Brain enzyme changes as markers of brain damage in rat cardiac arrest model. Effects of corticosteroid therapy

Apneic asphyxia to cardiac arrest (CA) in rats of 10 min was reversed by cardiopulmonary resuscitation (CPR), and after controlled ventilation and controlled normotension for 20 min, was followed by decapitation and brain freezing, and determination of brain concentrations of cytosolic and lysosomal enzymes. Normal values came from a control group of 10 rats without CA. In 20 rats with CA brain cytosolic enzymes CK, LD, and ASAT decreased post-arrest, while lysosomal enzyme changes were variable (Table I). Brain lactate increased 8-10-fold post-CA. To test the model, effect of methylprednisolone (MP) was studied. The 20 rats with CA were divided into 4 groups: Group I, received placebo pre-CA; Group II, MP 30 mg/kg i.v. pre-CA; Group III, placebo post-CA; and Group IV, MP post-CA. The post-CA MP Group IV was the only one without norepinephrine requirement and with return of EEG activity at 20 min. Brain CK, LD, and ASAT losses post-CA were not different between groups; and showed no differences between MP groups II and IV vs. placebo Groups I and III. When comparing both pre-CA Groups (I and II) with both post-CA Groups (III and IV), post-CA CK and ASAT levels were the same, but LD was higher in the post-CA treatment group. The lysosomal enzymes acid phosphatase, mannosidase, beta-glucuronidase and hexosaminidase showed variable concentration changes post-CA in the four groups, with a trend toward a lesser increase of some after MP or after post-treatment. Brain enzyme changes in our asphyxial CA rat model can serve as markers of brain damage. MP post-CA might enhance cardiovascular and EEG recovery, but does not seem to influence brain enzyme levels at 20 min post-CA.

New monkey model of severe-volume controlled hemorrhagic shock

Three series of experiments were conducted to develop a model of volume-controlled severe hemorrhagic shock in the unanesthetized analgesic cynomolgus monkey. This report concerns the insult without resuscitation. In Series I, seven monkeys were sedated with 75% N2O/25% O2, bled 40% of their measured blood volume over 20 min and observed until death. Mean arterial pressure (MAP) decreased to 21 +/- 6 mmHg, spontaneously increased to 46 +/- 5 mmHg, then gradually decreased to pulselessness at 146 +/- 42 min (range 101-213). Hemodynamic variables, lactate, base excess, electroencephalogram and sagittal sinus PO2 followed the same biphasic pattern. In Series II, eight monkeys were bled 27 ml/kg (43% of estimated blood volume) over 20 min under the same N2O analgesia and with similar responses as in Series I. In Series III 26 monkeys were bled 27 ml/kg over 20 min (time zero) as in Series II. Three developed apnea and pulselessness at end of hemorrhage. In 23 the shock period was prolonged for testing resuscitation therapies. Starting at 0 + 30 min, MAP was controlled with minute blood volume adjustments at 30 mmHg until 0 + 2 h. Three died due to inaccurate (preventable) MAP adjustments. At MAP 30 mmHg, all animals lost consciousness, EEG activity decreased, and brain stem reflexes disappeared. The "volume-pressure controlled" hemorrhagic shock model of Series III retains the initial natural response to bleeding, simulates the clinical picture of severe prolonged shock without anesthesia, and represents a more controllable insult than volume controlled hemorrhage alone.

Resuscitation from clinical death: pathophysiologic limits and therapeutic potentials

Modern cardiopulmonary-cerebral resuscitation (CPCR) for the reversal of clinical death (i.e., prolonged cardiac arrest) is a sequence of basic, advanced and prolonged life-support steps. This system was initiated by research that started in the 1950s. Present community-wide results are encouraging, but suboptimal. Maximal benefit from CPCR will be achievable: a) by minimizing response times; and b) by extending reversible arrest times--the topic of this symposium. For reperfusion, closed chest CPR is more readily available than, but physiologically inferior to, open chest CPR and emergency cardiopulmonary bypass. To optimize outcome, four components of the postresuscitation syndrome are being investigated: a) perfusion failure; b) reoxygenation injury cascades; c) self-intoxication; and d) blood derangements. Results from animal outcome studies so far suggest significant but still inconsistent benefit from several special postarrest treatments. The longest normothermic no-flow time yet reversed to good functional survival of heart, brain and the entire organism appears to be not 5 min, but between 10 and 20 min. The following is recommended and in part has been initiated: a) simultaneous investigation of pathophysiologic limits, therapeutic potentials, and prognosticating measurements; b) simultaneous basic research at cellular, organ, and organism levels; c) increased communication and consensus on research models between research centers; d) use of short-term and long-term animal models for systematic mechanism-oriented and empirical outcome-oriented studies; e) development of etiology-specific combination treatments; and f) community-wide case registries combined with epidemiologic studies and randomized clinical treatment trials.

