Introduction: Impact of global ischemia and reperfusion on brain in resuscitation animal models is well investigated. Investigations on vulnerability of spinal cord in such models are rarely reported. We investigated the spinal cord in a cardiopulmonary resuscitation ventricular fibrillation cardiac arrest (VFCA) rat model and hypothesized that an untreated CA of 6 and 8 min will lead to histological damage and dysfunction in the resuscitated animal′s spinal cord, depending on CA duration. Methods: Adult male Sprague-Dawley rats (350-450 g) were subjected to 6 (n=8) or 8 min (n=14) of VFCA and resuscitated with conventional chest compressions with a thumper device, mechanical ventilation and drugs (epinephrine, bicarbonate, heparin). After defibrillation and ROSC, rats survived for 14 days. The spinal cord was removed from the spine after fixation in formalin and embedded in paraffin. Transverse sections of cervical, thoracic and lumbar spinal cord were stained with hematoxylin and eosin (HE). Immunohistochemistry was performed with antibodies against GFAP for astrocytes and Iba1 for microglia. Sections were evaluated by a pathologist blinded to treatment regimens, and compared to sham animals (n=5). Results: Resuscitated animals showed high mortality; after 6 min CA four animals and after 8 min CA eleven animals died before endpoint. Surviving animals showed focal bilateral symmetrical loss of neurons and distinct gliosis in the gray matter of the thoracic spinal cord level with the central canal. Similar lesions were detected in other segments of the spinal cord, but were located predominantly in the ventral horn of the spinal cord. These lesions were accompanied by dilated myelin sheaths in the white matter. Immunohistochemistry showed activation of astrocytes and microglia in the damaged regions. There were no differences detectable between animals subjected to 6 or 8 min VFCA. Sham animals showed no lesions in the spinal cord. Conclusions: We found consistent histological damage in the spinal cords of rats resuscitated after 6 and 8 min untreated VFCA with CPR after 14 days survival but without clinical symptoms in these animals. However, similar lesions might be cause of paralysis and urinary retention found in animals that died before endpoint.

Background: The CA1 region of hippocampus is specifically vulnerable to global ischemia and is depopulated 14 days after 8min ventricular fibrillation cardiac arrests (VF-CA) and conventional resuscitation in a rat model. We have previously reported on the pyramidal cell repopulation of the CA1 region after long term survival after cardiac arrest in two thirds of animals. (Circulation. 2014;130:A80) The aim of this study was to investigate the distribution of microglia and astrocytes in the CA1 region of rat hippocampus after CA and to measure its diameter. Methods: After 8 min of VF-CA male Sprague-Dawley rats received mechanical chest compressions for 2 min and epinephrine 20 μg/kg. The animals were defibrillated thereafter every 2 min to achieve return of spontaneous circulation. Animals surviving with favorable neurologic recovery were sacrificed 140 days after CA (n=12, 8 with neuronal repopulation (R), 4 without R (nonR)) and compared to 14 day survivors (n=6) and control animals (n=20). Results: Microglia cells/ 75000μm 2 were 6±3 in controls, 53±9 in 14d survivors (p<0.001 vs controls), 12±4 in 140d-R and 19±12 in 140d-nonR. Astrocytes/75000μm 2 were 9±2 in controls, 15±3 in 14d survivors (p<0.001 vs controls), 21±4 in 140d-R and 43±13 in 140d-nonR animals (p<0.001 vs 140d-R). The hippocampal diameter (μm) was 543±36 in controls, 417±36 in 14d survivors (p<0.001 vs controls), 462±39 in 140d-R and 306±86 in 140d-nonR animals (p<0.001 vs 140d-R). Conclusions: The repopulation of pyramid cells in the CA1 that has taken place in two thirds of animals is accompanied by a significant increase in the diameter of the hippocampus and reduced astrocyte numbers compared to nonR-animals. Numbers of microglial cells are significantly increased after 14d survival removing cell debris after neuronal damage. This lifelong potential of the hippocampus for repair due to adult neurogenesis may open an additional late phase therapeutic window for CA recovery.

Introduction: Extracorporeal cardio pulmonary resuscitation (eCPR) is an invasive rescue option in patients with refractory out-of hospital cardiac arrest (OHCA). Recent literature shows evidence that the time frame from collapse till start of eCPR directly influences outcome. In most western countries, advanced life support is provided by emergency medical service (EMS) aiming return of spontaneous circulation at scene. We investigate the impact of EMS scene time interval on outcome in OHCA considering a possible following in-hospital eCPR treatment.

