Cardiopulmonary resuscitation in the rat

Association of diastolic blood pressure with coronary perfusion pressure during resuscitation in pediatric swine

BACKGROUND

Diastolic blood pressure (DBP) is suggested as a surrogate for coronary perfusion pressure (CPP) during cardiopulmonary resuscitation. We examined the correlation between DBP and CPP and hypothesized that both would be associated with survival in a pediatric swine model of asphyxial cardiac arrest.

METHODS

We performed a retrospective, secondary analysis of 102 pediatric swine resuscitations. DBP and CPP were recorded every 30 s during resuscitation. Values were compared between survivors and non-survivors.

RESULTS

DBP mirrored CPP in survivors and non-survivors throughout resuscitation and both were associated with survival. Improvements in DBP and CPP after the first epinephrine administration were greater in survivors (DBP: 25.1 ± 3.0 vs. 5.4 ± 0.8 mmHg, p < 0.01; CPP: 24.9 ± 3.2 vs. 4.8 ± 0.9 mmHg, p < 0.01). DBP and CPP after epinephrine administration were highly predictive of survival, with an area under the curve of 0.95 (0.89-1.00) for DBP and 0.90 (0.81-0.99) for CPP. The optimal threshold for DBP was 22.5 mmHg, whereas that for CPP was 14.5 mmHg.

CONCLUSIONS

DBP and CPP were associated with survival throughout resuscitation, and the response of both to the first epinephrine administration was highly predictive of survival in this model. Clinically, the availability of DBP makes it useful as a target for physiologic feedback during resuscitation.

IMPACT

Diastolic blood pressure (DBP) mirrored coronary perfusion pressure (CPP) throughout prolonged resuscitation in a pediatric model of asphyxial cardiac arrest. Mean DBP and CPP were significantly greater in survivors than in non-survivors both before and after administration of epinephrine. The response of both DBP and CPP to the first dose of epinephrine was highly predictive of return of spontaneous circulation. Given the clinical availability of DBP, these findings support its use as a surrogate for CPP to guide high-quality cardiopulmonary resuscitation in this pediatric swine model.

Post-cardiac arrest temporal evolution of left ventricular function in a rat model: speckle-tracking echocardiography and cardiac circulating biomarkers

Aims

There is little information from experimental studies regarding the evolution of post-resuscitation cardiac arrest [post-return of spontaneous circulation (post-ROSC)] myocardial dysfunction during mid-term follow-up. For this purpose, we assessed left ventricular (LV) function and circulating cardiac biomarkers at different time points in a rat model of cardiac arrest (CA).

Methods and results

Rats were divided into two groups: control and post-ROSC rats. Eight minutes of untreated ventricular fibrillation were followed by 8 min of cardiopulmonary resuscitation. Conventional and speckle-tracking echocardiographic (STE) parameters and cardiac circulating biomarkers concentrations were assessed, at 3, 4, 72, and 96 h post-ROSC. At 3 and 4 h post-ROSC, LV systolic function was severely impaired, and high-sensitivity cardiac troponin T and N-terminal pro-atrial natriuretic peptide (NT-proANP) plasma concentrations were significantly increased, compared with control rats (P < 0.0001 for all). At 72 and 96 h post-ROSC, LV ejection fraction (LVEF) normalized. At 96 h, the following variables were significantly different from control rats: early trans-mitral peak velocity, 56.8 ± 3.1 vs. 87.8 ± 3.8 cm/s, P < 0.0001; late trans-mitral peak velocity, 50.6 ± 4.7 vs. 73.7 ± 4.2 cm/s, P < 0.0001; mean s' wave velocity, 4.6 ± 0.3 vs. 5.9 ± 0.3 cm/s, P < 0.0001, global longitudinal strain (GLS) -7.5 ± 0.5 and vs. -11 ± 1.2%, P < 0.01; GLS rate (GLSR) -0.9 ± 0.4 and -2.3 ± 0.2 1/s, P < 0.01; and NT-proANP concentration, 2.5 (0.2; 6.0) vs. 0.4 (0.01; 1.0) nmol/L, P < 0.01.

Conclusion

s' velocity, GLS, and GLSR indicated that LV systolic function was still impaired 96 h post-ROSC. These findings agree with NT-proANP concentrations, which continue to be high. Normalization of LVEF supports the use of STE for its greater sensitivity for monitoring post-CA cardiac function. Further investigations are needed to provide evidence of the post-ROSC LV diastolic function pattern.

Effects of OP2113 on Myocardial Infarct Size and No Reflow in a Rat Myocardial Ischemia/Reperfusion Model

PURPOSE

The present study was to determine whether OP2113 could limit myocardial infarction size and the no-reflow phenomenon in a rat myocardial ischemia/reperfusion model.

METHODS

Rat heart-isolated mitochondria (RHM) were used to investigate mitochondrial respiration and mitochondrial reactive oxygen species (mtROS) generation both in normal conditions and in ischemia/reperfusion-mimicking conditions (using high concentrations of succinate). Human skeletal muscle myoblasts (HSMM) in culture were used to investigate the cellular intermittent deprivation in energy substrates and oxygen as reported in ischemia/reperfusion conditions. In vivo, rats were anesthetized and subjected to 30 min of left coronary artery occlusion followed by 3 h of reperfusion. Rats were randomized to receive OP2113 as an intravenous infusion starting either 5 min prior to coronary artery occlusion (preventive), or 5 min prior to reperfusion (curative), or to receive vehicle starting 5 min prior to coronary artery occlusion. Infusions continued until the end of the study (3 h of reperfusion).

RESULTS

RHM treated with OP2113 showed a concentration-dependent reduction of succinate-induced mtROS generation. In HSMM cells, OP2113 treatment (5-10 μM) during 48H prevented the reduction in the steady-state level of ATP measured just after reperfusion injuries and decreased the mitochondrial affinity to oxygen. In vivo, myocardial infarct size, expressed as the percentage of the ischemic risk zone, was significantly lower in the OP2113-treated preventive group (44.5 ± 2.9%) versus that in the vehicle group (57.0 ± 3.6%; p < 0.05), with a non-significant trend toward a smaller infarct size in the curative group (50.8 ± 3.9%). The area of no reflow as a percentage of the risk zone was significantly smaller in both the OP2113-treated preventive (28.8 ± 2.4%; p = 0.026 vs vehicle) and curative groups (30.1 ± 2.3%; p = 0.04 vs vehicle) compared with the vehicle group (38.9 ± 3.1%). OP2113 was not associated with any hemodynamic changes.

CONCLUSIONS

These results suggest that OP2113 is a promising mitochondrial ROS-modulating agent to reduce no-reflow as well as to reduce myocardial infarct size, especially if it is on board early in the course of the infarction. It appears to have benefit on no-reflow even when administered relatively late in the course of ischemia.

Brain Kynurenine Pathway and Functional Outcome of Rats Resuscitated From Cardiac Arrest

Background Brain injury and neurological deficit are consequences of cardiac arrest (CA), leading to high morbidity and mortality. Peripheral activation of the kynurenine pathway (KP), the main catabolic route of tryptophan metabolized at first into kynurenine, predicts poor neurological outcome in patients resuscitated after out-of-hospital CA. Here, we investigated KP activation in hippocampus and plasma of rats resuscitated from CA, evaluating the effect of KP modulation in preventing CA-induced neurological deficit. Methods and Results Early KP activation was first demonstrated in 28 rats subjected to electrically induced CA followed by cardiopulmonary resuscitation. Hippocampal levels of the neuroactive metabolites kynurenine, 3-hydroxy-anthranilic acid, and kynurenic acid were higher 2 hours after CA, as in plasma. Further, 36 rats were randomized to receive the inhibitor of the first step of KP, 1-methyl-DL-tryptophan, or vehicle, before CA. No differences were observed in hemodynamics and myocardial function. The CA-induced KP activation, sustained up to 96 hours in hippocampus (and plasma) of vehicle-treated rats, was counteracted by the inhibitor as indicated by lower hippocampal (and plasmatic) kynurenine/tryptophan ratio and kynurenine levels. 1-Methyl-DL-tryptophan reduced the CA-induced neurological deficits, with a significant correlation between the neurological score and the individual kynurenine levels, as well as the kynurenine/tryptophan ratio, in plasma and hippocampus. Conclusions These data demonstrate the CA-induced lasting activation of the first step of the KP in hippocampus, showing that this activation was involved in the evolving neurological deficit. The degree of peripheral activation of KP may predict neurological function after CA.

Establishing a Rodent Model of Ventricular Fibrillation Cardiac Arrest With Graded Histologic and Neurologic Damage With Different Cardiac Arrest Durations

Purpose:

The aim of the study was to establish a ventricular fibrillation (VF) cardiac arrest (CA) resuscitation model with consistent neurologic and neuropathologic damage as potential therapeutic target.

