Cerebral metabolic suppression during hypothermic circulatory arrest in humans

Near-Infrared Spectroscopy Monitoring of Brain Oxygen in Infant Cardiac Surgery

The use of near-infrared spectroscopy for monitoring cerebral oxygenation during different types of cardiopulmonary bypass was evaluated in 24 patients aged 5 to 13 months. They underwent open-heart surgery under cardiopulmonary bypass with moderate hypothermia, deep hypothermia with low flow, or deep hypothermia with circulatory arrest. Near-infrared spectroscopy data were compared with electroencephalography and biochemical indicators (neuron-specific enolase, lactate). Near-infrared spectroscopy data showed no correlation with biochemical indicators in patients undergoing cardiopulmonary bypass with moderate hypothermia or deep hypothermia with low flow. In the deep hypothermia with circulatory arrest group, the oxygenated hemoglobin signal declined to a nadir during circulatory arrest. The period from reaching the nadir until reperfusion and the minimum values of oxygenated hemoglobin correlated closely with increases in neuron-specific enolase and lactate. All patients with an oxygenated hemoglobin-signal nadir time < 35 min were free from behavioral evidence of brain injury. The oxygenated hemoglobin-signal nadir time may be useful in predicting the safe duration of circulatory arrest.

Rationale for Implementation of Warm Cardiac Surgery in Pediatrics

Cardiac surgery was developed thanks to the introduction of hypothermia and cardiopulmonary bypass in the early 1950s. The deep hypothermia protective effect has been essential to circulatory arrest complex cases repair. During the early times of open-heart surgery, a major concern was to decrease mortality and to improve short-term outcomes. Both mortality and morbidity dramatically decreased over a few decades. As a consequence, the drawbacks of deep hypothermia, with or without circulatory arrest, became more and more apparent. The limitation of hypothermia was particularly evident for the brain and regional perfusion was introduced as a response to this problem. Despite a gain in popularity, the results of regional perfusion were not fully convincing. In the 1990s, warm surgery was introduced in adults and proved to be safe and reliable. This option eliminates the deleterious effect of ischemia-reperfusion injuries through a continuous, systemic coronary perfusion with warm oxygenated blood. Intermittent warm blood cardioplegia was introduced later, with impressive results. We were convinced by the easiness, safety, and efficiency of warm surgery and shifted to warm pediatric surgery in a two-step program. This article outlines the limitations of hypothermic protection and the basic reasons that led us to implement pediatric warm surgery. After tens of thousands of cases performed across several centers, this reproducible technique proved a valuable alternative to hypothermic surgery.

Targeted temperature management for adult out-of-hospital cardiac arrest: current concepts and clinical applications

Targeted temperature management (TTM) (primarily therapeutic hypothermia (TH)) after out-of-hospital cardiac arrest (OHCA) has been considered effective, especially for adult-witnessed OHCA with a shockable initial rhythm, based on pathophysiology and on several clinical studies (especially two randomized controlled trials (RCTs) published in 2002). However, a recently published large RCT comparing TTM at 33 °C (TH) and TTM at 36 °C (normothermia) showed no advantage of 33 °C over 36 °C. Thus, this RCT has complicated the decision to perform TH after cardiac arrest. The results of this RCT are sometimes interpreted fever control alone is sufficient to improve outcomes after cardiac arrest because fever control was not strictly performed in the control groups of the previous two RCTs that showed an advantage for TH. Although this may be possible, another interpretation that the optimal target temperature for TH is much lower than 33 °C may be also possible. Additionally, there are many points other than target temperature that are unknown, such as the optimal timing to initiate TTM, the period between OHCA and initiating TTM, the period between OHCA and achieving the target temperature, the duration of maintaining the target temperature, the TTM technique, the rewarming method, and the management protocol after rewarming. RCTs are currently underway to shed light on several of these underexplored issues. In the present review, we examine how best to perform TTM after cardiac arrest based on the available evidence.

