Hypothermic aortic arch flush for preservation during exsanguination cardiac arrest of 15 minutes in dogs

Selective aortic arch perfusion: a first-in-human observational cadaveric study

BACKGROUND

Selective aortic arch perfusion (SAAP) is a novel endovascular technique that combines thoracic aortic occlusion with extracorporeal perfusion of the brain and heart. SAAP may have a role in both haemorrhagic shock and in cardiac arrest due to coronary ischaemia. Despite promising animal studies, no data is available that describes SAAP in humans. The primary aim of this study was to assess the feasibility of selective aortic arch perfusion in humans. The secondary aim of the study was to assess the feasibility of achieving direct coronary artery access via the SAAP catheter as a potential conduit for salvage percutaneous coronary intervention.

METHODS

Using perfused human cadavers, a prototype SAAP catheter was inserted into the descending aorta under fluoroscopic guidance via a standard femoral percutaneous access device. The catheter balloon was inflated and the aortic arch perfused with radio-opaque contrast. The coronary arteries were cannulated through the SAAP catheter.

RESULTS

The procedure was conducted four times. During the first two trials the SAAP catheter was passed rapidly and without incident to the intended descending aortic landing zone and aortic arch perfusion was successfully delivered via the device. The SAAP catheter balloon failed on the third trial. On the fourth trial the left coronary system was cannulated using a 5Fr coronary guiding catheter through the central SAAP catheter lumen.

CONCLUSIONS

For the first time using a perfused cadaveric model we have demonstrated that a SAAP catheter can be easily and safely inserted and SAAP can be achieved using conventional endovascular techniques. The SAAP catheter allowed successful access to the proximal aorta and permitted retrograde perfusion of the coronary and cerebral circulation.

Femoral vascular access for endovascular resuscitation

ABSTRACT

Endovascular resuscitation is an emerging area in the resuscitation of both severe traumatic hemorrhage and nontraumatic cardiac arrest. Vascular access is the critical first procedural step that must be accomplished to initiate endovascular resuscitation. The endovascular interventions presently available and emerging are routinely or potentially performed via the femoral vessels. This may require either femoral arterial access alone or access to both the femoral artery and vein. The time-critical nature of resuscitation necessitates that medical specialists performing endovascular resuscitation be well-trained in vascular access techniques. Keen knowledge of femoral vascular anatomy and skill with vascular access techniques are required to meet the needs of critically ill patients for whom endovascular resuscitation can prove lifesaving. This review article addresses the critical importance of femoral vascular access in endovascular resuscitation, focusing on the pertinent femoral vascular anatomy and technical aspects of ultrasound-guided percutaneous vascular access and femoral vessel cutdown that may prove helpful for successful endovascular resuscitation.

Renal Function: Implications on the Surgical Treatment of RCC

The good oncologic results after partial nephrectomy for stage 1 RCC show that radical nephrectomy is an overtreatment in most cases, and that many healthy nephrons are removed unnecessarily. However, partial nephrectomy is a difficult operation, with increased blood loss and a higher risk of complications. Therefore, the advantage of preserved function has to be weighed up against the increased trauma of surgery in each individual patient, and the assessment of preoperative function may influence this decision, among other factors such as comorbidities and age. In most studies, renal function has been assessed by means of estimated glomerular filtration rate, and this parameter is very helpful for long-term studies in large populations. However, more precise measurement based on clearance studies are sometimes required for more sophisticated investigations. The technique of partial nephrectomy has evolved substantially in recent years, resulting in the preservation of more nephrons, less damage to the remaining parenchyma, less blood loss, and a decreased risk of complications. The introduction of minimally invasive surgery for this purpose has also decreased the overall morbidity of surgery. In the long-term, chronic kidney disease may result in increased cardiac mortality. There is ongoing discussion on this problem, however, this potential negative influence on overall survival is not only influenced by the rate of renal insufficiency, but also to a great extent by other comorbidities such as hypertension and diabetes. Therefore, in addition to providing the best surgery for any given patient, we have to make sure that the treatment of the comorbidities will also be part of our patient management, since the risk of cardiac failure may be greater than the risk of poor oncologic outcome.

A New Vision for Therapeutic Hypothermia in the Era of Targeted Temperature Management: A Speculative Synthesis

Three decades of animal studies have reproducibly shown that hypothermia is profoundly cerebroprotective during or after a central nervous system (CNS) insult. The success of hypothermia in preclinical acute brain injury has not only fostered continued interest in research on the classic secondary injury mechanisms that are prevented or blunted by hypothermia but has also sparked a surge of new interest in elucidating beneficial signaling molecules that are increased by cooling. Ironically, while research into cold-induced neuroprotection is enjoying newfound interest in chronic neurodegenerative disease, conversely, the scope of the utility of therapeutic hypothermia (TH) across the field of acute brain injury is somewhat controversial and remains to be fully defined. This has led to the era of Targeted Temperature Management, which emphasizes a wider range of temperatures (33–36°C) showing benefit in acute brain injury. In this comprehensive review, we focus on our current understandings of the novel neuroprotective mechanisms activated by TH, and discuss the critical importance of developmental age germane to its clinical efficacy. We review emerging data on four cold stress hormones and three cold shock proteins that have generated new interest in hypothermia in the field of CNS injury, to create a framework for new frontiers in TH research. We make the case that further elucidation of novel cold responsive pathways might lead to major breakthroughs in the treatment of acute brain injury, chronic neurological diseases, and have broad potential implications for medicines of the distant future, including scenarios such as the prevention of adverse effects of long-duration spaceflight, among others. Finally, we introduce several new phrases that readily summarize the essence of the major concepts outlined by this review—namely, Ultramild Hypothermia, the “Responsivity of Cold Stress Pathways,” and “Hypothermia in a Syringe.”

Prolonged severe hemorrhagic shock at a mean arterial pressure of 40 mmHg does not lead to brain damage in rats

Aim

To examine whether prolonged hemorrhagic shock (HS) at a mean arterial pressure (MAP) of 40 mmHg leads to brain damage.

Methods

Rats were anesthetized with sevoflurane. The HS model consisted of the following phases: I, pressure‐controlled HS at a MAP of 40 mmHg; II, fluid resuscitation to normalize blood pressure; III, observations with outcome evaluations in terms of survival, overall performance categories, and neurological deficit scores, as well as evaluation of apoptosis in the hippocampus at 96 h. Each group of six rats was randomized into 60 min (group 1) or 75 min (group 2) each of phases I and II. Three sham rats were anesthetized for 150 min, and then awakened during phase III.

Results

The three sham rats as well as five and two of the six rats in groups 1 and 2 (P < 0.05), respectively, survived for up to 96 h. All survivors were functionally normal with overall performance category = 1 and neurological deficit score = 0 at 96 h. Apoptotic neurons were not found in the hippocampus.

Conclusions

The higher mortality in group 2 suggested a more profound effect of HS compared with group 1. However, prolonged HS for 60 or 75 min did not cause functional damage or apoptosis in the hippocampus. These findings suggest that prolonged HS at a MAP of 40 mmHg, as a level at which cerebral blood flow seems preserved by autoregulatory mechanisms, does not lead to brain damage.

Development of the emergency preservation and resuscitation for cardiac arrest from trauma clinical trial

BACKGROUND

Patients who suffer a cardiac arrest from trauma rarely survive, even with aggressive resuscitation attempts, including an emergency department thoracotomy. Emergency Preservation and Resuscitation (EPR) was developed to utilize hypothermia to buy time to obtain hemostasis before irreversible organ damage occurs. Large animal studies have demonstrated that cooling to tympanic membrane temperature 10°C during exsanguination cardiac arrest can allow up to 2 hours of circulatory arrest and repair of simulated injuries with normal neurologic recovery.

