Effect of mild hyperthermia on recovery of metabolic function after global cerebral ischemia in cats

2024 EACTS/EACTAIC/EBCP Guidelines on cardiopulmonary bypass in adult cardiac surgery

Clinical practice guidelines consolidate and evaluate all pertinent evidence on a specific topic available at the time of their formulation. The goal is to assist physicians in determining the most effective management strategies for patients with a particular condition. These guidelines assess the impact on patient outcomes and weigh the risk-benefit ratio of various diagnostic or therapeutic approaches. While not a replacement for textbooks, they provide supplementary information on topics relevant to current clinical practice and become an essential tool to support the decisions made by specialists in daily practice. Nonetheless, it is crucial to understand that these recommendations are intended to guide, not dictate, clinical practice, and should be adapted to each patient's unique needs. Clinical situations vary, presenting a diverse array of variables and circumstances. Thus, the guidelines are meant to inform, not replace, the clinical judgement of healthcare professionals, grounded in their professional knowledge, experience and comprehension of each patient's specific context. Moreover, these guidelines are not considered legally binding; the legal duties of healthcare professionals are defined by prevailing laws and regulations, and adherence to these guidelines does not modify such responsibilities. The European Association for Cardio-Thoracic Surgery (EACTS), the European Association of Cardiothoracic Anaesthesiology and Intensive Care (EACTAIC) and the European Board of Cardiovascular Perfusion (EBCP) constituted a task force of professionals specializing in cardiopulmonary bypass (CPB) management. To ensure transparency and integrity, all task force members involved in the development and review of these guidelines submitted conflict of interest declarations, which were compiled into a single document available on the EACTS website (https://www.eacts.org/resources/clinical-guidelines). Any alterations to these declarations during the development process were promptly reported to the EACTS, EACTAIC and EBCP. Funding for this task force was provided exclusively by the EACTS, EACTAIC and EBCP, without involvement from the healthcare industry or other entities. Following this collaborative endeavour, the governing bodies of EACTS, EACTAIC and EBCP oversaw the formulation, refinement, and endorsement of these extensively revised guidelines. An external panel of experts thoroughly reviewed the initial draft, and their input guided subsequent amendments. After this detailed revision process, the final document was ratified by all task force experts and the leadership of the EACTS, EACTAIC and EBCP, enabling its publication in the European Journal of Cardio-Thoracic Surgery, the British Journal of Anaesthesia and Interdisciplinary CardioVascular and Thoracic Surgery. Endorsed by the EACTS, EACTAIC and EBCP, these guidelines represent the official standpoint on this subject. They demonstrate a dedication to continual enhancement, with routine updates planned to ensure that the guidelines remain current and valuable in the ever-progressing arena of clinical practice.

Prediction model of early biomarkers of massive cerebral infarction caused by anterior circulation occlusion: Establishment and evaluation

Objective

The purpose of this study is to establish and evaluate an early biomarker prediction model of massive cerebral infarction caused by anterior circulation occlusion.

Methods

One hundred thirty-four patients with acute cerebral infarction from January 2018 to October 2020 were selected to establish the development cohort for the internal test of the nomogram. Ninety-one patients with acute cerebral infarction hospitalized in our hospital from December 2020 to December 2021 were constituted the validation cohort for the external validation. All patients underwent baseline computed tomography (CT) scans within 12 h of onset and early imaging signs (hyperdense middle cerebral artery sign, obscuration of the lentiform nucleus, insular ribbon sign) of acute cerebral infarction were identified on CT by two neurologists. Based on follow-up CT images, patients were then divided into a massive cerebral infarction group and a non-massive cerebral infarction group. The nomogram model was constructed based on logistic regression analysis with R language. The nomogram was subsequently validated in an independent external validation cohort. Accuracy and discrimination of the prediction model were evaluated by a calibration chart, receiver operating characteristic (ROC) curve, and decision curve.

Results

The indicators, including insular ribbon sign, reperfusion therapy, National Institutes of Health Stroke Scale (NHISS) score, previous cerebral infarction, and atrial fibrillation, were entered into the prediction model through binary logistic regression analysis. The prediction model showed good predictive ability. The area under the ROC curve of the prediction model was 0.848. The specificity, sensitivity, and Youden index were 0.864, 0.733, and 0.597, respectively. This nomogram to the validation cohort also showed good discrimination (AUC = 0.940, 95% CI 0.894–0.985) and calibration.

Conclusion

Demonstrating favorable predictive efficacy and reproducibility, this study successfully established a prediction model of CT imaging signs and clinical data as early biomarkers of massive cerebral infarction caused by anterior circulation occlusion.

Novel Quantitative Contrast-Enhanced Ultrasound Detection of Hypoxic Ischemic Injury in Neonates and Infants: Pilot Study 1

OBJECTIVES

To investigate whether quantitative contrast-enhanced ultrasound (CEUS) can accurately identify neonates and infants with hypoxic ischemic brain injury.

METHODS

In this prospective cohort study, 8 neonates and infants with a suspicion of hypoxic ischemic injury were evaluated with CEUS.

RESULTS

An interesting trend was observed in the central gray nuclei-to-cortex perfusion ratios. The ratios at the peak enhancement, wash-in area under the curve, perfusion index, and maximum wash-in slopes were lower in all of the affected cases compared to the normal group but not statistically significant given the small sample size (P = .0571). Additionally, when the central gray nuclei-to-cortex perfusion ratio was plotted for all time points along the time-intensity curve, it was observed that the affected cases showed a trend that was qualitatively different from that of the normal cases. In the affected cases, the ratio time-intensity curves either stayed below 1.0 for the entire enhancement period or reached 1.0 close to peak wash-in before falling just below 1.0 for the remaining period of enhancement. However, in the unaffected patients, there was a steep wash-in that crossed the 1.0 threshold and remained above 1.0 for most of the enhancement period.

CONCLUSIONS

Bedside CEUS is an easily obtainable brain-imaging modality that has the potential to effectively identify infants and neonates with evolving brain injury. A larger prospective study evaluating the correlation between CEUS findings and the reference standard of diffusion- and perfusion-weighted magnetic resonance imaging is needed to establish it as a diagnostic tool.

