Open-chest CPR: an old method whose time has returned

Resuscitative thoracotomies and open chest cardiac compressions in non-traumatic cardiac arrest

Since the popularisation of closed chest cardiac compressions in the 1960s, open chest compressions in non-traumatic cardiac arrest have become a largely forgotten art. Today, open chest compressions are only rarely performed outside operating theatres. Early defibrillation and high quality closed chest compressions is the dominating gold standard for the layman on the street as well as for the resuscitation specialist. In this paper we argue that the concept of open chest direct cardiac compressions in non-traumatic cardiac arrest should be revisited and that it might be due for a revival. Numerous studies demonstrate how open chest cardiac compressions are superior to closed chest compressions in regards to physiological parameters and outcomes. Thus, by incorporating resuscitative thoracotomies and open chest compressions in our algorithms for non-traumatic cardiac arrest we may improve outcomes.

Cerebral Resuscitation

Resuscitology is the science of reanimation from apparent death or from unconsciousness. Prior to the last quarter of this century, resuscitation was steeped in myth, supported only by anecdote, and founded on unphysiologic principles. The development of new, scientifically based, modern concepts and practice of cardiopulmonary resuscitation (CPR) injected great hope into improving the chances for survival and quality of life for cardiac patients.

Recent reports indicate that there are nearly 70,000 “successful” cardiac resuscitations annually. However, it is estimated that only 10% are able to resume their former lifestyles. It is anticipated that with the expansion of prehospital emergency medical services, this proportion will increase. These facts have stimulated intense research aimed at elucidating the pathophysiology of cellular death with the goal of protecting the brain during cardiac arrest.

Open-chest cardiopulmonary resuscitation: past, present and future

Out-of-hospital cardiac arrests account for approximately 1000 sudden cardiac deaths per day in the United States. Since its introduction in 1960 closed-chest cardiac massage (CCCM) often takes place as an attempt at resuscitation, although its survival rates are low. Other resuscitation techniques are available to physicians such as open-chest cardiopulmonary resuscitation (OCCPR). OCCPR has been shown by several scientists to be hemodynamically superior to CCCM as it increases arterial pressures, cardiac output, coronary perfusion pressures, return of spontaneous circulation and cerebral blood flow. Improved neurological and cardiovascular outcome and an increase in survival rate compared to CCCM have been described. Timing is one of the key variables in determining patient outcome when performing OCCPR. The American Heart Association in association with the International Liaison Committee (ILCOR) has specific indications for the use of OCCPR. Some investigators recommend starting OCCPR in out-of-hospital cardiac arrests on arrival at the scene instead of CCCM. Surprisingly, the incidence of infectious complications after thoracotomy in an unprepared chest is low. The vast majority of the patients' families accept OCCPR as a therapeutic choice for cardiac arrests and it has been showed to be economically viable. This paper reviews some of the basic and advanced concepts of this evolving technique.

Assessment of In-Hospital Cardiopulmonary Resuscitation Using Utstein Template in a University Hospital

The aim of this study was to evaluate the effectiveness of in-hospital cardiopulmonary resuscitation (CPR) strategies and identify key predictors of post-CPR survival in a university hospital setting. Using a form recommended by the European Resuscitation Council, data regarding in-hospital CPR attempts from January 2001 to December 2002 were recorded and analyzed. The main outcomes of interest were immediate survival after CPR and survival to hospital discharge. Of 307 patients who suffered cardiac arrest in the study period, 103 (33.5%) were resuscitated. Of these 103 patients, 28 (27.2%) survived immediately and 12 (11.7%) survived to hospital discharge. The key predictors of immediate survival were CPR duration and initial cardiac rhythm as monitored by ventricular fibrillation/pulseless ventricular tachycardia (VF/VT). The key predictors of survival to hospital discharge were CPR duration, immediate defibrillation, Glasgow Coma Scale score, and Early Prediction Score. Together, our results suggest that in-hospital CPR strategies require improvement. They also underscore the importance of data collection and analysis in evaluating the effectiveness of inhospital CPR strategies.