Predictors of electromechanical dissociation during cardiac arrest

ECG patterns observed during cardiac arrest were analyzed in 261 comatose cardiac arrest survivors. Forty-seven patients (18%) exhibited electromechanical dissociation (EMD) at some point before restoration of stable spontaneous circulation. These patients had a higher mortality (P = .05) and a lower rate of cerebral recovery (P = .01) during the one-year follow-up than study patients who did not exhibit EMD. Patients who developed EMD subsequent to defibrillation had better outcome than patients presenting with EMD. Multivariate analysis revealed that age more than 70 years old (P = .007), pulmonary disease (P less than .001), diabetes (P = .013, in-hospital arrests only), and prearrest hypoxemia (P = .013, outside-hospital arrests only) were independently predictive of the occurrence of EMD. Although the generalizability of these findings is limited, they may offer new clues to the pathophysiology of EMD.

Brain enzyme levels in CSF after cardiac arrest and resuscitation in dogs: markers of damage and predictors of outcome

Levels of brain creatine kinase (CK), aspartate aminotransferase (ASAT), and lactate dehydrogenase (LD) in CSF after cardiac arrest were studied in dog models. Ventricular fibrillation cardiac arrest lasting 10 min or asphyxiation cardiac arrest lasting 0-10 min was followed by cardiopulmonary resuscitation and 96-h intensive care. Outcome was scored as neurologic deficit (0% = normal, 100% = brain death) and overall performance category (1 = normal, 5 = death). Both measures correlated with EEG return time after asphyxiation cardiac arrest, but not after ventricular fibrillation cardiac arrest. Peak activity of enzymes in CSF at 48-72 h post arrest correlated with outcome, and CK was the best predictor. Brain histopathologic damage score at autopsy 96 h post arrest correlated with CK level in CSF (r = 0.79, n = 39) and neurologic deficit (r = 0.70, n = 50). Ischemic neuronal changes occurred after ventricular fibrillation cardiac arrest of 10 min, and neuronal changes plus microinfarcts occurred after asphyxiation cardiac arrest of 1.5-10 min. Brain enzymes were decreased at 6 h post arrest in regions with worst histologic damage (gray matter of neocortex, hippocampus, caudate nucleus, cerebellum). Brain CK decreased further, ASAT remained low, and LD increased at 72 h after arrest. The temporal changes in CK level paralleled the temporal ischemic neuronal changes in the brain, and time to peak activity was unaffected by the severity of the ischemic insult. Peak activity of individual enzymes in CSF was determined predominantly by the brain concentration, but was also influenced by rate of decomposition. This "chemical brain biopsy method" represents a useful adjunctive tool to predict permanent, severe brain damage during comatose states after cardiac arrest and resuscitation.

Protective effects of combined superoxide dismutase and deferoxamine on recovery of cerebral blood flow and function after cardiac arrest in dogs

Oxygen free radicals generated during reoxygenation after cardiac arrest may impair recovery of cerebral blood flow and function. In a randomized study in vivo, we tested the following anti-free radical combination therapy administered at the beginning of cardiopulmonary resuscitation after apnea-induced cardiac arrest of 7 minutes: 1) ventilation with 100% nitrogen for 30 seconds to allow the delivery of therapy before oxygen, 2) 10 mg/kg i.a. superoxide dismutase followed by 10 mg/kg i.v. over 1 hour to scavenge the superoxide anion radical, and 3) 20 mg/kg i.v. deferoxamine over 1 hour to prevent membrane lipid peroxidation. We evaluated the effects of this combined treatment on the recovery of cardiovascular variables, cerebral blood flow and oxygen consumption, and somatosensory evoked potentials in 20 dogs 6 hours after resuscitation. Compared with standard treatment (n = 10), the combined treatment (n = 10) did not affect cardiovascular variables, significantly mitigated cerebral blood flow changes after cardiac arrest, and enhanced recovery of somatosensory evoked potentials. We conclude that oxygen free radicals play a role in the pathogenesis of the arrest-related derangements of cerebral blood flow and function that are effectively reduced by this combined treatment; we recommend evaluation of its components in outcome studies.

