The history and present status of deep hypothermia and circulatory arrest in cerebrovascular surgery

Cerebral Perfusion and Protection During Repair of Type A Dissection

Patients with the highest risk of neurologic injury after cardiac surgery are those undergoing repair of type A aortic dissections. Since the 1950s, extensive research has been conducted to improve the safety and neurologic outcomes of these patients. Surgeons now routinely use hypothermia with circulatory arrest, and adjunctive cerebral perfusion methods. This article highlights the historic development of modern cerebral perfusion and protection, and discusses technical details and clinical outcomes of cannulation strategies, temperature management, and antegrade cerebral perfusion and retrograde cerebral perfusion.

Duration of deep hypothermic circulatory arrest for aortic arch surgery: is it a myth, fiction, or scientific leap?

INTRODUCTION

The use of deep hypothermic circulatory arrest (DHCA) to provide aortic surgeons with a bloodless operative field while simultaneously protecting the brain and peripheries from ischemic damage revolutionized cardiac and aortic surgery, and is currently used in specialist centers across the globe. However, it is associated with manifold adverse outcomes, including neurocognitive dysfunction and mortality. This review seeks to analyze the relationship between DHCA duration and clinical outcome, and evaluate the controversies and limitations surrounding its use.

EVIDENCE ACQUISITION

We performed a review of available literature with statistical analysis to evaluate the relationship between DHCA duration (<40 min and >40 min) and key clinical outcomes, including mortality, permanent and temporary neurological deficit, renal damage, admission length, and reintervention rate. The controversies surrounding DHCA use and future directions for care are also explored.

EVIDENCE SYNTHESIS

Statistical analysis revealed no significant association (P>0.05) between DHCA duration and clinical outcomes (early and late mortality rates, neurological deficit, admission length, and reintervention rate), both with and without adjunctive perfusion techniques.

CONCLUSIONS

Available literature suggests that the relationships between DHCA duration (with and without adjunctive perfusion) and clinical outcomes are unclear, and at present not statistically significant. Alternative surgical and endovascular techniques have been identified as promising novel approaches not requiring DHCA, as have the use of biomarkers to enable early diagnosis and intervention for aortic pathologies.

Therapeutic hypothermia after cardiac arrest: outcome predictors

OBJECTIVE

The determination of coma patient prognosis after cardiac arrest has clinical, ethical and social implications. Neurological examination, imaging and biochemical markers are helpful tools accepted as reliable in predicting recovery. With the advent of therapeutic hypothermia, these data need to be reconfirmed. In this study, we attempted to determine the validity of different markers, which can be used in the detection of patients with poor prognosis under hypothermia.

METHODS

Data from adult patients admitted to our intensive care unit for a hypothermia protocol after cardiac arrest were recorded prospectively to generate a descriptive and analytical study analyzing the relationship between clinical, neurophysiological, imaging and biochemical parameters with 6-month outcomes defined according to the Cerebral Performance Categories scale (good 1-2, poor 3-5). Neuron-specific enolase was collected at 72 hours. Imaging and neurophysiologic exams were carried out in the 24 hours after the rewarming period.

RESULTS

Sixty-seven patients were included in the study, of which 12 had good neurological outcomes. Ventricular fibrillation and electroencephalographic theta activity were associated with increased likelihood of survival and improved neurological outcomes. Patients who had more rapid cooling (mean time of 163 versus 312 minutes), hypoxic-ischemic brain injury on magnetic resonance imaging or neuron-specific enolase > 58ng/mL had poor neurological outcomes (p < 0.05).

CONCLUSION

Hypoxic-ischemic brain injury on magnetic resonance imaging and neuron-specific enolase were strong predictors of poor neurological outcomes. Although there is the belief that early achievement of target temperature improves neurological prognoses, in our study, there were increased mortality and worse neurological outcomes with earlier target-temperature achievement.