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.

Systemic perfusion pressure and blood flow before and after administration of epinephrine during experimental cardiopulmonary resuscitation

OBJECTIVES

To evaluate instantaneous blood flow variations in the compression and relaxation phases of cardiopulmonary resuscitation (CPR) and the effect of epinephrine administration.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Experimental laboratory in a university hospital.

SUBJECTS

Twenty-two anesthetized piglets.

INTERVENTIONS

A tracheostomy was performed and arterial, central venous, and pulmonary arterial catheters were inserted, followed by thoracotomy with placement of pulmonary arterial, aortic, and left anterior descending coronary arterial (extended study group) flow probes and a left atrial catheter. Ventricular fibrillation for 2 mins was followed by 10 mins of either open-chest (n = 10) or closed-chest (n = 12) CPR. Seven minutes after the initiation of CPR, all piglets received 0.5 mg of epinephrine iv; at 12 mins, direct current shocks were applied.

MEASUREMENTS AND MAIN RESULTS

Open-chest CPR generated greater systemic perfusion pressure than closed-chest CPR, especially during the relaxation phase, resulting in greater mean blood flow. With both open- and closed-chest CPR, antegrade pulmonary arterial and aortic blood flow occurred during compression, whereas antegrade left anterior descending coronary arterial blood flow occurred during relaxation. During relaxation, retrograde flow was found in the pulmonary artery and aorta. During compression, retrograde flow was found in the left anterior descending coronary artery. The administration of epinephrine had the following effects: a) increased the systemic perfusion pressure more during open- than closed-chest CPR; b) increased the systemic relaxation perfusion pressure more than the compression perfusion pressure; c) decreased mean pulmonary arterial and aortic blood flow, but substantially increased the mean left anterior descending coronary artery blood flow; and d) reduced the retrograde flow in the left anterior descending coronary artery.

CONCLUSIONS

Open-chest CPR generated greater systemic perfusion pressure and blood flow than closed-chest CPR. Epinephrine increased left anterior descending coronary artery blood flow but decreased total cardiac output, such that cerebral perfusion might be endangered. This problem will be studied separately.

Advanced cardiac life support: update on recent guidelines and a look at the future

The objectives of this article are to provide an update of the American Heart Association (AHA) 1992 National Conference guidelines for cardiopulmonary resuscitation (CPR) and emergency cardiac care and to review the investigation and development of new methods of CPR which may be considered in future recommendations. Despite an organized approach to sudden cardiac arrest, survival in patients receiving CPR is in the range of 5-15%. The new AHA guidelines recommend standard manual CPR performed at a rate of 80-100 compressions/min and organized algorithms of advanced cardiac life support. These guidelines stress widespread community training and rapid response in the following sequence: (1) recognition of early warning signs, (2) activation of the emergency medical system (EMS), (3) basic CPR, (4) early defibrillation, (5) intubation, and (6) intravenous medication. Several new recommendations pertain specifically to in-hospital care and are, therefore, particularly relevant to physician management of cardiac arrest. The best predictor of survival in patients requiring circulatory support after cardiac arrest is attainable coronary and cerebral perfusion. Unfortunately, the minimal levels of end-organ perfusion required to sustain life are often difficult or impossible to achieve with standard manual cardiopulmonary resuscitation and several new techniques have therefore been introduced. The most promising of these techniques are (1) interposed abdominal compression, (2) pneumatic vest, and (3) active compression-decompression resuscitation. Each of these techniques offers unique advantages when compared with standard manual cardiopulmonary resuscitation. The 1992 National Conference recommendations provide a rational framework for the resuscitation of cardiac arrest victims. New methods of cardiopulmonary resuscitation are now available and investigation into these methods continues.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood flow and perfusion pressure during open-chest versus closed-chest cardiopulmonary resuscitation in pigs

OBJECTIVE

To evaluate the blood flow and perfusion pressure differences observed during open- vs. closed-chest cardiopulmonary resuscitation (CPR), including the effects of epinephrine and sodium bicarbonate administration.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Experimental animal laboratory in a university hospital.