Methods:

Prospectively randomized groups of experiments in two phases. In phase 1 four groups of male Sprague–Dawley rats (n = 5) were resuscitated after 6 min VFCA with 2 and 6 min basic life support durations (BLS) with and without adrenaline. In phase 2 the most promising group regarding return of spontaneous circulation (ROSC) and survival was compared with a group of 8 min CA. Resuscitability, neurologic deficit scores (NDS), and overall performance category (OPC) were assessed daily; histolopathology of the hippocampal CA1 region [hematoxylin and eosin- (viable neurons), Fluoro-Jade- (dying neurons), and Iba-1 immunostaining (microglial activation–semiquantitative)] on day 14.

Results:

Two minutes BLS and with adrenaline as most promising group of phase 1 compared with an 8 min group in phase 2 exhibited ROSC in 8 (80%) vs. 9 (82%) animals and survivors till day 14 in 7 (88%) (all OPC 1, NDS 0 ± 0) vs. 6 (67%) (5 OPC 1, 1 OPC 2, NDS 0.83 ± 2.4) animals. OPC and NDS were only significantly different at day 1 (OPC: P = 0.035; NDS: P = 0.003). Histopathologic results between groups were not significantly different; however, a smaller variance of extent of lesions was found in the 8 min group. Both CA durations caused graded neurologic, overall, such as histopathologic damage.

Conclusions:

This dynamic global ischemia model offers the possibility to evaluate further cognitive and novel neuroprotective therapy testing after CA.

Heart defibrillation: relationship between pacing threshold and defibrillation probability

BACKGROUND

Considering the clinical importance of the ventricular fibrillation and that the most used therapy to reverse it has a critical side effect on the cardiac tissue, it is desirable to optimize defibrillation parameters to increase its efficiency. In this study, we investigated the influence of stimuli duration on the relationship between pacing threshold and defibrillation probability.

RESULTS

We found out that 0.5-ms-long pulses had a lower ratio of defibrillation probability to the pacing threshold, although the higher the pulse duration the lower is the electric field intensity required to defibrillate the hearts.

CONCLUSION

The appropriate choice of defibrillatory shock parameters is able to increase the efficiency of the defibrillation improving the survival chances after the occurrence of a severe arrhythmia. The relationship between pulse duration and the probability of reversal of fibrillation shows that this parameter cannot be underestimated in defibrillator design since different pulse durations have different levels of safety.

Sodium-Hydrogen Exchanger Isoform-1 Inhibition: A Promising Pharmacological Intervention for Resuscitation from Cardiac Arrest

Out-of-hospital sudden cardiac arrest is a major public health problem with an overall survival of less than 5%. Upon cardiac arrest, cessation of coronary blood flow rapidly leads to intense myocardial ischemia and activation of the sarcolemmal Na⁺-H⁺ exchanger isoform-1 (NHE-1). NHE-1 activation drives Na⁺ into cardiomyocytes in exchange for H⁺ with its exchange rate intensified upon reperfusion during the resuscitation effort. Na⁺ accumulates in the cytosol driving Ca²⁺ entry through the Na⁺-Ca²⁺ exchanger, eventually causing cytosolic and mitochondrial Ca²⁺ overload and worsening myocardial injury by compromising mitochondrial bioenergetic function. We have reported clinically relevant myocardial effects elicited by NHE-1 inhibitors given during resuscitation in animal models of ventricular fibrillation (VF). These effects include: (a) preservation of left ventricular distensibility enabling hemodynamically more effective chest compressions, (b) return of cardiac activity with greater electrical stability reducing post-resuscitation episodes of VF, (c) less post-resuscitation myocardial dysfunction, and (d) attenuation of adverse myocardial effects of epinephrine; all contributing to improved survival in animal models. Mechanistically, NHE-1 inhibition reduces adverse effects stemming from Na⁺–driven cytosolic and mitochondrial Ca²⁺ overload. We believe the preclinical work herein discussed provides a persuasive rationale for examining the potential role of NHE-1 inhibitors for cardiac resuscitation in humans.

Carotid artery and cerebral blood flow during experimental cardiopulmonary resuscitation: A systematic review of the literature

BACKGROUND

The carotid artery blood flow (CABF) or cerebral blood flow (CBF) achieved with current techniques of cardiac compression in humans are unknown. Animal experiments may provide useful information on such flows and on possible techniques to optimize them.

OBJECTIVES

To obtain an estimate of carotid and cerebral blood flows during cardiac compression with different techniques.

METHODS

We performed a systematic review of all studies in the English literature that measured the CABF and/or CBF during cardiac compression in experimental models of cardiac arrest, expressed as a percentage of baseline (pre-arrest) values. We compared the effect of vasopressor use, thoracic compression technique, pre-arrest infusion and animal model on maximum blood flows using standard statistical methodologies.

RESULTS

Overall, 133 studies were reviewed. Of these, 45 studies provided information only on CABF; 77 only on CBF, and 11 studies on both flows. The overall weighted mean (±SD) CABF was 35.2 ± 27.7% of baseline. Porcine studies showed lower CABF when vasopressors were used (p = 0.0002). Studies of CBF reported a weighted mean value of 66.5 ± 48.5% of baseline. Adjunctive vasopressor therapy significantly increased CBF (p = 0.007), as did fluid administration (P = 0.049). In studies reporting both CABF and CBF, the median CABF/CBF ratio was 0.67 (range 0.21-1.96).

CONCLUSIONS

During experimental cardiac compression, compared to baseline, CABF appears to decrease much more than CBF. However results should be regarded with caution. They are affected by ancillary interventions and measurement methods, variability is marked and, in experiments measuring CABF and CBF simultaneously, their ratios range well outside physiologically plausible values.

Neuroprotection with the P53-Inhibitor Pifithrin-μ after Cardiac Arrest in a Rodent Model

BACKGROUND

The small molecule pifithrin-μ reversibility inhibits the mitochondrial pathway of apoptosis. The neuronal effects of pifithrin-μ applied after cardiac arrest are unknown. We hypothesized that pifithrin-μ reduces neuronal damage in the most vulnerable brain region, the hippocampus, after cardiac arrest.

METHODS

In two randomized controlled series we administered pifithrin-μ or control in 109 rats resuscitated after 8 or 10 min of cardiac arrest. Neuronal damage was blindly assessed with histology (Fluoro Jade B: FJB, cresyl violet: CV) in the most vulnerable brain region (CA1 segment of hippocampus) and with a series of neurobehavioral tests (Open Field Task, Tape-Removal Test, Morris Water Maze test). Mixed ANOVA was used to combine both series, simple comparisons were done with t tests or Mann-Whitney U test.

RESULTS

Pifithrin-μ reduced the number of degenerating, FJB-positive neurons by 25% (mixed ANOVA p group = 0.014). This was more prominent after 8 min cardiac arrest (8 min arrest pifithrin-μ 94 ± 47 vs control 128 ± 37; n = 11 each; 10 min arrest pifithrin-μ 78 ± 44, n = 15 vs control 101 ± 31, n = 18; p group* arrest length interaction = 0.622). The reduction of ischemic CV-positive neurons in pifithrin-μ animals was not significant (ANOVA p group = 0.063). No significant group differences were found in neurobehavioral testing.

CONCLUSION

Temporarily inhibition of apoptosis with pifithrin-μ after cardiac arrest decreases the number of injured neurons in the CA1 segment of hippocampus in a cardiac arrest rat model, without clinical correlate. Further studies should elucidate the role of this neuroprotective agent in different settings and with longer cardiac arrest.

Diabetic aggravation of stroke and animal models

Cerebral ischemia in diabetics results in severe brain damage. Different animal models of cerebral ischemia have been used to study the aggravation of ischemic brain damage in the diabetic condition. Since different disease conditions such as diabetes differently affect outcome following cerebral ischemia, the Stroke Therapy Academic Industry Roundtable (STAIR) guidelines recommends use of diseased animals for evaluating neuroprotective therapies targeted to reduce cerebral ischemic damage. The goal of this review is to discuss the technicalities and pros/cons of various animal models of cerebral ischemia currently being employed to study diabetes-related ischemic brain damage. The rational use of such animal systems in studying the disease condition may better help evaluate novel therapeutic approaches for diabetes related exacerbation of ischemic brain damage.

Carvedilol Mitigates Adverse Effects of Epinephrine During Cardiopulmonary Resuscitation

Introduction: Earlier studies have implicated the adverse effects of β- and α1-adrenergic receptors during cardiopulmonary resuscitation (CPR). Because carvedilol is both a nonselective β- and α1-selective adrenergic receptor-blocking agent, we hypothesized that pre-treatment with carvedilol would convert the actions of epinephrine to that of a selective a2-agonist.

