Endothelin type A-antagonist improves long-term neurological recovery after cardiac arrest in rats

Brain vulnerability and viability after ischaemia

The susceptibility of the brain to ischaemic injury dramatically limits its viability following interruptions in blood flow. However, data from studies of dissociated cells, tissue specimens, isolated organs and whole bodies have brought into question the temporal limits within which the brain is capable of tolerating prolonged circulatory arrest. This Review assesses cell type-specific mechanisms of global cerebral ischaemia, and examines the circumstances in which the brain exhibits heightened resilience to injury. We suggest strategies for expanding such discoveries to fuel translational research into novel cytoprotective therapies, and describe emerging technologies and experimental concepts. By doing so, we propose a new multimodal framework to investigate brain resuscitation following extended periods of circulatory arrest.

Cerebral microcirculatory alterations and the no-reflow phenomenon in vivo after experimental pediatric cardiac arrest

Decreased cerebral blood flow (CBF) after cardiac arrest (CA) contributes to secondary ischemic injury in infants and children. We previously reported cortical hypoperfusion with tissue hypoxia early in a pediatric rat model of asphyxial CA. In order to identify specific alterations as potential therapeutic targets to improve cortical hypoperfusion post-CA, we characterize the CBF alterations at the cortical microvascular level in vivo using multiphoton microscopy. We hypothesize that microvascular constriction and disturbances of capillary red blood cell (RBC) flow contribute to cortical hypoperfusion post-CA. After resuscitation from 9 min asphyxial CA, transient dilation of capillaries and venules at 5 min was followed by pial arteriolar constriction at 30 and 60 min (19.6 ± 1.3, 19.3 ± 1.2 µm at 30, 60 min vs. 22.0 ± 1.2 µm at baseline, p < 0.05). At the capillary level, microcirculatory disturbances were highly heterogeneous, with RBC stasis observed in 25.4% of capillaries at 30 min post-CA. Overall, the capillary plasma mean transit time was increased post-CA by 139.7 ± 51.5%, p < 0.05. In conclusion, pial arteriolar constriction, the no-reflow phenomenon and increased plasma transit time were observed post-CA. Our results detail the microvascular disturbances in a pediatric asphyxial CA model and provide a powerful platform for assessing specific vascular-targeted therapies.

Therapeutic hypothermia attenuates paraplegia and neuronal damage in the lumbar spinal cord in a rat model of asphyxial cardiac arrest

Spinal cord ischemia can result from cardiac arrest. It is an important cause of severe spinal cord injury that can lead to serious spinal cord disorders such as paraplegia. Hypothermia is widely acknowledged as an effective neuroprotective intervention following cardiac arrest injury. However, studies on effects of hypothermia on spinal cord injury following asphyxial cardiac arrest and cardiopulmonary resuscitation (CA/CPR) are insufficient. The objective of this study was to examine effects of hypothermia on motor deficit of hind limbs of rats and vulnerability of their spinal cords following asphyxial CA/CPR. Experimental groups included a sham group, a group subjected to CA/CPR, and a therapeutic hypothermia group. Severe motor deficit of hind limbs was observed in the control group at 1 day after asphyxial CA/CPR. In the hypothermia group, motor deficit of hind limbs was significantly attenuated compared to that in the control group. Damage/death of motor neurons in the lumbar spinal cord was detected in the ventral horn at 1 day after asphyxial CA/CPR. Neuronal damage was significantly attenuated in the hypothermia group compared to that in the control group. These results indicated that therapeutic hypothermia after asphyxial CA/CPR significantly reduced hind limb motor dysfunction and motoneuronal damage/death in the ventral horn of the lumbar spinal cord following asphyxial CA/CPR. Thus, hypothermia might be a therapeutic strategy to decrease motor dysfunction by attenuating damage/death of spinal motor neurons following asphyxial CA/CPR.

Extracorporeal Life Support Increases Survival After Prolonged Ventricular Fibrillation Cardiac Arrest in the Rat

Background:

Extracorporeal life support (ECLS) for cardiopulmonary resuscitation (CPR) may increase end organ perfusion and thus survival when conventional CPR fails. The aim was to investigate, if after ventricular fibrillation cardiac arrest in rodents ECLS improves outcome compared with conventional CPR.

Methods:

In 24 adult male Sprague–Dawley rats (460–510 g) resuscitation was started after 10 min of no-flow with ECLS (consisting of an open reservoir, roller pump, and membrane oxygenator, connected to cannulas in the jugular vein and femoral artery, n = 8) or CPR (mechanical chest compressions plus ventilations, n = 8) and compared with a sham group (n = 8). After return of spontaneous circulation (ROSC), all rats were maintained at 33°C for 12 h. Survival to 14 days, neurologic deficit scores and overall performance categories were assessed.