Introduction: Epinephrine is an established vasopressor and the primary drug administrated during cardio pulmonary resuscitation (CPR). This study evaluates the influence of epinephrine on coronary perfusion pressure (CPP), mean atrial pressure (MAP) and end-tidal CO2 (ETCO2) in our rat VF CPR model.

Background: Outcome is generally poor in out of hospital cardiac arrests (OHCA) with initial non-shockable rhythms. Termination of resuscitation rules facilitate early prognostication at the scene to cease resuscitation attempts in futile situations and to proceed advanced life support in promising conditions. As pulseless electrical activity (PEA) is present as first rhythm in every 4th OHCA we were interested if the initial electrical frequency in PEA predicts survival. Methods: All patients > 18 years of age with non-traumatic OHCA and PEA as first rhythm between August 2013 and August 2015 from the Vienna Cardiac Arrest Registry were included in this retrospective observational study. Defibrillator and epidemiological data from the emergency medical system as survival data were processed considering the initial electrical activity in PEA and 30 days survival. Results: Out of 2149 OHCA patients, a total of 504 PEA patients were eligible for analyses. These patients were stratified into 4 groups according the initial electrical frequency in PEA: 10-24/min, 25-39/min, 40-59/min, > 60/min. Compared to a frequency > 60/min all other subgroups were associated with higher mortality especially those with an initial electrical frequency 10-24 (adjusted OR 0.56 (0.39-0.79) p =. 001 for each category chance). QRS duration in PEA did not influence outcome. Patients in the > 60/min group showed a 30-days-survival rate of 22% and a good neurological outcome in 15% of all patients - comparable to shockable cardiac arrest rhythms. Conclusion: Regardless of other resuscitation factors, higher initial electrical frequency in PEA is associated with increased odds of survival and good neurological outcome.

Introduction: High-quality cardiopulmonary resuscitation (CPR) aims to re-establish blood flow to vital organs until restoration of spontaneous circulation (ROSC). Coronary Perfusion Pressure (CPP) is an indicator for CPR effectiveness in the experimental setting. Direct CPP measurement from the coronary artery is not possible in small animal models. Several methods for calculating CPP from systemic blood pressure have been published. This study evaluates the reliability of calculated true mean CPP in assessing CPR quality in terms of ROSC rate in our ventricular fibrillation (VF) cardiac arrest (CA) model in rats.

Evaluating beneficial effects of potential protective therapies following cardiac arrest in rodent models could be enhanced by exploring behavior and cognitive functions. The Morris Water Maze is a well-known cognitive paradigm to test spatial learning and memory.

Cerebral metabolic alterations during cardiac arrest, cardiopulmonary resuscitation (CPR) and extracorporeal cardiopulmonary life support (ECLS) are poorly explored. Markers are needed for a more personalized resuscitation and post-resuscitation care. Aim of this study was to investigate early metabolic changes in the hippocampal CA1 region during ventricular fibrillation cardiac arrest (VF-CA) and ECLS versus conventional CPR. Male Sprague-Dawley rats (350g) underwent 8min untreated VF-CA followed by ECLS (n = 8; bloodflow 100ml/kg), mechanical CPR (n = 18; 200/min) until return of spontaneous circulation (ROSC). Shams (n = 2) were included. Glucose, glutamate and lactate/pyruvate ratio were compared between treatment groups and animals with and without ROSC. Ten animals (39%) achieved ROSC (ECLS 5/8 vs. CPR 5/18; OR 4,3;CI:0.7-25;p = 0.189). During VF-CA central nervous glucose decreased (0.32±0.1mmol/l to 0.04±0.01mmol/l; p<0.001) and showed a significant rise (0.53±0.1;p<0.001) after resuscitation. Lactate/pyruvate (L/P) ratio showed a 5fold increase (31 to 164; p<0.001; maximum 8min post ROSC). Glutamate showed a 3.5-fold increase to (2.06±1.5 to 7.12±5.1μmol/L; p<0.001) after CA. All parameters normalized after ROSC with no significant differences between ECLS and CPR. Metabolic changes during ischemia and resuscitation can be displayed by cerebral microdialysis in our VF-CA CPR and ECLS rat model. We found similar microdialysate concentrations and patterns of normalization in both resuscitation methods used. Institutional Protocol Number: GZ0064.11/3b/2011.