SUBJECTS

A total of 35 anesthetized piglets.

INTERVENTIONS

After tracheostomy and insertion of arterial, right atrial, and pulmonary arterial catheters, thoracotomy was performed with placement of a pulmonary arterial flow probe and left atrial catheter. Ventricular fibrillation was induced and followed by 15 mins of either open-chest (n = 14) or closed-chest (n = 21) CPR. A 4-min infusion of 50 mmol of sodium bicarbonate or saline was added at the start of CPR. After 8 mins of CPR, 0.5 mg of epinephrine was given intravenously, and after 15 mins, direct current (DC) shocks were used to revert the heart to sinus rhythm.

MEASUREMENTS AND MAIN RESULTS

Blood flow was studied using transit-time ultrasound flowmetry. In an extended group, intrathoracic pressure was measured for calculation of transmural pressure. Before epinephrine administration, mean pulmonary arterial flow (cardiac output) was reduced: a) during closed-chest CPR relatively more than pulmonary perfusion pressure but in proportion to systemic perfusion pressure; b) during open-chest CPR relatively less than pulmonary perfusion pressure but still in proportion to systemic perfusion pressure. Epinephrine administration temporarily increased systemic perfusion pressure during both closed- and open-chest CPR but temporarily decreased pulmonary perfusion pressure only during closed-chest CPR. After epinephrine administration, cardiac output temporarily decreased during both closed-and open-chest CPR.

CONCLUSIONS

Open-chest CPR resulted in better cardiac output and systemic perfusion pressure than closed-chest CPR. However, cardiac output values obtained with both methods were much lower than previously reported. After epinephrine administration, cardiac output became extremely low with both methods.

Mastering pediatric cardiopulmonary resuscitation

Premature and unexpected death, especially in children, is tragic and very unacceptable. Effective treatments for sudden death of pediatric patients continue to emerge. Modern cardiopulmonary resuscitation function began with the widespread introduction of closed-chest cardiac massage in 1960; however, despite 35 years of research and refinement, more than 90% of children who receive cardiopulmonary resuscitation do not survive. This article summarizes and expands on current treatment concepts for pediatric sudden death. Emphasis is placed on procedures and techniques that likely are accessible in most medical centers caring for critically ill and injured children.

The biphasic mechanism of blood flow during cardiopulmonary resuscitation: a physiologic comparison of active compression-decompression and high-impulse manual external cardiac massage

STUDY OBJECTIVE

Dismal survival in patients receiving standard manual CPR provided the rationale for the investigation of alternate methods of closed-chest circulatory support. Active compression-decompression (ACD) and high-impulse CPR are alternatives to standard manual CPR. This study was designed to test the hypothesis that ACD CPR provides superior cardiopulmonary hemodynamics due to an active decompression phase when compared with high-impulse manual CPR.

PARTICIPANTS

Hemodynamics were studied during ACD and high-impulse CPR in eight adult beagles.

DESIGN

Four animals were chronically instrumented and four were studied acutely. In an additional four animals, ACD was compared with sham ACD CPR. Each CPR technique was performed sequentially for 2 minutes, in random order, at a rate of 120, 50% duty cycle, and 1.5 to 2.0 in of compression depth. Measurements obtained included aortic, right atrial, left ventricular, and coronary perfusion pressures (in mm Hg); pulmonary artery flow, and left ventricular dimension.

RESULTS

ACD maximized cardiopulmonary hemodynamics, including coronary perfusion pressure and stroke volume, compared with both high-impulse manual and sham ACD CPR. ACD CPR also increased left ventricular pressure change per unit time during decompression, and these changes correlated well with left ventricular volume changes.

CONCLUSION

In the intact dog, ACD CPR generates physiologically and statistically superior hemodynamics when compared with high-impulse manual CPR. Improved blood flow seems to be related to more efficient ventricular filling and emptying. These findings emphasize the biphasic nature of CPR and the importance of active decompression.