Methods: Ventricular fibrillation (VF) was induced in Sprague-Dawley rats weighing approximately 500 g. Animals were randomized to 4 groups of 5 animals each: (1) placebo pretreatment and epinephrine treatment, (2) carvedilol pretreatment and placebo treatment, (3) carvedilol pretreatment and epinephrine treatment, and (4) placebo pretreatment and placebo treatment. Carvedilol (50 µg/kg) was injected as a bolus into the right atrium 15 minutes before VF was induced. VF was untreated for 8 minutes, after which CPR (chest compression and mechanical ventilation) was begun. Epinephrine (30 µg/kg) was injected into the right atrium 2 minutes after the start of CPR. Electrical defibrillation was attempted after 14 minutes of VF.

Results: All but 2 animals were successfully resuscitated. Approximately equivalent increases in coronary perfusion pressure from 23 ± 1 mm Hg to 30 ± 3 mm Hg were observed after the injection of epinephrine independently of carvedilol pretreatment. Carvedilol pretreatment followed by epinephrine treatment reduced early postresuscitation ventricular ectopy (116 ± 147 vs 834 ± 380, P < .01) and minimized increases in arterial blood lactate at 5 minutes after resuscitation (10.9 ± 2.1 mmol/L vs 17.4 ± 3.5 mmol/L, P < .01). The postresuscitation cardiac index measured 4 hours later was increased (307 ± 43 mL • min-1• kg-1 vs 210 ±6 mL • min-1• kg-1, P <.05). Left ventricular diastolic pressures were decreased (6 ± 1 vs 14 ± 1 mm Hg, P < .05). Animals pretreated with carvedilol survived longer (71 ± 1 vs 45 ± 22 hours, P < .05) and with less postresuscitation neurologic deficit.

Conclusion: After β- and α1-adrenergic blockade with carvedilol before inducing cardiac arrest, epinephrine administered during CPR yielded better postresuscitation myocardial and neurologic functions and significantly increased postresuscitation survival.

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.

PD98059 Protects Brain against Cells Death Resulting from ROS/ERK Activation in a Cardiac Arrest Rat Model

The clinical and experimental postcardiac arrest treatment has not reached therapeutic success. The present study investigated the effect of PD98059 (PD) in rats subjected to cardiac arrest (CA)/cardiopulmonary resuscitation (CPR). Experimental rats were divided randomly into 3 groups: sham, CA, and PD. The rats except for sham group were subjected to CA for 5 min followed by CPR operation. Once spontaneous circulation was restored, saline and PD were injected in CA and PD groups, respectively. The survival rates and neurologic deficit scores (NDS) were observed, and the following indices of brain tissue were evaluated: ROS, MDA, SOD, p-ERK1/2/ERK1/2, caspase-3, Bax, Bcl-2, TUNEL positive cells, and double fluorescent staining of p-ERK/TUNEL. Our results indicated that PD treatment significantly reduced apoptotic neurons and improved the survival rates and NDS. Moreover, PD markedly downregulated the ROS, MDA, p-ERK, and caspase-3, Bax and upregulated SOD and Bcl-2 levels. Double staining p-ERK/TUNEL in choroid plexus and cortex showed that cell death is dependent on ERK activation. The findings in present study demonstrated that PD provides neuroprotection via antioxidant activity and antiapoptosis in rats subjected to CA/CPR.

A Rat Model of Ventricular Fibrillation and Resuscitation by Conventional Closed-chest Technique

A rat model of electrically-induced ventricular fibrillation followed by cardiac resuscitation using a closed chest technique that incorporates the basic components of cardiopulmonary resuscitation in humans is herein described. The model was developed in 1988 and has been used in approximately 70 peer-reviewed publications examining a myriad of resuscitation aspects including its physiology and pathophysiology, determinants of resuscitability, pharmacologic interventions, and even the effects of cell therapies. The model featured in this presentation includes: (1) vascular catheterization to measure aortic and right atrial pressures, to measure cardiac output by thermodilution, and to electrically induce ventricular fibrillation; and (2) tracheal intubation for positive pressure ventilation with oxygen enriched gas and assessment of the end-tidal CO2. A typical sequence of intervention entails: (1) electrical induction of ventricular fibrillation, (2) chest compression using a mechanical piston device concomitantly with positive pressure ventilation delivering oxygen-enriched gas, (3) electrical shocks to terminate ventricular fibrillation and reestablish cardiac activity, (4) assessment of post-resuscitation hemodynamic and metabolic function, and (5) assessment of survival and recovery of organ function. A robust inventory of measurements is available that includes - but is not limited to - hemodynamic, metabolic, and tissue measurements. The model has been highly effective in developing new resuscitation concepts and examining novel therapeutic interventions before their testing in larger and translationally more relevant animal models of cardiac arrest and resuscitation.

Do different anesthesia regimes affect hippocampal apoptosis and neurologic deficits in a rodent cardiac arrest model?

Background

Different anesthesia regimes are commonly used in experimental models of cardiac arrest, but the effects of various anesthetics on clinical outcome parameters are unknown. We conducted a study in which we subjected rats to cardiac arrest under medetomidine/ketamine or sevoflurane/fentanyl anesthesia.

Methods

Asystolic cardiac arrest for 8 minutes was induced in 73 rats with a mixture of potassium chloride and esmolol. Daily behavioral and neurological examination included the open field test (OFT), the tape removal test (TRT) and a neurodeficit score (NDS). Animals were randomized for sacrifice on day 2 or day 5 and brains were harvested for histology in the hippocampus cornus ammonis segment CA1. The inflammatory markers IL-6, TNF-α, MCP-1 and MIP-1α were assessed in cerebrospinal fluid (CSF). Proportions of survival were tested with the Fisher’s exact test, repeated measurements were assessed with the Friedman’s test; the baseline values were tested using Mann–Whitney U test and the difference of results of repeated measures were compared.

Results

In 31 animals that survived beyond 24 hours neither OFT, TRT nor NDS differed between the groups; histology was similar on day 2. On day 5, significantly more apoptosis in the CA1 segment of the hippocampus was found in the sevoflurane/fentanyl group. MCP-1 was higher on day 5 in the sevoflurane/fentanyl group (p = 0.04). All other cyto- and chemokines were below detection threshold.

Conclusion

In our cardiac arrest model neurological function was not influenced by different anesthetic regimes; in contrast, anesthesia with sevoflurane/fentanyl results in increased CSF inflammation and histologic damage at day 5 post cardiac arrest.

Ventricular fibrillation-induced cardiac arrest in the rat as a model of global cerebral ischemia

Cardiopulmonary arrest remains one of the leading causes of death and disability in Western countries. Although ventricular fibrillation (VF) models in rodents mimic the "square wave" type of insult (rapid loss of pulse and pressure) commonly observed in adult humans at the onset of cardiac arrest (CA), they are not popular because of the complicated animal procedure, poor animal survival and thermal injury. Here we present a modified, simple, reliable, ventricular fibrillation-induced rat model of CA that will be useful in studying mechanisms of CA-induced delayed neuronal death as well as the efficacy of neuroprotective drugs. CA was induced in male Sprague Dawley rats using a modified method of von Planta et al. In brief, VF was induced in anesthetized, paralyzed, mechanically ventilated rats by an alternating current delivered to the entrance of the superior vena cava into the heart. Resuscitation was initiated by administering a bolus injection of epinephrine and sodium bicarbonate followed by mechanical ventilation and manual chest compressions and countershock with a 10-J DC current. Neurologic deficit score was higher in the CA group compared to the sham group during early reperfusion periods, suggesting brain damage. Significant damage in CA1 hippocampus (21% normal neurons compared to control animals) was observed following histopathological assessment at seven days of reperfusion. We propose that this method of VF-induced CA in rat provides a tool to study the mechanism of CA-induced neuronal death without compromising heart functions.

Differences of postresuscitation myocardial dysfunction in ventricular fibrillation versus asphyxiation

PURPOSE

This study aims to characterize postresuscitation myocardial dysfunction in 2 porcine models of cardiac arrest (CA): ventricular fibrillation cardiac arrest (VFCA) and asphyxiation cardiac arrest (ACA).

METHODS

Thirty-two pigs were randomized into 2 groups. The VFCA group (n = 16) were subject to programed electrical stimulation, and the ACA group (n = 16) underwent endotracheal tube clamping to induce CA. Once induced, CA remained untreated for 8 minutes. Two minutes after initiation of cardiopulmonary resuscitation (CPR), defibrillation was attempted until return of spontaneous circulation (ROSC) was achieved or animals died.