Hypothermia for neuroprotection in adults after cardiopulmonary resuscitation

BACKGROUND

Good neurological outcome after cardiac arrest is difficult to achieve. Interventions during the resuscitation phase and treatment within the first hours after the event are critical. Experimental evidence suggests that therapeutic hypothermia is beneficial, and several clinical studies on this topic have been published. This review was originally published in 2009; updated versions were published in 2012 and 2016.

OBJECTIVES

We aimed to perform a systematic review and meta-analysis to assess the influence of therapeutic hypothermia after cardiac arrest on neurological outcome, survival and adverse events.

SEARCH METHODS

We searched the following databases: the Cochrane Central Register of Controlled Trials (CENTRAL; 2014, Issue 10); MEDLINE (1971 to May 2015); EMBASE (1987 to May 2015); the Cumulative Index to Nursing and Allied Health Literature (CINAHL) (1988 to May 2015); and BIOSIS (1989 to May 2015). We contacted experts in the field to ask for information on ongoing, unpublished or published trials on this topic.The original search was performed in January 2007.

SELECTION CRITERIA

We included all randomized controlled trials (RCTs) conducted to assess the effectiveness of therapeutic hypothermia in participants after cardiac arrest, without language restrictions. We restricted studies to adult populations cooled by any cooling method, applied within six hours of cardiac arrest.

DATA COLLECTION AND ANALYSIS

We entered validity measures, interventions, outcomes and additional baseline variables into a database. Meta-analysis was performed only for a subset of comparable studies with negligible heterogeneity. We assessed the quality of the evidence by using standard methodological procedures as expected by Cochrane and incorporated the GRADE (Grades of Recommendation, Assessment, Development and Evaluation) approach.

MAIN RESULTS

We found six RCTs (1412 participants overall) conducted to evaluate the effects of therapeutic hypothermia - five on neurological outcome and survival, one on only neurological outcome. The quality of the included studies was generally moderate, and risk of bias was low in three out of six studies. When we compared conventional cooling methods versus no cooling (four trials; 437 participants), we found that participants in the conventional cooling group were more likely to reach a favourable neurological outcome (risk ratio (RR) 1.94, 95% confidence interval (CI) 1.18 to 3.21). The quality of the evidence was moderate.Across all studies that used conventional cooling methods rather than no cooling (three studies; 383 participants), we found a 30% survival benefit (RR 1.32, 95% CI 1.10 to 1.65). The quality of the evidence was moderate.Across all studies, the incidence of pneumonia (RR 1.15, 95% CI 1.02 to 1.30; two trials; 1205 participants) and hypokalaemia (RR 1.38, 95% CI 1.03 to 1.84; two trials; 975 participants) was slightly increased among participants receiving therapeutic hypothermia, and we observed no significant differences in reported adverse events between hypothermia and control groups. Overall the quality of the evidence was moderate (pneumonia) to low (hypokalaemia).

AUTHORS' CONCLUSIONS

Evidence of moderate quality suggests that conventional cooling methods provided to induce mild therapeutic hypothermia improve neurological outcome after cardiac arrest, specifically with better outcomes than occur with no temperature management. We obtained available evidence from studies in which the target temperature was 34°C or lower. This is consistent with current best medical practice as recommended by international resuscitation guidelines for hypothermia/targeted temperature management among survivors of cardiac arrest. We found insufficient evidence to show the effects of therapeutic hypothermia on participants with in-hospital cardiac arrest, asystole or non-cardiac causes of arrest.

How to Perfuse: Concepts of Cerebral Protection during Arch Replacement

Arch surgery remains undoubtedly among the most technically and strategically challenging endeavors in cardiovascular surgery. Surgical interventions of thoracic aneurysms involving the aortic arch require complete circulatory arrest in deep hypothermia (DHCA) or elaborate cerebral perfusion strategies with varying degrees of hypothermia to achieve satisfactory protection of the brain from ischemic insults, that is, unilateral/bilateral antegrade cerebral perfusion (ACP) and retrograde cerebral perfusion (RCP). Despite sophisticated and increasingly individualized surgical approaches for complex aortic pathologies, there remains a lack of consensus regarding the optimal method of cerebral protection and circulatory management during the time of arch exclusion. Many recent studies argue in favor of ACP with various degrees of hypothermic arrest during arch reconstruction and its advantages have been widely demonstrated. In fact ACP with more moderate degrees of hypothermia represents a paradigm shift in the cardiac surgery community and is widely adopted as an emergent strategy; however, many centers continue to report good results using other perfusion strategies. Amidst this important discussion we review currently available surgical strategies of cerebral protection management and compare the results of recent European multicenter and single-center data.