Open-chest cardiac massage. The possible rebirth of an old procedure

Open-chest cardiac massage was widely and successfully used for many decades before its virtual abandonment 25 years ago. Both experimental evidence and basic physiologic evidence indicate that it has many advantages over closed-chest massage (especially increased cardiac output). Both resuscitation techniques have specific and unique advantages and disadvantages: They are not mutually exclusive. However, significant increases in rates of survival after cardiac arrest cannot be expected with variations of closed-chest cardiac massage and standard advanced life support services. Therefore, physicians must be willing to support controlled human studies that can definitively determine the proper role of each in resuscitation after cardiac arrest.

Emergency cardiopulmonary bypass for resuscitation from prolonged cardiac arrest

After cardiac arrest (no flow) of more than approximately 5 minutes' duration, standard external cardiopulmonary resuscitation (CPR) basic, advanced, and prolonged life support (BLS, ALS, PLS) do not reliably produce cerebral and coronary perfusion pressures to maintain viability and achieve stable spontaneous normotension; nor do they provide prolonged control over pressure, flow, composition, and temperature of blood. Since these capabilities are often needed to achieve conscious survival, emergency closed-chest cardiopulmonary bypass (CPB) by veno-arterial pumping via oxygenator is presented in this review as a potential addition to ALS-PLS for selected cases. In six dog studies by the Pittsburgh group (n = 221; 1982 through 1988), all 179 dogs that received CPB after prolonged cardiac arrest (no flow) or after CPR (low flow) states had restoration of stable spontaneous circulation. The use of CPB enhanced survival and neurological recovery over those achieved with CPR-ALS attempts only. With CPB and standard intensive care, it was possible to reverse normothermic ventricular fibrillation (VF) cardiac arrest (no flow) of up to 15 minutes and to achieve survival without neurologic deficit; VF of 20 minutes to achieve survival but with neurologic deficit; and VF of 30 minutes to achieve transient restoration of spontaneous circulation followed by secondary cardiac death. CPB could restore stable spontaneous circulation after ice water submersion of up to 90 minutes. Other groups' laboratory and clinical results agree with these findings in general. Clinical feasibility trials are needed to work out logistic problems and to meet clinical challenges. Future possibilities for emergency CPB require further research and development.

Initiation of closed-chest cardiopulmonary resuscitation basic life support. A personal history

Modern external (closed-chest) cardiopulmonary resuscitation (CPR) basic life support (BLS) gives everyone anywhere a chance to initiate the reversal of death from airway obstruction, apnea, or pulselessness. The history of modern CPR has its roots around 1900, but lay dormant for half a century, until in the 1950s several fortunate circumstances merged to allow for documentation of Steps A (airway control by head-tilt and jaw-thrust), B (breathing control by mouth-to-mouth ventilation), and C (circulation control by closed-chest cardiac massage, i.e. chest compressions) and their combination into BLS Steps A-B-C. BLS is only for borderline emergency oxygenation, i.e. Phase I of the life support chain. Both the non-authoritarian environment of the U.S.A. and several role players with keen interest in resuscitation were needed to enable the systematic research (Steps A and B), a chance rediscovery (Step C), and the integration of BLS with advanced life support (ALS, drugs and defibrillation, transferred from open-chest CPR) and brain-oriented prolonged life support (PLS, intensive care) to result in the development of an effective cardiopulmonary-cerebral resuscitation system. A fertile environment led rapidly to the development of resuscitation delivery systems in hospitals and communities. This paper is a story told by one of the role players.