RESULTS

Return of spontaneous circulation was 100% successful in VFCA and 50% successful in ACA. Cardiopulmonary resuscitation duration in VFCA was about half as short as in ACA. The survival time of VFCA was significantly longer than that of ACA. Ventricular fibrillation cardiac arrest had better mean arterial pressure, cardiac output, and left ventricular ± dp/dt(max) after ROSC than ACA. Echocardiography revealed significantly lower left ventricular ejection fraction in ACA than in VFCA. Myocardial perfusion imaging using single-photon emission computed tomography demonstrated that myocardial injuries after ACA were more severe and widespread than after VFCA. Under a transmission electron microscope, the overall heart morphologic structure and the mitochondrial crista structure were less severely injured in the VFCA group than in the ACA group. Moreover, the percentage of apoptotic cardiomyocytes was higher in ACA than in VFCA.

CONCLUSIONS

Compared with VFCA, ACA causes more severe cardiac dysfunction associated with less successful resuscitation and shorter survival time.

Advances in recognition, resuscitation, and stabilization of the critically ill child

Advances in early recognition, effective response, and high-quality resuscitation before, during, and after cardiac arrest have resulted in improved survival for infants and children over the past 10 years. This review addresses several key factors that can make a difference in survival outcomes, including the etiology of pediatric cardiac arrests in and out of hospital, mechanisms and techniques of circulation of blood flow during cardiopulmonary resuscitation (CPR), quality of CPR, meticulous postresuscitative care, and effective training. Monitoring and quality improvement of each element in the system of resuscitation care are increasingly recognized as key factors in saving lives.

The neuroprotective effects of intraperitoneal injection of hydrogen in rabbits with cardiac arrest

OBJECTIVE

The purpose of this study was to investigate the neuroprotective effects of intraperitoneal injection of hydrogen (H2) in rabbits with cardiac arrest (CA).

METHODS

A rabbit model of CA was established by the delivery of alternating current between the esophagus and chest wall to induce ventricular fibrillation. Before CA, the animals were randomly divided into four groups: a sham group (no CA), a CA group, a CA + low dose (10 ml/kg) H2 group (CA + H2 group 1), and a CA + high dose (20 ml/kg) H2 group (CA + H2 group 2). In the first experiment, animals were observed for 72 h after the restoration of spontaneous circulation (ROSC). The neurological scores were assessed at 24, 48 and 72 h after ROSC. The rabbits that survived until 72 h were sacrificed using an overdose of anesthetic, and the brain tissues were collected and Nissl-stained to observe nerve cell damage in the hippocampal CA1 area. In addition, TUNEL assay was performed to detect apoptosis. In the second experiment, animals were observed for 6h after ROSC. Blood samples and brain hippocampal tissues were collected, and differences in oxidative stress indicators were compared among the four groups.

RESULTS

Intraperitoneal injection of H2 improved the 72-h survival rate and neurological scores, reduced neuronal injury and inhibited neuronal apoptosis. Intraperitoneal injection of H2 reduced oxidative stress indicators in the plasma and hippocampal tissues and enhanced antioxidant enzyme activity. No significant difference was observed between the two CA groups treated with different doses of H2.

CONCLUSIONS

Intraperitoneal injection of H2 is a novel hydrogen administration method and can reduce cerebral ischemia-reperfusion injury and improve the prognosis of cardiopulmonary cerebral resuscitation in a rabbit model of CA.

H(2) gas improves functional outcome after cardiac arrest to an extent comparable to therapeutic hypothermia in a rat model

Background

All clinical and biological manifestations related to postcardiac arrest (CA) syndrome are attributed to ischemia–reperfusion injury in various organs including brain and heart. Molecular hydrogen (H₂) has potential as a novel antioxidant. This study tested the hypothesis that inhalation of H₂ gas starting at the beginning of cardiopulmonary resuscitation (CPR) could improve the outcome of CA.

Methods and Results

Ventricular fibrillation was induced by transcutaneous electrical epicardial stimulation in rats. After 5 minutes of the subsequent CA, rats were randomly assigned to 1 of 4 experimental groups at the beginning of CPR: mechanical ventilation (MV) with 2% N₂ and 98% O₂ under normothermia (37°C), the control group; MV with 2% H₂ and 98% O₂ under normothermia; MV with 2% N₂ and 98% O₂ under therapeutic hypothermia (TH), 33°C; and MV with 2% H₂ and 98% O₂ under TH. Mixed gas inhalation and TH continued until 2 hours after the return of spontaneous circulation (ROSC). H₂ gas inhalation yielded better improvement in survival and neurological deficit score (NDS) after ROSC to an extent comparable to TH. H₂ gas inhalation, but not TH, prevented a rise in left ventricular end-diastolic pressure and increase in serum IL-6 level after ROSC. The salutary impact of H₂ gas was at least partially attributed to the radical-scavenging effects of H₂ gas, because both 8-OHdG- and 4-HNE-positive cardiomyocytes were markedly suppressed by H₂ gas inhalation after ROSC.

Conclusions

Inhalation of H₂ gas is a favorable strategy to mitigate mortality and functional outcome of post-CA syndrome in a rat model, either alone or in combination with TH.

Effect of cardiopulmonary resuscitation on restoration of myocardial ATP in prolonged ventricular fibrillation

BACKGROUND

There has been controversy over whether a short period of cardiopulmonary resuscitation (CPR) prior to defibrillation improves survival in patients who experienced a sudden cardiac arrest. However, there have been no reports about whether CPR restores the myocardial energy source during prolonged ventricular fibrillation (VF). The aim of this study is to investigate the effect of CPR in restoring myocardial high energy phosphates during prolonged VF.

METHODS AND RESULTS

Seventy-two adult male Sprague-Dawley rats were used in this study. Baseline adenosine triphosphate (ATP) and adenosine diphosphate (ADP) prior to induction of VF were measured in nine rats, the No-VF group. Sixty-three rats were subjected to 4 min of untreated VF. Animals were then randomized into two groups: No-CPR (n=37) and CPR (n=26). In the No-CPR group, ATPs and ADPs were measured at 4 min (No-CPR4), 6 min (No-CPR6), 8 min (No-CPR8) or 10 min (No-CPR10) after the induction of VF. The CPR group received 2 min (CPR2), 4 min (CPR4) or 6 min (CPR6) of mechanical chest compressions before ATP was measured. Myocardial ATP (nmol/mg protein) was decreased as VF duration was prolonged (No-VF: 5.49±1.71, No-CPR4: 4.27±1.58, No-CPR6: 4.13±1.31, No-CPR8: 3.77±1.42, No-CPR10: 3.52±0.90, p<0.05 between each of No-CPRs vs. No-VF). Two minutes of CPR restored myocardial ATP to the level of No-VF group (5.27±1.67 nmol/mg protein in CPR2, p>0.05 vs. No-VF group). However, myocardial ATP (nmol/mg protein) decreased if the duration of CPR was longer than 2 min (CPR4: 3.77±1.05, CPR6: 3.49±1.08, p<0.05 between CPR4 and CPR6 vs. No-VF).

CONCLUSIONS

CPR for 2 min helps to maintain myocardial ATP after prolonged VF.

Delayed high-quality CPR does not improve outcomes

AIM OF STUDY

The quality of cardiopulmonary resuscitation (CPR) is an important factor in the outcome of cardiac arrest. Our objective was to compare outcomes following either immediate low-quality (LQ) CPR or delayed high-quality (HQ) CPR. We hypothesized that delayed HQ CPR will improve the outcomes of CPR in comparison to immediately performing LQ CPR.

METHODS

Eighteen Sprague-Dawley rats were randomized into two groups: (1) Delayed HQ CPR (HQ group, n = 9). (2) Immediate LQ CPR (LQ group, n = 9). Ventricular fibrillation (VF) was induced and untreated for 8 mins. CPR was immediately performed in LQ group for 5 mins. Compression depth was set at 70% of the "optimal compression depth". VF was untreated for an additional 5 mins in HQ group. HQ CPR was started together with ventilation (100% oxygen) and external hypothermia for 8 mins in both groups. The "optimal compression depth" was approximately 30% of the anteroposterior chest diameter. Epinephrine was administrated 3 mins prior to defibrillation attempt. Restoration of spontaneous circulation, postresuscitation myocardial function and survival time were monitored.

RESULTS

All animals in the LQ group and 7 of 9 animals in the HQ group were resuscitated. Myocardial function, including ejection fraction and cardiac output was better in the LQ group than in the HQ group (p < 0.05) and survival time was longer in the LQ group (p < 0.05).

CONCLUSION

The outcomes after immediate LQ CPR, were better than those after delayed HQ CPR in this rat model of cardiac arrest and resuscitation.

Normothermic cardiac arrest and cardiopulmonary resuscitation: a mouse model of ischemia-reperfusion injury

Acute Kidney Injury (AKI) is a common, highly lethal, complication of critical illness which has a high mortality and which is most frequently caused by whole-body hypoperfusion. Successful reproduction of whole-body hypoperfusion in rodent models has been fraught with difficulty. Models which employ focal ischemia have repeatedly demonstrated results which do not translate to the clinical setting, and larger animal models which allow for whole body hypoperfusion lack access to the full toolset of genetic manipulation possible in the mouse. However, in recent years a mouse model of cardiac arrest and cardiopulmonary resuscitation has emerged which can be adapted to model AKI. This model reliably reproduces physiologic, functional, anatomic, and histologic outcomes seen in clinical AKI, is rapidly repeatable, and offers all of the significant advantages of a murine surgical model, including access to genetic manipulative techniques, low cost relative to large animals, and ease of use. Our group has developed extensive experience with use of this model to assess a number of organ-specific outcomes in AKI.