The incidence of hyperthermia during craniotomy

There is evidence that even mild hyperthermia may exacerbate brain injury. There seem reasonable grounds for considering patients undergoing craniotomy as at risk for brain injury. A retrospective observational study was undertaken to measure the incidence of mild hyperthermia in craniotomy cases in which the patient was initially normothermic. Auckland City Hospital's database of electronic anaesthetic records was searched for adult patients who were normothermic (≤37°C) prior to undergoing craniotomy procedures. For each case, demographic data, intraoperative naso- or oropharyngeal temperature measurements, and paracetamol use were extracted. We identified the proportion of patients whose temperature rose to exceed normal (>37°C) and subdivided that group into the proportion in whom the temperature rose to ≥38°C. Two thousand, nine hundred and thirty-five craniotomy cases began their operations while normothermic and had adequate temperature data collected. There were 984 (33.5%) cases that had at least one temperature reading >37°C, for a mean (standard deviation [SD]) time of 66.0 (64.6) minutes, and 49 (1.7%) cases that had at least one reading ≥38°C for a mean (SD) time of 40.4 (38.1) minutes. The majority (77.8%) who became mildly hyperthermic remained so at the end of the procedure. New mild hyperthermia occurs commonly during craniotomy. In view of the compelling evidence of potential harm arising from mild hyperthermia in brain injury, these findings suggest an opportunity for practice improvement in the anaesthetic management of craniotomy patients. Reasonable steps should be taken by anaesthetists to avoid intraoperative hyperthermia of any degree.

Brain temperature but not core temperature increases during spreading depolarizations in patients with spontaneous intracerebral hemorrhage

Spreading depolarizations (SDs) are highly active metabolic events, commonly occur in patients with intracerebral hemorrhage (ICH) and may be triggered by fever. We investigated the dynamics of brain-temperature (T_brain) and core-temperature (T_core) relative to the occurrence of SDs. Twenty consecutive comatose ICH patients with multimodal electrocorticograpy (ECoG) and T_brain monitoring of the perihematomal area were prospectively enrolled. Clusters of SDs were defined as ≥2 SDs/h. Generalized estimating equations were used for statistical calculations. Data are presented as median and interquartile range. During 3097 h (173 h [81-223]/patient) of ECoG monitoring, 342 SDs were analyzed of which 51 (15%) occurred in clusters. Baseline T_core and T_brain was 37.3℃ (36.9-37.8) and 37.4℃ (36.7-37.9), respectively. T_brain but not T_core significantly increased 25 min preceding the onset of SDs by 0.2℃ (0.1-0.2; p < 0.001) and returned to baseline 35 min following SDs. During clusters, T_brain increased to a higher level (+0.4℃ [0.1-0.4]; p = 0.006) when compared to single SDs. A higher probability (OR = 36.9; CI = 36.8-37.1; p < 0.001) of developing SDs was observed during episodes of T_brain ≥ 38.0℃ (23% probability), than during T_brain ≤ 36.6℃ (9% probability). Spreading depolarizations - and in particular clusters of SDs - may increase brain temperature following ICH.

Optimal Temperature Management During Cardiopulmonary Bypass: Warm, Cold, or Tepid?

Hypothermia permitted the advent of cardiac surgery and is considered by many the mainstay of cerebral protection during cardiopulmonary bypass (CPB). How ever, some clinicians have questioned the importance of reduced temperatures during CPB and advocate "normo thermic" heart surgery. Hypothermia (mild, moderate, and profound) provides protection during periods of inadequate oxygen delivery by at least two mecha nisms. First, metabolic rate is directly related to tempera ture ; therefore, reduced temperatures increase toler ance to inadequate oxygen delivery. Q10 values (the ratio of metabolic rates at temperature X°C and tempera ture X°C - 10°C) are controversial and are reported as varying between 2.0 and 5.0. During profound hypother mia (temperature = 17°C), metabolic requirements are 10% to 15% of normothermic values. Second, reduced temperatures (even minimal reductions [34°C to 35°C]) attenuate the release of glutamate and other excitatory amines from ischemic neuronal cells. This phenomenon is thought to play an important role in hypothermic cerebral protection. Many investigators have assessed the impact of normothermic temperatures on cerebral outcomes in cardiac surgery patients. Although seem ingly conflicting conclusions are reported, this much is clear: cerebral temperatures in excess of 37°C exacer bate ischemic injury and even mild hypothermia re duces central nervous system damage in the ischemic brain.

Cerebral Vascular Control and Metabolism in Heat Stress

This review provides an in-depth update on the impact of heat stress on cerebrovascular functioning. The regulation of cerebral temperature, blood flow, and metabolism are discussed. We further provide an overview of vascular permeability, the neurocognitive changes, and the key clinical implications and pathologies known to confound cerebral functioning during hyperthermia. A reduction in cerebral blood flow (CBF), derived primarily from a respiratory-induced alkalosis, underscores the cerebrovascular changes to hyperthermia. Arterial pressures may also become compromised because of reduced peripheral resistance secondary to skin vasodilatation. Therefore, when hyperthermia is combined with conditions that increase cardiovascular strain, for example, orthostasis or dehydration, the inability to preserve cerebral perfusion pressure further reduces CBF. A reduced cerebral perfusion pressure is in turn the primary mechanism for impaired tolerance to orthostatic challenges. Any reduction in CBF attenuates the brain's convective heat loss, while the hyperthermic-induced increase in metabolic rate increases the cerebral heat gain. This paradoxical uncoupling of CBF to metabolism increases brain temperature, and potentiates a condition whereby cerebral oxygenation may be compromised. With levels of experimentally viable passive hyperthermia (up to 39.5-40.0 °C core temperature), the associated reduction in CBF (∼ 30%) and increase in cerebral metabolic demand (∼ 10%) is likely compensated by increases in cerebral oxygen extraction. However, severe increases in whole-body and brain temperature may increase blood-brain barrier permeability, potentially leading to cerebral vasogenic edema. The cerebrovascular challenges associated with hyperthermia are of paramount importance for populations with compromised thermoregulatory control--for example, spinal cord injury, elderly, and those with preexisting cardiovascular diseases.

Neurologic Injury Associated with Rewarming from Hypothermia: Is Mild Hypothermia on Bypass Better than Deep Hypothermic Circulatory Arrest?

Many known risk factors for adverse cardiovascular and neurological outcomes in children with congenital heart defects (CHD) are not modifiable; however, the temperature and blood flow during cardiopulmonary bypass (CPB), are two risk factors, which may be altered in an attempt to improve long-term neurological outcomes. Deep hypothermic circulatory arrest, traditionally used for aortic arch repair, has been associated with short-term and long-term neurologic sequelae. Therefore, there is a rising interest in using moderate hypothermia with selective antegrade cerebral blood flow on CPB during aortic arch repair. Rewarming from moderate-to-deep hypothermia has been shown to be associated with neuronal injury, neuroinflammation, and loss of cerebrovascular autoregulation. A significantly lesser degree of rewarming is required following mild (33-35°C) hypothermia as compared with moderate (28-32°C), deep (21-27°C), and profound (less than 20°C) hypothermia. Therefore, we believe that mild hypothermia is associated with a lower risk of rewarming-induced neurologic injury. We hypothesize that mild hypothermia with selective antegrade cerebral perfusion during CPB for neonatal aortic arch repair would be associated with improved neurologic outcome.