Effect of cardiac arrest time on cortical cerebral blood flow during subsequent standard external cardiopulmonary resuscitation in rabbits

Standard external cardiopulmonary resuscitation (SECPR) produces high cerebral venous and intracranial pressure peaks, low cerebral perfusion pressure, and low cerebral blood flow (CBF). Cerebral viability seems to require 20% of normal CBF, which SECPR cannot reliably generate. We tested the hypothesis that SECPR can produce adequate CBF if started immediately, but not if started after a long period of cardiac arrest (no flow, stasis). Cardiac arrest times of 1, 3, 5, 7 and 9 min were studied in rabbits. We measured unifocal cortical CBF with H2 clearance curves after saturation with H2 10%, O2 50% and N2O 40% by intermittent positive-pressure ventilation (IPPV). Measurements were made during spontaneous circulation (control condition), and then after resaturation immediately before induction of asystole by KCl i.v., and H2 clearance starting at end of arrest time during SECPR-basic life support with IPPV 100% and manual chest compressions (120/min) during asystole. Control cortical CBF was 30-40 ml/100 g brain per min. During asystole and SECPR, CBF greater than 20% normal was achieved only after no-flow of 1 min. After longer arrest (no-flow) times, CBF was less than 20% normal. Values were near zero after 7 and 9 min of cardiac arrest. Decrease in mean arterial pressures (MAP) produced by SECPR during asystole paralleled CBF values. Thus, the longer the preceding period of stasis, the lower the MAP and CBF generated by SECPR without epinephrine. This effect may be the result of anoxia-induced vasoparalysis and stasis-induced increased blood viscosity.

Brain iron delocalization and lipid peroxidation following cardiac arrest

Brain injury after cardiac arrest and resuscitation may occur, in part, by oxygen radical mechanisms. The availability of a transition metal, such as iron, is essential for in vitro initiation of this type of reaction. The brain has significant stores of iron bound in large proteins. We conducted this study to determine whether iron availability is enhanced in the canine brain following resuscitation from 15 minutes of cardiac arrest, and whether this iron is associated with the appearance of products of radical-mediated lipid peroxidation (LP) after two hours of reperfusion. Examination of the data by the method of multivariate analysis revealed significant increases in the low molecular weight species (LMWS) iron (300% of nonischemic controls, P less than .01), malondialdehyde (MDA), a lipid peroxidation degradation product (145% of nonischemic controls, P less than .01), and conjugated dienes (CD) (204% of nonischemic controls, P = .07). Therapy with deferoxamine (50 mg/kg IV immediately post resuscitation) produced a reduction in MDA and CD to levels statistically indistinguishable from nonischemic controls. We conclude that brain tissue iron is delocalized from normal storage forms to a LMWS pool after two hours of reperfusion following resuscitation from a 15-minute cardiac arrest, and that this is associated with increased products of LP. The increase in LP products is blocked by treatment with deferoxamine.

Ischemia, resuscitation, and reperfusion: mechanisms of tissue injury and prospects for protection

Since its introduction in 1960, CPR has evolved into a complex program involving not only the medical community but also the lay public. Currently, program activities include instruction of the lay public in basic life support techniques, development and deployment of emergency medical systems, recommendations for drug protocols for advanced cardiac life support and, most recently, introduction of new methods for tissue protection following resuscitation. After 25 years of experience, we are beginning to understand the pathophysiology of tissue ischemia during cardiac arrest and the interventions required to improve chances of survival and quality of life of the cardiac arrest victim. Recent data in the literature suggest that modification of certain interventions in the resuscitation program may be needed. The poor neurologic outcomes with prolonged standard CPR show that it is not protective after 4 to 6 minutes of cardiac arrest. Modifications to this technique, including SVC-CPR or IAC-CPR, have not been shown to increase resuscitability or hospital discharge rates. Human studies of open-chest cardiac massage are needed to evaluate this option. Defibrillation is the definitive treatment for ventricular fibrillation. Greater emphasis should be placed on the earliest possible delivery of this treatment modality. Computerized defibrillators may provide greater and earlier access to defibrillation in the homes of patients at high risk of ventricular fibrillation. They may also be applicable by untrained public service personnel (police and firemen), individuals in geographically inaccessible areas (aircraft), or emergency medical technicians in rural areas where skill retention is a significant problem. Calcium has no proved benefit in cardiac resuscitation. There is biochemical evidence that it may be harmful in brain resuscitation. Its use in resuscitation should be discontinued. The dose of epinephrine currently advocated in the ACLS protocols may be inadequate to increase aortic diastolic pressure and coronary and cerebral perfusion pressures and thus aid resuscitation. Animal studies indicate that substantial increases in the current dosage are needed to achieve these effects. Human studies are needed to verify these results. A role for calcium antagonists in the treatment of postarrest encephalopathy has been demonstrated in animals and is currently undergoing clinical trials. Iron-dependent lipid peroxidative cell membrane injury may be important in the pathogenesis of postarrest encephalopathy. Animal studies suggest that the iron chelator deferoxamine may have a significant therapeutic role in the treatment of postarrest encephalopathy.

