Mild protective and resuscitative hypothermia for asphyxial cardiac arrest in rats

It has been shown in dogs that mild hypothermia (34 degrees C) during or immediately after ventricular fibrillation cardiac arrest can improve cerebral outcome. The effect of mild hypothermia on outcome after 8 minutes of asphyxiation (5 minutes' cardiac arrest) was studied for the first time in rats. Restoration of spontaneous circulation was with external cardiopulmonary resuscitation and observation to 72 hours. Three groups of 10 rats each were studied. At 72 hours postarrest, compared with the normothermic control group 1, final overall performance categories (OPC) and neurological deficit scores (NDS) were numerically better in the resuscitative (post-arrest) hypothermia group 2 and significantly better in the protective (pre-intra-arrest) hypothermia group 3 (P < .05). Total brain histopathological damage scores (HDS) were 17 +/- 5 in group 1, 14 +/- 6 in group 2 (NS), and 6 +/- 2 in group 3 (P < .001 versus group 1). HDS correlated with OPC (r = .6, P < .05) and NDS (r = .7, P < .05). Mild hypothermia improved cerebral outcome after asphyxial cardiac arrest in rats, more when induced before than after arrest. The model's insult is within the therapeutic window, which makes it also suitable for screening other cerebral resuscitation potentials.

Ischemic neurons in rat brains after 6, 8, or 10 minutes of transient hypoxic ischemia

The incidence and distribution of ischemic (necrotic) neurons in the brains of rats 72 hr after hypoxic ischemia induced via asphyxiation is described and scored. Anesthetized Sprague-Dawley rats (10/group) were endotracheally intubated and had their airways occluded for 6, 8, or 10 min, which resulted, respectively, in approximately 3, 5, or 7 min of pulselessness (MABP < 10 mm Hg). Survival was 10/10, 9/10, and 6/10 in the 6-, 8-, and 10-min groups: deaths occurred within 1 hr after resuscitation. At 72 hr, rats were reanesthetized and their brains were perfusion-fixed with 3% buffered paraformaldehyde. Paraffin-embedded, 5-micron-thick, H&E-stained sections at 5 coronal levels of the brain had shrunken, hypereosinophilic ischemic neurons in 12 anatomic regions. Ischemic neurons were most consistently found in the lateral reticular thalamic nucleus; lateral caudoputamen; CA1 region of the hippocampus; subiculum; and, with longer asphyxia times, among cerebellar Purkinje neurons. Categorical histologic damage scores were assigned to affected regions on the basis of manual counts of ischemic neurons and summed for the whole brain. Brain histologic damage scores were significantly (p < 0.01) different for the 6-, 8-, and 10-min groups (means of 8 +/- 2; 14 +/- 4; and 22 +/- 4). Brain regions where both the number of rats affected and ranked categorical scores for ischemic neurons increased with asphyxia time were the lateral caudoputamen and cerebellar Purkinje neurons.

Asphyxiation versus ventricular fibrillation cardiac arrest in dogs. Differences in cerebral resuscitation effects--a preliminary study

We explored the hypothesis that brain damage after cardiac arrest caused by ventricular fibrillation (VF) needs different therapies than that after asphyxiation, which has been studied less thoroughly. In 67 healthy mongrel dogs of both sexes cardiac arrest (at normothermia) by ventricular fibrillation (no blood flow lasting 10 min) or asphyxiation (no blood flow lasting 7 min) was reversed by normothermic external cardiopulmonary resuscitation, followed by intermittent positive-pressure ventilation for 20 h, and intensive care to 96 h. To ameliorate ischemic brain damage, the calcium entry blocker lidoflazine or a solution of free radical scavengers (mannitol and L-methionine in dextran 40) plus magnesium sulphate, was given intravenously immediately upon restoration of spontaneous circulation. Outcome was evaluated as functional deficit, brain creatine kinase (CK) leakage into the cerebrospinal fluid (CSF) and brain morphologic changes. Lidoflazine seemed to improve cerebral outcome after VF but not after asphyxiation. Free radical scavengers plus magnesium sulphate seemed to improve cerebral outcome after asphyxiation, but not after VF. After VF, scattered ischemic neuronal changes in multiple brain regions dominated, and total brain histopathologic damage scores correlated with final neurologic deficit scores at 96 h (r = 0.66) and with peak CK levels in CSF (r = 0.81). After asphyxiation, in addition to the same ischemic neuronal changes, microinfarcts occurred, and there was no correlation between total brain histopathologic damage scores and neurologic deficit scores or CK levels in CSF.