Emergence of cognitive deficits after mild traumatic brain injury due to hyperthermia

Mild elevations in core temperature can occur in individuals involved in strenuous activities that are risky for potentially sustaining a mild traumatic brain injury (mTBI) or concussion. Recently, we have discovered that mild elevations in brain temperature can significantly aggravate the histopathological consequences of mTBI. However, whether this exacerbation of brain pathology translates into behavioral deficits is unknown. Therefore, we investigated the behavioral consequences of elevating brain temperature to mildly hyperthermic levels prior to mTBI. Adult male Sprague Dawley rats underwent mild fluid-percussion brain injury or sham surgery while normothermic (37 °C) or hyperthermic (39 °C) and were allowed to recover for 7 days. Animals were then assessed for cognition using the water maze and cue and contextual fear conditioning. We found that mTBI alone at normothermia had no effect on long-term cognitive measures whereas mTBI animals that were hyperthermic for 15 min prior to and for 4h after brain injury were significantly impaired on long-term retention for both the water maze and fear conditioning. In contrast, hyperthermic mTBI animals cooled within 15 min to normothermia demonstrated no significant long-term cognitive deficits. Mild TBI irrespective of temperature manipulations resulted in significant short-term working memory deficits. Cortical atrophy and contusions were detected in all mTBI treatment groups and contusion volume was significantly less in hyperthermic mTBI animals that were cooled as compared to hyperthermic mTBI animals that remained hyperthermic. These results indicate that brain temperature is an important variable for mTBI outcome and that mildly elevated temperatures at the time of injury result in persistent cognitive deficits. Importantly, cooling to normothermia after mTBI prevents the development of long-term cognitive deficits caused by hyperthermia. Reducing temperature to normothermic levels soon after mTBI represents a rational approach to potentially mitigate the long-term consequences of mTBI.

Therapeutic hypothermia after cardiopulmonary resuscitation

Full cerebral recovery after cardiopulmonary resuscitation is still a rare event. Unfortunately, up to now, no specific and outcome-improving therapy was available after such events. From several cases it is known that low body and brain temperature during a cardiocirculatory arrest improves the neurological outcome following these events. As it is not possible in acute events to induce hypothermia beforehand, whether cooling after the insult could also be protective was evaluated. After animal studies in the 1990s and first clinical pilot trials of mild therapeutic and induced hypothermia, two randomized trials of hypothermic therapy after successful resuscitation after cardiac arrest were conducted. These studies demonstrated that hypothermia after cardiac arrest could improve neurological outcome as well as overall mortality.

Plasma protein denaturation with graded heat exposure

During cardiopulmonary bypass (CPB), perfusion at tepid temperatures (33-35 °C) is recommended to avoid high temperature cerebral hyperthermia during and after the operation. However, the ideal temperature for uncomplicated adult cardiac surgery is an unsettled question. Typically, the heat exchanger maximum temperature is monitored between 40-42 °C to prevent denaturation of plasma proteins, but studies have not been performed to make these conclusions. Therefore, our hypothesis was to determine the temperature in which blood plasma protein degradation occurs after 2 hours of heat exposure. As a result, blood plasma proteins were exposed to heat in the 37-50 °C range for 2 hours. Plasma protein samples were loaded onto an 8-12% gradient gel for SDS-PAGE and low molecular weight plasma protein degradation was detected with graded heat exposure. Protein degradation was first detected between 43-45 °C of heat exposure. This study supports the practice of monitoring the heat exchanger between 40-42 °C to prevent denaturation of plasma proteins.

Reliability of different body temperature measurement sites during aortic surgery

OBJECTIVE

We retrospectively performed a comparative analysis of temperature measurement sites during surgical repair of the thoracic aorta.

METHODS

Between January 2004 and May 2006, 22 patients (mean age: 63 ± 12 years) underwent operations on the thoracic aorta with arterial cannulation of the aortic arch concavity and selective antegrade cerebral perfusion (ACP) during deep hypothermic circulatory arrest (HCA). Indications for surgical intervention were acute type A dissection in 14 (64%) patients, degenerative aneurysm in 6 (27%), aortic infiltration of thymic carcinoma in 1 (4.5%) and intra-aortic stent refixation in 1 (4.5%). Rectal, tympanic and bladder temperatures were evaluated to identify the best reference to arterial blood temperature during HCA and ACP.

RESULTS

There were no operative deaths and the 30-day mortality rate was 13% (three patients). Permanent neurological deficits were not observed and transient changes occurred in two patients (9%). During re-warming, there was strong correlation between tympanic and arterial blood temperatures (r = 0.9541, p<0.001), in contrast to the rectal and bladder temperature (r = 0.7654, p = n.s; r = 0.7939, p = n.s., respectively).

CONCLUSION

We conclude that tympanic temperature measurements correlate with arterial blood temperature monitoring during aortic surgery with HCA and ACP and, therefore, should replace bladder and rectal measurements.

Extracorporeal membrane oxygenation and cerebral blood flow velocity in children

OBJECTIVE

To determine how extracorporeal membrane oxygenation affects cerebral blood flow velocity and to determine whether specific changes in cerebral blood flow velocity may be associated with neurologic injury.

DESIGN

Prospective, observational study.

SETTING

PICU in a tertiary care academic center.

PATIENTS

Children (age less than or equal to 18 yr) requiring extracorporeal membrane oxygenation support.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Eighteen patients (age 3.8 ± 7.2 years; venovenous neck, n = 5; venoarterial neck, n = 8; venoarterial chest, n = 5) requiring extracorporeal membrane oxygenation underwent daily transcranial Doppler ultrasound measurements of cerebral blood flow velocity in bilateral middle cerebral arteries. Cerebral blood flow velocity measurements were recorded as a percentage of age and gender normal value. On extracorporeal membrane oxygenation, cerebral blood flow velocities in patients not suffering clinically evident neurologic injury were decreased with systolic flow velocity (Vs) 54% ± 3% predicted and mean flow velocity (Vm) 52% ± 4% predicted. After decannulation, Vs and Vm were higher than while on extracorporeal membrane oxygenation at 73% ± 3% predicted (p = 0.0007 vs. value on extracorporeal membrane oxygenation) and 64% ± 4% predicted (p = 0.01 vs. value on extracorporeal membrane oxygenation).Patients who developed clinically evident cerebral hemorrhage had higher Vs, diastolic flow velocity (Vd), and Vm compared with those who did not: 123% ± 8% predicted, 130% ± 18% predicted, 127% ± 9% predicted (p < compared to values in children not suffering neurological injury). Supranormal flow velocities were noted 2-6 days before clinical recognition of cerebral hemorrhage in all four patients. There were no significant differences in mean arterial blood pressure, circuit flow, or hematocrit between the children who suffered cerebral hemorrhage and those who did not. Partial pressure of carbon dioxide was lower in the group of patients who experienced cerebral hemorrhage than in those who did not (38 ± 2 vs. 44 ± 1 mm Hg, p = 0.03).