Results:

ECLS leads to sustained ROSC in 8 of 8 (100%) and neurological intact survival to 14 days in 7 of 8 rats (88%), compared with 5 of 8 (63%) and 1 of 8 CPR rats. The median survival time was 14 days (IQR: 14–14) in the ECLS and 1 day (IQR: 0 to 5) for the CPR group (P = 0.004).

Conclusion:

In a rat model of prolonged ventricular fibrillation cardiac arrest, ECLS with mild hypothermia produces 100% resuscitability and 88% long-term survival, significantly better than conventional CPR.

Cerebral Perfusion and Cerebral Autoregulation after Cardiac Arrest

Out of hospital cardiac arrest is the leading cause of death in industrialized countries. Recovery of hemodynamics does not necessarily lead to recovery of cerebral perfusion. The neurological injury induced by a circulatory arrest mainly determines the prognosis of patients after cardiac arrest and rates of survival with a favourable neurological outcome are low. This review focuses on the temporal course of cerebral perfusion and changes in cerebral autoregulation after out of hospital cardiac arrest. In the early phase after cardiac arrest, patients have a low cerebral blood flow that gradually restores towards normal values during the first 72 hours after cardiac arrest. Whether modification of the cerebral blood flow after return of spontaneous circulation impacts patient outcome remains to be determined.

Comparing anesthesia with isoflurane and fentanyl/fluanisone/midazolam in a rat model of cardiac arrest

Only one in ten patients survives cardiac arrest (CA), underscoring the need to improve CA management. Isoflurane has shown cardio- and neuroprotective effects in animal models of ischemia-reperfusion injury. Therefore, the beneficial effect of isoflurane should be tested in an experimental CA model. We hypothesize that isoflurane anesthesia improves short-term outcome following resuscitation from CA compared with a subcutaneous fentanyl/fluanisone/midazolam anesthesia. Male Sprague-Dawley rats were randomized to anesthesia with isoflurane ( n = 11) or fentanyl/fluanisone/midazolam ( n = 11). After 10 min of asphyxial CA, animals were resuscitated by mechanical chest compressions, ventilations, and epinephrine and observed for 30 min. Hemodynamics, including coronary perfusion pressure, systemic O2 consumption, and arterial blood gases, were recorded throughout the study. Plasma samples for endothelin-1 and cathecolamines were drawn before and after CA. Compared with fentanyl/fluanisone/midazolam anesthesia, isoflurane resulted in a shorter time to return of spontaneous circulation (ROSC), less use of epinephrine, increased coronary perfusion pressure during cardiopulmonary resusitation, higher mean arterial pressure post-ROSC, increased plasma levels of endothelin-1, and decreased levels of epinephrine. The choice of anesthesia did not affect ROSC rate or systemic O2 consumption. Isoflurane reduces time to ROSC, increases coronary perfusion pressure, and improves hemodynamic function, all of which are important parameters in CA models.

NEW & NOTEWORTHY The preconditioning effect of volatile anesthetics in studies of ischemia-reperfusion injury has been demonstrated in several studies. This study shows the importance of anesthesia in experimental cardiac arrest studies as isoflurane raised coronary perfusion pressure during resuscitation, reduced time to return of spontaneous circulation, and increased arterial blood pressure in the post-cardiac arrest period. These effects on key outcome measures in cardiac arrest research are important in the interpretation of results from animal studies.

Alterations in Cerebral Blood Flow after Resuscitation from Cardiac Arrest

Greater than 50% of patients successfully resuscitated from cardiac arrest have evidence of neurological disability. Numerous studies in children and adults, as well as in animal models have demonstrated that cerebral blood flow (CBF) is impaired after cardiac arrest. Stages of cerebral perfusion post-resuscitation include early hyperemia, followed by hypoperfusion, and finally either resolution of normal blood flow or protracted hyperemia. At the level of the microcirculation the blood flow is heterogeneous, with areas of no flow, low flow, and increased flow. CBF directed therapies in animal models of cardiac arrest improved neurological outcome, and therefore, the alterations in CBF after cardiac arrest likely contribute to the development of hypoxic ischemic encephalopathy. Current intensive care after cardiac arrest is centered upon maintaining systemic oxygenation, normal blood pressure values for age, maintaining general homeostasis, and avoiding hyperthermia. Assessment of CBF and oxygenation is not routinely performed after cardiac arrest. Currently available and underutilized techniques to assess cerebral perfusion include transcranial doppler, near-infrared spectroscopy, and arterial spin labeling magnetic resonance imaging. Limited clinical studies established the role of CBF and oxygenation monitoring in prognostication after cardiac arrest and few studies suggest that guiding critical care post-resuscitation to mean arterial pressures above the minimal autoregulatory range might improve outcome. Important knowledge gaps thus remain in cerebral monitoring and CBF and oxygen goal-directed therapies post-resuscitation from cardiac arrest.