CONCLUSIONS

Different mechanisms of cardiac arrest, which cause different morphologic patterns of brain damage, may need different cerebral resuscitation treatments.

Future directions for resuscitation research. V. Ultra-advanced life support

Standard external cardiopulmonary resuscitation (SECPR) frequently produces very low perfusion pressures, which are inadequate to achieve restoration of spontaneous circulation (ROSC) and intact survival, particularly when the heart is diseased. Ultra-advanced life support (UALS) techniques may allow support of vital organ systems until either the heart recovers or cardiac repair or replacement is performed. Closed-chest emergency cardiopulmonary bypass (CPB) provides control of blood flow, pressure, composition and temperature, but has so far been applied relatively late. This additional low-flow time may preclude conscious survival. An easy, quick method for vessel access and a small preprimed system that could be taken into the field are needed. Open-chest CPR (OCCPR) is physiologically superior to SECPR, but has also been initiated too late in prior studies. Its application in the field has recently proven feasible. Variations of OCCPR, which deserve clinical trials inside and outside hospitals, include 'minimally invasive direct cardiac massage' (MIDCM), using a pocket-size plunger-like device inserted via a small incision and 'direct mechanical ventricular actuation' (DMVA), using a machine that pneumatically drives a cup placed around the heart. Other novel UALS approaches for further research include the use of an aortic balloon catheter to improve coronary and cerebral blood flow during SECPR, aortic flush techniques and a double-balloon aortic catheter that could allow separate perfusion (and cooling) of the heart, brain and viscera for optimal resuscitation of each. Decision-making, initiation of UALS methods and diagnostic evaluations must be rapid to maximize the potential for ROSC and facilitate decision-making regarding long-term circulatory support versus withdrawal of life support for hopeless cases. Research and development of UALS techniques needs to be coordinated with cerebral resuscitation research.

Introduction to Wolf Creek IV Conference

Early milestones of resuscitation research culminated in the 1950s in the documentation of modern external cardiovascular resuscitation (CPR) steps "ABC," followed by advanced and prolonged life support. Implementation of guidelines has been suboptimal. Self-training of the public in life-supporting first aid, including CPR-ABC-available since the 1970s-is only now being re-evaluated and hopefully implemented. Standard external CPR potency is inadequate for reliably restoring spontaneous circulation and saving the brain after prolonged arrests or in patients with sick hearts. Ultra-advanced life-support methods such as open-chest CPR and emergency cardiopulmonary bypass should be tried for bridging standard external CPR-resistant hearts to recovery or repair. Outcome studies in large animals can be fully controlled, in contrast to randomized clinical outcome trials, which have limitations. The HIV paranoia must not lead to abandoning the teaching of steps A and B, which are essential for any kind of coma, asphyxial arrest, and prolonged ventricular fibrillation arrest. Sternal compressions alone can produce some ventilation in animals, but not reliably in comatose humans. For cerebral resuscitation after cardiac arrest, the outcome benefit of the hypertensive bout, other cerebral blood flow-promoting measures, and mild resuscitative hypothermia have been documented in outcome models of large animals and are ready for clinical feasibility trials. The Wolf Creek CPR researchers' conferences I, II, and III were meant to advise the guidelines-setting committees of the American Heart Association and other agencies. The ten topics of Wolf Creek IV, published in this issue of New Horizons, were different in design and objective. There was an appropriate emphasis on fully automatic external defibrillation by lay rescuers, which has the potential for a breakthrough effect. Wolf Creek V, which we recommend to be conducted around the turn of the millennium, should focus on the pathophysiology and therapeutics of respiratory, cardiac, and cerebral resuscitation in general, and on organ, cellular, and molecular level research into how cells, organs, and organisms die, and how acute dying processes might be reversed. What to teach whom and how should be left to guideline conferences of agencies.

