Prolonged hypoperfusion in the cerebral cortex following cardiac arrest and resuscitation in dogs

Relationships of Jugular Bulb Parameters with Cerebral Perfusion and Metabolism After Resuscitation from Cardiac Arrest: A Post-Hoc Analysis of Experimental Studies Using a Minipig Model

BACKGROUND

Cerebral blood flow (CBF) decreases in the first few hours or days following resuscitation from cardiac arrest, increasing the risk of secondary cerebral injury. Using data from experimental studies performed in minipigs, we investigated the relationships of parameters derived from arterial and jugular bulb blood gas analyses and lactate levels (jugular bulb parameters), which have been used as indicators of cerebral perfusion and metabolism, with CBF and the cerebral lactate to creatine ratio measured with dynamic susceptibility contrast magnetic resonance imaging and proton magnetic resonance spectroscopy, respectively.

METHODS

We retrospectively analyzed 36 sets of the following data obtained during the initial hours following resuscitation from cardiac arrest: percent of measured CBF relative to that at the prearrest baseline (%CBF), cerebral lactate to creatine ratio, and jugular bulb parameters, including jugular bulb oxygen saturation, jugular bulb lactate, arterial-jugular bulb oxygen content difference, cerebral extraction of oxygen, jugular bulb-arterial lactate content difference, lactate oxygen index, estimated respiratory quotient, and arterial-jugular bulb hydrogen ion content difference. Linear mixed-effects models were constructed to examine the effects of each jugular bulb parameter on the %CBF and cerebral lactate to creatine ratio.

RESULTS

The arterial-jugular bulb oxygen content difference (P = 0.047) and cerebral extraction of oxygen (P = 0.030) had a significant linear relationship with %CBF, but they explained only 12.0% (95% confidence interval [CI] 0.002-0.371) and 14.2% (95% CI 0.005-0.396) of the total %CBF variance, respectively. The arterial-jugular bulb hydrogen ion content difference had a significant linear relationship with cerebral lactate to creatine ratio (P = 0.037) but explained only 13.8% (95% CI 0.003-0.412) of the total variance in the cerebral lactate to creatine ratio. None of the other jugular bulb parameters were related to the %CBF or cerebral lactate to creatine ratio.

CONCLUSIONS

In conclusion, none of the jugular bulb parameters appeared to provide sufficient information on cerebral perfusion and metabolism in this setting.

Feasibility of Magnetic Resonance-Based Conductivity Imaging as a Tool to Estimate the Severity of Hypoxic-Ischemic Brain Injury in the First Hours After Cardiac Arrest

BACKGROUND

Early identification of the severity of hypoxic-ischemic brain injury (HIBI) after cardiac arrest can be used to help plan appropriate subsequent therapy. We evaluated whether conductivity of cerebral tissue measured using magnetic resonance-based conductivity imaging (MRCI), which provides contrast derived from the concentration and mobility of ions within the imaged tissue, can reflect the severity of HIBI in the early hours after cardiac arrest.

METHODS

Fourteen minipigs were resuscitated after 5 min or 12 min of untreated cardiac arrest. MRCI was performed at baseline and at 1 h and 3.5 h after return of spontaneous circulation (ROSC).

RESULTS

In both groups, the conductivity of cerebral tissue significantly increased at 1 h after ROSC compared with that at baseline (P = 0.031 and 0.016 in the 5-min and 12-min groups, respectively). The increase was greater in the 12-min group, resulting in significantly higher conductivity values in the 12-min group (P = 0.030). At 3.5 h after ROSC, the conductivity of cerebral tissue in the 12-min group remained increased (P = 0.022), whereas that in the 5-min group returned to its baseline level.

CONCLUSIONS

The conductivity of cerebral tissue was increased in the first hours after ROSC, and the increase was more prominent and lasted longer in the 12-min group than in the 5-min group. Our findings suggest the promising potential of MRCI as a tool to estimate the severity of HIBI in the early hours after cardiac arrest.