Neuroprotective effects of deep hypothermia in refractory status epilepticus

Objective

Pharmacoresistance develops quickly during repetitive seizures, and refractory status epilepticus (RSE) remains a therapeutic challenge. The outcome of RSE is poor, with high mortality and morbidity. New treatments are needed. Deep hypothermia (20°C) is used clinically during reconstructive cardiac surgery and neurosurgery, and has proved safe and effective in those indications. We tested the hypothesis that deep hypothermia reduces RSE and its long‐term consequences.

Methods

We used a model of SE induced by lithium and pilocarpine and refractory to midazolam. Several EEG measures were recorded in both hypothermic (n = 17) and normothermic (n = 20) animals. Neuronal injury (by Fluoro‐Jade B), cell‐mediated inflammation, and breakdown of the blood–brain barrier (BBB) (by immunohistochemistry) were studied 48 h following SE onset.

Results

Normothermic rats in RSE seized for 4.1 ± 1.1 h, and at 48 h they displayed extensive neuronal injury in many brain regions, including hippocampus, dentate gyrus, amygdala, entorhinal and pyriform cortices, thalamus, caudate/putamen, and the frontoparietal neocortex. Deep hypothermia (20°C) of 30 min duration terminated RSE within 12 min of initiation of hypothermia, reduced EEG power and seizure activity upon rewarming, and eliminated SE‐induced neuronal injury in most animals. Normothermic rats showed widespread breakdown of the BBB, and extensive macrophage infiltration in areas of neuronal injury, which were completely absent in animals treated with hypothermia.

Interpretation

These results suggest that deep hypothermia may open a new therapeutic avenue for the treatment of RSE and for the prevention of its long‐term consequences.

Electroencephalography During Hemiarch Replacement With Moderate Hypothermic Circulatory Arrest

BACKGROUND

This study aimed to characterize intraoperative electroencephalography (EEG) during moderate hypothermic circulatory arrest (MHCA) with selective antegrade cerebral perfusion (SACP), which has not been described previously.

METHODS

This was a single-institution retrospective study of patients undergoing aortic hemiarch replacement using MHCA (temperatures <28°C at circulatory arrest [CA]) and unilateral SACP with EEG monitoring from July 1, 2013 to November 1, 2014. The EEG pattern was determined before and immediately after CA, as well as after establishment of SACP. Patient and procedural characteristics and outcomes were determined and compared after stratification by the presence of ischemic EEG changes.

RESULTS

The study included 71 patients. Before CA, 47 patients (66%) demonstrated a continuous EEG pattern, with or without periodic complexes, and 24 (34%) had a burst suppression EEG pattern. Immediately after CA, abrupt loss of electrocerebral activity occurred in 32 patients (45%), suggestive of cerebral ischemia. Establishment of unilateral SACP rapidly restored electrocerebral activity in all but 2 patients. One patient had persistent loss of left-sided activity, which resolved after transition to bilateral SACP. Another patient had persistent global loss of activity and was placed back on cardiopulmonary bypass for further cooling before reinitiation of CA. No significant differences in characteristics or outcomes were assessed between patients with and without loss of EEG activity.

CONCLUSIONS

Nearly half of patients undergoing hemiarch replacement with MHCA/SACP experience abrupt loss of electrocerebral activity after CA is initiated. Although unilateral SACP usually restores prearrest electrocerebral activity, intraoperative EEG may be particularly valuable for the identification of patients with persistent cerebral ischemia even after SACP.

Deep hypothermia for the treatment of refractory status epilepticus

In a rat model of status epilepticus (SE) induced by lithium and pilocarpine and refractory to midazolam, deep hypothermia (20 °C for 30 min) reduced EEG power over 50-fold, stopped SE within 12 min, and reduced EEG spikes by 87%. Hypothermia deserves further investigation as a treatment of last resort for refractory SE. This article is part of a Special Issue entitled "Status Epilepticus".