CONCLUSION

In children who did not suffer clinically apparent neurologic injury, cerebral blood flow velocities were lower than normal while on extracorporeal membrane oxygenation support and increased after decannulation. However, children who developed cerebral hemorrhage had higher than normal cerebral blood flow velocities noted for days prior to clinical recognition of bleeding. Cerebral blood flow velocity measurement may represent a portable, noninvasive way to predict cerebral complications of extracorporeal membrane oxygenation and deserves further study.

Mild hyperthermia worsens the neuropathological damage associated with mild traumatic brain injury in rats

The effects of slight variations in brain temperature on the pathophysiological consequences of acute brain injury have been extensively described in models of moderate and severe traumatic brain injury (TBI). In contrast, limited information is available regarding the potential consequences of temperature elevations on outcome following mild TBI (mTBI) or concussions. One potential confounding variable with mTBI is the presence of elevated body temperature that occurs in the civilian or military populations due to hot environments combined with exercise or other forms of physical exertion. We therefore determined the histopathological effects of pre- and post-traumatic hyperthermia (39°C) on mTBI. Adult male Sprague-Dawley rats were divided into 3 groups: pre/post-traumatic hyperthermia, post-traumatic hyperthermia alone for 2 h, and normothermia (37°C). The pre/post-hyperthermia group was treated with hyperthermia starting 15 min before mild parasagittal fluid-percussion brain injury (1.4-1.6 atm), with the temperature elevation extending for 2 h after trauma. At 72 h after mTBI, the rats were perfusion-fixed for quantitative histopathological evaluation. Contusion areas and volumes were significantly larger in the pre/post-hyperthermia treatment group compared to the post-hyperthermia and normothermic groups. In addition, pre/post-traumatic hyperthermia caused the most severe loss of NeuN-positive cells in the dentate hilus compared to normothermia. These neuropathological results demonstrate that relatively mild elevations in temperature associated with peri-traumatic events may affect the long-term functional consequences of mTBI. Because individuals exhibiting mildly elevated core temperatures may be predisposed to aggravated brain damage after mTBI or concussion, precautions should be introduced to target this important physiological variable.

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.

Hyperthermia Exacerbates Ischaemic Brain Injury

Hyperthermia frequently occurs in stroke patients. Hyperthermia negatively correlates with clinical outcome and adversely effects treatment regiments otherwise successful under normothermic conditions. Preclinical studies also demonstrate that hyperthermia converts salvageable penumbra to ischaemic infarct. The present article reviews the knowledge accumulated from both clinical and preclinical studies about hyperthermia and ischaemic brain injury, examines current treatment strategies and discusses future research directions.

Hyperthermia and fever control in brain injury

Fever in the neurocritical care setting is common and has a negative impact on outcome of all disease types. Meta-analyses have demonstrated that fever at onset and in the acute setting after ischemic brain injury, intracerebral hemorrhage, and cardiac arrest has a negative impact on morbidity and mortality. Data support that the impact of fever is sustained for longer durations after subarachnoid hemorrhage and traumatic brain injury. Recent advances have made eliminating fever and maintaining normothermia feasible. However, there are no prospective randomized trials demonstrating the benefit of fever control in these patient populations, and important questions regarding indications and timing remain. The purpose of this review is to analyze the data surrounding the impact of fever across a range of neurologic injuries to better understand the optimal timing and duration of fever control. Prospective randomized trials are needed to determine whether the beneficial impact of secondary injury prevention is outweighed by the potential risks of prolonged fever control.

Cooling therapy for acute stroke

BACKGROUND

Increased body temperatures are common in patients with acute stroke and are associated with poor outcome. In animal models of focal cerebral ischaemia, temperature-lowering therapy reduces infarct volume. In patients with acute stroke, lowering temperature may therefore improve outcome. This is an update of a Cochrane review first published in 1999.

OBJECTIVES

To assess the effects of pharmacological and physical strategies to reduce body or brain temperature in patients with acute stroke.

SEARCH STRATEGY

We searched the Cochrane Stroke Group trials register (last searched December 2007). In addition, we searched MEDLINE and EMBASE (January 1998 to December 2007). We scanned references and contacted authors of included trials. For the previous version of this review, the authors contacted pharmaceutical companies and manufactures of cooling equipment in this field.

SELECTION CRITERIA

We considered all completed randomised or non-randomised controlled clinical trials, published or unpublished, where pharmacological or physical strategies or both to reduce temperature were applied in patients with acute ischaemic stroke or intracerebral haemorrhage. Outcome measures were death or dependency (modified Rankin Scale score >/= 3) at the end of follow up, and adverse effects.

DATA COLLECTION AND ANALYSIS

Two review authors independently applied the inclusion criteria, assessed trial quality, and extracted and cross-checked the data.

MAIN RESULTS

We included five pharmacological temperature reduction trials and three physical cooling trials involving a total of 423 participants. We found no statistically significant effect of pharmacological or physical temperature-lowering therapy in reducing the risk of death or dependency (odds ratio (OR) 0.9, 95% confidence interval (CI) 0.6 to 1.4) or death (OR 0.9, 95% CI 0.5 to 1.5). Both interventions were associated with a non-significant increase in the occurrence of infections.

AUTHORS' CONCLUSIONS

There is currently no evidence from randomised trials to support routine use of physical or pharmacological strategies to reduce temperature in patients with acute stroke. Large randomised clinical trials are needed to study the effect of such strategies.

Interleukin-1beta: a bridge between inflammation and excitotoxicity?

Interleukin-1 (IL-1) is a proinflammatory cytokine released by many cell types that acts in both an autocrine and/or paracrine fashion. While IL-1 is best described as an important mediator of the peripheral immune response during infection and inflammation, increasing evidence implicates IL-1 signaling in the pathogenesis of several neurological disorders. The biochemical pathway(s) by which this cytokine contributes to brain injury remain(s) largely unidentified. Herein, we review the evidence that demonstrates the contribution of IL-1beta to the pathogenesis of both acute and chronic neurological disorders. Further, we highlight data that leads us to propose IL-1beta as the missing mechanistic link between a potential beneficial inflammatory response and detrimental glutamate excitotoxicity.

