to 9 and 10 minutes of cardiac arrest. Cardiac arrest was introduced with a mixture of the short-acting beta-blocking drug esmolol and potassium chloride.

RESULTS

All animals could be resuscitated within 1 minute, and survived until day 5. General health score and neurobehavioural testing indicated substantial impairment after cardiac arrest, without differences between groups. Histological examination of the hippocampus CA1 segment, the most vulnerable segment of the cerebrum, demonstrated extensive damage in the cresyl violet staining, as well as in the Fluoro-Jade B staining and in the Iba-1 staining, indicating recruitment of microglia after the hypoxic-ischaemic event. Again, there were no differences between the 9- and 10-minute cardiac arrest groups.

DISCUSSION

We were able to establish a simple and reproducible 9- and 10-minute rodent cardiac arrest model with a well-defined no-flow-time. Extensive damage can be found in the hippocampus CA1 segment. The lack of difference between 9- and 10-minute cardiac arrest time in the neuropsychological, the open field test and the histological evaluations is mainly due to the small sample size.

Decreased brainstem function following cardiac arrest and resuscitation in aged rat

There is a high incidence of cardiac arrest and poorer post-resuscitation outcome in the elderly population. Cardiac arrest and resuscitation results in ischemia/reperfusion injury associated with oxidative stress, leading to post-resuscitation mortality and delayed selective neuronal cell loss. In this study we investigated recovery following cardiac arrest and resuscitation in the aged rat brain. Male Fischer 344 rats (6, 12 and 24 months old) underwent 7 minute cardiac arrest before resuscitation. Overall survival and hippocampal neuronal counts were determined at 4 days of recovery. Brainstem function was assessed by hypoxic ventilatory response (HVR). Mitochondria of brainstem, cortex and hippocampus were isolated and assessed for respiratory function. Effect of an antioxidant, alpha-phenyl-tert-butyl-nitrone (PBN) was used as a treatment strategy against oxidative stress in the 6 and 24-month old rats. The time course of mitochondrial function was established using 3-month old Wistar rats with 12-minute cardiac arrest. In the 24-month old rats, overall survival rate, hippocampal CA1 neuronal counts, HVR, and brain mitochondrial respiratory control ratio were significantly reduced following cardiac arrest and resuscitation compared to the younger rats, and PBN treatment improved outcome. The data suggest that (i) there was increased susceptibility to ischemia/reperfusion in aged rat brain; (ii) HVR was decreased in the aged rats; (iii) brain mitochondrial respiratory function related to coupled oxidation was decreased following cardiac arrest and resuscitation in rats, more so in the aged; and (iv) treatment with an antioxidant, such as PBN, reduced the oxidative damage following cardiac arrest and resuscitation.