Adenosine-induced transient asystole

Cerebral aneurysms are an important health issue in the United States, and the mortality rate following aneurysm rupture, or SAH, remains high. The treatment of these aneurysms uses endovascular options which include coil placement, stent assistant coiling and, recently, flow diversion. However, microsurgical clipping remains an option in those aneurysms not suited for endovascular therapy. These are often the more complicated aneurysms such as in large, giant aneurysms or deep-seated aneurysms. Circumferential visualization of the aneurysm, parent vessels, branches, perforators, and other neurovascular structures is important to prevent residual aneurysms or strokes from vessel or perforator occlusion. Decompression of the aneurysm sac is often required and we believe that adenosine-induced transient asystole should be an important option for clipping of complex cerebral aneurysms.

The History of Deep Hypothermic Circulatory Arrest in Thoracic Aortic Surgery

Depending on the extent of aortic disease and surgical repair required, thoracic aortic surgery often involves periods of reduced cerebral perfusion. Historically, this resulted in detrimental neurological dysfunction, and high risk of mortality and morbidity. Over the last half century, rapid improvements have revolutionized aortic surgery. Among these, deep hypothermic circulatory arrest (DHCA) has drastically reduced the risk of mortality and morbidity following surgery on the thoracic aorta. This progress was facilitated by experimental pioneers such as Bigelow, who studied reduced oxygen expenditure consequent on induction of hypothermia in dogs. These encouraging findings led to trials in human cardiac surgery by Lewis in 1952 and further made possible the first successful aortic arch replacement by Denton Cooley and Michael De Bakey. Modern day surgery has come a long way from the use of immersion of the patient in ice baths and other primitive techniques previously described. This paper explores the development of deep hypothermic circulatory arrest from its origins to the present.

Use of hypothermia in the intensive care unit

Used for over 3600 years, hypothermia, or targeted temperature management (TTM), remains an ill defined medical therapy. Currently, the strongest evidence for TTM in adults are for out-of-hospital ventricular tachycardia/ventricular fibrillation cardiac arrest, intracerebral pressure control, and normothermia in the neurocritical care population. Even in these disease processes, a number of questions exist. Data on disease specific therapeutic markers, therapeutic depth and duration, and prognostication are limited. Despite ample experimental data, clinical evidence for stroke, refractory status epilepticus, hepatic encephalopathy, and intensive care unit is only at the safety and proof-of-concept stage. This review explores the deleterious nature of fever, the theoretical role of TTM in the critically ill, and summarizes the clinical evidence for TTM in adults.

Translational barriers and opportunities for emergency preservation and resuscitation in severe injuries

BACKGROUND

Hypothermia is commonly used for organ and tissue preservation in multiple clinical settings, but its role in the management of injured patients remains controversial. There is no doubt that temperature modulation is a powerful tool, and hypothermia has been shown to protect cells during ischaemia 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.

METHODS

A literature review was performed to include important papers that address the impact of hypothermia on key biological processes, and explore the potential therapeutic role of hypothermia in trauma/haemorrhage models.

RESULTS

No clinical studies have been conducted to test the therapeutic benefits of hypothermia in injured patients. However, numerous well designed animal studies support this concept. Despite excellent preclinical data, there are several potential barriers to translating hypothermia into clinical practice.

CONCLUSION

Therapeutic hypothermia is a promising life-saving strategy. Appropriate patient selection requires a thorough understanding of how temperature modulation affects various biological mechanisms.

Cardiac standstill for cerebral aneurysms in 103 patients: an update on the experience at the Barrow Neurological Institute. Clinical article

OBJECT

The aim of this study was to clarify the surgical indications, risks, and long-term clinical outcomes associated with the use of deep hypothermic circulatory arrest for the surgical treatment of intracranial aneurysms.

METHODS

The authors retrospectively reviewed 105 deep hypothermic circulatory arrest procedures performed in 103 patients (64 females and 39 males, with a mean age of 44.8 years) to treat 104 separate aneurysms. Patients' clinical histories, radiographs, and operative reports were evaluated. There were 97 posterior circulation aneurysms: at the basilar apex in 60 patients, midbasilar artery in 21, vertebrobasilar junction in 11, superior cerebellar artery in 4, and posterior cerebral artery in 1. Seven patients harbored anterior circulation aneurysms. Two additional patients harbored nonaneurysmal lesions.