Cervical Vagus Nerve Stimulation Improves Neurologic Outcome After Cardiac Arrest in Mice by Attenuating Oxidative Stress and Excessive Autophagy

BACKGROUND

Cerebral ischemia and reperfusion (I/R) induces oxidative stress and activates autophagy, leading to brain injury and neurologic deficits. Cervical vagus nerve stimulation (VNS) increases cerebral blood flow (CBF). In this study, we investigate the effect of VNS-induced CBF increase on neurologic outcomes after cardiac arrest (CA).

MATERIALS AND METHODS

A total of 40 male C57Bl/6 mice were subjected to ten minutes of asphyxia CA and randomized to vagus nerve isolation (VNI) or VNS treatment group. Eight mice received sham surgery and VNI. Immediately after resuscitation, 20 minutes of electrical stimulation (1 mA, 1 ms, and 10 Hz) was started in the VNS group. Electrocardiogram, blood pressure, and CBF were monitored. Neurologic and histologic outcomes were evaluated at 72 hours. Oxidative stress and autophagy were assessed at 3 hours and 24 hours after CA.

RESULTS

Baseline characteristics were not different among groups. VNS mice had better behavioral performance (ie, open field, rotarod, and neurologic score) and less neuronal death (p < 0.05, vs VNI) in the hippocampus. CBF was significantly increased in VNS-treated mice at 20 minutes after return of spontaneous circulation (ROSC) (p < 0.05). Furthermore, levels of 8-hydroxy-2'-deoxyguanosine in the blood and autophagy-related proteins (ie, LC-3Ⅱ/Ⅰ, Beclin-1, and p62) in the brain were significantly decreased in VNS mice. Aconitase activity was also reduced, and the p-mTOR/mTOR ratio was increased in VNS mice.

CONCLUSIONS

Oxidative stress induced by global brain I/R following CA/ROSC leads to early excessive autophagy and impaired autophagic flux. VNS promoted CBF recovery, ameliorating these changes. Neurologic and histologic outcomes were also improved.

Bench to bedside: resuscitation from prolonged ventricular fibrillation

Ventricular fibrillation (VF) remains the most common cardiac arrest heart rhythm. Defibrillation is the primary treatment and is very effective if delivered early within a few minutes of onset of VF. However, successful treatment of VF becomes increasingly more difficult when the duration of VF exceeds 4 minutes. Classically, successful cardiac arrest resuscitation has been thought of as simply achieving restoration of spontaneous circulation (ROSC). However, this traditional approach fails to consider the high early post-cardiac arrest mortality and morbidity and ignores the reperfusion injuries, which are manifest in the heart and brain. More recently, resuscitation from cardiac arrest has been divided into two phases; phase I, achieving ROSC, and phase II, treatment of reperfusion injury. The focus in both phases of resuscitation remains the heart and brain, as prolonged VF remains primarily a two-organ disease. These two organs are most sensitive to oxygen and substrate deprivation and account for the vast majority of early post-resuscitation mortality and morbidity. This review focuses first on the initial resuscitation (achieving ROSC) and then on the reperfusion issues affecting the heart and brain.

Alkaline buffers for correction of metabolic acidosis during cardiopulmonary resuscitation with focus on Tribonat--a review

A combined hypercarbic and metabolic acidosis develops during the low flow state of cardiac arrest treated with cardiopulmonary resuscitation. Several negative consequences of the acidosis have been demonstrated, two of the most important being reduced contractility of the ischaemic but still beating myocardium and impaired resuscitability of the arrested heart. Even though interventions to re-establish a spontaneous circulation should be the number one priority during cardiopulmonary resuscitation, attempts to treat the acidosis are often carried out in order to avoid the reported negative inotropic effect. Different alkaline buffers have been used, but it has been demonstrated over the years that such treatment may aggravate the situation due to a variety of deleterious side-effects of the buffers. A mixture of THAM, acetate, sodium bicarbonate and phosphate registered as Tribonat has been suggested as a suitable alternative to conventional buffer substances. The problems preceding the designation of Tribonat as well as studies evaluating its effects are reviewed in this article. Tribonat seems to offer a more well-balanced buffering without any major disadvantages compared with previously used alkaline buffers, even though improved survival has not been reported.