Background: Comparison of ischemia- and reperfusion markers determined by brain microdialysis in a model of two different reperfusion methods after ventricular fibrillation (VF) cardiac arrest in rats. The goal was to establish online measurement of ischemic stress and reperfusion to guide an experimental approach and future therapies. Methods: Male Sprague-Dawley rats were used in a model of 8 minutes VF cardiac arrest. Microdialysis assessment was performed in the right hippocampal CA1 region with 4 baseline and 6 intervention samples. Probe placement was verified histologically after necropsy. Sampling was performed at 1μl/min with 8 minutes intervals. Lactate and pyruvate were assessed. Lactate/pyruvate ratios, reflecting ischemia, were calculated during extracorporeal life support (ECLS), with cardiopulmonary bypass and were compared to cardiopulmonary resuscitation (CPR). A sham group was used for baseline assessment. In this preliminary analysis one animal was used in each group. Results: Return of spontaneous circulation (ROSC) was achieved in both intervention animals after 4 minutes of reperfusion. The lactate/ pyruvate ratio increased 6 fold in intervention animals after cardiac arrest, while sham measurements showed a constant baseline (Figure 1). The normalization of lactate/pyruvate ratio after ROSC differed in intervention animals, showing faster normalization in CPR and slower decline in ECLS. Conclusions: To our knowledge this is the first report of cerebral microdialysis in a cardiac arrest reperfusion model in rats comparing ECLS and CPR. Reperfusion strategies seem to affect the release of hypoxia markers. This model could be used for investigation of different resuscitation regimens and subsequently for guiding clinical strategies. Further data is needed to validate these results. Figure: Lactate/pyruvate ratios of Sham (red), CPR (blue) and ECLS (black) animal. X-axis: count of measurements. Y-axis: lactate pyruvate ratio.

Background: Rodent models of ventricular fibrillation (VF) cardiac arrest (CA) are useful to investigate new treatment strategies for successful resuscitation. Emergency cardiopulmonary bypass (ECPB) is a promising concept for advanced life support of prolonged VF CA. Establishing a rat model of ECPB resuscitation is associated with procedural pitfalls. Methods: Anaesthetized male Sprague Dawley rats (350g) underwent surgical preparation. VF was induced via neonatal pacing catheter placed into the jugular cannula. Rats were resuscitated with ECPB, mechanical ventilation, defibrillation and drugs. Catheter and cannula explantation was performed if return of spontaneous circulation (ROSC) was achieved. Serious adverse events were collected and analyzed. Results: A total of 65 serious adverse events occurred in 130 experiments. Most were catheter related. Hemorrhage was a common adverse event during surgical blood vessel cannulation (12 animals). No ROSC was achieved in 7 animals due to anemia caused by blood loss during surgery. The most challenging part in establishing our ECPB model is the insertion of the jugular CPB cannula. In 23 rats lethal hemothorax occurred, due to injury of the heart or the inferior vena cava. We tested different cannulas and techniques without avoiding completely the risk of rupture. In 6 cases blood could not be drained from the venous circulation caused by occlusion or dislocation of the jugular cannula. Disconnection from the bypass oxygen flow occurred three times. During the explantation of the jugular CPB cannula after achieving ROSC, pulmonary air embolism followed by instantaneous death occurred in 12 animals. We observed in 2 animals lethal pulmonary edema. Conclusion: Establishing an ECBP resuscitation model in rats has confronted us with considerable technical challenges. We report our procedural failures during model implementation to prevent other experimental researchers repeating these potential avoidable errors in their model. Exchange of technical and procedural resources between research groups would help minimize loss of animals.

Background: Rodent models of cardiac arrest help to investigate detailed pathophysiologic mechanisms of cerebral ischemia and reperfusion. Sensitive neurologic and behavioral tests would enhance the ability of such models to evaluate possible beneficial effects of protective therapies. The Morris Water Maze (MWM) is a procedure to study spatial learning and memory. The aim of this study was to investigate behavioral testing with the MWM in rats resuscitated from ventricular fibrillation (VF) cardiac arrest (CA) via emergency cardiopulmonary bypass (ECPB). Methods: Sprague-Dawley rats (450g, male, anesthetized) were put into VF CA. After 10 min of CA the animals were resuscitated with ECPB, epinephrine and defibrillations and cooled to mild hypothermia (33°C) . Ten surviving animals with favorable neurologic recovery were compared to 8 healthy rats. MWM was performed in each animal 2 times on 4 consecutive days for maximal 60 s with a hidden platform in a 22°C cold water tank and on day 7 and 14 with the platform removed for memory testing. Results: The latency time to find the hidden platform decreased in the CPB group and the control group from 60(IQR 39-60) s and 60(IQR 60-60) s to 9(IQR 6-29) s and 10(IQR 6-19) s respectively (p=0.46). After removal of the platform the time within the target sector on day 7 in 60 s was 17±6 s and 22±5 s (p=0.08) and on day 14 12±4 s and 13±4 s (p=0.76) respectively. Conclusions: Spatial learning and memory in clinical neurologically intact animals resuscitated from a 10 min VF CA cooled to mild hypothermia was comparable to normal healthy controls. With this MWM setup learning was performed well, the remembrance of platform position was kept for one week in both groups equally.