RESULTS

Perioperatively, 14 patients (14%) died. Five patients (5%) were lost to late follow-up. At a mean long-term follow-up of 9.7 years, 65 patients (63%) had the same or a better status after surgical intervention, 10 (10%) were worse, and 9 (9%) had died. There were 19 cases (18%) of permanent or severe complications. The combined rate of permanent treatment-related morbidity and mortality was 32%. The mean late follow-up Glasgow Outcome Scale score was 4, and the annual hemorrhage rate after microsurgical clipping during cardiac standstill was 0.5%/year. Ninety-two percent of patients required no further treatment of their aneurysm at the long-term follow-up.

CONCLUSIONS

Cardiac standstill remains an important treatment option for a small subset of complex and giant posterior circulation aneurysms. Compared with the natural history of the disease, the risk associated with this procedure is acceptable.

Alterations in gene expression after induction of profound hypothermia for the treatment of lethal hemorrhage

INTRODUCTION

We have previously demonstrated that induction of profound hypothermia improves long-term survival in animal models of complex injuries/lethal hemorrhage. However, the precise mechanisms have not been well defined. The aim of this high-throughput study was to investigate the impact of profound hypothermia on gene expression profiles.

METHODS

Wistar-Kyoto rats underwent 40% blood volume arterial hemorrhage over 10 minutes and were randomized into two groups based on core body temperatures (n = 7 per group): hypothermia (H, 15 degrees C) and normothermia (N, 37 degrees C). Hypothermia was induced by infusing cold isotonic solution using a cardiopulmonary bypass (CPB) setup. After reaching target body temperature, low-flow state (CPB flow rate of 20 mL x kg x min) was maintained for 60 minutes. Hypothermic rats were rewarmed to baseline temperature, and all rats were resuscitated on CPB and monitored for 3 hours. The N group underwent identical CPB management. Sham rats (no hemorrhage and no instrumentation) were used as controls. Blood samples were collected serially, and hepatic tissues were harvested after 3 hours. Affymatrix Rat Gene 1.0 ST Array (27,342 genes, >700,000 probes) was used to determine gene expression profiles (n = 3 per group), which were further analyzed using GeneSpring (Agilent Technologies, Santa Clara, CA) and GenePattern (Broad Institute, Cambridge, MA) programs. Data were further queried using network analysis tools including Gene Ontology, and Ingenuity Pathway Analysis (Ingenuity Systems). Key findings were verified using real-time polymerase chain reaction and Western blots.

RESULTS

Induction of hypothermia significantly (p < 0.05) decreased the magnitude of lactic acidosis and increased the survival rates (100% vs. 0% in normothermia group). Five hundred seventy-one of 23,000 genes had altered expression in response to the induction of hypothermia: 382 were up-regulated and 187 were down-regulated. Twelve key pathways were specifically modulated by hypothermia. Interleukin-6, interleukin-10, p38 mitogen-activated protein kinase (MAPK), nuclear factor kappa-light-chain-enhancer of activated B cells, glucocorticoids, and other signaling pathways involved with acute phase reactants were up-regulated. Multiple metabolic pathways were down- regulated. The largest change was in the peroxisome proliferator-activated receptor gamma gene that codes for a transcriptional coactivator, which in turn controls mitochondrial biogenesis, glycerolipid, and other metabolic pathways in the liver. Apoptotic cell death cascades were activated in response to blood loss (H and N groups), but multiple specific anti-apoptotic genes (baculoviral Inhibitor of apoptosis protein repeat-containing 3, BCL3L1, NFKB2) displayed an increased expression specifically in the hypothermia treated animals, suggesting an overall pro-survival phenotype.

CONCLUSIONS

Profound hypothermia increases survival in a rodent model of hemorrhagic shock. In addition to decreasing tissue oxygen consumption, induction of hypothermia directly alters the expression profiles of key genes, with an overall up-regulation of pro-survival pathways and a down- regulation of metabolic pathways.

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.

Circulatory arrest and deep hypothermia for the treatment of complex intracranial aneurysms--results from a single European center

BACKGROUND

Vascular neurosurgery faces the controversial discussion about the need for deep hypothermia and circulatory arrest (dh/ca) for the treatment of complex cerebral aneurysms. In this retrospective analysis, we present our experience in the treatment of 26 giant and large cerebral aneurysms under profound hypothermia and circulatory arrest.