AVE4454B--a novel sodium-hydrogen exchanger isoform-1 inhibitor--compared less effective than cariporide for resuscitation from cardiac arrest

We compared the efficacy of the novel sodium-hydrogen exchanger (NHE-1) inhibitor AVE4454B with cariporide for resuscitation from ventricular fibrillation (VF) assessing the effects on left ventricular myocardial distensibility during chest compression, myocardial function after the return of spontaneous circulation, and survival. Three groups of 10 rats each were subjected to 10 min of untreated VF and resuscitation attempted by providing chest compression for up to 8 min with the depth of compression adjusted to attain an aortic diastolic pressure between 26 and 28 mmHg (to secure a coronary perfusion pressure above 20 mmHg) followed by electrical shocks. Rats received AVE4454B (1 mg/kg), cariporide (1 mg/kg), or vehicle control immediately before chest compression. We observed that NHE-1 inhibition (NHEI) preserved left ventricular myocardial distensibility during chest compression evidenced by less depth of compression required to attain the target aortic diastolic pressure corresponding to (mean ± standard deviation) 14.1 ± 1.1 mm in the AVE4454B group (P < 0.001 versus control), 15.0 ± 1.4 mm in the cariporide group (P < 0.01 versus control), and 17.0 ± 1.2 mm in controls. When the depth of compression was related to the coronary perfusion pressure generated-an index of left ventricular distensibility-only the cariporide group attained statistical significance. Postresuscitation, both compounds ameliorated myocardial dysfunction evidenced by lesser reductions in mean aortic pressure and the maximal rate of left ventricular pressure increase as well as earlier normalization of left ventricular end-diastolic pressure increases. This effect was associated with improved survival corresponding to 55% in the AVE4454B group (not significant) and 70% in the cariporide group (P < 0.01 versus control by Gehan-Breslow analysis) at 240 min postresuscitation. An inverse correlation was found between plasma cytochrome c and indices of left ventricular function at 240 min postresuscitation suggesting that NHEI exerts beneficial effects in part by attenuating mitochondrial injury. We conclude that cariporide is more effective than AVE4454B for resuscitation from cardiac arrest given its more prominent effect on preserving left ventricular myocardial distensibility and promoting survival.

Increased susceptibility to cardiovascular effects of dihydrocapcaicin in resuscitated rats. Cardiovascular effects of dihydrocapsaicin

Background

Survivors of a cardiac arrest often have persistent cardiovascular derangements following cardiopulmonary resuscitation including decreased cardiac output, arrhythmias and morphological myocardial damage. These cardiovascular derangements may lead to an increased susceptibility towards the external and internal environment of the cardiovascular system as compared to the healthy situation.

Methods

Here we tested the hypothesis that the cardiovascular system in healthy rats and rats resuscitated from a cardiac arrest may be differentially affected by a transient receptor potential vanilloid type 1 agonist, by continuous intravenous infusion of dihydrocapsaicin (DHC).

Results

Compared to baseline, infusion of DHC caused an initial increase in mean arterial blood pressure in both healthy and resuscitated rats of 25% and 10%, respectively. Also, we observed an initial response of tachycardia in both healthy and resuscitated rats of 30% and 20%, respectively. Then, at high levels of DHC infusion (> 2.0 mg/kg/hr) we observed two single episodes of transient bradycardia and hypotension in 33% of the healthy rats, which was consistent with a TRPV1 agonist induced Bezold-Jarisch reflex. In contrast, in resuscitated rats we observed multiple episodes of bradycardia/hypotension in 100% of the rats and at a dose of DHC of 0.65 mg/kg/hr. Notably, this DHC effect could be completely blocked in the resuscitated rats by pre-treatment with atropine, a muscarinic acetylcholine antagonist.

Conclusions

Our results indicate that the susceptibility of the rats towards TRPV1 agonist induced Bezold-Jarisch reflex is increased in those resuscitated from cardiac arrest compared to the healthy situation.

Continued breathing followed by gasping or apnea in a swine model of ventricular fibrillation cardiac arrest

BACKGROUND

Continued breathing following ventricular fibrillation has here-to-fore not been described.

METHODS

We analyzed the spontaneous ventilatory activity during the first several minutes of ventricular fibrillation (VF) in our isoflurane anesthesized swine model of out-of-hospital cardiac arrest. The frequency and type of ventilatory activity was monitored by pneumotachometer and main stream infrared capnometer and analyzed in 61 swine during the first 3 to 6 minutes of untreated VF.

RESULTS

During the first minute of VF, the air flow pattern in all 61 swine was similar to those recorded during regular spontaneous breathing during anesthesia and was clearly different from the patterns of gasping. The average rate of continued breathing during the first minute of untreated VF was 10 breaths per minute. During the second minute of untreated VF, spontaneous breathing activity either stopped or became typical of gasping. During minutes 2 to 5 of untreated VF, most animals exhibited very slow spontaneous ventilatory activity with a pattern typical of gasping; and the pattern of gasping was crescendo-decrescendo, as has been previously reported. In the absence of therapy, all ventilatory activity stopped 6 minutes after VF cardiac arrest.

CONCLUSION

In our swine model of VF cardiac arrest, we documented that normal breathing continued for the first minute following cardiac arrest.

Model of cardiac arrest in rats by transcutaneous electrical epicardium stimulation

OBJECTIVE

To establish a new model of cardiac arrest (CA) in rats by transcutaneous electrical epicardium stimulation.

METHODS

Two acupuncture needles connected to the anode and cathode of a stimulator were transcutaneously inserted into the epicardium as electrodes. The stimulating current was steered to the epicardium and the stimulation was maintained for 3 min to induce CA. Cardiopulmonary resuscitation (CPR) was performed at 6 min after a period of nonintervention.

RESULTS

CA was successfully induced in a total of 20 rats. The success rate of induction was 12/20 at the current intensity of 1 mA; and reached 20/20 when the current intensity was increased to 2 mA. After the electrical stimulation, the femoral blood pressure quickly dropped below 25 mmHg and the arterial pulse waveform disappeared. The average time from the electrical stimulation to CA induction was 5.10 (+/-2.81) s. When the electrical stimulation stopped, 18/20 rats had ventricular fibrillation and 2/20 rats had pulseless electrical activity. CPR was performed for averagely 207.4 (+/-148.8) s. The restoration of spontaneous circulation (ROSC) was 20/20. The death rate within 4h after ROSC was 5/20, and the 72-h survival rate was 10/20. There were only two cases of complications, a minor muscle contraction and a minor lung lobe injury.

CONCLUSION

The model of CA in rats induced by transcutaneous electrical epicardium stimulation is a stable model that requires low-intensity current and has fewer complications. This model may provide another option for experimental research of CA induced by malignant arrhythmia (especially VF).

Intravenous infusion of bone marrow mesenchymal stem cells improves brain function after resuscitation from cardiac arrest

OBJECTIVE

Allogeneic bone marrow mesenchymal stem cells were previously shown to improve myocardial function when administered intravenously after resuscitation from cardiac arrest in rats. Coincidental evidence of improved brain function prompted the present study.

DESIGN

Prospective, randomized, controlled study.

SETTING

University-affiliated research institute.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Using an established model in 20 male Sprague-Dawley rats in which 6 mins of untreated cardiac arrest was followed by cardiopulmonary resuscitation, animals were randomized to receive 5 x 10(6) mesenchymal stem cells labeled with PKH26 in phosphate buffer solution or phosphate buffer solution alone as a placebo at 2 hrs after restoration of spontaneous circulation. The stem cells or buffer diluent were injected into a catheter advanced from the jugular vein into the right atrium.

MEASUREMENTS AND MAIN RESULTS

Outcome measurements in addition to 35-day survival included somatosensor testing of capability for removal of an adhesive patch applied to both front paws, testing of motor function using a rotating cylinder, and observational scoring of the severity of neurologic impairment. Labeled mesenchymal stem cells were subsequently identified and counted in 5 microm sections obtained from defined sites in the harvested brain. Immunohistochemistry was used to identify neural cells differentiation of mesenchymal stem cells. Adhesive removal, motor function test, neurologic severity score, and 35-day survival were each significantly improved in comparison with control animals. Labeled mesenchymal stem cells were identified in the hippocampus, cortex, pons, medulla, and cerebellum and expressed protein markers phenotypic neural cells.