Augmentation of methamphetamine-induced toxicity in the rat striatum by unpredictable stress: contribution of enhanced hyperthermia

Stress is known to enhance the abuse of various drugs. Although the effects of chronic stress and the neurotoxicity of methamphetamine (METH) are influenced, in part, by hyperthermia, the role of hyperthermia in the hypothesized stress-induced enhancement of METH-induced dopamine (DA) and serotonin depletions and decreases in vesicular monoamine transporter 2 (VMAT-2) immunoreactivity is unknown. Rats were exposed to 10 days of unpredictable stress and then challenged with METH (7.5 mg/kg, i.p., once every 2 hx4 injections). There were no differences in the extracellular DA concentrations of stressed and non-stressed rats administered METH. Prior exposure to chronic unpredictable stress augmented the acute METH-induced hyperthermia, the decreases in VMAT-2 immunoreactivity, and the depletions of striatal DA and serotonin content. Prevention of enhanced hyperthermia through cooling of chronically stressed rats to levels exhibited by non-stressed but METH-exposed rats blocked the enhanced depletions. This study reports the novel finding that chronic stress enhances METH toxicity through enhanced hyperthermia and suggests that this effect may be mediated by early METH-induced decreases in VMAT-2 immunoreactivity.

Therapeutic hypothermia in acute ischemic stroke

Increased body temperatures are common in the acute phase of stroke. Experimental and clinical studies have suggested that increased body temperatures are related to poor outcome. In animal studies of focal cerebral ischemia, early hypothermia consistently reduced infarct volume. Based on these findings, several Phase II clinical trials have been performed to study physical methods to reduce body temperature in patients with acute stroke. The feasibility and safety of these methods have not yet been established with sufficient certainty. Pharmacological lowering of body temperature may be an attractive alternative approach. In guidelines for the treatment of acute stroke, antipyretics are generally recommended to reduce fever, although their effect on functional outcome is unknown. There is currently no evidence from randomized trials to support routine use of physical or pharmacological cooling in acute stroke. Large randomized clinical trials are needed to study the effect of both physical and medical cooling on functional outcome after stroke.

Cellular mechanisms of neuronal damage from hyperthermia

Hyperthermia can cause brain damage and also exacerbate the brain damage produced by stroke and amphetamines. The developing brain is especially sensitive to hyperthermia. The severity of, and mechanisms underlying, hyperthermia-induced neuronal death depend on both temperature and duration of exposure. Severe hyperthermia can produce necrotic neuronal death. For a window of less severe heat stresses, cultured neurons exhibit a delayed death with apoptotic characteristics including cytochrome c release and caspase activation. Little is known about mechanisms of hyperthermia-induced damage upstream of these late apoptotic effects. This chapter considers several possible upstream mechanisms, drawing on both in vivo and in vitro studies of the nervous system and other tissues. Hyperthermia-induced damage in some non-neuronal cells includes endoplasmic reticular stress due to denaturing of nascent polypeptide chains, as well as nuclear and cytoskeletal damage. Evidence is presented that hyperthermia produces mitochondrial damage, including depolarization, in cultured mammalian neurons.

Hyperthermia and central nervous system injury

Fever is a common occurrence in patients following brain and spinal cord injury (SCI). In intensive care units, large numbers of patients demonstrate febrile periods during the first several days after injury. Over the last several years, experimental studies have reported the detrimental effects of fever in various models of central nervous system (CNS) injury. Small elevations in temperature during or following an insult have been shown to worsen histopathological and behavioral outcome. Thus, the control of fever after brain or SCI may improve outcome if more effective strategies for monitoring and treating hyperthermia were developed. Because of the clinical importance of fever as a potential secondary injury mechanism, mechanisms underlying the detrimental effects of mild hyperthermia after injury have been evaluated. To this end, studies have shown that mild hyperthermia (>37 degrees C) can aggravate multiple pathomechanisms, including excitotoxicity, free radical generation, inflammation, apoptosis, and genetic responses to injury. Recent data indicate that gender differences also play a role in the consequences of secondary hyperthermia in animal models of brain injury. The observation that dissociations between brain and body temperature often occur in head-injured patients has again emphasized the importance of controlling temperature fluctuations after injury. Thus, increased emphasis on the ability to monitor CNS temperature and prevent periods of fever has gained increased attention in the clinical literature. Cooling blankets, body vests, and endovascular catheters have been shown to prevent elevations in body temperature in some patient populations. This chapter will summarize evidence regarding hyperthermia and CNS injury.

Temperature During Cardiopulmonary Bypass: The Discrepancies Between Monitored Sites

We performed studies in patients to determine whether temperature recordings from sites commonly monitored during hypothermic cardiopulmonary bypass adequately reflect cerebral temperature. In Study I (n = 12), temperatures monitored in the jugular bulb (JB) were compared with those recorded in the nasopharynx, esophagus, bladder, and rectum. In Study II (n = 30), temperature was also monitored in the arterial outlet of the membrane oxygenator. A calibrated recorder continuously and simultaneously recorded all temperatures. Study I found large temperature discrepancies between the JB and all other body sites during cooling and rewarming. There was considerable interindividual variability in the degree of discrepancy between the JB and other sites. Study II produced similar results but also showed that JB temperature reached equilibration with the temperature of blood entering the patient via the arterial outlet of the membrane oxygenator after cooling for 3.3 +/- 1.3 min and after rewarming for 16.5 +/- 5.5 min. Analysis of variance revealed that this arterial outlet site had the smallest average discrepancy of all temperature sites relative to the JB site (P < 0.001). In summary, temperatures measured in body sites over-estimated JB temperature during cooling and under-estimated it during rewarming, whereas arterial outlet blood temperature provided a good approximation.

Neuroprotection in cardiac surgery

This article reviews past and present neuroprotective efforts and outlines a framework for the future development of techniques for neuroprotection during cardiac surgery.

Animal models of focal and global cerebral ischemia

The use of appropriate animal models is essential to predict the value and effect of therapeutic approaches in human subjects. Focal (stroke) and global (cardiac arrest) cerebral ischemia represents diseases that are common in the human population. Stroke and cardiac arrest, which are major causes of death and disability, affect millions of individuals around the world and are responsible for the leading health care costs of all diseases. Understanding the mechanisms of injury and neuroprotection in these diseases is critical if we are ever to learn new target sites to treat ischemia. There are many animal models available to investigate injury mechanisms and neuroprotective strategies. This review summarizes many (but not all) small and large animal models of focal and global cerebral ischemia and discusses their advantages and disadvantages.

Effects of hyperthermia on hypoxic-ischemic brain damage in the immature rat: its influence on caspase-3-like protease

OBJECTIVE

Recent clinical studies suggested that intrapartum maternal fever is a strong independent risk factor for neonatal encephalopathy. With use of a well-studied rat model of neonatal hypoxic-ischemic encepalopathy, this study investigated the hypothesis that intraischemic hyperthermia accelerates and worsens brain injury in immature animals and examined whether apoptotic cell death machinery is involved in the underlying mechanisms.