STUDY DESIGN

The Emergency Preservation and Resuscitation for Cardiac Arrest from Trauma trial has been developed to test the feasibility and safety of initiating EPR. Select surgeons will be trained in the EPR technique. If a trained surgeon is available, the subject will undergo EPR. If not, the subject will be followed as a control subject. For this feasibility study, 10 EPR and 10 control subjects will be enrolled.

STUDY PARTICIPANTS

Study participants will be those with penetrating trauma who remain pulseless despite an emergency department thoracotomy.

INTERVENTIONS

Emergency Preservation and Resuscitation will be initiated via an intra-aortic flush of a large volume of ice-cold saline solution. Following surgical hemostasis, delayed resuscitation will be accomplished with cardiopulmonary bypass.

OUTCOME MEASURES

The primary outcome will be survival to hospital discharge without significant neurologic deficits. Secondary outcomes include long-term survival and functional outcome.

IMPLICATIONS

Once data from these 20 subjects are reviewed, revisions to the inclusion criteria and/or the EPR technique may then be tested in a second set of EPR and control subjects.

Emergency preservation and resuscitation for cardiac arrest from trauma

The advent of cardiopulmonary resuscitation (CPR) revolutionized the care of patients with cardiac arrest, now allowing survival of up to 30% after out-of-hospital arrest due to arrhythmia; however, outcomes for cardiac arrest after trauma remain dismal, with less than 10% survival despite the most aggressive modern resuscitation techniques. The short time interval between cardiac arrest and brain ischemia, the reduced efficacy of CPR in the patient with profound hypovolemia due to hemorrhage, and the speed of exsanguination from major vascular injury all conspire to limit the effectiveness of standard CPR in the critically injured patient. Beginning in the 1980s, researchers began to harness the effects of profound hypothermia in order to extend the window of survivability after traumatic arrest, allowing the critical time needed to obtain surgical hemostasis in otherwise lethal exsanguinating injuries. These studies have culminated in the emergency preservation and resuscitation (EPR) of the trauma patient. Rapid central arterial access is obtained and profound (<10 °C) hypothermia induced with aortic infusion of cold saline. During this window of up to 1 h, damage control surgical techniques are applied to control hemorrhage and repair injuries, followed by controlled rewarming and reperfusion using cardiopulmonary bypass. In this review, we trace these techniques from their early theoretical development, through refinement in clinically relevant animal models, and into their present application in a currently-enrolling human clinical trial of EPR for cardiac arrest from trauma (EPR-CAT), as well as examine current topics, ongoing challenges, and future directions for emergency preservation and resuscitation research.

Salvage techniques in traumatic cardiac arrest: thoracotomy, extracorporeal life support, and therapeutic hypothermia

PURPOSE OF REVIEW

Survival from traumatic cardiac arrest is associated with a very high mortality despite aggressive resuscitation including an Emergency Department thoracotomy (EDT). Novel salvage techniques are needed to improve these outcomes.

RECENT FINDINGS

More aggressive out-of-hospital interventions, such as chest decompression or thoracotomy by emergency physicians or anesthesiologists, seem feasible and show some promise for improving outcomes. For trauma patients who suffer severe respiratory failure or refractory cardiac arrest, there seems to be an increasing role for the use of extracorporeal life support (ECLS), utilizing heparin-bonded systems to avoid systemic anticoagulation. The development of exposure hypothermia is associated with poor outcomes in trauma patients, but preclinical studies have consistently demonstrated that mild, therapeutic hypothermia (34 °C) improves survival from severe hemorrhagic shock. Sufficient data exist to justify a clinical trial. For patients who suffer a cardiac arrest refractory to EDT, induction of emergency preservation and resuscitation by rapid cooling to a tympanic membrane temperature of 10 °C may preserve vital organs long enough to allow surgical hemostasis, followed by resuscitation with cardiopulmonary bypass.

SUMMARY

Salvage techniques, such as earlier thoracotomy, ECLS, and hypothermia, may allow survival from otherwise lethal injuries.

In cold blood: intraarteral cold infusions for selective brain cooling in stroke

Hypothermia is a promising therapeutic option for stroke patients and an established neuroprotective treatment for global cerebral ischemia after cardiac arrest. While whole body cooling is a feasible approach in intubated and sedated patients, its application in awake stroke patients is limited by severe side effects: Strong shivering rewarms the body and potentially worsens ischemic conditions because of increased O2 consumption. Drugs used for shivering control frequently cause sedation that increases the risk of aspiration and pneumonia. Selective brain cooling by intraarterial cold infusions (IACIs) has been proposed as an alternative strategy for patients suffering from acute ischemic stroke. Preclinical studies and early clinical experience indicate that IACI induce a highly selective brain temperature decrease within minutes and reach targeted hypothermia 10 to 30 times faster than conventional cooling methods. At the same time, body core temperature remains largely unaffected, thus systemic side effects are potentially diminished. This review critically discusses the limitations and side effects of current cooling techniques for neuroprotection from ischemic brain damage and summarizes the available evidence regarding advantages and potential risks of IACI.

Feasibility of blind aortic catheter placement in the prehospital environment to guide resuscitation in cardiac arrest

BACKGROUND

Aortic catheter-based resuscitation therapies are emerging with laboratory investigations showing benefit in models of trauma-related noncompressible torso hemorrhage and nontraumatic cardiac arrest. For these investigational aortic catheter-based therapies to reach their greatest potential clinical benefit, the ability to initiate them in the prehospital setting will be important. Feasibility of prehospital aortic catheterization without imaging capability supports this potential and is described in this report.

METHODS

A physician prehospital response system was created in cooperation with the local emergency medical services system to provide invasive hemodynamic monitoring during cardiac arrest. Physicians were dispatched to all known or suspected prehospital cardiac arrests covered by the emergency medical services system. Physicians responded with a specialized vascular catheterization pack and a monitor with invasive pressure monitoring capability. The physicians performed blind thoracic aortic and central venous catheterizations in cardiac arrest patients in the prehospital setting to measure coronary perfusion pressure, to optimize closed-chest cardiopulmonary resuscitation technique, and to administer intra-aortic epinephrine.

RESULTS

During a 2-year period, 22 medical cardiac arrest patients underwent prehospital invasive hemodynamic monitoring to guide resuscitation. Most patients had both aortic and central venous catheters inserted. The combination of intra-aortic epinephrine and adjustments in closed-chest cardiopulmonary resuscitation technique resulted in improved coronary perfusion pressure. Return of spontaneous circulation with survival to hospital admission was achieved in 50% (11 of 22) of these patients.

CONCLUSION

This report demonstrates the feasibility of successful blind aortic and central venous catheterizations in the prehospital environment and supports the potential feasibility of other emerging aortic catheter-based resuscitation therapies.

Induced hypothermia in comatose survivors of asphyxia: a case series of 14 consecutive cases

BACKGROUND

Induced hypothermia is widely used for comatose survivors of cardiac arrest. Other causes of hypoxic brain injury carry a poor prognosis when treated using traditional methods. At our hospital, hypothermia has also been used for the management of all comatose survivors of asphyxiation. The aim of the present study was to report the results of the management of these patients.

METHODS

Hospital charts of all patients admitted unconscious after asphyxiation during a 7-year period were reviewed. This included patients after hanging, drowning, carbon monoxide intoxication and other gas intoxications. In all patients, hypothermia with a target temperature of 32-34 degrees C was induced with external or intravascular cooling for 24 h. The primary outcome was neurologic function at discharge.