CONCLUSIONS

Mesenchymal stem cells injected into the right atrium of rats after resuscitation from cardiac arrest were identified in brains harvested 35 days later. Brain function was significantly improved. Accordingly, venous injection of mesenchymal stem cells after cardiopulmonary resuscitation has promise of minimizing the severity of postresuscitation neurologic impairment.

Gasping in response to basic resuscitation efforts: observation in a Swine model of cardiac arrest

Objective. To analyze the effect of basic resuscitation efforts on gasping and of gasping on survival. Methods. This is secondary analysis of a previously reported study comparing continuous chest compressions (CCC CPR) versus chest compressions plus ventilation (30:2 CPR) on survival. 64 swine were randomized to 1 of these 2 basic CPR approaches after either short (3 or 4 minutes) or long (5 or 6 minutes) durations of untreated VF. At 12 minutes of VF, all received the same Guidelines 2005 Advanced Cardiac Life Support. Neurologically status was evaluated at 24 hours. A score of 1 is normal, 2 is abnormal, such as not eating or drinking normally, unsteady gait, or slight resistance to restraint, 3 severely abnormal, where the animal is recumbent and unable to stand, 4 is comatose, and 5 is dead. For this analysis a neurological outcome score of 1 or 2 was classified as “good”, and a score of 3, 4, or 5 was classified as “poor.” Results. Gasping was more likely to continue or if absent, to resume in the animals with short durations of untreated VF before basic resuscitation efforts. With long durations of untreated VF, the frequency of gasping and survival was better in swine receiving CCC CPR. In the absence of frequent gasping, intact survival was rare in the long duration of untreated VF group. Conclusions. Gasping is an important phenomenon during basic resuscitation efforts for VF arrest and in this model was more frequent with CCC-CPR.

Apoptosis is not involved in the mechanism of myocardial dysfunction after resuscitation in a rat model of cardiac arrest and cardiopulmonary resuscitation

OBJECTIVE

To investigate the presence of apoptosis after the global myocardial ischemia of cardiopulmonary resuscitation and the regional myocardial ischemia after left anterior descending coronary artery occlusion and relate it to the severity of postresuscitation myocardial dysfunction.

DESIGN

Prospective animal study.

SETTING

University-affiliated animal research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Fifteen male Sprague-Dawley rats weighing 450-550 g were randomized to: (1) 8 mins of untreated cardiac arrest followed by 6 mins of cardiopulmonary resuscitation; (2)left anterior descending coronary artery occlusion for 45 mins followed by 4 hrs of reperfusion; and (3) left anterior descending coronary artery sham group. Cardiac functions, including ejection fraction, analog differentiation of left ventricular pressure at 40 mm Hg, and rate of maximal left ventricular pressure decline were continuously measured for 4 hrs. The hearts were then harvested for the terminal transferase-mediated 2'-deoxyuridine, 5'-triphosphate nick end-labeling assay analysis.

MEASUREMENTS AND MAIN RESULTS

Myocardial function was significantly impaired after resuscitation from cardiac arrest and reperfusion from left anterior descending coronary artery occlusion(p < .01). There was no difference in the percentage of apoptotic cells between the cardiopulmonary resuscitation animals and sham-operated animals. Fewer apoptotic cells were observed in cardiac arrest/cardiopulmonary resuscitation animals in comparison to left anterior descending coronary artery occlusion animals (p < .05), even though myocardial function was more severely impaired after resuscitation (p < .01).

CONCLUSIONS

Myocardial function was significantly impaired after cardiac arrest/cardiopulmonary resuscitation and ischemia/reperfusion. However, apoptosis was not involved in the mechanism of postresuscitation myocardial dysfunction in this setting.

Opioid receptor agonist reduces myocardial ischemic injury when administered during early phase of myocardial ischemia

AIM OF THE STUDY

Postresuscitation myocardial dysfunction is one of the leading causes of early death after initial success of resuscitation, the mechanisms of postresuscitation myocardial dysfunction remain controversial. We hypothesize that ischemia injury, rather than reperfusion injury is the major cause of postresuscitation myocardial dysfunction. We proposed to investigate the separate effects of ischemia and reperfusion injury on postresuscitation myocardial dysfunction.

METHODS

Thirty-three Langendorff-perfused isolated rat hearts were subjected to 15 min of global ischemia followed by 120 min of reperfusion. Pentazocine was utilized as a myocardial protective agent, either before ischemia or during reperfusion. All hearts were randomized into 3 groups: (1) "ischemia protection", in which pentazocine was infused 10 min prior to global ischemia, (2) "reperfusion protection", in which pentazocine was infused during 2h of reperfusion and (3) "control", with no pentazocine infusion. Left ventricular (LV) functions were measured by the maximal rate of LV pressure rise (dP/dt(max)) and decline (-dP/dt(max)), the maximal LV diastolic pressure (LVDP). The incidences of postischemic arrhythmias were measured.

RESULTS

When pentazocine was administered before onset of ischemia, the LV systolic and diastolic functions were significantly greater, and the postischemic arrhythmias were significantly less in comparison to those with reperfusion protection (p<0.05) and the control group (p<0.05).

CONCLUSIONS

In this model, the severity of postischemic myocardial dysfunction was less when the heart was protected during ischemia. Ischemia injury may therefore be the major cause of postresuscitation myocardial dysfunction.

What is the optimal dose of epinephrine during cardiopulmonary resuscitation in a rat model?

OBJECTIVE

Because different species may require different doses of drug to produce the same physiologic response, we were provoked to evaluate the dose-response of epinephrine during cardiopulmonary resuscitation (CPR) and identify what is the optimal dose of epinephrine in a rat cardiac arrest model.

METHODS

Rat cardiac arrest was induced via asphyxia, and then the effects of different doses of epinephrine (0.04, 0.2, and 0.4 mg/kg IV, respectively) and saline on the outcome of CPR were compared (n = 10/each group). The primary outcome measure was restoration of spontaneous circulation (ROSC), and the secondary was the change of spontaneous respiration and hemodynamics after ROSC.

RESULTS

Rates of ROSC were 9 of 10, 8 of 10, 7 of 10, and 1 of 10 in the low-dose, medium-dose, and high-dose epinephrine groups and saline group, respectively. The rates of withdrawal from the ventilator within 60 minutes in the low-dose (7 of 9) and medium-dose epinephrine groups (7 of 8) were higher than in the high-dose epinephrine group (1 of 7, P < .05). Mean arterial pressures were comparable, but the heart rate in the high-dose epinephrine group was the lowest among epinephrine groups after ROSC. These differences in part of time points reached statistical significance (P < .05).

CONCLUSION

Different doses of epinephrine produced the similar rate of ROSC, but high-dose epinephrine inhibited the recovery of spontaneous ventilation and caused relative bradycardia after CPR in an asphyxial rat model. Therefore, low and medium doses of epinephrine were more optimal for CPR in a rat asphyxial cardiac arrest model.

The effects of phase duration on defibrillation success of dual time constant biphasic waveforms

AIM OF STUDY

The effects of first and second phase duration of biphasic waveforms on defibrillation success were evaluated in a guinea pig model of ventricular fibrillation (VF). We hypothesized that waveform duration, and especially the first phase duration, played a main role on defibrillation efficacy in comparison to energy, current and voltage, when a dual time constant biphasic shock was employed.

METHODS

VF was induced and untreated for 5s in 30 male guinea pigs, prior to attempting a single defibrillatory shock with one of 5 defibrillation waveforms which had different durations of the first and second phase. A five step up-down protocol was utilized for determining the defibrillation efficacy. After a 3-min interval, the procedure was repeated. A total of 25 cardiac arrest events and defibrillations were investigated for each animal.

RESULTS

The defibrillation waveforms with an intermediate first phase of 5 ms, yielded the highest defibrillation success (p<0.05). These waveforms also presented significantly lower energy, current and voltage in comparison to waveforms with shorter or longer first phase durations (p<0.001). However, no differences on defibrillation success were observed among waveforms with different second phase durations varying from 1.5 ms to 3.5 ms.

CONCLUSIONS

For dual time constant biphasic waveforms, the first phase duration played a main role on defibrillation success. The intermediate first phase duration of 5 ms, yielded the best defibrillation efficacy compared with shorter or longer first phase durations. While the second phase duration did not affect defibrillation outcomes.

A rodent model of emergency cardiopulmonary bypass resuscitation with different temperatures after asphyxial cardiac arrest

BACKGROUND

The use of emergency cardiopulmonary bypass (ECPB) resuscitation after cardiac arrest may offer hope for survival when standard ACLS therapies fail. However, whether cooling adds benefit to ECPB is unknown and we lack an ECPB rodent model for experimental studies. We sought to (a) develop a 72 h survival rodent model using ECPB to treat asphyxial cardiac arrest and (b) use this new model to evaluate early mild and moderate hypothermia versus normothermia during ECPB resuscitation.