Hyperthermia-induced cardiac arrest in monkeys: limited efficacy of standard CPR

BACKGROUND

Successful resuscitation from heatstroke cardiopulmonary arrest has been only partially explored and the data covering the post resuscitation pathophysiology leading to secondary arrest is, in most cases, insufficient.

HYPOTHESIS

Following heatstroke-cardiopulmonary arrest, successful resuscitation may be achieved by standard CPR with surface cooling and administration of glucose. We ponder the sequence of early circulatory responses and the pathophysiological changes following successful resuscitation.

METHODS

We exposed 12 pigtail monkeys to total-body hyperthermia (cerebral T 42 degrees C) until cardiac arrest ensued. Standard external CPR with surface cooling and glucose 5% IV were administered for up to 30 min. Control group A (n = 6) was compared with experimental group B (n = 6), which received additional steroid, glucagon and hypertonic glucose during CPR attempts.

RESULTS

No significant differences were found between the outcome of the two groups. The 30-min CPR attempt succeeded in restoration of spontaneous circulation (ROSC) in 8/12 monkeys-5 animals from group A and 3 in group B. The animals in whom resuscitation was unsuccessful had significantly prolonged periods of rectal temperature exceeding 42.5 degrees C (p < 0.05), and significantly higher rectal temperatures at the end of 30 min of CPR and cooling (p < 0.05). All the resuscitated animals later rearrested at 158 +/- 68 (95-228) min after ROSC; pulmonary edema occurred in 6/8 animals.

CONCLUSIONS

We conclude that experimentally-induced heatstroke can be transiently reversed by standard resuscitative procedures, but is followed by a delayed, irreversible, secondary shock state, which could not be prevented by the treatment we employed. We were, however, able to document in detail the pathophysiologic processes involved in the resuscitation, and the irreversible shock one sees after "successful" CPR.

Hypothermia and minimal fluid resuscitation increase survival after uncontrolled hemorrhagic shock in rats

OBJECTIVE

To test the hypothesis that protective-preservative moderate hypothermia during uncontrolled hemorrhagic shock (UHS) in rats increases survival.

DESIGN

Randomized outcome study in rats.

MATERIALS AND METHODS

UHS phase I of 90 minutes, with initial withdrawal of 3 mL/100 g of blood plus tail amputation, was followed by hemostasis and all-out resuscitation phase II from 90 to 150 minutes, and observation phase III to 72 hours. Forty male rats under light anesthesia and spontaneous breathing were randomized into four groups: Group 1 received no fluid resuscitation during UHS and normothermia (37.5 degrees C) throughout. Group 2 received no fluid resuscitation and hypothermia (30 degrees C) from 15 to 120 minutes. Group 3 received lactated Ringer's solution to maintain mean arterial pressure at 40 mm Hg during UHS and normothermia. Group 4 received lactated Ringer's solution to a mean arterial pressure of 40 mm Hg during UHS and hypothermia from 15 to 120 minutes.

RESULTS

UHS phase I was survived by 0 of 10 rats in group 1, 7 of 10 in group 2, 5 of 10 in group 3, and 10 of 10 in group 4 (p < 0.01 for group 1 vs. 2, 3, or 4; p < 0.05 for group 4 vs. 3). Survival to 72 hours was achieved by 0 of 10 rats in group 1, 3 of 10 in group 2 (p < 0.001 vs. group 1), 1 of 10 in group 3, and 7 of 10 in group 4 (p < 0.001 vs. group 1, and p < 0.01 vs. group 3). All 72-hour survivors were neurologically normal. Necropsies in rats that died early during phase III showed edema and gastrointestinal hemorrhages.

CONCLUSIONS

Moderate hypothermia or limited (hypotensive) fluid resuscitation --best both combined--increases survival during and after UHS in rats.