Association between initial prescribed minute ventilation and post-resuscitation partial pressure of arterial carbon dioxide in patients with post-cardiac arrest syndrome

BACKGROUND

Post-cardiac arrest hypocapnia/hypercapnia have been associated with poor neurological outcome. However, the impact of arterial carbon dioxide (CO2) derangements during the immediate post-resuscitation period following cardiac arrest remains uncertain. We sought to test the correlation between prescribed minute ventilation and post-resuscitation partial pressure of CO2 (PaCO2), and to test the association between early PaCO2 and neurological outcome.

METHODS

We retrospectively analyzed a prospectively compiled single-center cardiac arrest registry. We included adult (age ≥ 18 years) patients who experienced a non-traumatic cardiac arrest and required mechanical ventilation. We analyzed initial post-resuscitation ventilator settings and initial arterial blood gas analysis (ABG) after initiation of post-resuscitation ventilator settings. We calculated prescribed minute ventilation:MVmL/kg/min=tidalvolumeTV/idealbodyweightIBWxrespiratoryrateRRfor each patient. We then used Pearson's correlation to test the correlations between prescribed MV and PaCO2. We also determined whether patients had normocapnia (PaCO2 between 30 and 50 mmHg) on initial ABG and tested the association between normocapnia and good neurological function (Cerebral Performance Category 1 or 2) at hospital discharge using logistic regression analyses.

RESULTS

Seventy-five patients were included. The majority of patients were in-hospital arrests (85%). Pulseless electrical activity/asystole was the initial rhythm in 75% of patients. The median (IQR) TV, RR, and MV were 7 (7 to 8) mL/kg, 14 (14 to 16) breaths/minute, and 106 (91 to 125) mL/kg/min, respectively. Hypocapnia, normocapnia, and hypercapnia were found in 15%, 62%, and 23% of patients, respectively. Good neurological function occurred in 32% of all patients, and 18%, 43%, and 12% of patients with hypocapnia, normocapnia, and hypercapnia respectively. We found prescribed MV had only a weak correlation with initial PaCO2, R = -0.40 (P < 0.001). Normocapnia was associated with good neurological function, odds ratio 4.44 (95% CI 1.33 to 14.85).

CONCLUSIONS

We found initial prescribed MV had only a weak correlation with subsequent PaCO2 and that early Normocapnia was associated with good neurological outcome. These data provide rationale for future research to determine the impact of PaCO2 management during mechanical ventilation in post-cardiac arrest patients.

Association Between Postresuscitation Partial Pressure of Arterial Carbon Dioxide and Neurological Outcome in Patients With Post–Cardiac Arrest Syndrome

Background—

Partial pressure of arterial CO 2 (Pa co 2 ) is a regulator of cerebral blood flow after brain injury. Recent guidelines for the management of cardiac arrest recommend maintaining Pa co 2 at 40 to 45 mm Hg after successful resuscitation; however, there is a paucity of data on the prevalence of Pa co 2 derangements during the post–cardiac arrest period and its association with outcome.

Methods and Results—

We analyzed a prospectively compiled and maintained cardiac arrest registry at a single academic medical center. Inclusion criteria are as follows: age ≥18, nontrauma arrest, and comatose after return of spontaneous circulation. We analyzed arterial blood gas data during 0 to 24 hours after the return of spontaneous circulation and determined whether patients had exposure to hypocapnia and hypercapnia (defined as Pa co 2 ≤30 mm Hg and Pa co 2 ≥50 mm Hg, respectively, based on previous literature). The primary outcome was poor neurological function at hospital discharge, defined as Cerebral Performance Category ≥3. We used multivariable logistic regression, with multiple sensitivity analyses, adjusted for factors known to predict poor outcome, to determine whether post–return of spontaneous circulation hypocapnia and hypercapnia were independent predictors of poor neurological function. Of 193 patients, 52 (27%) had hypocapnia only, 63 (33%) had hypercapnia only, 18 (9%) had both hypocapnia and hypercapnia exposure, and 60 (31%) had no exposure; 74% of patients had poor neurological outcome. Hypocapnia and hypercapnia were independently associated with poor neurological function, odds ratio 2.43 (95% confidence interval, 1.04–5.65) and 2.20 (95% confidence interval, 1.03–4.71), respectively.

Conclusions—

Hypocapnia and hypercapnia were common after cardiac arrest and were independently associated with poor neurological outcome. These data suggest that Pa co 2 derangements could be potentially harmful for patients after resuscitation from cardiac arrest.