Cardiopulmonary bypass after prolonged cardiac arrest in dogs

Ventricular fibrillation (VF) cardiac arrest of more than ten minutes can be survived by cerebral neurons, but restoration of spontaneous circulation (ROSC) by external CPR is unreliable. Cardiopulmonary bypass (CPB) permits control of pressure, flow, oxygenation, temperature, and composition of blood. After 12 1/2 minutes of normothermic VF cardiac arrest, CPB was used as a research tool for reperfusion and assisted circulation for two hours in ten dogs without thoracotomy, with plasma substitute priming, and without preceding CPR (a deliberately nonclinical scenario). Recovery was compared with that in ten control dogs in which standard CPR with advanced life support (ALS) for up to 30 minutes was used to achieve ROSC. Both groups subsequently had blood pressure, blood gases, ventilation, and other parameters controlled for 20 hours, and intensive therapy to 72 hours. CPB achieved ROSC more successfully (ten of ten vs six of ten controls) (P less than .05), and more rapidly, with fewer defibrillation attempts and with less epinephrine (P less than .05). CPB improved 72-hour survival (seven of ten vs two of ten controls) (P = .025). Between two and 24 hours, of those with ROSC, intractable cardiogenic shock killed four of six control dogs (NS). CPB was followed by fewer arrhythmias. CPB increased recovery of consciousness (five of ten CPB vs zero of six controls with ROSC) (P = .037), but achieved neurologic normality in only one of ten. Cardiac arrest and CPB (without CPR) resulted in less myocardial morphologic damage than did standard CPR (P less than .025).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiopulmonary bypass after cardiac arrest and prolonged closed-chest CPR in dogs

We studied a clinically realistic field-to-hospital scenario in dogs with four-minute ventricular fibrillation (VF) cardiac arrest followed by 30-minute standard external CPR basic life support (BLS). At the end of this 34-minute insult, cardiopulmonary bypass (CPB) was used for early defibrillation and assisted circulation for one hour (n = 10). Recovery was compared with that of control dogs (n = 10) in which standard CPR with advanced life support (ALS) for another 30 minutes was used for restoration of spontaneous circulation (ROSC). Both groups had hemodilution and heparinization; controlled blood pressure, blood gases, ventilation, and other parameters for 20 hours; and intensive care to 72 hours. During CPR-BLS of 30 minutes in both groups signs of cerebral viability returned. CPB achieved ROSC more successfully (ten of ten vs five of ten CPR-ALS controls) (P less than .02); and more rapidly, with less defibrillation energy (first countershock in eight of ten) and with less epinephrine (P less than .01). CPB improved 72-hour survival (seven of ten vs three of ten controls) (P less than .05). Between two and 24 hours, of those with ROSC, cardiac complications killed three of ten CPB dogs (after weaning), and two of five CPR-ALS dogs (NS). All seven CPB survivors to 72 hours were neurologically normal; of the three CPR-ALS survivors, one remained with severe neurologic deficit and two were neurologically normal (seven of ten CPB vs two of ten controls, P = .025). Starting CPR-BLS within four minutes of arrest can maintain cerebral viability.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral resuscitation after cardiac arrest: a review

Cerebral neurons can tolerate at least 20 min of normothermic ischemic anoxia. Cerebral recovery from more than 5 min of cardiac arrest is hampered by complex secondary derangements of multiple organ systems after reperfusion. There is increasing support of our hypothesis that this "postresuscitation syndrome" includes the following: secondary cerebral perfusion failure, cerebral reoxygenation injury (cell-necrotizing cascades), and cerebral "intoxication" from derangements of extracerebral organs. To be optimal for the brain, CPR with optimal perfusion pressure must be started as promptly as possible. Significant though inconsistent mitigation of permanent brain damage after prolonged complete global brain ischemia has been achieved in animal outcome preparations with the use of the following treatments initiated at the start of reperfusion: brain-oriented extracerebral life support by protocol, intra-arterial hemodilution, hypertension, and artificial circulation, barbiturates, calcium-entry blockers, free-radical scavengers, and multifaceted treatments. We currently recommend treatment 1 for patient care and treatment 2 for clinical feasibility trials. Treatment 3, thiopental loading (starting 10 to 50 min after restoration of spontaneous circulation), was tested in a randomized clinical trial and was not shown to confer a statistically significant benefit. A calcium-entry blocker is under clinical investigation. Many other novel treatments appear promising but further animal studies are required. The complex multifactorial pathogenesis of postcardiac arrest encephalopathy requires systematic multicenter development of etiology-specific combination therapies.

Calcium uptake during insulin-aggravated ischemic myocardial contracture in the rat heart

Perfusion of isolated, nondiabetic rat hearts with high concentrations of regular insulin (10 mU/ml) produced earlier onset of myocardial contracture during ischemia than control perfusions without insulin. High insulin concentrations also increased total myocardial calcium content (p less than .001) and myocardial Ca-45 uptake postischemia (p less than .05). Insulin perfusion before ischemia did not enhance calcium uptake. These results support the hypothesis that insulin may increase calcium movement across myocardial cell membranes, which may lead to increased ischemic contracture. Insulin-aggravated myocardial ischemia in cardiothoracic surgery and cardiac resuscitation deserves further investigation.