Ischemia-mediated neuronal injury

Resuscitation of the brain after a period of global ischemia is limited by two classes of post-ischemic pathologies: hemodynamic disturbances which prevent the adequate re-oxygenation of the ischemic brain, and metabolic disturbances which may lead to delayed neuronal death in so-called selectively vulnerable brain regions. The hemodynamic disturbances can be classified into the no-reflow phenomenon and the post-ischemic hypoperfusion syndrome. The no-reflow phenomenon results from a combination of increased blood viscosity and perivascular edema; the severity increases with the duration of ischemia, and the treatment is by combining arterial hypertension with dehydration and anticoagulation. The post-ischemic hypoperfusion syndrome is independent of the duration of ischemia, it develops after a delay and is due to an impairment of the metabolic/hemodynamic coupling mechanisms; there is no specific treatment at the present. The most important metabolic disturbance leading to delayed neuronal death is prolonged inhibition of protein synthesis. The injury is manifested already after 5 min ischemia but it progresses little if ischemia is prolonged to 1 h. Inhibition occurs at the translation level due to selective inhibition of polypeptide chain initiation. After brief periods of ischemia, the disturbance can be reversed by various anesthetics and hypothermia but there is no treatment if ischemia is prolonged. Exitotoxity, free radical-mediated reactions, disturbances of polyamine metabolism, acidosis and selective disturbances of gene expression may also be involved but are probably of lesser importance.

Magnetic resonance imaging findings associated with cardiac arrest

BACKGROUND AND PURPOSE

The frequency and prognostic significance of neuroradiological findings after cardiac arrest are unknown. Using healthy volunteers as control subjects, we studied the magnetic resonance imaging (MRI) findings associated with cardiac arrest, adjusted for confounding factors.

METHODS

The presence of cerebral infarcts, leukoaraiosis, atrophy, and edema on ultra-low-field MRI was assessed in 88 community volunteers and 52 cardiac arrest survivors enrolled in a placebo-controlled, randomized, double-blind trial of nimodipine in out-of-hospital ventricular fibrillation.

RESULTS

Cardiac arrest was an independent risk factor for the presence of infarcts in a logistic regression model adjusted for age, sex, and history of myocardial infarction, stroke, coronary heart disease, cardiac failure, and hypertension (odds ratio, 3.6; 95% confidence interval, 1.3 to 9.9; P = .01). Leukoaraiosis was associated with increasing age but not with cardiac arrest. Adjusted for age, the delay of advanced life support had an inverse correlation with the degree of atrophy in placebo-treated patients (r = -.62, P < .0001) but not in patients treated with nimodipine (r = -.10, P = .43). Lack of age-related atrophy, possibly implicating the presence of brain edema, predicted poor outcome after cardiac arrest (odds ratio, 4.6; 95% confidence interval, 1.4 to 15.8; P = .01).

CONCLUSIONS

Cardiac arrest was associated with deep cerebral infarcts but not with leukoaraiosis. MRI findings did not predict the functional outcome at 1 year. Nimodipine treatment had no significant effect on the MRI findings, but delayed resuscitation was associated with probable brain edema only in placebo-treated patients.