[Comments on the 2010 guidelines on cardiopulmonary resuscitation of the European Resuscitation Council]

ADULTS

Administer chest compressions (minimum 100/min, minimum 5 cm depth) at a ratio of 30:2 with ventilation (tidal volume 500-600 ml, inspiration time 1 s, F(I)O₂ if possible 1.0). Avoid any interruptions in chest compressions. After every single defibrillation attempt (initially biphasic 120-200 J, monophasic 360 J, subsequently with the respective highest energy), chest compressions are initiated again immediately for 2 min independent of the ECG rhythm. Tracheal intubation is the optimal method for securing the airway during resuscitation but should be performed only by experienced airway management providers. Laryngoscopy is performed during ongoing chest compressions; interruption of chest compressions for a maximum of 10 s to pass the tube through the vocal cords. Supraglottic airway devices are alternatives to tracheal intubation. Drug administration routes for adults and children: first choice i.v., second choice intraosseous (i.o.). Vasopressors: 1 mg epinephrine every 3-5 min i.v. After the third unsuccessful defibrillation amiodarone (300 mg i.v.), repetition (150 mg) possible. Sodium bicarbonate (50 ml 8.4%) only for excessive hyperkaliemia, metabolic acidosis, or intoxication with tricyclic antidepressants. Consider aminophylline (5 mg/kgBW). Thrombolysis during spontaneous circulation only for myocardial infarction or massive pulmonary embolism; during on-going cardiopulmonary resuscitation (CPR) only when indications of massive pulmonary embolism. Active compression-decompression (ACD-CPR) and inspiratory threshold valve (ITV-CPR) are not superior to good standard CPR.

CHILDREN

Most effective improvement of outcome by prevention of full cardiorespiratory arrest. Basic life support: initially five rescue breaths, followed by chest compressions (100-120/min depth about one third of chest diameter), compression-ventilation ratio 15:2. Foreign body airway obstruction with insufficient cough: alternate back blows and chest compressions (infants), or abdominal compressions (children >1 year). Treatment of potentially reversible causes: ("4 Hs and 4 Ts") hypoxia and hypovolaemia, hypokalaemia and hyperkalaemia, hypothermia, and tension pneumothorax, tamponade, toxic/therapeutic disturbances, thrombosis (coronary/pulmonary). Advanced life support: adrenaline (epinephrine) 10 µg/kgBW i.v. or i.o. every 3-5 min. Defibrillation (4 J/kgBW; monophasic or biphasic) followed by 2 min CPR, then ECG and pulse check. NEWBORNS: Initially inflate the lungs with bag-valve mask ventilation (p(AW) 20-40 cmH₂O). If heart rate remains <60/min, start chest compressions (120 chest compressions/min) and ventilation with a ratio 3:1. Maintain normothermia in preterm babies by covering them with foodgrade plastic wrap or similar. POSTRESUSCITATION PHASE: Early protocol-based intensive care stabilization; initiate mild hypothermia early regardless of initial cardiac rhythm [32-34°C for 12-24 h (adults) or 24 h (children); slow rewarming (<0.5°C/h)]. Consider percutaneous coronary intervention (PCI) in patients with presumed cardiac ischemia. Prediction of CPR outcome is not possible at the scene, determine neurological outcome <72 h after cardiac arrest with somatosensory evoked potentials, biochemical tests and neurological examination. ACUTE CORONARY SYNDROME: Even if only a weak suspicion of an acute coronary syndrome is present, record a prehospital 12-lead ECG. In parallel to pain therapy, administer aspirin (160-325 mg p.o. or i.v.) and clopidogrel (75-600 mg depending on strategy); in ST-elevation myocardial infarction (STEMI) and planned PCI also prasugrel (60 mg p.o.). Antithrombins, such as heparin (60 IU/kgBW, max. 4000 IU), enoxaparin, bivalirudin or fondaparinux depending on the diagnosis (STEMI or non-STEMI-ACS) and the planned therapeutic strategy. In STEMI define reperfusion strategy depending on duration of symptoms until PCI, age and location of infarction. TRAUMA: In severe hemorrhagic shock, definitive control of bleeding is the most important goal. For successful CPR of trauma patients a minimal intravascular volume status and management of hypoxia are essential. Aggressive fluid resuscitation, hyperventilation and excessive ventilation pressure may impair outcome in patients with severe hemorrhagic shock.

TRAINING

Any CPR training is better than nothing; simplification of contents and processes is the main aim.

Amelioration of hypoperfusion after traumatic brain injury by in vivo endothelin-1 knockout

Endothelin 1 (ET-1) is one of the most powerful vasoconstrictors in the brain. Its expression is upregulated after traumatic brain injury (TBI) and is a major factor in the ensuing hypoperfusion. Attenuation of ET-1 effects has been mainly achieved by blockade of its receptors. The result of a direct blockade of ET-1 mRNA synthesis is not known. We used the Marmarou's model to inflict injury to male Sprague-Dawley rats injected with antisense ET-1 oligodeoxynucleotides (ODNs) before injury. Laser Doppler flowmetry in noninjured rats (2 groups, i.e., untreated and animals that received cODNs) revealed a constant cerebral blood flow of approximately 14 mL.min-1.100 g-1, whereas the values from injured animals pretreated with control ODNs (cODNs) or from animals subjected to TBI alone were approximately 8.0 mL.min-1.100 g-1 during the 18-48 h time period post-TBI. After antisense ET-1 ODNs pretreatment, however, cerebral blood flow in injured animals was approximately 17 mL.min-1.100 g-1 during the 6-48 h time period. Antisense ET-1 ODNs-treated animals also had 19%-29% larger microvessel cross-sectional area and approximately one-third less ET-1 immunoreactivity in the 50-75% range after injury than did cODNs-treated animals after TBI. The results indicate that this direct in vivo approach is an effective therapeutic intervention for the restoration of cerebral blood flow after TBI.