RESULTS

Fourteen male patients were treated with hypothermia, eight after hanging, three after drowning, two after carbon monoxide intoxication and one after methane intoxication. All were deeply comatose (Glasgow Coma Score 3-5) on arrival to hospital. Nine had been resuscitated from cardiac arrest. There were nine survivors (65%), all with good neurological recovery (Cerebral Performance Category 1-2). Four out of five non-survivors showed cerebral edema already on arrival computed tomographic (CT) scan while none of the nine survivors did.

CONCLUSIONS

The results of this study suggest that an early abnormal CT scan of the brain in patients resuscitated after asphyxiation carries an adverse prognosis. The favorable outcome of the patients in the present study suggests that a randomized clinical trial on the use of induced hypothermia in patients exposed to severe asphyxia might be warranted.

Induced hypothermia for trauma: current research and practice

Induction of hypothermia with the goal of providing therapeutic benefit has been accepted for use in the clinical setting of adult cardiac arrest and neonatal hypoxic-ischemic encephalopathy (HIE). However, its potential as a treatment in trauma is not as well defined. This review discusses potential benefits and complications of induced hypothermia (IH) with emphasis on the current state of knowledge and practice in various types of trauma. There is excellent preclinical research showing that in cases of penetrating trauma with cardiac arrest, inducing hypothermia to 10 degrees C using cardiopulmonary bypass (CPB) could possibly save those otherwise likely to die without causing neurologic sequelae. A human trial of this intervention is about to get underway. Preclinical studies suggest that inducing hypothermia may be useful to delay cardiac arrest in penetrating trauma victims who are hypotensive. There is potential for IH to be used in cases of blunt trauma, but it has not been well studied. In the case of traumatic brain injury (TBI), clinical trials have shown conflicting results, despite almost uniform efficacy seen in preclinical experiments. Major studies are analyzed and ways to standardize its use and optimize future clinical trials are discussed. More preclinical and clinical research is needed to better define whether there could be a role for IH in the case of spinal cord injuries.

Hypothermia in bleeding trauma: a friend or a foe?

The induction of hypothermia for cellular protection is well established in several clinical settings. Its role in trauma patients, however, is controversial. This review discusses the benefits and complications of induced hypothermia--emphasizing the current state of knowledge and potential applications in bleeding patients. Extensive pre-clinical data suggest that in advanced stages of shock, rapid cooling can protect cells during ischemia and reperfusion, decrease organ damage, and improve survival. Yet hypothermia is a double edged sword; unless carefully managed, its induction can be associated with a number of complications. Appropriate patient selection requires a thorough understanding of the pre-clinical literature. Clinicians must also appreciate the enormous influence that temperature modulation exerts on various cellular mechanisms. This manuscript aims to provide a balanced view of the published literature on this topic. While many of the advantageous molecular and physiological effects of induced hypothermia have been outlined in animal models, rigorous clinical investigations are needed to translate these promising findings into clinical practice.

Hypothermia in multisystem trauma

Exsanguinating hemorrhage is a common clinical feature of multisystem trauma that results in death or severe disability. Cardiovascular collapse resulting from hemorrhage is unresponsive to conventional methods of cardiopulmonary resuscitation. Even when bleeding is controlled rapidly, adequate circulation cannot be restored in time to avoid neurologic consequences that appear after only 5 mins of cerebral ischemia and hypoperfusion. Reperfusion adds further insult to injury. A novel solution to this problem would be to institute a therapy that makes cells and organs more resistant to ischemic injury, thereby extending the time they can tolerate such an insult. Hypothermia can attenuate some effects of ischemia and reperfusion. Accumulating preclinical data demonstrate that hypothermia can be induced safely and rapidly to achieve emergency preservation for resuscitation during lethal hemorrhage. Hypothermia may be an effective therapeutic approach for otherwise lethal traumatic hemorrhage, and a clinical trial to determine its utility is warranted.

Therapeutic hypothermia for neuroprotection

This review briefly discusses induced therapeutic hypothermia (TH), which represents the intentional induction of a lowered core body temperature of 35 degrees C or less. The focus is on resuscitative or postarrest hypothermia, the data that support it, and the practical issues pertaining to TH implementation.

Emergency preservation and resuscitation improve survival after 15 minutes of normovolemic cardiac arrest in pigs*

OBJECTIVE

Outcome after prolonged normovolemic cardiac arrest is poor, and new resuscitation strategies have to be found. We hypothesized that the induction of deep hypothermia for emergency preservation and resuscitation (EPR) during prolonged cardiac arrest, before the start of reperfusion, will mitigate the deleterious cascades leading to neuronal death and will thus improve outcome.

DESIGN

Prospective experimental study.

SETTING

University research laboratory.

SUBJECTS

Thirteen pigs, Large White breed (27-37 kg).

INTERVENTIONS

After 15 mins of ventricular fibrillation, pigs were subjected to 1) EPR (n = 6), 20 mins of hypothermic stasis induced with a cold saline aortic flush; or 2) 20 mins of conventional resuscitation (n = 7). Then cardiopulmonary bypass was initiated in both groups, followed by defibrillation. Controlled ventilation and mild hypothermia were continued for 20 hrs; survival was for 9 days. For neurologic evaluation, neurologic deficit score (100% = brain dead, 0-10% = normal), overall performance category (1 = normal, 5 = dead or brain dead), and brain histologic damage score were used.

MEASUREMENTS AND MAIN RESULTS

In the EPR group, brain temperature decreased from 38.5 degrees C +/- 0.2 degrees C to 16.7 degrees C +/- 2.5 degrees C within 235 +/- 27 secs. Five animals achieved restoration of spontaneous circulation and survived to 9 days: two pigs with overall performance category 2 and three pigs with overall performance category 3. Their neurologic deficit score was 45% (interquartile range 35, 50) and histologic damage score was 142 (interquartile range 109, 159). In the control group, four pigs achieved restoration of spontaneous circulation: one survived to 9 days with overall performance category 3, neurologic deficit score 45%, and histologic damage score 226 (restoration of spontaneous circulation, p = .6; survival, p = .03; overall performance category, p = .02).

CONCLUSIONS

EPR is feasible in an experimental pig model and improves survival after prolonged cardiac arrest in pigs. Further experimental studies are needed before this concept can be brought into clinical practice.

Suspended animation for delayed resuscitation

'Suspended animation for delayed resuscitation' is a new concept for attempting resuscitation from cardiac arrest of patients who currently (totally or temporarily) cannot be resuscitated, such as traumatic exsanguination cardiac arrest. Suspended animation means preservation of the viability of brain and organism during cardiac arrest, until restoration of stable spontaneous circulation or prolonged artificial circulation is possible. Suspended animation for exsanguination cardiac arrest of trauma victims would have to be induced within the critical first 5 min after the start of cardiac arrest no-flow, to buy time for transport and resuscitative surgery (hemostasis) performed during no-flow. Cardiac arrest is then reversed with all-out resuscitation, usually requiring cardiopulmonary bypass. Suspended animation has been explored and documented as effective in dogs in terms of long-term survival without brain damage after very prolonged cardiac arrest. In the 1990s, the Pittsburgh group achieved survival without brain damage in dogs after cardiac arrest of up to 90 min no-flow at brain (tympanic) temperature of 10 degrees C, with functionally and histologically normal brains. These studies used emergency cardiopulmonary bypass with heat exchanger or a single hypothermic saline flush into the aorta, which proved superior to pharmacologic strategies. For the large number of normovolemic sudden cardiac death victims, which currently cannot be resuscitated, more research in large animals is needed.