Epinephrine in cardiopulmonary resuscitation

This review assesses the role of epinephrine in cardiopulmonary resuscitation from the perspective of mechanisms of action, cardiac and cerebral effects, and use in human beings. We reviewed the literature from 1966 onward, using a Medline Search of the National Library of Medicine with the key words: "heart arrest," "resuscitation," and "epinephrine." Pertinent articles that represented original research were critically appraised by at least two authors. We concluded that the Advanced Cardiac Life Support recommended dose of epinephrine (1 mg or 0.007 to 0.014 mg/kg) has little scientific basis. Evidence from animal studies demonstrates that doses of 0.1 to 0.2 mg/kg are required to significantly improve myocardial and cerebral blood flow and resuscitation rates. Limited human data confirm the dose-dependent vasopressor response to epinephrine and the potential for improved immediate survival with higher doses. We suggest that randomized controlled human trials are needed to document the usefulness of higher doses of epinephrine in cardiopulmonary resuscitation.

Early effects of nimodipine on intracranial and cerebral perfusion pressures in cerebral anoxia after out-of-hospital cardiac arrest

Some calcium entry blockers seem to improve the neurological survival of anoxic comas. The early monitoring of intracranial pressure shows the frequency of intracranial hypertension. A calcium channel blocker has been shown to increase the cerebral blood flow which can potentially lead to deleterious increases of the intracranial pressure. This study presents 39 out-of-hospital cardiac arrests resuscitated with success. The intracranial pressures were registered by means of an extra dural screw set up as soon as possible. Nineteen patients received an early continuous 5 days nimodipine treatment (0.58 gamma/kg weight/min. after a 12.3 gamma/kg weight bolus). The other 20 patients did not receive any calcium entry blocker. The two groups were similar in terms of age, origin and electrical type of cardiac arrest, duration of cardiac arrest before BLS and before ACLS, principles of the treatment, initial neurological status and biological values. The maximum and mean intracranial pressures of the nimodipine group were always lower than the intracranial pressure of the control group. The cerebral perfusion pressure was never significantly different in both groups. If the nimodipine treatment proves to be efficient on neurological survival, it would be all the more interesting because it seems to limit the intracranial hypertension phenomenon which aggravates the neurological prognosis.

Brain hypoperfusion post-resuscitation

Post-resuscitation brain hypoperfusion is an all too common problem following successful CPR in dogs and cats. The deterioration of neurologic status may occur, regardless of the clinician's ability to restore and maintain heart rate and rhythm, mucous membrane color, capillary refill time, and arterial blood pressure. New insight has been gained into the mechanisms responsible for post-resuscitation brain hypoperfusion, which has improved current treatment regimens and the development of new therapeutic modalities. Proper use of fluids (isotonic or hypertonic saline, oncotic solutions), diuretics, corticosteroids, and sedatives, combined with appropriate CPR techniques, can improve outcome. New drugs and therapeutic techniques offer exciting potential for the future limitation of this problem.

Flunarizine i.v. after cardiac arrest (FLUNA-study): study design and organisational aspects of a double-blind, placebo-controlled randomized study

To investigate the cerebro-protective effect of flunarizine i.v. in patients successfully resuscitated from ventricular fibrillation outside hospital, a double-blind, placebo-controlled randomized study was started in February 1988 in West-Berlin with all eight Mobile Intensive Care Units and ten major hospitals participating. Start of treatment was in the patient's home immediately after restoration of stable circulatory conditions. Primary endpoints reduction of mortality due to hypoxic brain damage and more rapid improvement after cardiac arrest and resuscitation. Inclusion criteria men and women without age limit, ventricular fibrillation prior to or upon arrival of a MICU, primarily successful cardiac resuscitation with continuing unconsciousness. Recruitment of patients will end January 31st, 1990. An inclusion of about 500 patients is expected.