Insulin worsens ischemia-induced myocardial contracture in the isolated rat heart

We used a modification of Langendorff's isolated perfused nonworking rat-heart model to study the effects of diabetes, insulin-treated diabetes, and hyperinsulinemia on left ventricular pressure, force of ventricular contraction, and myocardial contracture, before, during, and after 20 min of complete normothermic global ischemia. Untreated diabetic rat hearts behaved the same as normal hearts, but insulin-treated diabetic hearts had more ischemic and postischemic contracture (p less than .01), and less return of left ventricular function. Chronic insulin treatment potentiated ischemic contracture in diabetic and nondiabetic rat hearts. These results support the hypotheses that insulin can increase Ca++ actin-myosin ATPase activity, and increase the affinity of myofibrillar receptors for calcium, which may lead to increased ischemic contracture. Insulin as a risk factor in myocardial ischemia, cardiothoracic surgery and cardiac resuscitation, and other pathogenetic factors of "stone heart" development, deserve further investigation.

Deferred consent. A new approach for resuscitation research on comatose patients

Methodological constraints inherent in the rapidly growing field of resuscitation research have created an apparent conflict with newly promulgated federal regulations, especially those concerning informed consent requirements. We propose that two new concepts be applied to resuscitation research to satisfy the current federal regulations governing biomedical research. The first of these concepts is "minimal differential risk," ie, in resuscitation medicine, the difference between the risk of an undesirable outcome when standard, commonly accepted therapy may be used and the risk of an undesirable outcome with experimental therapy is minimal. The second concept is "deferred consent," ie, obtaining consent to continue with an experimental therapy after administration of that therapy has already begun. We believe that the emergency exception to informed consent applies to resuscitation research. Recognition of the applicability of these concepts to resuscitation research should allow compliance with federal and state regulations that otherwise might inhibit or preclude such research endeavors.

Comparison of open-chest cardiac massage techniques in dogs

Manual compression of the heart during open-chest cardiac massage (OCPR) has been shown to be superior to closed-chest compression. Our study sought to determine, in a canine model, the optimal hand position for manual compression of the heart. Twelve dogs were anesthetized with ketamine, an orotracheal tube was placed, and anesthesia was maintained with halothane and nitrous oxide. Cannulae were placed to monitor diastolic (DBP) and systolic (SBP) blood pressures, intracranial pressure (ICP), and common carotid blood flow (CCBF). Control values were obtained under light general anesthesia, and ventricular fibrillation was induced. External CPR (ECPR) was performed with a mechanical compressor before opening the chest and pericardium through the left fifth interspace. The following sequence of three hand positions was used for OCPR: technique A, one-handed technique with thumb on left ventricle, fingers over the right ventricle, and apex in palm; technique B, two-handed technique with right ventricle cupped in left hand and fingers of right hand over left ventricle; and technique C, one-handed technique with fingers of right hand over left ventricle and heart against sternum. Each was done at a rate of 60 compressions per minute with the operator blind to results during performance. All three techniques produced significantly (P less than .05) greater DBPs and CCBFs when compared with ECPR. All three also produced significantly lower (P less than .05) ICPs when compared with ECPR. DBPs, SBPs, CCBFs, and cerebral perfusion pressures were similar for techniques B and C, and all were significantly greater (P less than .05) than those achieved with technique A.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term animal outcome models for cardiopulmonary-cerebral resuscitation research

Controlled clinically relevant animal models are essential in the ongoing search for increasingly cost-effective methods to reverse clinical death. Acute (up to 12 h) and short-term (up to 24 h) experiments are useful for the study of dying mechanisms and restoration of spontaneous circulation. Although long-term models are difficult and expensive, they are essential to permit lesions to mature, treatments to take effect, secondary deterioration to be recognized, and survival and brain damage to be quantified and compared between treatment groups. The insults studied include temporary complete global head ischemia in monkeys, ventricular fibrillation cardiac arrest in dogs, asphyxial cardiac arrest in rats and dogs, and exsanguination arrest in dogs. Standard external CPR combined with advanced life support is less successful than open-chest CPR or emergency cardiopulmonary bypass after prolonged ventricular fibrillation. Postinsult monitoring of multiple organ systems can be used to explore the postresuscitation syndrome and evaluate novel treatment potentials. Outcome measurements include brain enzyme leakage into the cerebrospinal fluid, neurologic deficit scoring, overall performance categorization, incidence of secondary deterioration, and histopathologic damage scoring of brain and viscera.