An update on fluid resuscitation

Hemorrhagic shock is the leading cause of death in civilian and military trauma. Effective hemorrhage control and better resuscitation strategies have the potential of saving lives. However, if not performed properly, resuscitation can actually exacerbate cellular injury caused by hemorrhagic shock, and the type of fluid used for resuscitation plays an important role in this injury pattern. It is logical to prevent this cellular injury through wiser resuscitation strategies than attempting immunomodulation after the damage has already occurred. It is important to recognize that unlike numerous other variables, resuscitation is completely under our control. We decide who, when and how should get resuscitated. This paper summarizes data from a number of studies to illustrate the differential effects of commonly used resuscitation fluids on cellular injury, and how these relate to clinical practice. In addition, some novel resuscitation strategies are described that may become clinically available in the near future.

Suspended animation can allow survival without brain damage after traumatic exsanguination cardiac arrest of 60 minutes in dogs

BACKGROUND

We have previously shown in dogs that exsanguination cardiac arrest of up to 120 minutes without trauma under profound hypothermia induced by aortic flush (suspended animation) can be survived without neurologic deficit. In the present study, the effects of major trauma (laparotomy, thoracotomy) are explored. This study is designed to better mimic the clinical scenario of an exsanguinating trauma victim, for whom suspended animation may buy time for resuscitative surgery and delayed resuscitation.

METHODS

Fourteen dogs were exsanguinated over 5 minutes to cardiac arrest. Flush of saline at 2 degrees C into the femoral artery was initiated at 2 minutes of cardiac arrest and continued until a tympanic temperature of 10 degrees C was achieved. The dogs were then randomized into a control group without trauma (n = 6) or a trauma group (n = 8) that underwent a laparotomy and isolation of the spleen before hemorrhage and then, at the start of cardiac arrest, spleen transection and left thoracotomy. During cardiac arrest, splenectomy was performed. After 60 minutes of no-flow cardiac arrest, reperfusion with cardiopulmonary bypass was followed by intensive care to 72 hours.

RESULTS

All 14 dogs survived to 72 hours with histologically normal brains. All control dogs were functionally neurologically intact. Four of eight trauma dogs were also functionally normal. Four had neurologic deficits, although three required prolonged mechanical ventilation because of airway edema and evidence of multiple organ failure. Blood loss from the chest and abdomen was variable and was associated with poor functional outcomes.

CONCLUSION

Rapid induction of profound hypothermic suspended animation (tympanic temperature, 10 degrees C) can enable survival without brain damage after exsanguination cardiac arrest of 60 minutes even in the presence of trauma, although prolonged intensive care may be required. This technique may allow survival of exsanguinated trauma victims, who now have almost no chance of survival.

Rapid induction of cerebral hypothermia by aortic flush during normovolemic cardiac arrest in pigs

OBJECTIVE

Induction of deep cerebral hypothermia before reperfusion might improve neurologic outcome after cardiac arrest. We hypothesized that an aortic flush with cold saline during cardiac arrest is able to induce deep cerebral hypothermia and that the cooling efficiency can be enhanced by a) increasing the arteriovenous pressure gradient during the flush with vasopressin; b) improving the cerebral microcirculation during the flush with the thrombolytic agent alteplase; and c) increasing the arteriovenous pressure gradient further with venting the right heart by draining blood during the flush.

DESIGN

Prospective randomized experimental study.

SETTING

University research laboratory.

SUBJECTS

Twenty-four pigs Large White breed (31-42 kg).

INTERVENTIONS

After 10 mins of ventricular fibrillation, pigs received an aortic flush (100 mL/kg, 4 degrees C, flow rate 35 mL/kg/min) into the descending aorta via a balloon catheter. The animals were subjected randomly to either an aortic flush with saline, saline plus vasopressin 1.2 IU/kg, saline plus alteplase 1 mg/kg, saline plus a combination of vasopressin 1.2 IU/kg and alteplase 1 mg/kg, or saline plus vasopressin 1.2 IU/kg and venting the right heart. Arterial and venous pressures and brain temperatures were recorded for an observation time of 10 mins after flush.

MEASUREMENTS AND MAIN RESULTS

A sufficient arteriovenous pressure gradient and deep cerebral hypothermia were only achieved with a flush containing vasopressin (brain temperature 16.1+/-1.3 degrees C in the vasopressin group vs. 35.4+/-1.5 degrees C in the saline group, p<.001); combining vasopressin with alteplase, or venting the right heart, did not further enhance the cooling efficiency of the flush.

CONCLUSIONS

A cold saline aortic flush with vasopressin rapidly decreases brain temperature during prolonged normovolemic cardiac arrest in pigs. Whether deep cerebral hypothermia induced before reperfusion can improve neurologic outcome after cardiac arrest needs further investigation in large animal outcome studies.

Therapeutic hypothermia after cardiac arrest

PURPOSE OF REVIEW

Most patients who suffer a cardiac arrest die after the event. Full neurological recovery occurs in only 6-23%. Until recently no specific post-arrest therapy was available to improve outcome. Application of therapeutic hypothermia (32-34 degrees C for 12-24 h) applied after cardiac arrest could help to improve this dreadful situation. This review covers the background of and recent clinical studies into hypothermia after cardiac arrest, and gives some insights into the future of resuscitation, namely suspended animation.

RECENT FINDINGS

Two randomized clinical trials of mild therapeutic hypothermia applied after successful resuscitation from cardiac arrest showed that hypothermia after cardiac arrest improves neurological outcome as well as overall mortality.

SUMMARY

The introduction of therapeutic hypothermia after cardiac arrest into routine intensive care practice could save thousands of lives worldwide, because only six patients must be treated to yield one additional patient with favourable neurological recovery. New developments in cooling techniques will make early induction of therapeutic hypothermia simple and convenient. The optimal duration and depth of hypothermia will be determined by future trials. Suspended animation is cooling during cardiac arrest to preserve the organism under conditions of prolonged controlled clinical death, followed by delayed resuscitation, resulting in survival without brain damage. This concept was initially introduced for trauma victims who rapidly bleed to death, and proved to be feasible in studies evaluating outcomes following exsanguination cardiac arrest in large animals. Whether the concept of suspended animation is applicable to normovolemic cardiac arrest is under investigation.

The rate of induction of hypothermic arrest determines the outcome in a Swine model of lethal hemorrhage

BACKGROUND

Lethal injuries can be surgically repaired under asanguineous hypothermic condition (suspended animation) with excellent outcome. However, the optimal rate for the induction of hypothermic metabolic arrest following uncontrolled lethal hemorrhage (ULH) is unknown.

METHODS

ULH was induced in 32 female swine (80-120 lbs) by creating an iliac artery and vein injury, followed 30 minutes later by laceration of the descending thoracic aorta. Through a left thoracotomy approach, total body hypothermic hyperkalemic metabolic arrest was induced by infusing organ preservation fluids into the aorta. Experimental groups were: normothermic controls (no cooling, NC), or hypothermia induced at a rate of 0.5 degrees C/min (slow, SC), 1 degrees C/min (medium, MC), or 2 degrees C/min (fast, FC). Vascular injuries were repaired during the 60 minutes of profound (10 degrees C) hypothermic arrest. Hyperkalemia was reversed by hypokalemic fluid exchange, and blood was infused for resuscitation during the re-warming (0.5 degrees C/ minute) period. The survivors were monitored for 6 weeks.

RESULTS

The 6 week survival rates were 0% (NC), 37.5% (SC), 62.5% (MC), and 87.5% (FC) respectively (p < 0.05 MC&FC versus NC). All of the surviving hypothermic arrest animals were neurologically intact and displayed no long term organ dysfunction.