Comparison of thermal clearance measurement of regional cerebral blood flow with radiolabelled microspheres

A thermal clearance technique for measuring cerebral blood flow is described and compared with the radiolabelled microsphere technique. The thermal technique involves measurement of the rewarming curve generated after bolus infusion of 4-5 ml of ice-cold saline into the common carotid artery with a subdural thermistor placed on the parietal cortex. Evaluation of the biexponential decay curves obtained with this technique demonstrated a close correlation with total hemispheric, parietal, and parietal gray blood flow determined by simultaneous microsphere measurement. Despite significant correlations (p less than 0.001), scatter in the data produced a broad 95% confidence interval, thus making interpretation of blood flow with the thermal clearance technique impossible. Furthermore, instrumentation with the thermal probe, which required opening of the dura, blunted the cerebral blood flow response to hypercapnia. We conclude that the major limitations of the thermal clearance technique include: nonhomogeneous clearance function, significant variability, and depression of CO2 reactivity. These limitations must be addressed before this technique can be used reliably in the laboratory.

Cerebral resuscitation after cardiac arrest using hetastarch hemodilution, hyperbaric oxygenation and magnesium ion

This study was done to investigate the effects of hemodilution, hyperbaric oxygenation, and magnesium sulfate on cerebral resuscitation. Sixteen mongrel dogs were anesthetized, and monitored via pulmonary artery catheter, arterial catheter and electrocardiogram. A left lateral thoracotomy was done. Ventricular fibrillation was obtained by application of a 6-volt AC current. Mechanical ventilation was stopped. Total arrest time was 12 min. All dogs were cardiac resuscitated within 6 min using internal massage, ventilation, bicarbonate, epinephrine and internal defibrillation. The animals were then randomized into three groups. Group I represented controls, and were not treated. Group II dogs received normvolemic hemodilution using hetastarch (Hespan) containing magnesium sulfate (2000 mg/l), resulting in a hematocrit of 20%-30%. Group III dogs received the above hemodilution plus compression in a hyperbaric oxygen chamber to 2 atmospheres absolute. Critical care management and hourly neurologic scoring was performed for 7 days by blinded observers. All dogs at the time of death underwent autopsies for gross study. Data analysis revealed no statistical difference among the three groups with respect to survival time, cardiac function or neurologic scoring.

Ibuprofen improves survival and neurologic outcome after resuscitation from cardiac arrest

Post-ischemic inflammatory changes in the central nervous system (CNS) following cardiac arrest and resuscitation are potentially responsible for ultimate survival and much of the neurologic damage, producing greater morbidity and mortality in successfully resuscitated patients. This study was undertaken to assess the non-steroidal anti-inflammatory agent, ibuprofen, in a controlled and monitored experimental model of canine cardiac arrest and resuscitation. With the investigator blinded as to the intervention, eight of 21 dogs were randomly assigned to receive ibuprofen as an i.v. bolus (10 mg/kg) and a 6-h i.v. infusion (5 mg/kg per h). The other 13 dogs received an equivalent volume of 0.9% NaCl to serve as controls. No statistically significant differences between the two groups were detected in any pre-arrest variables. All 21 dogs were successfully resuscitated. At 24 h, dogs receiving ibuprofen exhibited 100% survival, while control dogs exhibited only 54% survival (P = 0.03). The majority of deaths for the control group occurred within the first 6 h. Neurologic deficit scores were assigned at 1, 2, 6 and 24 h after resuscitation. A general trend occurred such that dogs treated with ibuprofen improved over time, while the control dogs remained severely impaired. A significant difference in neurologic deficit score was detected at 6 h (P = 0.01). At 24 h the ibuprofen group exhibited minimal neurologic deficit (5.9 +/- 3.2), and the control group exhibited significantly more severe neurologic impairment (52.2 +/- 13.0, P = 0.01). These results suggest that ibuprofen may be helpful in the pharmacologic management of cardiac arrest as a means of increasing survival and decreasing neurologic impairment.