Background: Rodent models of cardiac arrest (CA) help to investigate pathophysiologic mechanisms of cerebral ischemia and reperfusion. Sensitive neurologic tests would enhance the ability of such models to evaluate possible beneficial effects of protective therapies. The Morris Water Maze (MWM) is a procedure to test spatial learning and memory. The aim of this study was to investigate behavioral testing with the Morris Water Maze in rats resuscitated from ventricular fibrillation (VF) CA. Methods: Sprague-Dawley rats (379±13g, male, anesthetized) were put into VF CA. After 8 min of CA the animals received mechanical chest compressions for 2 min and epinephrine 20 μg/kg. The animals were defibrillated thereafter every 2 min to achieve return of spontaneous circulation. Ten animals surviving with favorable neurologic recovery were compared to 10 naive rats. MWM testing was performed in each animal 3 times on 4 consecutive days for maximal 120 s with a hidden platform and on day 5 and day 12 with the platform removed. Results: The latency time to find the hidden platform (reflecting spatial learning) decreased in the CPR group and the control group from 107±31 s and 75±42 s to 10±5 s and 17±14 s between day 1 and day 4 (p=0.11). After removal of the platform, the time within the target sector on day 5 (reflecting short term memory) in 60 s was 24±6 s and 25±8 s (p=0.87).Time within the target sector on day 12 (reflecting long term memory) was significantly reduced in the CPR group vs. naive rats with 15±3 s and 18±2 s (p=0.03) Conclusions: Spatial learning and short-term memory in clinical neurologically intact animals resuscitated from an 8 min VF CA was comparable to normal healthy controls. Long term memory after a 7-day period without training was reduced. Memory retention rather than short term may prove valuable in this global ischemia model as behavioral testing strategy.

Introduction: The ideal rodent model of ventricular fibrillation (VF) cardiac arrest (CA) produces consistent histologic and neurologic damage as target for novel therapies and shows a high survival rate to minimize animal use and allow for long term outcome. VF induction, chest compressions and ventilation are crucial techniques and published in many variants in literature. We report our experiences during model development. Materials and Methods: A non-randomized cohort study evaluating different methods of VF induction, chest compressions techniques, mechanical ventilation and defibrillation was performed with regards to it’s feasibility, complications, ROSC rate and survival. Results: Male Sprague-Dawley rats (350g, anesthetised, instrumented) underwent VF induction with 2 min endocardial fibrillation via a transjugular neonatal pacing catheter with minimal current use, low incidence of autodefibrillation and good resuscitability. Mechanical chest compressions with approx. 30% of thorax diameter depth were applied with a pneumatic thumper 200/min placed mid-sternally, tilted upwards. Strong fixation with tapes avoided throrax-instability. Epinephrine (20μg/kg) and NaHCO3 (1mmol/ kg) were administered before CPR start and epinephrine repeatedly given after defibrillations every 2min. For defibrillations (5J, biphasic) modified paediatric defi pads were used. ROSC was achieved in 7/10 animals in a 6 min CA group and 6/11 in a 8 min CA group. CPR time was 2.6±1.0 min (mean±SD), number of defibrillations needed 2±1 and a cumulative epinephrine dose of 46±10 μg/kg with no differences between groups. Conclusions: Researchers developing a VF CA model are facing a multitude of difficulties, a lack of data on model development and many variations published in literature, often without detailed description. We developed a CPR rat model for VF CA with graded cognitive deficits and long-term survival. We propose detailed description of model development, including ineffective methods, to facilitate experience exchange between research groups, to avoid that future experimental groups repeat possible mistakes.