Prolonged Antegrade Cerebral Perfusion via Right Axillary Artery (≥60 min) Does Not Affect Early Outcomes in a Repair of Type A Acute Aortic Dissection

PURPOSE

We aim to investigate whether the duration of antegrade cerebral perfusion (ACP) via right axillary artery with an 8-mm prosthetic graft affects early outcomes in a repair of type A acute aortic dissection (AAD).

METHODS

Over the 24 months from April 2010, a repair of AAD under ACP via the right axillary artery and mild hypothermic circulatory arrest (rectum temperature, 28-30°C) was performed in 34 patients. Mean age was 64.5 ± 13.7 years of age.Preoperative shock status was in three due to cardiac tamponade. Organ malperfusion occurred in 11 patients preoperatively. Mean follow-up period was 9.6 ± 8.4 months and follow-up rate was 100%.

RESULTS

Hospital mortality rate was 8.8%. No newly required hemodialysis and new onset of temporary or permanent neurologic deficits were present in survivors.There were no statistically significant differences of mortality rate, new onset of permanent or temporary neurologic deficits and distal organ dysfunction between ACP duration <60 min and ≥60 min. The 12-month survival was 84.4% ± 6.4%. And, freedom from aorta-related events at 12 and 18 months were 100% ± 0.0% and 88.9% ± 10.5%, respectively.

CONCLUSIONS

The duration of ACP via right axillary artery does not affect early outcomes following a repair of AAD.

Evidence base for restrictive transfusion triggers in high-risk patients

Liberal versus restrictive red blood cell (RBC) transfusion triggers have been debated for years. This review illustrates the human body's physiologic response to acute anemia and summarizes the evidence from prospective randomized trials (RCTs) for restrictive use of RBC transfusions in high-risk patients. During progressive anemia, the human body maintains the oxygen delivery to the tissues by an increase in cardiac output and peripheral oxygen extraction. Seven RCTs with a total of 5,566 high-risk patients compared a restrictive hemoglobin (Hb) transfusion trigger (Hb < 70 or < 80 g/l) with a liberal Hb transfusion trigger (Hb < 90 or < 100 g/l). Unanimously these studies show non-inferiority, safety, and a significant reduction in RBC transfusions in the restrictive groups. In one RCT mortality was higher in the liberal Hb transfusion group, and in two additional RCTs mortality of subgroups or after risk adjustment was significantly higher in the liberal Hb transfusion trigger groups.

CONCLUSION

Strong RCT evidence suggests the safety of restrictive transfusion triggers. As a consequence, an Hb transfusion trigger of <70 g/l is recommended for high risk patients.

Brain activity monitoring by compressed spectral array during deep hypothermic circulatory arrest in acute aortic dissection surgery

INTRODUCTION

Monitoring the central nervous system during aortic dissection repair may improve the understanding of the intraoperative changes related to its bioactivity.

AIM

The aim of the study was to evaluate the influence of deep hypothermia on intraoperative brain bioactivity measured by the compressed spectral array (CSA) method and to assess the influence of the operations on postoperative cognitive function.

MATERIAL AND METHODS

The study enrolled 40 patients (31 men and 9 women) at the mean age of 60.2 ± 8.6 years, diagnosed with acute aortic dissection. They underwent emergency operations in deep hypothermic circulatory arrest (DHCA). During the operations, brain bioactivity was monitored with the compressed spectral array method.

RESULTS

There were no intraoperative deaths. Electrocerebral silence during DHCA was observed in 31 patients (74%). The lowest activity was observed during DHCA: it was 0.01 ± 0.05 nW in the left hemisphere and 0.01 ± 0.03 nW in the right hemisphere. The postoperative results of neurological tests deteriorated statistically significantly (26.9 ± 1.7 points vs. 22.0 ± 1.7 points; p < 0.001), especially among patients who exhibited brain activity during DHCA.