Guidelines for discontinuing prehospital CPR in the emergency department--a review

We provide information that we believe should allow the establishment of rational guidelines for discontinuing, with physician supervision, unsuccessful prehospital CPR. Goldberg has advocated that CPR be terminated only after evidence of brain or cardiac death has persisted for more than one hour of adequately applied advanced CPR. This recommendation was made for inhospital resuscitation and does not reflect the limited capabilities of basic and advanced CPR techniques to sustain life outside the hospital. In addition, White and associates have demonstrated that after resuscitation from prolonged cardiac arrest, cerebral cortical blood flow is reduced severely. This state of hypoperfusion may last up to 18 hours. Because this condition can result in extensive neurologic damage, it may explain the poor survival rates after prolonged resuscitation. We propose that CPR be terminated in the ED when, despite adequate rescue attempts (intubation, defibrillation, IV medications, CCCM en route) by those responding at the scene of cardiac arrest, intrinsic cardiac activity has not been achieved in patients brought to the hospital with asystole or bradyarrhythmia. Additionally patients who have had advanced prehospital CPR for more than 45 minutes without generation of any intrinsic cardiac activity are not resuscitatable by current standard techniques, and CPR may be discontinued. These criteria must not be used for victims of hypothermia before a core temperature of 35 C to 36.1 C is achieved by active core rewarming during CPR. The available data suggest that if these criteria are implemented, many unproductive hospital-based resuscitative efforts can be eliminated without jeopardizing potential survivors.(ABSTRACT TRUNCATED AT 250 WORDS)

Prolonged cardiac arrest and resuscitation in dogs: brain mitochondrial function with different artificial perfusion methods

Clinical techniques for artificial perfusion have not previously been examined directly for their effects on brain high-energy metabolism. Our study involved 24 large mongrel dogs that were anesthetized, instrumented for central venous intravenous access, and subjected to craniotomy to expose the dura and underlying parietal cortex. The animals were divided into the following six experimental groups of four animals each: nonischemic controls; 15-minute cardiac arrest without resuscitation; 45-minute cardiac arrest without resuscitation; 15-minute cardiac arrest plus 30 minutes resuscitation with conventional cardiopulmonary resuscitation (CPR); 15-minute cardiac arrest plus 30 minutes resuscitation with interposed abdominal compression (IAC) CPR; and 15-minute cardiac arrest plus 30 minutes resuscitation with internal cardiac massage. Cardiac arrest was induced by central venous injection of KCl 0.6 mEq/kg, and it was confirmed by continuous ECG monitoring. The three active resuscitation models included administration of NaHCO3 and epinephrine, but no attempt was made to restart the heart by defibrillation during resuscitation. At the indicated time in each group, a 4- to 5-g sample of brain was removed through the craniotomy, immediately cooled to 0 C and processed for isolation of mitochondria. The mitochondria were studied for their content of superoxide dismutase and for quantitative oxygen consumption with glutamate/malate substrate during resting and ADP-stimulated respiration. Our results show a significant drop in brain mitochondrial superoxide dismutase activity during the first 15 minutes of cardiac arrest. There is minimal injury to brain mitochondrial oxygen consumption during both 15 and 45 minutes of complete ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurological recovery after cardiac arrest: clinical feasibility trial of calcium blockers

In order to determine whether the calcium blockers verapamil and/or magnesium sulfate decrease neurological morbidity after cardiac arrest, all out-of-hospital cardiac arrests (290) occurring during a nine-month period in five participating hospitals were retrospectively studied. Twenty-nine patients met the criteria for inclusion in this study. Each had an unwitnessed, out-of-hospital cardiac arrest and was comatose (no purposeful response to pain) 20 minutes after the restoration of spontaneous circulation (ROSC). Eighteen patients (calcium blocker group) received verapamil and/or magnesium sulfate at some point after ROSC, while eleven patients received standard ACLS therapy (control group). Age, arrest time, cardiopulmonary resuscitation (CPR) time, and cerebral ischemic time were comparable in the two groups. In the calcium blocker group, seven of 18 patients regained consciousness, and six of these seven survived. All six survivors appeared neurologically normal upon discharge and at three and six months of follow-up. While no demonstrably adverse effects were seen after the administration of magnesium sulfate, 56% of the patients who received verapamil had a significant drop in blood pressure. In the control group, three of 11 patients regained consciousness and two of the three left the hospital alive. Both survivors were disabled--one severely and one moderately. Follow-up after three and six months revealed no significant improvement in their disability. Overall, six of 18 patients experienced clinically complete neurological recovery in the calcium blocker group, while none of the 11 patients in the control group made a complete neurological recovery (P = 0.06).