STUDY DESIGN

Seven-day-old rats underwent a combination of left common carotid artery ligation and exposure to 8% oxygen for 15 minutes (n = 32 rats). During the 15-minute hypoxic insult, body temperature was elevated to 40 degrees C in 16 animals (hyperthermic hypoxic insult group), and was maintained at 37 degrees C in 16 animals (normothermic hypoxic insult group). Then both groups were placed in the same chamber in a water bath at 37 degrees C for 24 hours and finally returned to the mothers. Caspase-3-like activity was assessed 36 hours after the hypoxic-ischemic insult. One week later, microtubule-associated protein-2 immunostaining was used to examine neuronal damage.

RESULTS

Intraischemic hyperthermia was shown to activate the caspase-3 activity 36 hours after hypoxia-ischemia while caspase-3 was activated insignificantly in the normothermic hypoxic insult group at that time. The hyperthermic hypoxic insult group also showed a reduced microtubule-associated protein-2-positive area 7 days after hypoxia-ischemia compared with that in the normothermia group.

CONCLUSION

Hyperthermia during hypoxia-ischemia makes the immature brain inordinately susceptible to hypoxic-ischemic insult and causes brain injury, even if hypoxic-ischemic insult is so mild that it causes no or little injury by itself. This effect may be mediated by the escalation of the apoptotic cell death pathway in the immature animal.

Microalbuminuria and hyperthermia independently predict long-term mortality in acute ischemic stroke patients

OBJECTIVES

To investigate the association between microalbuminuria (MA) and hyperthermia in acute ischemic stroke and to evaluate their significance as the predictors of long-term mortality after stroke.

MATERIAL AND METHODS

We assessed neurologic deficit, urinary albumin excretion and body temperature in 60 patients admitted within 24 h after the onset of their first ischemic stroke. Outcome was assessed by 90-day and 1-year mortality.

RESULTS

MA was found in 46.7% of patients. Hyperthermia was found in 18.3% patients on Day 1 and in 25% patients on Day 2. The correlation between albuminuria on Day 2 and the body temperature on Days 1 and 2 was found (r = 0.45, and r = 0.30, respectively; both P < 0.05). The mortality was significantly higher in the group of patients with both MA and hyperthermia on Day 2 (73% vs 10% after 90 days; P < 0.0001 and 73% vs 18% after 1 year, P < 0.005). In the logistic regression analysis, albuminuria (P = 0.017), hyperthermia on Day 1 (P = 0.028) and neurologic deficit on admission (P = 0.044) independently predicted 1-year mortality after ischemic stroke.

CONCLUSION

Daily urinary albumin excretion correlates with the body temperature in acute stroke patients, but the predictive power of both these variables is independent of that association.

Hyperthermia in the forty-eight hours after cardiopulmonary bypass

The adverse consequences of perioperative hypothermia have been emphasized. However, postoperative hyperthermia may be equally hazardous after cardiac surgery, owing to increased oxygen demand and potential exacerbation of neurologic injury. To determine the incidence of hyperthermia (bladder temperature [BT] > or = 38.5 degrees C) after cardiopulmonary bypass, we recorded hourly postoperative BT (n = 305), nasopharyngeal (n = 40), and jugular venous bulb (n = 20) temperatures for up to 48 h after admission to the intensive care unit (ICU). At least 38% of the patients developed postoperative hyperthermia, although all patients did not remain in the ICU for 48 h. The incidence of hyperthermia peaked with a bimodal distribution at 9.1 +/- 4.0 h (26%) and at 27.7 +/- 6.3 h (26%). Of these, 14% of the patients were hyperthermic at both times. For the first 5 postoperative h, jugular venous bulb temperature was 0.4 degrees C higher than the BT (P < 0.05). There was no difference between BT and nasopharyngeal temperature. Higher temperature on ICU entry and age <60 yr were independently associated with hyperthermia (P < 0.05). In summary, postoperative hyperthermia is common, with both early and late occurrences during the first 48 h after cardiac surgery with cardiopulmonary bypass.

IMPLICATIONS

Postoperative hyperthermia is common in cardiac surgery patients, with a bimodal distribution during the first 48 h. Jugular venous bulb temperature is slightly higher than bladder temperature for several hours. Postoperative cerebral hyperthermia may contribute to the severity of cerebral injury after cardiopulmonary bypass.

Hyperthermia in the neurosurgical intensive care unit

OBJECTIVE

In patients with traumatic or ischemic brain injury, hyperthermia is thought to worsen the neurological injury. We studied fever in the neurosurgical intensive care unit (ICU) population using a definition common to surgical practice (rectal temperature >38.5 degrees C). We sought to determine fever incidence, fever duration, and peak temperature and to quantify the use of antipyretic therapy. We also attempted to determine the patient subgroups that are at highest risk for development of fever.

METHODS

In a retrospective chart review of a 6-month period, all febrile episodes that occurred in a consecutive series of neurosurgical ICU patients in a university hospital setting were studied. A febrile episode was defined as a rectal temperature of at least 38.5 degrees C; an episode lasted until the temperature fell below this threshold.

RESULTS

The 428 patients studied had 946 febrile episodes. Fever occurred in 47% of patients, with a mean of 4.7 febrile episodes in each febrile patient. Fevers occurred in more than 50% of patients who were admitted to the ICU for subarachnoid hemorrhage, a central nervous system infection, seizure control, or hemorrhagic stroke, but they occurred in only 27% of patients admitted for spinal disorders. Fevers occurred in 15% of the patients who stayed in the ICU less than 24 hours, but in 93% of those who remained longer than 14 days. Despite the use of antipyretic therapy for 86% of the febrile episodes, 57% lasted longer than 4 hours and 5% lasted longer than 12 hours.

CONCLUSION

Fever is common in critically ill neurosurgical patients, especially those with a prolonged length of stay in the ICU or a cranial disease. If hyperthermia worsens the functional outcome after a primary ischemic or traumatic injury, as has been suggested by several studies of stroke patients, treatment of fever is a clinical issue that requires better management.