CONCLUSIONS

The compressed spectral array method is clinically useful in monitoring brain bioactivity during emergency operations of acute aortic dissections. Electrocerebral silence occurs in 75% of patients during DHCA. The cognitive function of patients deteriorates significantly after operations with DHCA.

Brain resuscitation and prognosis after cardiac arrest

Brain injury represents the major cause of long-term disability and mortality among patients resuscitated from cardiac arrest. Brain-directed therapies include maintenance of normal oxygenation, hemodynamic support to optimize cerebral perfusion, glycemic control, and targeted temperature management. Pertinent guidelines and recommendations are reviewed for brain-directed treatment. The latest clinical trial data regarding targeted temperature management are also reviewed. Contemporary prognostication among initially comatose cardiac arrest survivors uses a combination of clinical and electrophysiologic tests. The most recent guidelines for prognostication after cardiac arrest are reviewed. Ongoing research regarding the effects of induced hypothermia on prognostic algorithms is also reviewed.

Cardiopulmonary bypass with brain perfusion for renal cell carcinoma with caval thrombosis

AIM: To compare a modified technique preserving brain circulation during cardiopulmonary by-pass (CPB) for radical nephrectomy and caval thrombectomy, to the standard technique.

METHODS: Retrospective evaluation of an institutional database that collects the data of patients submitted to nephrectomy and removal of caval thrombosis with CPB since 1998. In period between 1998 and 2007, CPB followed a standard technique (group sCPB); then, since 2008, a variation in the perfusional technique was introduced, allowing the anterograde perfusion of brain circulation during circulatory arrest (group CPB + BP) with the aim to reduce the risk of ischemic damage to the brain and also the need of deeper hypothermia. Patients (age, gender, comorbidity) and tumor characteristics (side, histology, staging, level of thrombosis), as well as parameters of CPB (times of CPB, aortic clamping and circulatory arrest, minimum temperature reached during hypothermia), intra- and perioperative morbidity (complications in general, bleeding, renal and hepatic failure) and mortality were analyzed and compared between 2 groups (sCPB vs CPB + BP)

RESULTS: The data of 24 patients, respectively 9 in sCPB group and 15 in CPB + BP group, have been reviewed. No differences in the characteristics of patients and tumors were observed. Only 1 (11.1%) and 4 (26.0%) of sCPB and CPB + BP patients, respectively, didn’t experience any event of complication. In sCPB group were observed 15 events of complication (5 of which Clavien ≥ 3, 33% of the events), for a mean of 1.66 events/patient; 29 events (10 Clavien ≥ 3, 30.3%), in the CPB + BP group, for a mean of 2.1 events/patient. 1 (11.1%) and 2 (14.2%) deaths occurred, respectively. For patients submitted to CPB + BP, the minimum temperature reached was significantly higher (29.9 °C vs 26.4 °C, P = 0.001), the time of circulatory arrest was longer (17.4 min vs 13.7 min, NS), but the overall time of CPB shorter (76.1 min vs 92.5 min, NS), albeit these latter differences were not statistically significant. No differences in terms of bleeding, impairment of renal function (post-operative Cr > 2.0 mg/dL respectively in 44.4% vs 35.7% of cases, in the two groups, NS) or hepatic insufficiency (post-operative GOT or GPT > 50 U/L respectively in 44.4% and 66.7% of patients, NS) were noted. Average follow-up was 51 mo in patients undergoing a sCPB and 12 mo in the CPB + BP group of patients; at the last follow-up, 7 patients had died of progression of the condition (4 in the first group and 3 in the second group, respectively), 7 were alive in progression and 10 had no evidence of the disease.

CONCLUSION: The perfusional technique that maintains brain perfusion during circulatory arrest limits hypothermia and lowers time of CPB, without rising the risk of renal and hepatic injury.

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.

Antegrade versus retrograde cerebral perfusion for hemiarch replacement with deep hypothermic circulatory arrest: does it matter? A propensity-matched analysis

OBJECTIVE

The choice of cerebral perfusion strategy for aortic arch surgery has been debated, and the superiority of antegrade (ACP) or retrograde (RCP) cerebral perfusion has not been shown. We examined the early and late outcomes for ACP versus RCP in proximal (hemi-) arch replacement using deep hypothermic circulatory arrest (DHCA).