Blood flow in the cerebral cortex during cardiac resuscitation in dogs

Regional cerebral cortical blood flow (rCCBF) in 15 large dogs was determined using the double thermistor dilution method during standard closed-chest massage (CCM), CCM with an epinephrine infusion at 30 micrograms/kg/min (CCM + Epi), and open-chest cardiac massage (OCCM). As a percentage of prearrest flow values, the rCCBF was 9.8% with CCM, 35% with CCM + Epi, and 156% with OCCM. The rCCBF was reduced significantly with CCM (P less than .005) and CCM + Epi (P less than .01). OCCM generated flows indistinguishable from prearrest values. The use of high-dose epinephrine significantly increased the rCCBF during CCM. The implications for intact neurologic resuscitation of these reductions in rCCBF with CCM are important.

Perfusion of the cerebral cortex by use of abdominal counterpulsation during cardiopulmonary resuscitation

Perfusion of the cerebral cortex (rCCBF) during resuscitation from cardiac arrest was studied using 24 large dogs and three different resuscitation models. Conventional cardiopulmonary resuscitation (CPR) was compared with interposed abdominal compression CPR (IAC-CPR) and with IAC-CPR together with infusion of epinephrine. Conventional CPR produced a mean rCCBF of only 11% (0.057 +/- 0.07 ml/min/g) normal perfusion (0.54 +/- 0.14 ml/min/g). Even without epinephrine, IAC-CPR produced mean rCCBF equal to 51% (0.27 +/- 0.17 ml/min/g) of normal. With epinephrine, IAC-CPR produced rCCBF (0.93 +/- 0.49 ml/min/g) statistically indistinguishable from normal. Both models of IAC-CPR were significantly superior to conventional CPR in perfusion of the cerebral cortex.

Brain injury by ischemic anoxia: hypothesis extension--a tale of two ions?

The understanding of the pathophysiology of cerebral ischemic anoxia depends on elucidation of cellular neuronal changes during this event and under conditions of cardiopulmonary resuscitation. Current knowledge of these metabolic developments is reviewed, and a hypothesis of the role of iron in this situation is presented.

Early amelioration of neurologic deficit by lidoflazine after fifteen minutes of cardiopulmonary arrest in dogs

A prospective, controlled, blind study was done to test the effect of a calcium entry blocker on the neurologic integrity of dogs after cardiopulmonary arrest. Ten male mongrel dogs were anesthetized, prepared with sterile technique, and instrumented for pulmonary arterial (PA) and systematic arterial pressure monitoring. A left thoracotomy and pericardotomy were performed. Cardiac arrest was produced by injecting KCl (1 mEq/kg) through the PA line, and the respirator was stopped. Full arrest was maintained for 15 minutes. Thereafter, the dogs were resuscitated with ventilation, internal massage, fluids, bicarbonate, epinephrine, and internal defibrillation. All dogs were resuscitated within 6 to 10 minutes. Five control dogs received saline placebo, and five dogs were treated with lidoflazine (1 mg/kg) IV drip immediately post resuscitation. All dogs were scored neurologically every two hours by a deficit grading scale. All treated dogs had spontaneous ventilation, reactive pupils and corneals, voluntary movements, and responses to tactile stimulation at 12 hours post resuscitation. Four of five control dogs had maximum deficit scores without improvement. The difference in neurologic scores between the treated and control groups became increasingly divergent with time, and was statistically significant (P less than .05) by four hours post resuscitation. Thus the calcium antagonist lidoflazine produces improvement in neurologic recovery in the first 12 hours after cardiopulmonary arrest in dogs.