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.

Changes in cerebral blood flow and oxygen extraction during post-resuscitation syndrome

INTRODUCTION

Most survivors of out-of-hospital cardiac arrest (OHCA) will die subsequently from post-anoxic encephalopathy. In animals, the severity of brain damage is mainly influenced by the duration of cardiac arrest and also by the cerebral blood flow (CBF) and oxygen extraction (CEO2) abnormalities observed during the post-resuscitation period. The aim of our study was to describe CBF and CEO2 modifications during the first 72 h in OHCA patients treated by induced mild hypothermia.

METHODS

Consecutive OHCA patients were studied every 12 h over 72 h. Diastolic flow velocities (dFV), mean flow velocities (mFV) and pulsatility index (PI) were assessed by transcranial doppler (TCD) as an estimate of CBF changes. Simultaneous measurements of CEO2 were obtained using retrograde jugular catheterisation.

RESULTS

Eighteen patients (61 [47-74] years) were studied (12 non-survivors and 6 survivors). At admission, mFV values were low (27.3 [21.5-33.6]cm/s) but reached normal values after 72 h (50.5 [36.7-58.1]cm/s). Initial PI values were high (1.6 [1.3-1.9]) but reached normal values after 72 h (1.04 [0.82-1.2]). No differences were found between survivors and non-survivors regarding these CBF estimates. CEO2 values were quite normal at admission (20.4 [11-27%]) but decreased over time in non-survivors until H72 (25.8% [19.3-31.1] versus 5.7% [5.1-11.5], p=0.02).

CONCLUSION

Cerebral haemodynamic and oxygenation values are altered considerably but evolve during the first 72 h following resuscitation after cardiac arrest. In particular, these changes may lead to a mismatch between CBF and CEO2 leading to a "luxurous perfusion" in non-survivors.

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.

[The new 2005 resuscitation guidelines of the European Resuscitation Council: comments and supplements]

The new CPR guidelines are based on a scientific consensus which was reached by 281 international experts. Chest compressions (100/min, 4-5 cm deep) should be performed in a ratio of 30:2 with ventilation (tidal volume 500 ml, Ti 1 s, FIO2 if possible 1.0). After a single defibrillation attempt (initially biphasic 150-200 J, monophasic 360 J, subsequently with the respective highest energy), chest compressions are initiated again immediately for 2 min. Endotracheal intubation is the gold standard; other airway devices may be employed as well depending on individual skills. Drug administration routes for adults and children: first choice IV, second choice intraosseous, third choice endobronchial [epinephrine dose 2-3x (adults) or 10x (pediatric patients) higher than IV]. Vasopressors: 1 mg epinephrine every 3-5 min IV. After the third unsuccessful defibrillation attempt amiodarone IV (300 mg); repetition (150 mg) possible. Sodium bicarbonate (1 ml/kg 8.4%) only in excessive hyperkalemia, metabolic acidosis, or intoxication with tricyclic antidepressants. Consider atropine (3 mg) and aminophylline (5 mg/kg). Thrombolysis during spontaneous circulation only in myocardial infarction or massive pulmonary embolism; during CPR only during massive pulmonary embolism. Cardiopulmonary bypass only after cardiac surgery, hypothermia or intoxication. Pediatrics: best improvement in outcome by preventing cardiocirculatory collapse. Alternate chest thumps and chest compression (infants), or abdominal compressions (>1-year-old) in foreign body airway obstruction. Initially five breaths, followed by chest compressions (100/min; approximately 1/3 of chest diameter): ventilation ratio 15:2. Treatment of potentially reversible causes (4 "Hs", "HITS": hypoxia, hypovolemia, hypo- and hyperkaliemia, hypothermia, cardiac tamponade, intoxication, thrombo-embolism, tension pneumothorax). Epinephrine 10 microg/kg IV or intraosseously, or 100 microg (endobronchially) every 3-5 min. Defibrillation (4 J/kg; monophasic oder biphasic) followed by 2 min CPR, then ECG and pulse check. Newborns: inflate the lungs with bag-valve mask ventilation. If heart rate<60/min chest compressions:ventilation ratio 3:1 (120 chest compressions/min). Postresuscitation phase: initiate mild hypothermia [32-34 degrees C for 12-24 h; slow rewarming (<0.5 degrees C/h)]. Prediction of CPR outcome is not possible at the scene; determining neurological outcome within 72 h after cardiac arrest with evoked potentials, biochemical tests and physical examination. Even during low suspicion for an acute coronary syndrome, record a prehospital 12-lead ECG. In parallel to pain therapy, aspirin (160-325 mg PO or IV) and in addition clopidogrel (300 mg PO). As antithrombin, heparin (60 IU/kg, max. 4000 IU) or enoxaparine. In ST-segment elevation myocardial infarction, define reperfusion strategy depending on duration of symptoms until PCI (prevent delay>90 min until PCI). Stroke is an emergency and needs to be treated in a stroke unit. A CT scan is the most important evaluation, MRT may replace a CT scan. After hemorrhage exclusion, thrombolysis within 3 h of symptom onset (0.9 mg/kg rt-PA IV; max 90 mg within 60 min, 10% of the entire dosage as initial bolus, no aspirin, no heparin within the first 24 h). In severe hemorrhagic shock, definite control of bleeding is the most important goal. For successful CPR of trauma patients, a minimal intravascular volume status and management of hypoxia are essential. Aggressive fluid resuscitation, hyperventilation, and excessive ventilation pressure may impair outcome in severe hemorrhagic shock. Despite bad prognosis, CPR in trauma patients may be successful in select cases. Any CPR training is better than nothing; simplification of contents and processes remains important.