METHODS

A retrospective analysis of a prospectively maintained database was performed for all patients undergoing elective and nonelective hemiarch replacement at a single referral institution from June 2005 to February 2013. Total arch cases were excluded to limit the analysis to shorter DHCA times and a more uniform patient population for whom clinical equipoise regarding ACP versus RCP exists. A total of 440 procedures were identified, with 360 (82%) using ACP and 80 (18%) using RCP. The endpoints included 30-day/in-hospital and late outcomes. A propensity score with 1:1 matching of 40 pre- and intraoperative variables was used to adjust for differences between the 2 groups.

RESULTS

All 80 RCP patients were propensity matched to a cohort of 80 similar ACP patients. The pre- and intraoperative characteristics were not significantly different between the 2 groups after matching. No differences were found in 30-day/in-hospital mortality or morbidity outcomes. The only significant difference between the 2 groups was a shorter mean operative time in the RCP cohort (P = .01). No significant differences were noted in late survival (P = .90).

CONCLUSIONS

In proximal arch operations using DHCA, equivalent early and late outcomes can be achieved with RCP and ACP, although the mean operative time is significantly less with RCP, likely owing to avoidance of axillary cannulation. Questions remain regarding comparative outcomes with straight DHCA and lesser degrees of hypothermia.

Surviving two hours of ventricular fibrillation in accidental hypothermia

BACKGROUND

Cardiac arrest as a consequence of deep accidental hypothermia is associated with high mortality. Standardized prehospital management as well as rewarming with extracorporeal circulation (ECC) are important factors to improve survival. The objective of this case report is to illustrate the importance of effective cardiopulmonary resuscitation (CPR) and ECC in a cardiac arrest following deep accidental hypothermia.

CASE REPORT

A 42-year-old man was found unresponsive to external stimuli and pulseless at an outdoor temperature of 1°C. CPR was started at the scene by laypersons, and the emergency medical services (EMS) arrived 5 minutes after the emergency call. Resuscitation according to International Liaison Committee on Resuscitation (ILCOR) guidelines was initiated by EMS. The first recorded rhythm was ventricular fibrillation (VF), which persisted, despite repeated defibrillation. The patient showed signs of severe hypothermia and, during ongoing CPR, was transported to hospital where on arrival the patient's rectal temperature was measured at 22°C. Resuscitation measures were continued and warming was started at the emergency room. Due to persistent VF and deep hypothermia, the patient was transferred to a cardiothoracic surgical unit for rewarming with ECC. At commencement of ECC, CPR had been going for approximately 130 minutes and a total of 38 defibrillations had been made. During this time interval the patients was pulseless. At a core temperature of 30°C, one defibrillation restored sinus rhythm and subsequently stable circulation was achieved. The patient received a further 24 hours of hypothermia treatment at 32-34°C. He was discharged to rehabilitation facilities after 3 weeks of hospital care. Three months after the cardiac arrest the patient was fully recovered, was back to work, and had resumed normal activities.

CONCLUSIONS

We demonstrate a case of cardiac arrest due to deep accidental hypothermia that stresses the importance of effective CPR and early-stage consideration of the use of ECC for safe and effective rewarming.

Preconditioning provides neuroprotection in models of CNS disease: paradigms and clinical significance

Preconditioning is a phenomenon in which brief episodes of a sublethal insult induce robust protection against subsequent lethal injuries. Preconditioning has been observed in multiple organisms and can occur in the brain as well as other tissues. Extensive animal studies suggest that the brain can be preconditioned to resist acute injuries, such as ischemic stroke, neonatal hypoxia/ischemia, surgical brain injury, trauma, and agents that are used in models of neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease. Effective preconditioning stimuli are numerous and diverse, ranging from transient ischemia, hypoxia, hyperbaric oxygen, hypothermia and hyperthermia, to exposure to neurotoxins and pharmacological agents. The phenomenon of "cross-tolerance," in which a sublethal stress protects against a different type of injury, suggests that different preconditioning stimuli may confer protection against a wide range of injuries. Research conducted over the past few decades indicates that brain preconditioning is complex, involving multiple effectors such as metabolic inhibition, activation of extra- and intracellular defense mechanisms, a shift in the neuronal excitatory/inhibitory balance, and reduction in inflammatory sequelae. An improved understanding of brain preconditioning should help us identify innovative therapeutic strategies that prevent or at least reduce neuronal damage in susceptible patients. In this review, we focus on the experimental evidence of preconditioning in the brain and systematically survey the models used to develop paradigms for neuroprotection, and then discuss the clinical potential of brain preconditioning.