CONCLUSION

Hypothermic metabolic arrest can be used to maintain viability of key organs during repair of lethal injuries. Survival is influenced by the rate of cooling with the best outcome following rapid induction of hypothermia.

Hypothermia and injury

PURPOSE OF REVIEW

Recent studies demonstrating that mild therapeutic hypothermia can improve the outcome from several ischemic and traumatic insults have led to increased interest in the potential benefits of hypothermia after injury. Previous clinical studies, however, have suggested that hypothermia is detrimental to trauma patients. This most likely is a result of differences in the physiologic effects between uncontrolled exposure hypothermia and controlled therapeutic hypothermia. The laboratory and clinical data regarding traumatic hemorrhagic shock and hypothermia are presented, as well as a novel approach to the patient with exsanguinating trauma: suspended animation. Therapeutic hypothermia for traumatic brain injury is discussed.

RECENT FINDINGS

Laboratory studies of hemorrhagic shock demonstrate improved survival with mild hypothermia. For the first time, this was shown in a study in a large animal outcome model of hemorrhagic shock with trauma and intensive care. Because clinical studies continue to suggest an association between the development of hypothermia and worse outcomes in trauma patients, clinicians are continuing efforts to prevent and treat hypothermia. For exsanguination cardiac arrest, laboratory studies have demonstrated the feasibility of inducing hypothermic preservation via a rapid aortic flush (suspended animation). For traumatic brain injury, the most recent clinical trial did not show an overall benefit, but it seems that patients who arrive mildly hypothermic have better outcomes if hypothermia is maintained.

SUMMARY

The dichotomy between laboratory findings that show a benefit of hypothermia and clinical findings that suggest detrimental effects remains difficult to explain. For now, preventing hypothermia remains prudent. Suspended animation seems promising for patients with exsanguinating trauma. Clinical trials of mild hypothermia during hemorrhagic shock and suspended animation for exsanguination are indicated. Clinical trials of hypothermia for traumatic brain injury are in progress.

Suspended animation for resuscitation from exsanguinating hemorrhage

In dogs, isotonic saline at 0-4 degrees C, flushed into the aorta at a rate of 1-2 L/min, with drainage of the vena cava, can achieve deep to profound hypothermia of vital organs at a cooling rate of up to 3 degrees C per minute. This achieves preservation of viability of the organism during predictable durations of no flow: cardiac arrest of 15-20 mins at Tty of 30-35 degrees C, cardiac arrest of 30 mins at Tty of 25 degrees C, cardiac arrest of 60 mins at Tty of 15 degrees C, and cardiac arrest of 90 mins at Tty of 10 degrees C. So far, pharmacologic approaches have not resulted in any breakthrough effect on outcome above that achieved with hypothermia, except perhaps the antioxidant tempol. Additional studies of novel drugs and, perhaps, combination therapies remain warranted. The optimal fluids to have in the circulation during circulatory arrest and reperfusions need to be determined. As laboratory studies to optimize suspended animation proceed, clinical trials should be initiated. In addition, devices should be developed to facilitate induction of suspended animation, eventually in the field.

Hypothermic retrograde jugular perfusion reduces brain damage in rats with heatstroke

OBJECTIVE

To determine whether direct retrograde ice saline infusion in the jugular vein without cardiopulmonary bypass protects rat brains after heatstroke.

DESIGN

Randomized, controlled, prospective study.

SETTING

University physiology research laboratory.

SUBJECTS

Sprague-Dawley rats (270-320 g, males).

INTERVENTIONS

Rats were randomized into three groups and given a) no resuscitation after onset of heat stroke (HS, n = 8); b) ice saline infusion in the femoral vein after onset of heat stroke (HS + F, n = 8); or c) retrograde ice saline infusion in the external jugular vein after onset of heat stroke (HS + J, n = 8). Rats were exposed to an ambient temperature of 43 degrees C after vessel cannulation. Their mean arterial pressure, heart rate, colonic temperature, and brain temperature were continuously recorded. Survival time and brain pathology were checked.

MEASUREMENTS AND MAIN RESULTS

Although colonic temperature decreased 0.8-1.0 degrees C 15 mins after heatstroke in all groups, no treatment-related changes in colonic temperature were noted in any group. However, significant changes were observed in brain temperature. Fifteen minutes after heatstroke, brain temperature was 37.6 +/- 0.4 degrees C, 36.1 +/- 0.4 degrees C, and 33.6 +/- 0.8 degrees C in HS, HS + F, and HS + J, respectively. Survival time was 16.1 +/- 2.1, 33.0 +/- 3.8, and >120 mins in these groups, respectively. Neuron damage score was significantly lower in HS + J and without lateralization.

CONCLUSIONS

We successfully demonstrated that direct retrograde hypothermic perfusion via the jugular vein without cardiopulmonary bypass protected the brain after heat stroke. This technique cooled the brain but did not significantly interfere with body temperature.

Induced hypothermia in critical care medicine: a review

BACKGROUND

Clinical trials of induced hypothermia have suggested that this treatment may be beneficial in selected patients with neurologic injury.

OBJECTIVES

To review the topic of induced hypothermia as a treatment of patients with neurologic and other disorders.

DESIGN

Review article.

INTERVENTIONS

None.

MAIN RESULTS

Improved outcome was demonstrated in two prospective, randomized, controlled trials in which induced hypothermia (33 degrees C for 12-24 hrs) was used in patients with anoxic brain injury following resuscitation from prehospital cardiac arrest. In addition, prospective, randomized, controlled trials have been conducted in patients with severe head injury, with variable results. There also have been preliminary clinical studies of induced hypothermia in patients with severe stroke, newborn hypoxic-ischemic encephalopathy, neurologic infection, and hepatic encephalopathy, with promising results. Finally, animal models have suggested that hypothermia that is induced rapidly following traumatic cardiac arrest provides significant neurologic protection and improved survival.

CONCLUSIONS

Induced hypothermia has a role in selected patients in the intensive care unit. Critical care physicians should be familiar with the physiologic effects, current indications, techniques, and complications of induced hyperthermia.

Survival without brain damage after clinical death of 60-120 mins in dogs using suspended animation by profound hypothermia

OBJECTIVES

This study explored the limits of good outcome of brain and organism achievable after cardiac arrest (no blood flow) of 60-120 mins, with preservation (suspended animation) induced immediately after the start of exsanguination cardiac arrest.

DESIGN

Prospective experimental comparison of three arrest times, without randomization.

SETTING

University research laboratory.

SUBJECTS

Twenty-seven custom-bred hunting dogs (17-25 kg).

INTERVENTIONS

Dogs were exsanguinated over 5 mins to cardiac arrest no-flow of 60 mins, 90 mins, or 120 mins. At 2 mins of cardiac arrest, the dogs received, via a balloon-tipped catheter, an aortic flush of isotonic saline at 2 degrees C (at a rate of 1 L/min), until tympanic temperature reached 20 degrees C (for 60 mins of cardiac arrest), 15 degrees C (for 60 mins of cardiac arrest), or 10 degrees C (for 60, 90, or 120 mins of cardiac arrest). Resuscitation was by closed-chest cardiopulmonary bypass, postcardiac arrest mild hypothermia (tympanic temperature 34 degrees C) to 12 hrs, controlled ventilation to 20 hrs, and intensive care to 72 hrs.