METHODS

All patients were treated surgically under dh/ca. Seventeen patients had aneurysms of the anterior circulation, and nine patients had aneurysms of the posterior circulation. Thrombosis or calcification was found in ten patients. Eleven patients presented with subarachnoid hemorrhage. The seven patients with the longest circulation arrest time were analyzed in detail.

RESULTS

Subarachnoid hemorrhage led to hospital admission in 42% (n = 11) of cases. The overall mortality was 11.5%, and the overall morbidity was 15%. Ten patients deteriorated transiently but fully recovered. The mean age, Glasgow Coma Score, Fisher, and Hunt and Hess Score correlated significantly with the long-term outcome. Circulation arrest time correlated significantly to the neurological outcome on discharge. All patients with prolonged circulation arrest times had wide aneurysmal necks, and four had adjacent vessels to the dome or the parent vessel included in the neck. We observed a significant increase of neurological deficits immediately postoperatively, but this neurological deterioration resolved over time.

CONCLUSIONS

We observed neurological deterioration immediately postoperatively in 13 patients, but all patients fully recovered within 6 months except for four patients. A long cardiac arrest time reflected complex pathoanatomical conditions. We conclude that the clipping procedure under deep hypothermia and circulatory arrest remains a pivotal armament in complex vascular neurosurgery.

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.

Putting life on hold-for how long? Profound hypothermic cardiopulmonary bypass in a Swine model of complex vascular injuries

BACKGROUND

Rapid induction of profound hypothermia for emergency preservation and resuscitation can improve survival from uncontrolled lethal hemorrhage in large animal models. We have previously demonstrated that profound hypothermia (10 degrees C) must be induced rapidly (2 degrees C/min) and reversed gradually (0.5 degrees C/min) for best results. However, the maximum duration of hypothermic arrest in a clinically relevant trauma model remains unknown.

METHODS

Uncontrolled lethal hemorrhage was induced in 22 swine by creating an iliac artery and vein injury, followed 30 minutes later (simulating transport time) by laceration of the descending thoracic aorta. Through a thoracotomy approach, a catheter was placed in the aorta, and cold organ preservation solution was infused using a roller pump to rapidly induce profound hypothermia (10 degrees C) which was maintained with low-flow cardiopulmonary bypass. Vascular injuries were repaired during the asanguinous hypothermic low flow period. Profound hypothermia was maintained (n = 10-12 per group) for either 60 minutes or 120 minutes. After repair of injuries, animals were rewarmed (0.5 degrees C/min) and resuscitated on cardiopulmonary bypass, and whole blood was infused during this period. Animals were monitored for 4 weeks for neurologic deficits, organ dysfunction, and postoperative complications.

RESULTS

The 4-week survival rates in 60- and 120-minute groups were 92% and 50%, respectively (p < 0.05). The surviving animals were neurologically intact and had no long-term organ dysfunction, except for one animal in the 120-minute group. The animals subjected to 120 minutes of hypothermia had significantly worse lactic acidosis, displayed markedly slower recovery, and had significantly higher rates of postoperative complications, including late deaths because of infections.

CONCLUSION

In a model of lethal injuries, rapid induction of profound hypothermia can prevent death. Profound hypothermia decreases but does not abolish metabolism. With current methods, the upper limit of hypothermic arrest in the setting of uncontrolled hemorrhage is 60 minutes.

Hypothermia treatment potentiates ERK1/2 activation after traumatic brain injury

Traumatic brain injury (TBI) results in significant hippocampal pathology and hippocampal-dependent memory loss, both of which are alleviated by hypothermia treatment. To elucidate the molecular mechanisms regulated by hypothermia after TBI, rats underwent moderate parasagittal fluid-percussion brain injury. Brain temperature was maintained at normothermic or hypothermic temperatures for 30 min prior and up to 4 h after TBI. The ipsilateral hippocampus was assayed with Western blotting. We found that hypothermia potentiated extracellular signal-regulated kinase 1/2 (ERK1/2) activation and its downstream effectors, p90 ribosomal S6 kinase (p90RSK) and the transcription factor cAMP response element-binding protein. Phosphorylation of another p90RSK substrate, Bad, also increased with hypothermia after TBI. ERK1/2 regulates mRNA translation through phosphorylation of mitogen-activated protein kinase-interacting kinase 1 (Mnk1) and the translation factor eukaryotic initiation factor 4E (eIF4E). Hypothermia also potentiated the phosphorylation of both Mnk1 and eIF4E. Augmentation of ERK1/2 activation and its downstream signalling components may be one molecular mechanism that hypothermia treatment elicits to improve functional outcome after TBI.