A comparison of prolonged manual and mechanical external chest compression after cardiac arrest in dogs

The effects of manual and a new mechanical chest compression device (Heartsaver 2000) during prolonged CPR with respect to haemodynamics and outcome were tested in a prospective, randomized, controlled experimental trial during ventricular fibrillation in 12 dogs of 9-13 kg body weight after 1 min of cardiac arrest. During the first 10 min of CPR the dogs were resuscitated according to the Basic Life Support (BLS) algorithm, followed by 20 min of Advanced Life Support (ALS) algorithm. After 30 min of CPR both manual and mechanical CPR groups were resuscitated following a standardized ALS protocol. During CPR, coronary perfusion pressure and end tidal CO2 were greater with mechanical CPR. All animals were successfully resuscitated and neurological deficit scores were not different. The CPR trauma score was less in the mechanical group. Mechanical external chest compression provided better haemodynamics than the manual technique, though outcome did not differ. Both optimally performed manual and mechanical techniques produce flow sufficient to maintain organ viability for 30 min of CPR after a 1 min arrest interval.

Resuscitation medicine research: quo vadis

Laboratory research should have clinical relevance. Topics should be selected according to need, gaps in knowledge, and opportunities; the investigator's background, expertise, interests, and ambitions; scientific, clinical, and socioeconomic importance; and feasibility of successful performance and conclusion. The current explosion of knowledge and sophistication of methods will require research by multidisciplinary teams. Systematic goal-oriented studies should be conducted in environments that encourage serendipitous discoveries. Mechanism- and outcome-oriented research, in laboratories and on patients, is needed. In cardiac arrest research, hearts and brains "too good to die" offer many challenges. In trauma research, particular challenges include protection-preservation during uncontrolled hemorrhagic shock, suspended animation for delayed resuscitation in exsanguination, and prevention of brain swelling after traumatic brain injury. Emergency physicians have the unique opportunity to initiate clinical resuscitation research in unexplored territory: the prehospital arena.

Sodium bicarbonate in cardiac arrest: a reappraisal

The routine use of sodium bicarbonate in patients with cardiac arrest has been discouraged, with the benefit of outcome evaluation. Current recommendations include an elaborate stratification of circumstances in which bicarbonate is to be used. The physiological and clinical aspects of bicarbonate administration during cardiopulmonary resuscitation in animal and human studies were reviewed. The onset of significant acidemia or alkalemia is associated with adverse system specific effects. The administration of bicarbonate may mitigate the adverse physiological effects of acidemia, improve response to exogenously administered vasopressor agents, or simply increase venous return due to an osmolar effect, resulting in increased coronary perfusion pressure. Likewise, bicarbonate may have adverse effects in each of these areas. The preponderance of evidence suggests that bicarbonate is not detrimental and may be helpful to outcome from cardiac arrest. An objective reappraisal of the empirical use of bicarbonate or other buffer agents in the appropriate "therapeutic window" for cardiac patients may be warranted.

Complete recovery after normothermic hemorrhagic shock and profound hypothermic circulatory arrest of 60 minutes in dogs

OBJECTIVE

We hypothesize that during severe normothermic hemorrhagic shock (HS), induction of profound hypothermic circulatory arrest (PHCA) of 60 minutes to allow repair of otherwise lethal injuries in a bloodless field, can be survived without brain damage. In previous dog studies, normothermic HS with mean arterial pressure (MAP) of 40 mm Hg for 30 minutes, followed by PHCA of 2 hours at brain (tympanic membrane) temperature of 5 to 10 degrees C and core temperature of 10 degrees C, induced and reversed with cardiopulmonary bypass, resulted in survival with mild histopathologic brain damage. This study was designed to determine the severity of HS that can safely allow 1 hour of PHCA. In pilot studies with HS at MAP 30 mm Hg for 90 minutes with or without subsequent PHCA of 60 minutes there were no survivors.

METHODS

In the definitive study, outcomes in four groups of five dogs each were compared: group I, HS at MAP 30 mm Hg for 60 minutes and normothermic fluid resuscitation; group II, HS at MAP 30 mm Hg for 60 minutes, PHCA for 60 minutes, and resuscitation; group III, HS at MAP 40 mm Hg for 60 minutes and normothermic fluid resuscitation; and group IV, HS at MAP 40 mm Hg for 60 minutes, PHCA for 60 minutes, and resuscitation. Controlled ventilation was maintained for at least 20 hours and intensive care for 72 hours.

RESULTS

In groups I and II, two of five dogs in each group survived to 72 hours. In groups III and IV, all ten dogs survived. All survivors were functionally normal, with neurologic deficit scores (0% = normal, 100% = brain dead) of < 10%. Light microscopic scoring of 18 brain regions revealed no ischemic changes. All nonsurvivors had a severe metabolic acidemia after HS and developed multiple organ failure, including pulmonary edema, pneumonia, and intestinal necrosis.