MEASUREMENTS AND MAIN RESULTS

We assessed overall performance categories (OPC 1, normal; 2, moderate disability; 3, severe disability; 4, coma; 5, death), neurologic deficit scores (NDS 0-10%, normal; 100%, brain death), regional and total brain histologic damage scores at 72 hrs (total HDS >0-40, mild; 40-100, moderate; >100, severe damage), and morphologic damage of extracerebral organs. For 60 mins of cardiac arrest (n = 14), tympanic temperature 20 degrees C (n = 6) was achieved after flush of 3 mins and resulted in two dogs with OPC 1 and four dogs with OPC 2: median NDS, 13% (range 0-27%); and median total HDS, 28 (range, 4-36). Tympanic temperature of 15 degrees C (n = 5) was achieved after flush of 7 mins and resulted in all five dogs with OPC 1, NDS 0% (0-3%), and HDS 8 (0-48). Tympanic temperature 10 degrees C (n = 3) was achieved after flush of 11 mins and resulted in all three dogs with OPC 1, NDS 0%, and HDS 16 (2-18). For 90 mins of cardiac arrest (n = 6), tympanic temperature 10 degrees C was achieved after flush of 15 mins and resulted in all six dogs with OPC 1, NDS 0%, and HDS 8 (0-37). For 120 mins of cardiac arrest (n = 7), three dogs had to be excluded. In the four dogs within protocol, tympanic temperature 10 degrees C was achieved after flush of 15 mins. This resulted in one dog with OPC 1, NDS 0%, and total HDS 14; one with OPC 1, NDS 6%, and total HDS 20; one with OPC 2, NDS 13%, and total HDS 10; and one with OPC 3, NDS 39%, and total HDS 22.

CONCLUSIONS

In a systematic series of studies in dogs, the rapid induction of profound cerebral hypothermia (tympanic temperature 10 degrees C) by aortic flush of cold saline immediately after the start of exsanguination cardiac arrest-which rarely can be resuscitated effectively with current methods-can achieve survival without functional or histologic brain damage, after cardiac arrest no-flow of 60 or 90 mins and possibly 120 mins. The use of additional preservation strategies should be pursued in the 120-min arrest model.

Veno-venous extracorporeal blood shunt cooling to induce mild hypothermia in dog experiments and review of cooling methods

Mild hypothermia (33-36 degrees C) might be beneficial when induced during or after insults to the brain (cardiac arrest, brain trauma, stroke), spinal cord (trauma), heart (acute myocardial infarction), or viscera (hemorrhagic shock). Reaching the target temperature rapidly in patients inside and outside hospitals remains a challenge. This study was to test the feasibility of veno-venous extracorporeal blood cooling for the rapid induction of mild hypothermia in dogs, using a simple pumping-cooling device. Ten custom-bred hunting dogs (21-28 kg) were lightly anesthetized and mechanically ventilated. In five dogs, two catheters were inserted through femoral veins, one peripheral and the other into the inferior vena cava. The catheters were connected via a coiled plastic tube as heat exchanger (15 m long, 3 mm inside diameter, 120 ml priming volume), which was immersed in an ice-water bath. A small roller-pump produced a veno-venous flow of 200 ml/min (about 10% of cardiac output). In five additional dogs (control group), a clinically practiced external cooling method was employed, using alcohol over the skin of the trunk and fanning plus ice-bags. During spontaneous normotension, veno-venous cooling delivered blood into the vena cava at 6.2 degrees C standard deviation (SD 1.4) and decreased tympanic membrane (Tty) temperature from 37.5 to 34.0 degrees C at 5.2 min (SD 0.7), and to 32.0 degrees C at 7.9 min (SD 1.3). Skin surface cooling decreased tympanic temperature from 37.5 to 34.0 degrees C at 19.9 min (SD 3.7), and to 32.0 degrees C at 29.9 (SD 5.1) (P=0.001). Heart rates at Tty 34 and 32 degrees C were significantly lower than at baseline in both groups, but within physiological range, without difference between groups. There were no arrhythmias. We conclude that in large dogs the induction of mild systemic hypothermia with extracorporeal veno-venous blood shunt cooling is simple and four times more rapid than skin surface cooling.

Cerebral resuscitation potentials for cardiac arrest

Permanent brain damage after cardiac arrest and resuscitation is determined by many factors, predominantly arrest (no-flow) time, cardiopulmonary resuscitation (low-flow) time, and temperature. Research since around 1970 into cardiopulmonary-cerebral resuscitation has attempted to mitigate the postischemic-anoxic encephalopathy. These efforts' results have recently shown outcome benefits as documented in clinically relevant outcome models in dogs and in clinical trials. Pharmacologic strategies have so far yielded relatively disappointing results. In a recent exploration of 14 drugs in dogs, only the antioxidant tempol administered at the start of prolonged cardiac arrest improved functional outcome in dogs. Cerebral blood flow promotion by hypertensive reperfusion and hemodilution has resulted in improved outcome in dogs, and brief hypertension after restoration of spontaneous circulation is associated with improved outcome in patients. Postarrest hypercoagulability of blood seems to yield to therapeutic thrombolysis, which is associated with improved cerebral outcome in animals and patients. In a clinically relevant dog outcome model, mild postarrest cerebral hypothermia (34 degrees C), initiated with reperfusion and continued for 12 hrs, combined with cerebral blood-flow promotion increased from 5 to >10 mins the previously longest normothermic no-flow time that could be reversed to complete cerebral recovery. Mild hypothermia by surface cooling after prolonged cardiac arrest in patients has been found effective in recent clinical studies in Australia and Europe. Preliminary data on the recent randomized study in Europe have been reported. For presently unresuscitable cardiac arrests, research since the 1980s in dog outcome models of prolonged exsanguination cardiac arrest has culminated in brain and organism preservation during cardiac arrest (no-flow) durations of up to 90 mins, perhaps 120 mins, at a tympanic temperature of 10 degrees C and complete recovery of function and normal histology. This "suspended animation for delayed resuscitation" strategy includes use of an aortic flush of cold saline (or preservation solution) within the first 5 mins of no flow. This strategy should also be explored for the larger number of patients with unresuscitable out-of-hospital cardiac arrests. Suspended animation for prolonged preservation of viability could buy time for transport and repair during hypothermic no flow followed by resuscitation, or it could serve as a bridge to prolonged cardiopulmonary bypass.

Antioxidant Tempol enhances hypothermic cerebral preservation during prolonged cardiac arrest in dogs

The authors are systematically exploring pharmacologic preservation for temporarily unresuscitable exsanguination cardiac arrest in dogs. They hypothesized that the antioxidant Tempol improves cerebral outcome when added to aortic saline flush at the start of cardiac arrest. In study A, no drug (n = 8), Tempol 150 mg/kg (n = 4), or Tempol 300 mg/kg (n = 4) was added to 25 mL/kg saline flush at 24 degrees C (achieving mild cerebral hypothermia) at the start of 20-minute cardiac arrest. In study B, no drug (n = 8) or Tempol 300 mg/kg (n = 7) was added to 50 mL/kg saline flush at 2 degrees C (achieving moderate cerebral hypothermia) at the start of 40-minute cardiac arrest. Cardiac arrest was reversed with cardiopulmonary bypass. Mild hypothermia lasted for 12 hours, controlled ventilation was sustained to 24 hours, and intensive care was provided for up to 72 hours. In study A, overall performance category 1 or 2 (good outcome) was achieved in all eight dogs treated with Tempol compared with three of eight dogs in the control group ( P = 0.03). In study B, good outcome was achieved in all seven dogs treated with Tempol versus only two of 8 dogs in the control group ( P = 0.007). In both studies, neurologic deficit scores were significantly better in the Tempol group, but not total histologic damage scores. At 72 hours, electron paramagnetic resonance spectroscopy of Tempol revealed direct evidence for its presence in the brain. Single- and double-strand DNA damage, nitrotyrosine immunostaining, total antioxidant reserve, and ascorbate acid levels were similar between groups, and thiol levels were decreased after Tempol in study B. The authors conclude that when added to aortic saline flush at the start of prolonged cardiac arrest, the antioxidant Tempol can enhance mild or moderate hypothermic cerebral preservation in terms of improved functional outcome. The mechanisms involved in this beneficial effect need further clarification.