METHODS

After 8 min of normothermic asphyxia, three groups of rats were resuscitated with ECPB at 37 degrees C (NORM), 34 degrees C (MILD) and 30 degrees C (MOD) for 1h (n=10 each). During the second resuscitation hour, ECPB was discontinued, ventilatory support was provided and body temperatures were maintained at 37 degrees C for NORM, 34 degrees C for MILD, and from 30 degrees C gradually up to 34 degrees C in 1h for MOD animals. From hours 3 to 8, body temperature was maintained at 37 degrees C for NORM and 34 degrees C for MILD and MOD animals.

RESULTS

All rats were initially resuscitated by ECPB. After 72 h, neurological outcome and survival in the MILD (60% survival) and MOD (80%) groups were significantly better than in the NORM (0%) group (p<0.05). Overall performance recovery in the MOD group was best (vs. the NORM group), while the MILD group had an intermediate outcome.

CONCLUSIONS

A rodent model of ECPB is feasible and useful for resuscitation studies. The addition of early mild and moderate hypothermia to ECPB resuscitation significantly improves survival compared with normothermic ECPB in rats.

Buccal capnometry for quantitating the severity of hemorrhagic shock

We have recently demonstrated that measurement of buccal mucosal PCO2 (PBUCO2) is a reliable alternative to sublingual mucosal PCO2 for measuring the severity of hemorrhagic shock. We hypothesized that measurement of PBUCO2 would serve as a continuous and a more sensitive and specific measurement for predicting survival during hemorrhagic shock than conventional measurements and thereby better guide initial management. Four groups of five pentobarbital anesthetized Sprague-Dawley rats were randomly assigned to be bled over 30 min in amounts estimated to be 25%, 30%, 35%, or 40% of total blood volume. With an optical PCO2 sensor applied noninvasively to the mucosa of the left inner cheek, PBUCO2 was continuously measured together with arterial pressure, end-tidal PCO2, and intermittent measurement of cardiac output, arterial blood lactate, and base deficit. Surviving animals had free access to water and food but no other treatment during the 72-h interval after recovery from anesthesia. After an estimated 40% blood loss, all animals died within 1 h. In the remaining animals, arterial pressure, end-tidal carbon dioxide, cardiac index, blood lactate, and base deficit each failed to discriminate among animals with 35%, 30%, and 25% acute blood losses. This contrasted with PBUCO2, which discriminated between the magnitude of massive blood loss and untreated survival. Buccal mucosal PCO2 was predictive of outcome after rapid bleeding when compared with arterial pressure, end-tidal carbon dioxide, cardiac index, arterial blood lactate, and base deficit. This measurement is therefore likely to serve as a useful guide for the immediate management of hemorrhagic shock.

Improved outcomes of cardiopulmonary resuscitation in rats with myocardial infarction treated with allogenic bone marrow mesenchymal stem cells

OBJECTIVE

We hypothesized that rats in which myocardial infarction had been treated with mesenchymal stem cells (MSCs) would have better outcomes following the global myocardial ischemia of cardiac arrest and cardiopulmonary resuscitation (CPR) compared with rats in which myocardial infarction had been treated with phosphate buffer solution (PBS).

DESIGN

Prospective, randomized controlled study.

SETTING

University-affiliated research institute.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Myocardial infarction was induced in 18 male Sprague-Dawley rats. Four weeks later, animals were randomized to receive 5 x 10 MSCs labeled with red fluorescent dye gel (PKH26) in PBS or a PBS-alone injection into right femoral vein.

MEASUREMENTS AND MAIN RESULTS

Echocardiographically measured myocardial function, including ejection fraction, left ventricular end-diastolic volume, and left ventricular end-systolic volume, was quantitated 2 and 4 weeks after administering MSCs or PBS. Four weeks after MSCs or PBS injection, 6 minutes of ventricular fibrillation (VF) and 6 minutes of CPR were performed before defibrillation. Myocardial function, including cardiac index, left ventricular, dP/dt max (dP/dt max), left ventricular negative dP/dt min (-dP/dt min), and left ventricular diastolic pressure, was measured before inducing VF and hourly following return of spontaneous circulation. Labeled MSCs were observed in 5-mum cryostat sections from each harvested heart. Significant improvements in ejection fraction, left ventricular end-diastolic volume, left ventricular end-systolic volume, cardiac index, dP/dt max, -dP/dt min, and left ventricular diastolic pressure followed injection of MSCs before inducing VF. Following return of spontaneous circulation, myocardial function was significantly better in animals pretreated with MSCs; this was associated with significantly increased duration of postresuscitation survival.

CONCLUSIONS

Myocardial function before and after CPR and duration of survival after CPR were significantly improved in animals in which myocardial infarction was treated with MSCs. MSCs existing in the myocardium resisted a secondary ischemic event and provided better postresuscitation myocardial function.

Activation of caspase-3 may not contribute to postresuscitation myocardial dysfunction

We have previously reported that postresuscitation myocardial dysfunction is accompanied by the release of cytochrome c and caspase-3 activation. We now investigated the role of caspase-3 activation by examining whether such process prompts apoptotic DNA fragmentation, whether caspase-3 inhibition attenuates myocardial dysfunction, and whether myocardial protective effects of sodium-hydrogen exchanger isoform-1 (NHE-1) inhibition involve caspase-3 inhibition using a rat model of ventricular fibrillation (VF) of closed-chest resuscitation. Resuscitation after 4 or 8 min of untreated VF caused significant reductions in left ventricular stroke work index averaging 23% of sham control rats at 4 h postresuscitation. Left ventricular dysfunction was accompanied by increases in cytosolic cytochrome c, decreases in pro- and cleaved caspase-9 fragments, increases in 17-kDa caspase-3 fragments, and increases in caspase-3 activity indicating the activation of the mitochondrial apoptotic pathway but without evidence of apoptotic DNA fragmentation. In addition, levels of heat shock protein 70 were increased and levels of X-linked inhibitor of apoptosis protein and alphabeta-crystallin were preserved, all of which can exert antiapoptotic effects. In a separate series, the caspase-3 inhibitor z-Asp-Glu-Val-Asp chloromethyl ketone given before the induction of VF failed to prevent postresuscitation myocardial dysfunction despite reductions in caspase-3 activity (2.3 +/- 0.5 vs. 1.3 +/- 0.5 pmol fluorophore AFC released.mg protein(-1).min-1; P < 0.03). Treatment with the NHE-1 inhibitor cariporide had no effect on caspase-3 activity. Accordingly, in this rat model of VF and severe postresuscitation myocardial dysfunction, activation of caspase-3 did not lead to DNA fragmentation or contribute to myocardial dysfunction. Concomitant activation of intrinsic antiapoptotic mechanisms could play a protective role downstream to caspase-3 activation.

The use of mice and rats as animal models for cardiopulmonary resuscitation research

Cardiopulmonary resuscitation (CPR) after the induction of cardiac arrest (CA) has been studied in mice and rats. The anatomical and physiological parameters of the cardiopulmonary system of these two species have been defined during experimental studies and are comparable with those of humans. Moreover, these animal models are more ethical to establish and are easier to manipulate, when compared with larger experimental animals. Accordingly, the effects of successful CPR on the function of vital organs, such as the brain, have been investigated because damage to these vital organs is of concern in CA survivors. Furthermore, the efficacy of several drugs, such as adrenaline (epinephrine), vasopressin and nitroglycerin, has been evaluated for use in CA in these small animal models. The purpose of these studies is not only to increase the rate of survival of CA victims, but also to improve their quality of life by reducing damage to their vital organs after CA and during CPR.

Myocardial protection by erythropoietin during resuscitation from ventricular fibrillation

Human recombinant erythropoietin (rhEPO) can protect the myocardium during ischemia and reperfusion. We investigated whether rhEPO could ameliorate previously identified functional myocardial abnormalities that develop during resuscitation from cardiac arrest, using a rat model of ventricular fibrillation (VF) and closed-chest resuscitation. VF was electrically induced and maintained, untreated, for 10 minutes. Chest compression and ventilation were then started and electrical defibrillation was attempted 8 minutes later. Rats were randomized to receive rhEPO (5000 U/kg) in the right atrium at baseline, 15 minutes before induction of VF (rhEPOBL -15-min), or at 10 minutes of VF, immediately before the start of chest compression (rhEPOVF 10-min), or to receive 0.9% NaCl solution instead (control). rhEPO given at the time of resuscitation (rhEPOVF 10-min group) -- but not at baseline -- prompted more effective chest compression, yielding higher coronary perfusion pressures for a given compression depth (1.95 +/- 0.27 mm Hg/mm; P < 0.05 in comparison with rhEPOBL -15-min [1.63 +/- 0.23 mm Hg/mm] and control [1.62 +/- 0.26 mm Hg/mm], by Dunnett's multicomparison method). Post-resuscitation, rats in the rhEPOVF 10-min group displayed higher mean aortic pressure associated with numerically higher cardiac index, stroke work index, and systemic vascular resistance index. rhEPO may rapidly induce myocardial protection during resuscitation from cardiac arrest.