CONCLUSIONS

The critical level of hypotension during 60 minutes normothermic HS that is compatible with survival in dogs is a MAP of between 30 and 40 mm Hg. After otherwise survivable severe normothermic HS of 60 minutes, PHCA of 60 minutes does not add brain damage or mortality, and may allow survival from injuries that would otherwise be irreparable.

On the history of modern resuscitation

The development of modern cardiopulmonary-cerebral resuscitation (CPCR) has given every person the ability to challenge death anywhere. Despite sparks of knowledge and occasional applications of possibly effective lifesaving efforts since antiquity, the possibility to reverse acute terminal states or clinical death by modern, physiologically sound, and effective measures did not come about until around 1900 inside hospitals, and around 1960 outside hospitals. Additional potentially effective cerebral resuscitation, research since around 1970, may be taken to clinical trials before the year 2000. The history of resuscitation medicine around 1900, when many opportunities to assemble existing bits of knowledge into an effective system were missed, should be a warning for those individuals who will lead CPCR beyond the year 2000. History has shown the need for continuing communication and collaboration among investigators of different countries, and between laboratory researchers, clinicians of various disciplines, and prehospital rescuers. The lessons learned from history, for research challenges in the near future, include: a) the development of ultra-advanced life support to be initiated outside the hospital, to bridge cardiopulmonary resuscitation (CPR)-resistant cases to definitive cardiac procedures in the hospital; and b) cerebral resuscitation to complete recovery after 10 to 15 mins of normothermic cardiac arrest without blood flow. Both challenges above will require research projects at multiple levels--from the molecular and cellular levels, to the use of small and large animal models (with organs' and organisms' process and outcome evaluations), to studies of patients and communities. Beyond the year 2000, resuscitation research might become more challenging and cost-effective in the area of multiple trauma, which concerns the young and fit. Research challenges concerning brain trauma, uncontrolled hemorrhagic shock, and "suspended animation" for delayed resuscitation have their own histories, and are not covered here. The author apologizes for not having recognized many important contributors to the history of CPCR because of space constraints or lack of knowledge about such contributions. Input on this subject from readers of this paper is hereby invited.

Resuscitative hypothermia

Resuscitative (postinsult) hypothermia is less well studied than protective-preservative (pre- and intra-arrest) hypothermia. The latter is in wide clinical use, particularly for protecting the brain during cardiac surgery. Resuscitative hypothermia was explored in the 1950s and then lay dormant until the 1980s when it was revived. This change occurred through the discoveries of brain damage mitigating effects after cardiac arrest in dogs, and after forebrain ischemia in rats, of mild (34 degrees C) hypothermia (which is safe), and of benefits derived from moderate hypothermia (30 degrees C) after traumatic brain injury or focal brain ischemia in various species. The idea that protection-preservation or resuscitation by hypothermia is mainly explained by its ability to reduce cerebral oxygen demand has been replaced by an increasingly documented synergism of many beneficial mechanisms. Deleterious chemical cascades during and after these insults are suppressed even by mild hypothermia. Prolonged moderate hypothermia carries some risks, e.g., arrhythmias, infection and coagulopathies. These side effects need further study. In global brain ischemia, protective-preservative mild hypothermia provides lasting mitigation of brain damage. Resuscitative mild hypothermia, however, may be beneficial in terms of long-term outcome or may merely delay the inevitable loss of selectively vulnerable neurons. Even if the latter is true, mild hypothermia may extend the therapeutic window for other interventions. This extension of the therapeutic window requires further documentation. After normothermic cardiac arrest of 11 mins in dogs, mild resuscitative hypothermia from 15 mins to 12 hours after reperfusion plus cerebral blood flow promotion normalized functional recovery with the least histologic damage seen thus far. Optimal duration of, and rewarming methods from, resuscitative hypothermia need clarification. The earliest possible induction of mild hypothermia after cardiac arrest seems desirable. Head-neck surface cooling alone is too slow. Among many clinically feasible rapid cooling methods, carotid cold flush and peritoneal cooling look promising. After traumatic brain injury or focal brain ischemia, which seem to still benefit from even later cooling, surface cooling methods may be adequate. Resuscitative hypothermia after cardiac arrest, traumatic brain injury, or focal brain ischemia should be considered for clinical trials.