A meta-analysis of deep hypothermic circulatory arrest versus moderate hypothermic circulatory arrest with selective antegrade cerebral perfusion

INTRODUCTION

A recent concern of deep hypothermic circulatory arrest (DHCA) in aortic arch surgery has been its potential association with increased risk of coagulopathy, elevated inflammatory response and end-organ dysfunction. Recently, moderate hypothermic circulatory arrest (MHCA) with selective antegrade circulatory arrest (SACP) seeks to negate potential hypothermia-related morbidities, while maintaining adequate neuroprotection. The present meta-analysis aims to compare postoperative outcomes in arch surgery using DHCA or MHCA+SACP as neuroprotective strategies.

METHODS

Electronic searches were performed using six databases from their inception to January 2013. Two reviewers independently identified all relevant studies comparing DHCA with MHCA+SACP, as defined by a recent hypothermia temperature consensus. Data were extracted and meta-analyzed according to pre-defined clinical endpoints.

RESULTS

Nine comparative studies were identified for inclusion in the present meta-analysis. Stroke rates were significantly lower in patients undergoing MHCA+SACP (P=0.0007, I(2)=0%), while comparable results were observed with temporary neurological deficit, mortality, renal failure or bleeding. Infrequent and inconsistent reporting of systemic outcomes precluded analysis of other systemic outcomes.

CONCLUSIONS

The present meta-analysis indicated the superiority of MHCA+SACP in terms of stroke risk.

Consensus on hypothermia in aortic arch surgery

Considered a standard part of aortic arch surgery, hypothermia can sufficiently reduce cerebral metabolic demand to permit reasonable periods of circulatory arrest. Yet despite its ubiquitous application and critical importance, temperature classification in hypothermic circulatory arrest is still without clear definition. The following Consensus from experts in high-volume aortic institutions defines 'profound', 'deep', 'moderate', and 'mild' hypothermia and recommends standardized monitoring sites, so as to facilitate more consistent reporting and robust analysis.

A meta-analysis of deep hypothermic circulatory arrest alone versus with adjunctive selective antegrade cerebral perfusion

INTRODUCTION

Recognizing the importance of neuroprotection in aortic arch surgery, deep hypothermic circulatory arrest (DHCA) now underpins operative practice as it minimizes cerebral metabolic activity. When prolonged periods of circulatory arrest are required, selective antegrade cerebral perfusion (SACP) is supplemented as an adjunct. However, concerns exist over the risks of SACP in introducing embolism and hypo- and hyper-perfusing the brain. The present meta-analysis aims to compare postoperative outcomes in arch surgery using DHCA alone or DHCA + SACP as neuroprotection strategies.

METHODS

Electronic searches were performed using six databases from their inception to January 2013. Two reviewers independently identified all relevant studies comparing DHCA alone with DHCA + SACP. Data were extracted and meta-analyzed according to pre-defined clinical endpoints.

RESULTS

Nine comparative studies were identified in the present meta-analysis, with 648 patients employing DHCA alone and 370 utilizing DHCA + SACP. No significant differences in temporary or permanent neurological outcomes were identified. DHCA + SACP was associated with significantly better survival outcomes (P=0.008, I(2)=0%), despite longer cardiopulmonary bypass time. Infrequent and inconsistent reporting of other clinical results precluded analysis of systemic outcomes.

CONCLUSIONS

The present meta-analysis indicate the superiority of DHCA + SACP in terms of mortality outcomes.