Fructose-1,6-bisphosphate and MK-801 by aortic arch flush for cerebral preservation during exsanguination cardiac arrest of 20 min in dogs. An exploratory study

In our exsanguination cardiac arrest (CA) outcome model in dogs we are systematically exploring suspended animation (SA), i.e. preservation of brain and heart immediately after the onset of CA to enable transport and resuscitative surgery during CA, followed by delayed resuscitation. We have shown in dogs that inducing moderate cerebral hypothermia with an aortic arch flush of 500 ml normal saline solution at 4 degrees C, at start of CA 20 min no-flow, leads to normal functional outcome. We hypothesized that, using the same model, but with the saline flush at 24 degrees C inducing minimal cerebral hypothermia (which would be more readily available in the field), adding either fructose-1,6-bisphosphate (FBP, a more efficient energy substrate) or MK-801 (an N-methyl-D-aspartate (NMDA) receptor blocker) would also achieve normal functional outcome. Dogs (range 19-30 kg) were exsanguinated over 5 min to CA of 20 min no-flow, and resuscitated by closed-chest cardiopulmonary bypass (CPB). They received assisted circulation to 2 h, mild systemic hypothermia (34 degrees C) post-CA to 12 h, controlled ventilation to 20 h, and intensive care to 72 h. At CA 2 min, the dogs received an aortic arch flush of 500 ml saline at 24 degrees C by a balloon-tipped catheter, inserted through the femoral artery (control group, n=6). In the FBP group (n=5), FBP (total 1440 or 4090 mg/kg) was given by flush and with reperfusion. In the MK-801 group (n=5), MK-801 (2, 4, or 8 mg/kg) was given by flush and with reperfusion. Outcome was assessed in terms of overall performance categories (OPC 1, normal; 2, moderate disability; 3, severe disability; 4, coma; 5, brain death or death), neurologic deficit scores (NDS 0-10%, normal; 100%, brain death), and brain histologic damage scores (HDS, total HDS 0, no damage; >100, extensive damage; 1064, maximal damage). In the control group, one dog achieved OPC 2, one OPC 3, and four OPC 4; in the FBP group, two dogs achieved OPC 3, and three OPC 4; in the MK-801 group, two dogs achieved OPC 3, and three OPC 4 (P=1.0). Median NDS were 62% (range 8-67) in the control group; 55% (range 34-66) in the FBP group; and 50% (range 26-59) in the MK-801 group (P=0.2). Median total HDS were 130 (range 56-140) in the control group; 96 (range 64-104) in the FBP group; and 80 (range 34-122) in the MK-801 group (P=0.2). There was no difference in regional HDS between groups. We conclude that neither FBP nor MK-801 by aortic arch flush at the start of CA, plus an additional i.v. infusion of the same drug during reperfusion, can provide cerebral preservation during CA 20 min no-flow. Other drugs and drug-combinations should be tested with this model in search for a breakthrough effect.

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

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

Thiopental and phenytoin by aortic arch flush for cerebral preservation during exsanguination cardiac arrest of 20 minutes in dogs. An exploratory study

We are systematically exploring in our exsanguination cardiac arrest (CA) outcome model in dogs suspended animation (SA), i.e. immediate preservation of brain and heart for resuscitative surgery during CA, with delayed resuscitation. We have shown in dogs that inducing moderate cerebral hypothermia with an aortic arch flush of 500 ml normal saline solution of 4 degrees C, at start of CA 20 min no-flow, leads to normal functional outcome. We hypothesized that, using the same model, adding thiopental (or even better thiopental plus phenytoin) to the flush at ambient temperature (24 degrees C), which would be more readily available in the field, will also achieve normal functional outcome. Thirty dogs (20-28 kg) were exsanguinated over 5 min to CA of 20 min no-flow, and resuscitated by closed-chest cardiopulmonary bypass. They received assisted circulation to 2 h, 34 degrees C post-CA to 12 h, controlled ventilation to 20 h, and intensive care to 72 h. At CA 2 min, the dogs received an aortic arch flush of 500 ml saline at 24 degrees C by a balloon-tipped catheter, inserted through the femoral artery (control group 1, n=14). In group 2 (n=9), thiopental (variable total doses of 15-120 mg/kg) was added to the flush and given with reperfusion. In group 3 (n=7), thiopental (15 or 45 mg/kg) plus phenytoin (10, 20, or 30 mg/kg) was given by flush and with reperfusion. Outcome was assessed in terms of overall performance categories (OPC 1, normal; 2, moderate disability; 3, severe disability; 4, coma; 5, brain death), neurologic deficit scores (NDS 0-10%, normal; 100%, brain death), and histologic deficit scores (HDS, total and regional). The flush reduced tympanic temperature to about 36 degrees C in all groups. In control group 1, one dog achieved OPC 1, three OPC 2, six OPC 3, and four OPC 4. In thiopental group 2, two dogs achieved OPC 1, two OPC 3, and five OPC 4. In thiopental/phenytoin group 3, one dog achieved OPC 1, two OPC 3, and four OPC 4 (p=0.5). Median NDS were 36% (IQR 22-62%) in group 1; 51% (IQR 22-56%) in group 2; and 55% (IQR 38-59%) in group 3 (p=0.7). Median total HDS were 67 (IQR 56-127) in group 1; 60 (IQR 52-138) in group 2; and 76 (IQR 48-132) in group 3 (p=1.0). Thiopental and thiopental/phenytoin dogs achieved significantly lower HDS only in the putamen. Thiopental in large doses caused side effects. We conclude that neither thiopental alone nor thiopental plus phenytoin by flush, with or without additional intravenous infusion, can consistently provide 'clinically significant' cerebral preservation for 20 min no-flow. Other drugs and drug-combinations should be tested with this model in search for a breakthrough effect.

Long-term mild hypothermia with extracorporeal lung and heart assist improves survival from prolonged cardiac arrest in dogs

BACKGROUND AND PURPOSE

although normothermic extracorporeal lung and heart assist (ECLHA) improves cardiac outcomes, patients can not benefit from hypothermia-mediated brain protection. The present study evaluated the effects of long-term ECLHA with mild to moderate hypothermia (33 degrees C) in a canine model of prolonged cardiac arrest.

METHODS

15 dogs were assigned to either the hypothermic (seven dogs, 33 degrees C) or normothermic group (eight dogs, 37.5 degrees C). All dogs were induced to normothermic ventricular fibrillation (VF) for 15 min, followed by 24 h of ECLHA and 72 h of intensive care. The hypothermia group maintained core (pulmonary artery) temperature at 33 degrees C for 20 h starting from resuscitation, then were rewarmed by 28 h. Outcome evaluations included: (1) mortality; (2) catecholamine dose; (3) time to extubation; (4) necrotic myocardial mass (g); and (5) neurological deficits score (NDS).

RESULTS

in the normothermic group five dogs died of cardiogenic shock and one dog succumbed to poor oxygenation. The two surviving dogs remained comatose (NDS 60.5 +/- 4.9%) with necrotic myocardial mass of 14.5 +/- 3.5 g. In the hypothermic group, one dog died from pulmonary dysfunction, the other six dogs survived. The surviving dogs showed brain damage (29.8 +/- 2.5%), but there was evidence of some brain-protective effect. The mass of necrotic myocardium was 4.2 +/- 1.3 g in the hypothermic group or 3.4 times smaller than in the normothermic group. The survival rate was significantly higher in the hypothermic than in the normothermic group (P < 0.05). The catecholamine requirement was also lower in the hypothermic than in the normothermic dogs (P < 0.05).