Ventricular fibrillation induced by transoesophageal cardiac pacing: A new model of cardiac arrest in rats

OBJECTIVE

To investigate whether transoesophageal cardiac pacing can induce ventricular fibrillation (VF) and how long the cardiac pacing has to be sustained to prevent the reversion of the VF induced.

METHODS

A pacing electrode was inserted orally into the oesophagus and high-frequency ventricular pacing was performed so as to elicit VF in 25 Sprague-Dawley rats. Incidences of VF and time of cardiac pacing were observed and recorded. Four minutes after onset of VF cardiopulmonary resuscitation (CPR) was initiated.

RESULTS

A short interval of high-frequency ventricular pacing caused an immediate drop of blood pressure, loss of pulse and increase of right atrial pressure in the same time frame. When the cardiac pacing was terminated, VF was elicited at least once or more than once in all of the 25 rats. However, the VF elicited by the burst stimulation could be defibrillated spontaneously. With the prolongation (120-180 s) of cardiac pacing, the incidence of defibrillation of VF decreased from 100 to 0%. VF persisted in 19 of 25 animals, developed into asystole in 5 of 25 animals and converted into pulseless electrical activity in 1 of 25 animals prior to CPR. Following CPR 22 of 25 animals were resuscitated.

CONCLUSIONS

Transoesophageal cardiac pacing can induce VF in rats. However, the cardiac pacing is required for at least 120-180 s to ensure that VF does not spontaneously convert. We can use the technique to establish a new and simpler rat cardiac arrest (CA) model, which may facilitate experimental investigation on CPR.

A simpler cardiac arrest model in rats

Two disadvantages of electrical induction of cardiac arrest used currently are that it is a technically complicated procedure and the consequent thermal injury, which prompts us to search for a simpler method with less adverse effect to induce ventricular fibrillation (VF) in rats. Different potential (18, 24, 30, and 36 V) of alternating current (AC) were administered to elicit VF in 15 rats via pacing electrode placed in esophagus. Four minutes after onset of VF, conventional cardiopulmonary resuscitation (CPR) was initiated. Restoration of spontaneous circulation was defined as the return of supraventricular rhythm with a mean aortic pressure of 20 mm Hg or greater for a minimum of 5 minute. Ventricular fibrillation was achieved by short interval of AC stimulation in all of the rats. After the termination of prolonged AC stimulation, electrocardiogram indicated VF occurred in 6 of 15 rats, asystole in 3 of 15 rats and pulseless electrical activity in 6 of 15 rats. Before CPR, however, electrocardiogram indicated that only 2 of 15 and 4 of 15 animals remained in VF and pulseless electrical activity, respectively, whereas 9 of 15 animals presented as asystole. After CPR, 11 of 15 animals were resuscitated. Necropsy showed that there was no gross evidence of thermal injury on the surface layer of the heart. Therefore, development of a rat cardiac arrest model by transesophageal AC stimulation is simpler and less adverse effect, which may have practical significance for facilitating experimental investigation on cardiac arrest and CPR.

Limiting sarcolemmal Na+ entry during resuscitation from ventricular fibrillation prevents excess mitochondrial Ca2+ accumulation and attenuates myocardial injury

BACKGROUND

intracellular Na+ accumulation during ischemia and reperfusion leads to cytosolic Ca2+ overload through reverse-mode operation of the sarcolemmal Na+ -Ca2+ exchanger. Cytosolic Ca2+ accumulation promotes mitochondrial Ca2+ (Ca2+ m) overload, leading to mitochondrial injury. We investigated whether limiting sarcolemmal Na+ entry during resuscitation from ventricular fibrillation (VF) attenuates Ca2+ m overload and lessens myocardial dysfunction in a rat model of VF and closed-chest resuscitation.

METHODS

hearts were harvested from 10 groups of 6 rats each representing baseline, 15 min of untreated VF, 15 min of VF with chest compression given for the last 5 min (VF/CC), and 60 min postresuscitation (PR). VF/CC and PR included four groups each randomized to receive before starting chest compression the new NHE-1 inhibitor AVE4454B (1.0 mg/kg), the Na+ channel blocker lidocaine (5.0 mg/kg), their combination, or vehicle control. The left ventricle was processed for intracellular Na+ and Ca2+ m measurements.

RESULTS

limiting sarcolemmal Na+ entry attenuated cytosolic Na+ increase during VF/CC and the PR phase and prevented Ca2+ m overload yielding levels that corresponded to 77% and 71% of control hearts at VF/CC and PR, without differences among specific Na+ -limiting interventions. Limiting sarcolemmal Na+ entry attenuated reductions in left ventricular compliance during VF and prompted higher mean aortic pressure (110 +/- 7 vs. 95 +/- 11 mmHg, P < 0.001) and higher cardiac work index (159 +/- 34 vs. 126 +/- 29 g x m x min(-1) x kg(-1), P < 0.05) with lesser increases in circulating cardiac troponin I at 60 min PR.

CONCLUSIONS

Na+ -limiting interventions prevented excess Ca2+ m accumulation induced by ischemia and reperfusion and ameliorated myocardial injury and dysfunction.

Vasopressors are essential during cardiopulmonary resuscitation in rats: Is vasopressin superior to adrenaline?

BACKGROUND

Vasopressors are recommended for cardiopulmonary resuscitation (CPR) after cardiac arrest. In order to assess possible benefits regarding neurological recovery, vasopressin versus adrenaline and the combination of both was tested against placebo in a cardiac arrest model in rats.

METHODS

Under anaesthesia with halothane and N2O, cardiac arrest was initiated via transoesophageal electrical fibrillation. After 7 min of global ischaemia, CPR was performed by external chest compression combined with defibrillation. Animals were randomly assigned to three groups receiving adrenaline, vasopressin and a combination of both (n = 15 per group) versus placebo (n = 8). At 1, 3 and 7 days animals were tested according to a neurological deficit score (NDS). After 7 days of reperfusion, coronal brain sections were analysed by Nissl- and TUNEL-staining. Viable as well as TUNEL-positive neurons were counted in the hippocampal CA-1 sector. For statistical analysis, the log rank and the Kruskal-Wallis ANOVA test were used. All data are given as mean+/-S.D.; a p-value <0.05 was considered significant.

RESULTS

Mean arterial blood pressure (MAP) measured in the aorta did not differ between the vasopressor groups, whereas placebo animals had significantly lower levels. Survival to 7 days revealed significant differences between the placebo (n = 0/8) and all vasopressor groups (adrenaline, 10/15; adrenaline/vasopressin, 8/15; vasopressin, 12/15). Histological deficit scoring by quantitative analysis of the Nissl- and TUNEL-staining showed no difference in the amount of viable and apoptotic neurons in the vasopressin group (viable: 33+/-18; apoptotic: 63+/-23) versus the adrenaline group (viable: 21+/-12; apoptotic: 67+/-17) and the adrenaline/vasopressin group (viable: 31+/-26; apoptotic: 61+/-27). Neurological deficit scoring did not show any differences between the vasopressor groups.

CONCLUSION

Administration of arginine-vasopressin during CPR does not improve behavioural and cerebral histopathological outcome, compared to the use of adrenaline or the combination of both vasopressors, after cardiac arrest in rats.

Preterminal gasping and effects on the cardiac function

OBJECTIVE

Gasping, also known as agonal respirations, is the terminal pattern that occurs after anoxia or ischemia and is a universal phenomenon in mammals. In this article we review the physiology of gasping, the prevalence and significance of gasping in cardiac arrest, and the effects of gasping on cardiac function.

DESIGN

Review relevant human and animal literature on gasping and cardiac function during gasping.

RESULTS

Gasping originates in the medullary area of the central nervous system. Gasping is prevalent during cardiac arrest: it occurs in all animals during ventricular fibrillation, in a majority of infants (31 of 32) with sudden infant death syndrome, and in 30-40% of witnessed episodes of cardiac arrest in adults. Animal studies demonstrated that gasping is associated with a decrease in intrathoracic pressure during the inspiratory phase, which promotes venous return and an increase in intrathoracic pressure during the expiratory phase, which favors coronary perfusion. Gasping increases cardiac output and cardiac contractility in immature animals exposed to anoxia.

CONCLUSIONS

Gasping is auto-resuscitative in immature mammals and improves the outcome of cardiopulmonary resuscitation in mature mammals. Gasping is associated with important cardiorespiratory changes: improved pulmonary gas exchange, increased venous return to the heart, increased cardiac output, cardiac contractility, aortic pressure, and coronary perfusion pressure.