Quantitative evaluation of extracellular glutamate concentration in postischemic glutamate re-uptake, dependent on brain temperature, in the rat following severe global brain ischemia

Changes in brain temperature are known to modulate the marked neuronal damage caused by an approximately 10-min intra-ischemic period. Numerous studies have suggested that the extracellular glutamate concentration ([Glu](e)) in the intra-ischemic period and the initial postischemia period is strongly implicated in such damage. In this study, the effects of intra-ischemic brain temperature (32, 37, 39 degrees C) on [Glu](e) were investigated utilizing a dialysis electrode combined with ferrocene bovine serum albumin (BSA), which allows oxygen-independent real-time measurement of [Glu](e). This system allowed separate quantitative evaluation of intra-ischemic biphasic glutamate release from the neurotransmitter and metabolic pools, and of postischemic glutamate re-uptake in ischemia-reperfusion models. The biphasic [Glu](e) elevation in the intra-ischemic period did not differ markedly among intra-ischemic brain temperatures ranging from 32 to 39 degrees C. Intra-ischemic normothermia (37 degrees C) and mild hyperthermia (39 degrees C) markedly inhibited [Glu](e) re-uptake during the postischemic period, although the intra-ischemic [Glu](e) elevation did not differ from that during intra-ischemic hypothermia (32 degrees C). It was assumed that normothermia or mild hyperthermia in the intra-ischemic period influences intracellular functional abnormalities other than the intra-ischemic [Glu](e) elevation, thereby inhibiting glutamate re-uptake after reperfusion rather than directly modulating intra-ischemic [Glu](e) dynamics.

Moderate hypothermia and brain temperature in patients with severe middle cerebral artery infarction

Elevated temperature is known to facilitate neuronal injury after ischemia. After head injury a gradient between temperature and body temperature of up to 3 degrees C higher in the brain has been reported. Hypothermia may limit some of the deleterious metabolic consequences of such increased temperature. In 20 patients who had suffered severe ischemic stroke in the middle cerebral artery (MCA) territory, intracerebral temperature combined with ICP monitoring was recorded using two different thermocouples, with epidural, and parenchymatous measurements. Mild hypothermia was induced using cooling blankets. Patients were kept at 33 degrees C core temperature for 48 to 72 hours. In all patients brain temperature exceeded body-core temperature by at least up to 1 degree C (range 1.0-2.1 degrees C). Systemic cooling was effective and sustained hypothermic (33-34 degrees C) brain temperatures. With mild hypothermia critically elevated ICP values could be controlled. 12 patients survived the hemispheric stroke with a mean Barthel index of 70. Severe side effects of hypothermia were not detected. After MCA stroke, human intracerebral temperature is higher than central body-core temperature. Mild hypothermia in the treatment of severe cerebral ischemia using cooling blankets is safe and does not lead to severe side effects. Mild hypothermia can help to control critically elevated ICP values in severe space-occupying stroke and may improve clinical outcome in these patients.

Mild hypothermia--a revived countermeasure against ischemic neuronal damages

Although hypothermia as a means of cerebral protection against and resuscitation from ischemic damage has a history of approximately six decades, extensive studies, both in basic and clinical fields, on the mechanisms, effects and methods of mild hypothermia at temperatures no less than 31 degrees C have started only in the last decade. In experiments on rodents, hypothermia in the postischemic period that is introduced up to several hours after reperfusion and is maintained for one day followed by a slow rewarming, significantly protects hippocampal neurons against damage. The mode of action of hypothermia is apparently non-specific and multi-focal in widely progressing cascade reactions in ischemic cells; namely, suppressing: (1) glutamate surge followed by; (2) intraneuronal calcium mobilization; (3) sustained activation of glutamate receptors; (4) dysfunction of blood brain barrier; (5) proliferation of microglial cells; and (6) production of superoxide anions and nitric oxide. In addition, mild hypothermia modulates processes in ischemic condition at the level of cell nucleus, such as the binding of transcription factor AP-1 to DNA, and ameliorates the depression of protein synthesis. This non-specific and widely affecting manner might explain why hypothermia is superior to any medicine developed. Recent clinical trials of mild hypothermia in various individual institutions have revealed significantly beneficial outcomes in some cases, along with an accumulation of practical knowledge of techniques and treatments. Large scale randomized studies involving multiple institutions as well as exchange of informations and ideas are needed for further development of hypothermia treatment.

Indomethacin in the management of elevated intracranial pressure: a review

Elevated intracranial pressure occurs frequently in patients with severe head injury. A number of studies in recent years suggest that indomethacin may be useful in the management of elevated intracranial pressure. Indomethacin acts primarily by reducing cerebral blood flow and decreasing cerebral edema following head injury. This review summarizes the basic and clinical studies of the effects of indomethacin on cerebral blood flow, brain edema, and intracranial pressure. The pharmacology of indomethacin, and issues for future investigation in the use of indomethacin in severe head injury, are discussed.

Perioperative Stroke, Encephalopathy, and Central Nervous System Dysfunction

The leading cause of mortality in adult populations throughout the world is atherosclerosis, which results in cardiovascular and cerebrovascular complications and consumes substantive health care resources. The impact of atherosclerosis on patients undergoing surgery is also considerable, given the multiple stresses occurring during, and especially following, the surgical procedures, thereby precipitating vascular morbidity. Perioperative cerebrovascular morbidity and mortality occur in approximately 10% of the 600,000 patients who undergo cardiac surgery annually, consuming approximately $13 billion, which is expended on in-hospital, intensive care unit (ICU), and long-term specialized care for these neurological complications of stroke, encephalopathy, and cognitive dysfunction. Furthermore, risk of these outcomes will continue to increase as the surgical population ages. Principal among the etiologies of focal stroke and encephalopathy appear to be perioperative hypotension and precipitation of macroemboli and microemboli. As a result, new detection techniques for these events have been instituted, including (1) continuous hemodynamic monitoring, for detection of hypotensive episodes; (2) transesophageal echocardiography, for detection of aortic atherosclerosis, a potential source for emboli; and (3) transcranial Doppler sonography, for detection of cerebral emboli, as well as determination of cerebral blood flow. Recent large-scale multicenter studies have identified risk factors and indices for perioperative central nervous system (CNS) morbidity. Regarding therapy, a number of pharmacological approaches are currently under consideration; principal among these approaches are agents that can modulate the excitotoxic response, including glutamate receptor antagonists (NMDA, AMPA, metabotrophic), calcium channel blockers, free radical scavengers, and agents that modify the inflammatory white cell response. Although a number of laboratory, animal, and smaller clinical trials have been conducted, only one large-scale multicenter program to date has been conducted to assess the efficacy of adenosine modulation. These data, collected in more than 4,000 patients undergoing cardiac surgery, suggest that in addition to mitigation of myocardial injury, stroke also may be modulated by enhancing adenosine concentration in the area of cerebral ischemia. However, these preliminary findings must be validated in appropriately powered clinical trials. Finally, postoperative stroke and encephalopathy consume substantive resources, resulting in prolonged length-of-stay (17 days in-hospital 10 days for patients suffering Q-wavc infarction, vs 7 days for patients having no adverse outcome) and prolonged length-of-stay in the ICU following surgery (5 vs 3 vs 2 days, respectively). Hospital costs increase by approximately 3- to 4-fold in patients who suffer CNS outcomes following surgery. In conclusion, perioperative CNS morbidity and mortality is a critical problem that affects a substantial portion of the surgical population and consumes considerable health care resources. Over the next several years, attention must be focused on this important problem, and clinical and research resources should be redirected toward the solution of perioperative CNS morbidity.