Neuronal damage in rat brain and spinal cord after cardiac arrest and massive hemorrhagic shock*

OBJECTIVE

Severe global ischemia often results in severe damage to the central nervous system of survivors. Hind-limb paralysis is a common deficit caused by global ischemia. Until recently, most studies of global ischemia of the central nervous system have examined either the brain or spinal cord, but not both. Spinal cord damage specifically after global ischemia has not been studied in detail. Because the exact nature of the neuronal damage to the spinal cord and the differences in neuronal damage between the brain and spinal cord after global ischemia are poorly understood, we developed a new global ischemia model in the rat and specifically studied spinal cord damage after global ischemia. Further, we compared the different forms of neuronal damage between the brain and spinal cord after global ischemia.

DESIGN

Randomized, controlled study using three different global ischemia models in the rat.

SETTING

University research laboratory.

SUBJECTS

Male, adult Sprague-Dawley rats (300 g).

INTERVENTIONS

Animals were divided into three experimental groups, group A (n = 6, survived for 7 days), 12 mins of hemorrhagic shock; group B (n = 6, survived for 7 days), 5 mins of cardiac arrest; or group C (n = 6, each for 6 hrs, 12 hrs, 1 day, 3 days, and 7 days), 7 mins of hemorrhagic shock and 5 mins of cardiac arrest. Motor deficit of the hind limbs was studied 6 hrs to 7 days after resuscitation. Also, nonoperated animals (n = 6) were used as the control. Histologic analysis (hematoxylin and eosin, Fluoro-Jade B, terminal deoxynucleotidyl transferase- mediated dUTP end-labeling [TUNEL], Klüver-Barrera) and ultrastructural analysis using electron microscopy were performed on samples from the CA1 region of the hippocampus and lumbar spinal cord. Demyelination of the white matter of the lumbar spinal cord was analyzed semiquantitatively using Scion Image software.

MAIN RESULTS

No paraplegic animals were observed in either group A or B. All group C animals showed severe hind-limb paralysis. Severe neuronal damage was found in the CA1 region of the hippocampus in all groups, and the state of delayed neuronal cell death was similar among the three groups. Neuronal damage in the lumbar spinal cord was detected only in group C animals, mainly in the dorsal horn and intermediate gray matter. Demyelination was prominent in the ventral and ventrolateral white matter in group C. A significant difference was observed between control and group C rats with Scion Image software. Ultrastructural analysis revealed extensive necrotic cell death in the intermediate gray matter in the lumbar spinal cord in group C rats.

CONCLUSION

The combination in the global ischemia model (i.e., hemorrhagic shock followed by cardiac arrest) caused severe neuronal damage in the central nervous system. Thereby, hind-limb paralysis after global ischemia might result from spinal cord damage. These results suggest that therapeutic strategies for preventing spinal cord injury are necessary when treating patients with severe global ischemia.