Profound hypothermic cardiopulmonary bypass facilitates survival without a high complication rate in a swine model of complex vascular, splenic, and colon injuries

BACKGROUND

Induction of a profound hypothermia for emergency preservation and resuscitation in severe hemorrhagic shock can improve survival from lethal injuries, but the impact of hypothermia on bleeding and infectious complications has not been completely determined.

STUDY DESIGN

Uncontrolled hemorrhage was induced in 26 swine (95 to 135 lbs) by creating an iliac artery and vein injury, and 30 minutes later, by lacerating the descending thoracic aorta. Through a left thoracotomy approach, profound total body hypothermia (10 degrees C) was induced (2 degrees C/min) by infusing cold organ preservation solution into the aorta. The experimental groups were: vascular injuries alone (group 1, n=10), vascular and colon injuries (group 2, n=8), and vascular, colon, and splenic injuries (group 3, n=8). All injuries were repaired during 60 minutes of low-flow cardiopulmonary bypass (CPB) with hemodilution and profound hypothermia; then the animals were slowly rewarmed (0.5 degrees C/min) back to normothermia. Survivors were monitored for 6 weeks for postoperative bleeding, neurologic deficits, cognitive function (learning new skills), organ dysfunction, and septic complications.

RESULTS

Six-week survival rates were 90% in group 1, 87.5% in group 2, and 75% in group 3 (p > 0.05). One animal in each group died from acute cardiac failure during the early postoperative phase. Splenic salvage was possible in all animals, and none required complete splenectomy for hemorrhage control. All surviving animals were neurologically intact, displayed normal learning capacity, and had no longterm organ dysfunction. None of the animals had postoperative hemorrhage or experienced septic complications. One animal in group 3 died on the ninth postoperative day because of bowel obstruction (volvulus).

CONCLUSIONS

Induction of profound hypothermia can preserve the viability of key organs during repair of lethal injuries. This strategy can be used even in the presence of solid organ and bowel injuries to improve survival, without any considerable increase in postoperative complication rates.

Mild hypothermia reduces cardiac post-ischemic reactive hyperemia

Background

In experimentally induced myocardial infarction, mild hypothermia (33–35°C) is beneficial if applied prior to ischemia or reperfusion. Hypothermia, when applied after reperfusion seems to confer little or no benefit. The mechanism by which hypothermia exerts its cell-protective effect during cardiac ischemia remains unclear. It has been hypothesized that hypothermia reduces the reperfusion damage; the additional damage incurred upon the myocardium during reperfusion. Reperfusion results in a massive increase in blood flow, reactive hyperemia, which may contribute to reperfusion damage. We postulated that hypothermia could attenuate the post-ischemic reactive hyperemia.

Methods

Sixteen 25–30 kg pigs, in a closed chest model, were anesthetized and temperature was established in all pigs at 37°C using an intravascular cooling catheter. The 16 pigs were then randomized to hypothermia (34°C) or control (37°C). The left main coronary artery was then catheterized with a PCI guiding catheter. A Doppler flow wire was placed in the mid part of the LAD and a PCI balloon was then positioned proximal to the Doppler wire but distal to the first diagonal branch. The LAD was then occluded for ten minutes in all pigs. Coronary blood flow was measured before, during and after ischemia/reperfusion.

Results

The peak flow seen during post-ischemic reactive hyperemia (during the first minutes of reperfusion) was significantly reduced by 43 % (p < 0.01) in hypothermic pigs compared to controls.

Conclusion

Mild hypothermia significantly reduces post-ischemic hyperemia in a closed chest pig model. The reduction of reactive hyperemia during reperfusion may have an impact on cardiac reperfusion injury.