Brain cooling during transient focal ischemia provides complete neuroprotection

A review of the effects of reducing brain temperature on ischemic brain injury is presented together with original data describing the systematic evaluation of the effects of brain cooling on brain injury produced by transient focal ischemia. Male spontaneously hypertensive rate were subjected to transient middle cerebral artery occlusion (TMCAO; 80, 120 or 160 min) followed by 24 h of reperfusion. During TMCAO, the exposed skull was bathed with isotonic saline at various temperatures to control skull and deeper brain temperatures. Rectal temperature was always constant at 37 degrees C. Initial studies indicated that skull temperature was decreased significantly (i.e. to 32-33 degrees C) just as a consequence of surgical exposure of the artery. Subsequent studies indicated that maintaining skull temperature at 37 degrees C compared to 32 degrees C significantly (p < 0.05) increased the infarct size following 120 or 160 min TMCAO. In other studies, 80 min TMCAO was held constant, but deeper brain temperature could be varied by regulating skull temperature at different levels. At 36-38 degrees C brain temperature, infarct volumes of 102 +/- 10 to 91 +/- 9 mm3 occurred following TMCAO. However, at a brain temperature of 34 degrees C, a significantly (p < 0.05) reduced infarct volume of 37 +/- 10 mm3 was observed. Absolutely no brain infarction was observed if the brain was cooled to 29 degrees C during TMCAO. Middle cerebral artery exposure and maintaining brain temperature at 37 degrees C without artery occlusion did not produce any cerebral injury. These data indicated the importance of controlling brain temperature in cerebral ischemia and that reducing brain temperature during ischemia produces a brain temperature-related decrease in focal ischemic damage. Brain cooling of 3 degrees C and 8 degrees C can provide dramatic and complete, respectively, neuroprotection from transient focal ischemia. Multiple mechanisms for reduced brain temperature-induced neuroprotection have been identified and include reduced metabolic rate and energy depletion, decreased excitatory transmitter release, reduced alterations in ion flux, and reduced vascular permeability, edema, and blood-brain barrier disruption. Cerebral hypothermia is clearly the most potent therapeutic approach to reducing experimental ischemic brain injury identified to date, and this is emphasized by the present data which demonstrate complete neuroprotection in transient focal stroke. Certainly all available information warrants the evaluation of brain cooling for potential implementation in the treatment of human stroke.

The effect of temperature management during cardiopulmonary bypass on neurologic and neuropsychologic outcomes in patients undergoing coronary revascularization

Several studies suggest that normothermic ("warm") bypass techniques may improve myocardial outcomes for patients undergoing cardiac operations. Normothermic temperatures during cardiopulmonary bypass may, however, decrease the brain's tolerance to the ischemic insults that accompany all cardiac procedures. To assess the effect of bypass temperature management strategy on central nervous system outcomes in patients undergoing coronary revascularization, 138 patients were randomly assigned to two treatment groups: (1) hypothermia (n = 70), patients cooled to a temperature less than 28 degrees C during cardiopulmonary bypass, or (2) normothermia (n = 68), patients actively warmed to a temperature of at least 35 degrees C. Patients underwent detailed neurologic examination before the operation, on postoperative days 1 to 3 and 7 to 10, and at approximately 1 month after operation. In addition, a battery of five neuropsychologic tests was administered before operation, on postoperative days 7 to 10, and at the 4- to 6-week follow-up visit. Patients in the normothermic treatment group were older (65 +/- 10 vs 61 +/- 11 years in the hypothermic group), had statistically less likelihood of preexisting cerebrovascular disease, and had higher bypass blood glucose values (276 +/- 100 mg/% vs. 152 +/- 66 mg/% in the hypothermic group). All other patient characteristics and intraoperative variables were similar in the two treatment groups. Seven of 68 patients in the normothermic group were found to have a central neurologic deficit, compared with none of the patients cooled to 28 degrees C (p = 0.006). Performance on at least one neuropsychologic test deteriorated in the immediate postoperative period in more than one half of all patients in both treatment groups but returned to preoperative levels approximately 1 month after the operation in most (85%). This pattern was not related to bypass temperature management strategy. We conclude that active warming during cardiopulmonary bypass to maintain systemic temperatures > or = 35 degrees C increases the risk of perioperative neurologic deficit in patients undergoing elective coronary revascularization.

Normothermic versus hypothermic cardiopulmonary bypass: central nervous system outcomes

The recent advent of "warm heart" surgery has resulted in reexamination of the neuroprotective effects of hypothermia in the setting of cardiopulmonary bypass (CPB). Hypothermia has been shown to confer significant protection in the setting of transient, but not permanent, ischemia. The mechanism of this neuroprotection is unclear at this time. Reduction in cerebral metabolic rate is believed to be less important compared with the effect of hypothermia on the release of excitatory neurotransmitters, catecholamines, or other mediators of cellular injury. It is for this reason that mild hypothermia (33-35 degrees C) is believed to confer significant neuroprotection. Two large randomized trials of warm versus cold heart surgery have been reported. Neither study found a difference in terms of neuropsychologic dysfunction. However, one study identified a threefold increase in strokes in the "warm" patients. The reasons for this difference are not clear; however, there were various differences in technique and patient population that may have been important. There are other reports of large series of patients undergoing normothermic bypass, with no increase in stroke rate over what is reported elsewhere in the literature. To date, the evidence would suggest that neuropsychologic function is not affected by CPB temperature, suggesting that the transient ischemia is not an important mechanism in this injury. Stroke after CPB is usually the result of permanent ischemia, and hypothermia's effect in this setting is minimal. It would seem unlikely that hypothermia offers anything more than modest benefits in the clinical situation where there is no circulatory arrest.

Intracerebral temperature monitoring in severely head injured patients

In a series of 6 severely head injured patients, intraventricular as well as rectal, bladder and jugular vein temperature is recorded. The relationship between these temperatures in different conditions is evaluated. Intracerebral temperature is 0.5 +/- 0.2 degrees C (mean +/- SD) higher than bladder temperature except in conditions such as brain death. It is concluded that rectal temperature is not representative and therefore not a good alternative to the measurement of brain temperature. More data on human intracerebral temperature are mandatory as well as prospective studies correlating intracerebral temperature with final outcome in head injury.