A selective endothelin ETA receptor antagonist, SB 234551, improves cerebral perfusion following permanent focal cerebral ischemia in rats

In recent experimental studies, a selective antagonist of endothelin ET(A) receptors, SB 234551, improved neurological and histological outcome in both head trauma and transient focal cerebral ischemia. The present study was conducted to ascertain the degree to which hemodynamic alterations are responsible for this therapeutic effect in a model of permanent middle cerebral artery occlusion (MCAo) in rats. Anesthetized Sprague-Dawley rats were subjected to permanent MCAo by insertion of an intraluminal nylon suture coated with poly-L-lysine. The agent (SB 234551, 30 microg/kg/min = 1.8 mg/kg/h) or vehicle (PBS; 0.6 ml/h) was administered by i.v. infusion beginning 15 min after onset of MCAo and lasting for 23.75 h. Autoradiographic measurement of local cerebral blood flow (lCBF) was performed at 24 h. Physiological data were similar among groups. SB 234551 augmented perfusion by 1.7- to 1.8-fold in both the ischemic hemisphere and in the contralateral (non-ischemic) hemisphere when compared to vehicle-treated ischemic animals. In the ischemic hemisphere, the brain regions significantly benefited were those lying outside the zone of most dense ischemia (i.e., paramedian cortex and thalamus), while in the non-ischemic hemisphere all regions measured showed significant lCBF augmentation. This study demonstrates that SB 234551 therapy results in significant improvement of local cerebral perfusion in the ischemic as well as in the non-ischemic hemispheres after permanent MCAo.

Effects of hypertonic versus isotonic infusion therapy on regional cerebral blood flow after experimental cardiac arrest cardiopulmonary resuscitation in pigs

OBJECTIVE

To evaluate the effects of hypertonic, isooncotic, and isotonic infusion therapy on cerebral blood flow (CBF) during and after cardiopulmonary resuscitation (CPR) from experimental cardiac arrest (CA).

METHODS

In 32 domestic swine (13-23 kg) open chest CPR was initiated after 8 min of ventricular fibrillation. With the onset of CPR animals randomly received 2 ml/kg per 10 min of either hypertonic saline (HS: 7.2% NaCl), hypertonic-isooncotic HES-saline (HHS: 7.2% NaCl in 6% HES 200,000/0.5), isooncotic HES (6% HES 200,000/0.5), or isotonic (normal) saline (NS: 0.9% NaCl). Haemodynamic variables were monitored continuously, and coloured microspheres were used to measure CBF quantitatively before CA, during CPR, and 20, 90 and 240 min after restoration of spontaneous circulation (ROSC).

RESULTS

In HES/NaCl treated animals, CBF significantly decreased during CPR compared to the prearrest level (P < 0.01, respectively; MANOVA). In contrast, CBF was sustained during CPR in HS/HHS treated animals and significantly higher compared to animals receiving NS (P < 0.05, respectively). During recirculation severe postischaemic hypoperfusion as indicated by a decrease of CBF below the prearrest level, was present only in animals receiving HES and NS.

CONCLUSIONS

Hypertonic solutions (HS/HHS) applied during internal cardiac massage enhanced CBF during CPR and after ROSC.

Vasopressor agents: old and new components

PURPOSE OF REVIEW

In settings of cardiac arrest, reestablishing vital organ perfusion plays an important role in initial CPR. As a pharmacologic intervention, vasopressor agents aim to improve aortic diastolic pressure and, consequently, coronary and cerebral perfusion pressures.

RECENT FINDINGS

Historically, adrenergic agonists such as epinephrine have been suggested for routine use in CPR. However, epinephrine's efficacy is controversial because of its unfavorable inotropic and chronotropic action. This has prompted research into the use of alternative pressor agents with more promising hemodynamic features; these include selective alpha 2-adrenergic agonists and other nonadrenergic vasoconstrictors such as vasopressin.

SUMMARY

In this article, the main traditional and novel adrenergic and nonadrenergic vasopressor drugs are reviewed.

Time course of circulatory and metabolic recovery of cat brain after cardiac arrest assessed by perfusion- and diffusion-weighted imaging and MR-spectroscopy

Brain recovery after cardiac arrest (CA) was assessed in cats using arterial spin tagging perfusion-weighted imaging (PWI), diffusion-weighted imaging (DWI), and 1H-spectroscopy (1H-MRS). Cerebral reperfusion and metabolic recovery was monitored in the cortex and in basal ganglia for 6 h after cardiopulmonary resuscitation (CPR). Furthermore, the effects of an hypertonic/hyperoncotic solution (7.5% NaCl/6% hydroxyl ethyl starch, HES) and a tissue-type plasminogen activator (TPA), applied during CPR, were assessed on brain recovery. CA and CPR were carried out in the MR scanner by remote control. CA for 15-20 min was induced by electrical fibrillation of the heart, followed by CPR using a pneumatic vest. PWI after successful CPR revealed initial cerebral hyperperfusion followed by delayed hypoperfusion. Initial cerebral recirculation was improved after osmotic treatment. Osmotic and thrombolytic therapy were ineffective in ameliorating delayed hypoperfusion. Calculation of the apparent diffusion coefficient (ADC) from DWI demonstrated complete recovery of ion and water homeostasis in all animals. 1H-MRS measurements of lactate suggested an extended preservation of post-ischaemic anaerobic metabolism after TPA treatment. The combination of noninvasive MR techniques is a powerful tool for the evaluation of therapeutical strategies on circulatory and metabolic cerebral recovery after experimental cerebral ischaemia.