CONCLUSIONS

Long-term mild to moderate hypothermia with ECLHA induced immediately after cardiac arrest improved survival as well as cerebral and cardiac outcomes.

Rapid induction of mild cerebral hypothermia by cold aortic flush achieves normal recovery in a dog outcome model with 20-minute exsanguination cardiac arrest

OBJECTIVES

Resuscitation attempts in trauma victims who suffer cardiac arrest (CA) from exsanguination almost always fail. The authors hypothesized that an aortic arch flush with cold normal saline solution (NSS) at the start of exsanguination CA can preserve cerebral viability during 20-minute no-flow.

METHODS

Twelve dogs were exsanguinated over 5 minutes to CA of 20-minute no-flow, resuscitated by cardiopulmonary bypass, followed by post-CA mild hypothermia (34 degrees C) continued to 12 hours, controlled ventilation to 20 hours, and intensive care to 72 hours. At CA 2 minutes, the dogs received a 500-mL flush of NSS at either 24 degrees C (group 1, n = 6) or 4 degrees C (group 2, n = 6), using a balloon-tipped catheter inserted via the femoral artery into the descending thoracic aorta.

RESULTS

The flush at 24 degrees C (group 1) decreased tympanic membrane temperature [mean (+/-SD)] from 37.5 degrees C (+/-0.1) to 35.7 degrees C (+/-0.2); the flush at 4 degrees C (group 2) to 34.0 degrees C (+/-1.1) (p = 0.005). In group 1, one dog achieved overall performance category (OPC) 2 (moderate disability), one OPC 3 (severe disability), and four OPC 4 (coma). In group 2, four dogs achieved OPC 1 (normal), one OPC 2, and one OPC 3 (p = 0.008). Neurologic deficit scores (0-10% normal, 100% brain death) [median (25th-75th percentile)] were 62% (40-66) in group 1 and 5% (0-19) in group 2 (p = 0.01). Total brain histologic damage scores were 130 (62-137) in group 1 and 24 (10-55) in group 2 (p = 0.008).

CONCLUSIONS

Aortic arch flush of 4 degrees C at the start of CA of 20 minutes rapidly induces mild cerebral hypothermia and can lead to normal functional recovery with minimal histologic brain damage. The same model with aortic arch flush of 24 degrees C results in survival with brain damage in all dogs, which makes it suitable for testing other (e.g., pharmacologic) preservation potentials.

Suspended animation for delayed resuscitation from prolonged cardiac arrest that is unresuscitable by standard cardiopulmonary-cerebral resuscitation

Standard cardiopulmonary-cerebral resuscitation fails to achieve restoration of spontaneous circulation in approximately 50% of normovolemic sudden cardiac arrests outside hospitals and in essentially all victims of penetrating truncal trauma who exsanguinate rapidly to cardiac arrest. Among cardiopulmonary-cerebral resuscitation innovations since the 1960s, automatic external defibrillation, mild hypothermia, emergency (portable) cardiopulmonary bypass, and suspended animation have potentials for clinical breakthrough effects. Suspended animation has been suggested for presently unresuscitable conditions and consists of the rapid induction of preservation (using hypothermia with or without drugs) of viability of the brain, heart, and organism (within 5 mins of normothermic cardiac arrest no-flow), which increases the time available for transport and resuscitative surgery, followed by delayed resuscitation. Since 1988, we have developed and used novel dog models of exsanguination cardiac arrest to explore suspended animation potentials with hypothermic and pharmacologic strategies using aortic cold flush and emergency portable cardiopulmonary bypass. Outcome evaluation was at 72 or 96 hrs after cardiac arrest. Cardiopulmonary bypass cannot be initiated rapidly. A single aortic flush of cold saline (4 degrees C) at the start of cardiac arrest rapidly induced (depending on flush volume) mild-to-deep cerebral hypothermia (35 degrees to 10 degrees C), without cardiopulmonary bypass, and preserved viability during a cardiac arrest no-flow period of up to 120 mins. In contrast, except for one antioxidant (Tempol), explorations of 14 different drugs added to the aortic flush at room temperature (24 degrees C) have thus far had disappointing outcome results. Profound hypothermia (10 degrees C) during 60-min cardiac arrest induced and reversed with cardiopulmonary bypass achieved survival without functional or histologic brain damage. Further plans for the systematic development of suspended animation include the following: a) aortic flush, combining hypothermia with mechanism-specific drugs and novel fluids; b) extension of suspended animation by ultraprofound hypothermic preservation (0 degrees to 5 degrees C) with cardiopulmonary bypass; c) development of the most effective suspended animation protocol for clinical trials in trauma patients with cardiac arrest; and d) modification of suspended animation protocols for possible use in normovolemic ventricular fibrillation cardiac arrest, in which attempts to achieve restoration of spontaneous circulation by standard external cardiopulmonary resuscitation-advanced life support have failed.

Adenosine by aortic flush fails to augment the brain preservation effect of mild hypothermia during exsanguination cardiac arrest in dogs - an exploratory study

Most trauma cases with rapid exsanguination to cardiac arrest (CA) in the field, as well as many cases of normovolemic sudden cardiac death are 'unresuscitable' by standard cardiopulmonary-cerebral resuscitation (CPCR). We are presenting a dog model for exploring pharmacological strategies for the rapid induction by aortic arch flush of suspended animation (SA), i.e. preservation of cerebral viability for 15 min or longer. This can be extended by profound hypothermic circulatory arrest of at least 60 min, induced and reversed with (portable) cardiopulmonary bypass (CPB). SA is meant to buy time for transport and repair during pulselessness, to be followed by delayed resuscitation to survival without brain damage. This model with exsanguination over 5 min to CA of 15-min no-flow, is to evaluate rapid SA induction by aortic flush of normal saline solution (NSS) at room temperature (24 degrees C) at 2-min no-flow. This previously achieved normal functional recovery, but with histologic brain damage. We hypothesized that the addition of adenosine would achieve recovery with no histologic damage, because adenosine delays energy failure and helps repair brain injury. This dog model included reversal of 15-min no-flow with closed-chest CPB, controlled ventilation to 20 h, and intensive care to 72 h. Outcome was evaluated by overall performance, neurologic deficit, and brain histologic damage. At 2 min of CA, 500 ml of NSS at 24 degrees C was flushed (over 1 min) into the brain and heart via an aortic balloon catheter. Controls (n=5) received no drug. The adenosine group (n=5) received 2-chloro-adenosine (long acting adenosine analogue), 30 mg in the flush solution, and, after reperfusion, adenosine i.v. over 12 h (210 microg/kg per min for 3 h, 140 microg/kg per min for 9 h). The 24 degrees C flush reduced tympanic membrane temperature (T(ty)) within 2 min of CA from 37.5 to approximately 36.0 degrees C in both groups. At 72 h, final overall performance category (OPC) 1 (normal) was achieved by all ten dogs of the two groups. Final neurologic deficit scores (NDS; 0-10% normal, 100% brain death) were 5+/-3% in the control group versus 6+/-5% in the adenosine group (NS). Total brain histologic damage scores (HDS) at 72 h were 74+/-9 (64-80) in the control group versus 68+/-19 (40-88) in the adenosine group (NS). In both groups, ischemic neurons were as prevalent in the basal ganglia and neocortex as in the cerebellum and hippocampus. The mild hypothermic aortic flush protocol is feasible in dogs. The adenosine strategy used does not abolish the mild histologic brain damage.