Post-hypothermia fever is associated with increased mortality after out-of-hospital cardiac arrest

OBJECTIVE

Post-cardiac arrest fever has been associated with adverse outcome before implementation of therapeutic hypothermia (TH), however the prognostic implications of post-hypothermia fever (PHF) in the era of modern post-resuscitation care including TH has not been thoroughly investigated. The aim of the study was to assess the prognostic implication of PHF in a large consecutive cohort of comatose survivors after out-of-hospital cardiac arrest (OHCA) treated with TH.

METHODS

In the period 2004-2010, a total of 270 patients resuscitated after OHCA and surviving a 24-h protocol of TH with a target temperature of 32-34°C were included. The population was stratified in two groups by median peak temperature (≥38.5°C) within 36h after rewarming: PHF and no-PHF. Primary endpoint was 30-days mortality and secondary endpoint was neurological outcome assessed by Cerebral Performance Category (CPC) at hospital discharge.

RESULTS

PHF (≥38.5°C) was associated with a 36% 30-days mortality rate compared to 22% in patients without PHF, plog-rank=0.02, corresponding to an adjusted hazard rate (HR) of 1.8 (95% CI: 1.1-2.7), p=0.02). The maximum temperature (HR=2.0 per °C above 36.5°C (95% CI: 1.4-3.0), p=0.0005) and the duration of PHF (HR=1.6 per 8h (95% CI: 1.3-2.0), p<0.0001) were also independent predictors of 30-days mortality in multivariable models. Good neurological outcome (CPC1-2) versus unfavourable outcome (CPC3-5) at hospital discharge was found in 61% vs. 39% in the PHF group compared to 75% vs. 25% in the No PHF group, p=0.02.

CONCLUSIONS

Post-hypothermia fever ≥38.5°C is associated with increased 30-days mortality, even after controlling for potential confounding factors. Avoidance of PHF as a therapeutic target should be evaluated in prospective randomized trials.

Modern temperature management in aortic arch surgery: the dilemma of moderate hypothermia

Arch surgery is undoubtedly among the most technically and strategically challenging endeavours in aortic surgery, requiring thorough understanding not only of cardiovascular physiology, but also in particular, of neurophysiology (cerebral and spinal cord), and is still associated with significant mortality and morbidity. In the late 1980s, when deep hypothermic circulatory arrest (HCA) had gained widespread acceptance as the standard approach for arch surgery, antegrade selective cerebral perfusion (SCP), as an adjunct to deep HCA, began its triumphal march, offering excellent neuroprotection and improved overall outcome. This encouraged the use of antegrade SCP in combination with steadily increasing body core temperatures--a trend culminating in the progressive advocation of moderate-to-mild temperatures up to 35 °C, and even normothermia. The impetus for progressive temperature elevation was the limitation of adverse effects of profound hypothermia and the most welcome side effect of significantly shorter cooling and rewarming periods on cardiopulmonary bypass (CPB), and thereby, potentially, the alleviation of the systemic inflammatory response and, in particular, the risk of severe postoperative bleeding (and other organ dysfunctions). The safe limits of prolonged distal circulatory arrest, particularly with regard to the ischaemic tolerance of the viscera and the spinal cord, have not yet been clearly defined. Adverse outcomes due to inappropriate temperature management (core temperatures too high for the required duration of distal arrest) are probably highly underreported. Complications historically associated with hypothermia, namely excessive bleeding, are possibly overestimated. Trading effective neuroprotection and excellent outcomes for the risk of prolonged 'warm' distal ischaemia might constitute a significant step back, jeopardizing visceral and, in particular, spinal cord integrity, with unpredictable consequences for long-term outcome and quality of life, particularly affecting those in need of more complex surgery or with previous neurological deficits.

Hypothermia for aortic surgery

Hypothermic circulatory arrest has been used during aortic arch repairs with acceptable neurologic outcomes. Through the years, we have studied the effects of deep hypothermia on brain metabolism and perfusion both in a pig model and in surgical patients. Hypothermic circulatory arrest has also been used as a method of organ protection in the repair of thoracoabdominal aortic aneurysms. We summarize the clinical and laboratory studies to support the routine use of hypothermic circulatory arrest in clinical practice.