Dependence of early cerebral reperfusion and long-term outcome on resuscitation efficiency after cardiac arrest in rats

BACKGROUND AND PURPOSE

While it is well known that longer duration of cardiac arrest (CA) is often associated with poorer long-term outcome, the influence of resuscitation efficacy on postischemia recovery is less clear. The objective of the present study is to investigate whether an inadequate and prolonged resuscitation after a shorter CA can lead to worse long-term outcomes than an effective resuscitation after a longer CA, provided that the total time from the onset of CA to the return of spontaneous circulation is comparable.

METHODS

Thirty-eight rats were randomized into 2 groups with nominal 9 minutes (group 1) and 15 minutes (group 2) of normothermic asphyxial CA. Each group was further divided into 2 subgroups on the basis of the duration of resuscitation efforts (labeled as S and L for short and long, respectively). Thus, the asphyxia and nominal resuscitation times were 8 and 1 minute, respectively, for group 1S, 5 and 4 minutes for group 1L, 14 and 1 minute for group 2S, and 11 and 4 minutes for group 2L. Cerebral perfusion was measured continuously at the dorsal hippocampus level before, during, and after the CA, with the use of the arterial spin labeling MRI technique. The survival time, histological damage, and neurological deficit were evaluated 5 days after resuscitation.

RESULTS

Groups 1S and 1L had nearly the same duration of CA (9.02 +/- 0.17 minutes, n=6 versus 8.58 +/- 0.80 minutes, n=6). The same is true for groups 2S and 2L (15.51 +/- 0.59 minutes, n=11 versus 15.65 +/- 1.25 minutes, n=15). Despite longer asphyxia, shorter and more effective resuscitation was associated with significantly improved long-term outcomes and higher cerebral perfusion at the early stage of reperfusion.

CONCLUSIONS

Effective resuscitation increased early reperfusion and improved survival after CA. The clinical implication is that inadequate and prolonged resuscitation may have detrimental effects on the recovery of CA patients.

Regional dependence of cerebral reperfusion after circulatory arrest in rats

The severity of neurologic dysfunction after circulatory arrest depends on cerebral reperfusion during and after resuscitation. The objective of current study was to investigate the temporal and spatial patterns of the cerebral perfusion immediately after resuscitation. Precise control of circulatory arrest was achieved in rats by combination of asphyxia and transient blockage of cardiac-specific beta-adrenergic receptors with esmolol, an ultra-short-acting beta-blocker. Animals were randomized into 3 groups with resuscitation starting 0.5 (sham group, no asphyxia, n = 5), 4 (Group 2, n = 5), or 12 minutes (Group 3, n = 8) later by retrograde intraarterial infusion of donor blood along with a resuscitation mixture. Cerebral perfusion was measured by magnetic resonance imaging (MRI) using arterial spin labeling. The average perfusion before arrest was 163 +/- 27 mL 100 g(-1) min(-1) under isoflurane anesthesia. Resuscitation led to transient perfusion increase, which started from thalamus and hypothalamus and later shifted to the cortex. Severe hypoperfusion to as low as 6% to 20% of the normal level developed in the first 10 to 20 minutes of reperfusion and lasted for at least 2 hours. On the fifth day after circulatory arrest, all animals showed a normal level of perfusion (159 +/- 57 mL 100 g(-1) min(-1) ) and minimal neurologic deficit. Nevertheless, histologic examination revealed extensive changes in the CA1 region of the hippocampus consistent with global ischemia and reperfusion damage. The combination of an improved circulatory arrest model and noninvasive MRI cerebral perfusion measurements provides a powerful tool for investigations of circulatory arrest and resuscitation, allowing for evaluation of therapies aimed at modulating cerebral reperfusion.

Cerebral resuscitation after traumatic brain injury and cardiopulmonary arrest in infants and children in the new millennium

As outlined in Figure 1, it is likely that a series of interventions beginning in the field and continuing through the emergency department, ICU, rehabilitation center, and possibly beyond, will be needed to optimize clinical outcome after severe TBI or asphyxial CA in infants and children. Despite the many differences between these two important pediatric insults, it is likely that many of the therapies targeting neuronal death, in either condition, will need to be administered early after the insult, possibly at the injury scene. Even cerebral swelling, a pathophysiologic derangement routinely treated in the PICU, almost certainly is better prevented rather than treated. Finally, this review includes, for one of the first times, a brief discussion of additional horizons in the management of patients with severe brain injury, namely, manipulation of the injured circuitry and stimulation of regeneration. Further research is needed to define better the pathobiology of these two important conditions at the bedside, to understand the optimal application of contemporary therapies, and to develop and apply novel therapies. The tools necessary to carry out these studies are materializing, although the obstacles are great. This difficult but important challenge awaits further investigation by clinician-scientists in pediatric neurointensive care.