BACKGROUND: Emergency cardiopulmonary bypass (ECPB) may achieve successful resuscitation after prolonged cardiac arrest (CA) when conventional cardiopulmonary resuscitation (CPR) fails. A rodent model of ventricular fibrillation (VF) CA would allow optimizing ECPB use. In this study, we assessed the feasibility of a 10 min ventricular fibrillation (VF) CA model with ECPB resuscitation in rats in terms of return of spontaneous circulation (ROSC) rate and long-term survival with neurologic and histologic outcome. METHODS: The ECPB setup consisted of an open reservoir, a roller pump, a capillary membrane oxygenator, primed with 15 mL of heparinized crystalloid solution, connected by silicone tubing to a draining catheter in the right jugular vein and an inflow catheter in the right femoral artery, and a circulating water bath. VF was initiated in adult male Sprague-Dawley rats (450 g, anesthetized) endocardially. After 10 min of CA, rats were resuscitated with ECPB at a flow rate of 50 mL/min, mechanical ventilations and drugs (epinephrine, bicarbonate, heparin). With start of ECPB, rats were cooled to mild therapeutic hypothermia. After defibrillation and ROSC, rats were weaned from CPB and maintained at 33°C for 5 hours. Outcome parameters included resuscitability, survival to 1 month with neurologic deficit score (NDS; 0% = normal, 100% = dead), overall performance category (OPC; 1 = normal, 5 = dead) and a histologic damage score (HDS, pending). All data is presented as mean±SD. RESULTS: ROSC was achieved in 14 / 14 animals within 3.3±0.9 min on bypass, 10 / 14 animals survived to 1 month (7 OPC 1, 3 OPC 2). NDS was 1.9±2.5. All animals experienced marked neurologic (motoric, sensory and cognitive) and overall improvement over the long observation period. The deficits that persisted were motoric on the lower extremities. CONCLUSION: In a rat model of prolonged VF CA, ECPB resuscitation with mild hypothermia leads to 100% resuscitability and favorable functional outcome and long-term survival after 10 min of VF.

BACKGROUND: Exact and valid temperature measurement is crucial to assess the effects of temperature levels on outcome after cardiac arrest (CA). In this study, we assessed the temperature profile in different body locations in our rat ventricular fibrillation (VF) CA model with emergency cardiopulmonary bypass (ECPB) resuscitation. METHODS: Adult Sprague-Dawley rats (400g) were equipped with esophagus (Tes), tympanic (Ttym) and rectal (Trec) temperature probes along standard instrumentation. Following 10 min of VF CA, rats were randomized to normothermic control (NT, 37±0.5°C), mild hypothermic (MH, 33±0.5°C) or deep hypothermic (DH, 27±0.5°C) reperfusion and put on ECPB for 15 min. On ECPB rats were rapidly cooled to and maintained at target temperature. After ECPB and return of spontaneous circulation (ROSC), MH and DH were maintained mild hypothermic with surface cooling/warming. Temperature profiles for the first five rats in the DH group are presented as mean±SD, variances tested by ANOVA and post-hoc Tukey analysis. Results: Before CA, all rats were normothermic with all three probes and cooled passively by 0.8±0.6°C during CA. In the MH and NT group, no differences in temperature measurements were found during the entire experiment, whereas in the DH group, temperature profile of the three probes significantly differed, which is presented below. With start of ECPB, cooling rate was significantly higher according to Tes (2.5±0.7°C/min) versus Ttym (1.4±0.6, p=0.44) or Trec (0.6±0.2, p=0.002) and target temperature reached by Tes within 2.8±1.0 min, but only in two animals by Ttym (4.5±0.7 min) and not at all by Trec. Rewarming rate to mild hypothermia at the end of ECPB did not vary significantly between probes (0.12±0.02) and was reached by 33±4 min. CONCLUSION: Even in a small animal model, temperature differs significantly in measurement locations. But what is true brain temperature? In future studies, measurement of brain temperature might be indicated.

Aim of the studyTo determine the incidence of out-of-hospital cardiac arrest and the survival rate of those patients who received CPR in the city of Vienna.MethodsA cohort of patients with out-of-hospital cardiac arrests and who were treated by the Vienna Ambulance Service between January 1, 2009, and December 31, 2010, were followed up until either death or hospital discharge. The associations of survival and neurological outcome with their potential predictors were analysed using simple logistic regression models. Odds ratios were estimated for each factor.ResultsDuring the observation period, a total of 7030 (206.8/100,000 inhabitants/year) patients without signs of circulation were assessed by teams of the Vienna Ambulance Service, and 1448 adult patients were resuscitated by emergency medical service personnel. A sustained return of spontaneous circulation was reported in 361 (24.9%) of the treated patients, and in all 479 (33.0%) of the patients were taken to the emergency department. A total of 164 (11.3%) of the patients were discharged from the hospital alive, and 126 (8.7%) of the patients showed cerebral performance categories of 1 or 2 at the time of discharge. Younger age, an arrest in a public area, a witnessed arrest and a shockable rhythm were associated with a higher probability of survival to hospital discharge.ConclusionSurvival rates for out-of-hospital cardiac arrests remain low. Efforts should be focused on rapidly initiating basic life support, early defibrillation, and high-quality CPR by emergency medical services and state-of-the art post-resuscitation care.