Cerebral resuscitation from cardiac arrest: pathophysiologic mechanisms

Both the period of total circulatory arrest to the brain and postischemic-anoxic encephalopathy (cerebral postresuscitation syndrome or disease), after normothermic cardiac arrests of between 5 and 20 mins (no-flow), contribute to complex physiologic and chemical derangements. The best documented derangements include the delayed protracted inhomogeneous cerebral hypoperfusion (despite controlled normotension), excitotoxicity as an explanation for selectively vulnerable brain regions and neurons, and free radical-triggered chemical cascades to lipid peroxidation of membranes. Protracted hypoxemia without cardiac arrest (e.g., very high altitude) can cause angiogenesis; the trigger of it, which lyses basement membranes, might be a factor in post-cardiac arrest encephalopathy. Questions to be explored include: What are the changes and effects on outcome of neurotransmitters (other than glutamate), of catecholamines, of vascular changes (microinfarcts seen after asphyxia), osmotic gradients, free-radical reactions, DNA cleavage, and transient extracerebral organ malfunction? For future mechanism-oriented studies of the brain after cardiac arrest and innovative cardiopulmonary-cerebral resuscitation, increasingly reproducible outcome models of temporary global brain ischemia in rats and dogs are now available. Disagreements exist between experienced investigative groups on the most informative method for quantitative evaluation of morphologic brain damage. There is agreement on the desirability of using not only functional deficit and chemical changes, but also morphologic damage as end points.

Cerebral resuscitation from cardiac arrest: treatment potentials

In 1961, in Pittsburgh, PA, "cerebral" was added to the cardiopulmonary resuscitation system (CPR --> CPCR). Cerebral recovery is dependent on arrest and cardiopulmonary resuscitation times, and numerous factors related to basic, advanced, and prolonged life support. Postischemic-anoxic encephalopathy (the cerebral postresuscitation disease or syndrome) is complex and multifactorial. The prevention or mitigation of this syndrome requires that there be development and trials of special, multifaceted, combination treatments. The selection of therapies to mitigate the postresuscitation syndrome should continue to be based on mechanistic rationale. Therapy based on a single mechanism, however, is unlikely to be maximally effective. For logistic reasons, the limit for neurologic recovery after 5 mins of arrest must be extended to achieve functionally and histologically normal human brains after 10 to 20 mins of circulatory arrest. This goal has been approached, but not quite reached. Treatment effects on process variables give clues, but long-term outcome evaluation is needed for documentation of efficacy and to improve clinical results. Goals have crystallized for clinically relevant cardiac arrest-intensive care outcome models in large animals. These studies are expensive, but essential, because positive treatment effects cannot always be confirmed in the rat forebrain ischemia model. Except for a still-elusive breakthrough effect, randomized clinical trials of CPCR are limited in their ability to statistically document the effectiveness of treatments found to be beneficial in controlled outcome models in large animals. Clinical studies of feasibility, side effects, and acceptability are essential. Hypertensive reperfusion overcomes multifocal no-reflow and improves outcome. Physical combination treatments, such as mild resuscitative (early postarrest) hypothermia (34 degrees C) plus cerebral blood flow promotion (e.g., with hypertension, hemodilution, and normocapnia), each having multiple beneficial effects, achieved complete functional and near-complete histologic recovery of the dog brain after 11 mins of normothermic, ventricular fibrillation cardiac arrest. Calcium entry blockers appear promising as a treatment for postischemic-anoxic encephalopathy. However, the majority of single or multiple drug treatments explored so far have failed to improve neurologic outcome. Assembling and evaluating combination treatments in further animal studies and determining clinical feasibility inside and outside hospitals are challenges for the near future. Treatments without permanent beneficial effects may at least extend the therapeutic window. All of these investigations will require coordinated efforts by multiple research groups, pursuing systematic, multilevel research--from cell cultures to rats, to large animals, and to clinical trials. There are still many gaps in our knowledge about optimizing extracerebral life support for cerebral outcome.