Postischemic tissue injury by iron-mediated free radical lipid peroxidation

Cell damage initiated during ischemia matures during reperfusion. Mechanisms involved during reperfusion include the effects of arachidonic acid and its oxidative products prostaglandins and leukotrienes, reperfusion tissue calcium overloading, and damage to membranes by lipid peroxidation. Lipid peroxidation occurs by oxygen radical mechanisms that require a metal with more than one ionic state (transitional metal) for catalysis. We have shown that cellular iron is delocalized from the large molecules where it is normally stored to smaller chemical species during postischemic reperfusion. Postischemic lipid peroxidation is inhibited by the iron chelator deferoxamine. Intervention in the reperfusion injury of membranes by chelation of transitional metals is a new and promising therapeutic possibility for protection of the heart and brain.

Ischemic brain protection

Despite advances in the understanding of the pathophysiology of cerebral ischemia, no single brain resuscitation therapy has yet been shown to be clinically superior to brain-oriented intensive care. Basic concepts in cardiopulmonary-cerebral resuscitation (CPCR) are discussed, as are two specific phases of CPCR, cerebral preservation and cerebral resuscitation. Cerebral preservation is initiated during cardiac arrest (ie, prior to restoration of spontaneous circulation [ROSC]) and includes use of artificial perfusion techniques and drugs to produce cerebral perfusion during this phase. Cerebral resuscitation is brain-oriented therapy initiated after ROSC. Pharmacologic agents currently under study for cerebral resuscitation include the barbiturates, calcium antagonists, and iron chelators. With respect to defining efficacy of the pharmacologic agents, the concept of therapeutic window is important. Although no agent has been proven clinically, several appear to be promising.

Resuscitation of dogs from cold-water submersion using cardiopulmonary bypass

In cold-water drowning, attempts at restoration of spontaneous circulation (ROSC) by external cardiopulmonary resuscitation (CPR) often fail. We explored the longest period of asphyxial cardiac arrest from cold-water submersion (without inhalation of water) from which ROSC is possible using cardiopulmonary bypass (CPB). In 19 lightly anesthetized dogs the tracheal tube was clamped (simulating laryngospasm) and the dogs were immersed in ice water from 20, 40, 60, 90, or 120 minutes. Cardiac arrest occurred after six to 11 minutes of submersion. At start of resuscitation, rectal temperature ranged from 21 C (after 60 minutes) to 34 C (after 20 minutes of submersion), and cerebral temperature was between 7 C (after 120 minutes) and 27 C (after 20 minutes submersion). Resuscitation attempts were performed according to protocol in 16 dogs, using only CPB by venoarterial pumping with an oxygenator and a heat exchanger. Priming was with 400 to 800 mL Dextran 40 and Ringer's solution 1:1 plus heparin. CPB flows were 10 mL/kg/min, and they increased to achieve normotension and return of rectal temperature to 32 C. After one-half to three hours, of CPB, ROSC was successful in 75%. This percentage included one of three dogs after 90 minutes submersion, but not in the one dog after 120 minutes submersion. Spontaneous breathing and EEG activity returned in 56% at two to 24 hours, after 20 to 90 minutes of submersion. Failure of ROSC attempts apparently were due to clotting in large vessels during arrest and capillary leakage during reperfusion. CPB is effective for ROSC after prolonged hypothermic cardiac arrest, and it should be evaluated in animal outcome studies.