The significance of altered temperature after traumatic brain injury: an analysis of investigations in experimental and human studies: part 2

Proinflammatory and amyloidogenic S100A9 induced by traumatic brain injury in mouse model

Traumatic brain injury (TBI) represents a significant risk factor for development of neurodegenerative diseases such as Alzheimer's and Parkinson's. The S100A9-driven amyloid-neuroinflammatory cascade occurring during primary and secondary TBI events can serve as a mechanistic link between TBI and Alzheimer's as demonstrated recently in the human brain tissues. Here by using immunohistochemistry in the controlled cortical impact TBI mouse model we have found pro-inflammatory S100A9 in the brain tissues of all mice on the first and third post-TBI days, while 70% of mice did not show any S100A9 presence on seventh post-TBI day similar to controls. This indicates that defensive mechanisms effectively cleared S100A9 in these mouse brain tissues during post-TBI recovery. By using sequential immunohistochemistry we have shown that S100A9 was produced by both neuronal and microglial cells. However, Aβ peptide deposits characteristic for Alzheimer's disease were not detected in any post-TBI animals. On the first and third post-TBI days S100A9 was found to aggregate intracellularly into amyloid oligomers, similar to what was previously observed in human TBI tissues. Complementary, by using Rayleigh scatting, intrinsic fluorescence and atomic force microscopy we demonstrated that in vitro S100A9 self-assembles into amyloid oligomers within minutes. Its amyloid aggregation is highly dependent on changes of environmental conditions such as variation of calcium levels, pH, temperature and reduction/oxidation, which might be relevant to perturbation of cellular and tissues homeostasis under TBI. Present results demonstrate that S100A9 induction mechanisms in TBI are similar in mice and humans, emphasizing that S100A9 is an important marker of brain injury and therefore can be a potential therapeutic target.

S100A9-Driven Amyloid-Neuroinflammatory Cascade in Traumatic Brain Injury as a Precursor State for Alzheimer's Disease

Pro-inflammatory and amyloidogenic S100A9 protein is an important contributor to Alzheimer's disease (AD) pathology. Traumatic brain injury (TBI) is viewed as a precursor state for AD. Here we have shown that S100A9-driven amyloid-neuroinflammatory cascade was initiated in TBI and may serve as a mechanistic link between TBI and AD. By analyzing the TBI and AD human brain tissues, we demonstrated that in post-TBI tissues S100A9, produced by neurons and microglia, becomes drastically abundant compared to Aβ and contributes to both precursor-plaque formation and intracellular amyloid oligomerization. Conditions implicated in TBI, such as elevated S100A9 concentration, acidification and fever, provide strong positive feedback for S100A9 nucleation-dependent amyloid formation and delay in its proteinase clearance. Consequently, both intracellular and extracellular S100A9 oligomerization correlated with TBI secondary neuronal loss. Common morphology of TBI and AD plaques indicated their similar initiation around multiple aggregation centers. Importantly, in AD and TBI we found S100A9 plaques without Aβ. S100A9 and Aβ plaque pathology was significantly advanced in AD cases with TBI history at earlier age, signifying TBI as a risk factor. These new findings highlight the detrimental consequences of prolonged post-TBI neuroinflammation, which can sustain S100A9-driven amyloid-neurodegenerative cascade as a specific mechanism leading to AD development.

Endovascular Cooling Method for Hypothermia in Injured Swine

We evaluated an endovascular cooling method to modulate core temperature in trauma swine models with and without fluid support. Anesthetized swine (N = 80) were uninjured (SHAM) or injured through a bone fracture plus soft tissue injury or an uncontrolled hemorrhage and then subdivided to target body temperatures of 38°C (normothermia) or 33°C (hypothermia) by using a Thermogard endovascular cooling device (Zoll Medical). Temperature regulation began simultaneously at onset of injury (T0). Body temperatures were recorded from a rectal probe (Rec Temp) and from a central pulmonary artery catheter (PA Temp). At T15, swine received 500 mL IV Hextend over 30 minutes or no treatment (NONE) with continued monitoring until 3 hours from injury. Hypothermia was attained in 105 ± 39 minutes, at a cooling rate of -0.061°C ± 0.007°C/min for NONE injury groups. Postinjury Hextend administration resulted in faster cooling (-0.080°C ± 0.006°C/min); target temperature was reached in 83 ± 11 minutes (p < 0.05). During active cooling, body temperature measured by the PA Temp was significantly cooler than the Rec Temp due to the probe's closer proximity to the blood-cooling catheter balloons (p < 0.05). This difference was smaller in SHAM and fluid-supported injury groups (1.1°C ± 0.4°C) versus injured NONE groups (2.1°C ± 0.3°C). Target temperatures were correctly maintained thereafter in all groups. In normothermia groups, there was a small initial transient overshoot to maintain 38°C. Despite the noticeable difference between PA Temp and Rec Temp until target temperature was attained, this endovascular method can safely induce moderate hypothermia in anesthetized swine. However, likely due to their compromised hemodynamic state, cooling in hypovolemic and/or injured patients will be different from those without injury or those that also received fluids.

Lateral (Parasagittal) Fluid Percussion Model of Traumatic Brain Injury

Fluid percussion was first conceptualized in the 1940s and has evolved into one of the leading laboratory methods for studying experimental traumatic brain injury (TBI). Over the decades, fluid percussion has been used in numerous species and today is predominantly applied to the rat. The fluid percussion technique rapidly injects a small volume of fluid, such as isotonic saline, through a circular craniotomy onto the intact dura overlying the brain cortex. In brief, the methods involve surgical production of a circular craniotomy, attachment of a fluid-filled conduit between the dura overlying the cortex and the outlet port of the fluid percussion device. A fluid pulse is then generated by the free-fall of a pendulum striking a piston on the fluid-filled cylinder of the device. The fluid enters the cranium, producing a compression and displacement of the brain parenchyma resulting in a sharp, high magnitude elevation of intracranial pressure that is propagated diffusely through the brain. This results in an immediate and transient period of traumatic unconsciousness as well as a combination of focal and diffuse damage to the brain, which is evident upon histological and behavioral analysis. Numerous studies have demonstrated that the rat fluid percussion model reproduces a wide range of pathological features associated with human TBI.

The Effect of Paracetamol on Core Body Temperature in Acute Traumatic Brain Injury: A Randomised, Controlled Clinical Trial

Background

Strategies to prevent pyrexia in patients with acute neurological injury may reduce secondary neuronal damage. The aim of this study was to determine the safety and efficacy of the routine administration of 6 grams/day of intravenous paracetamol in reducing body temperature following severe traumatic brain injury, compared to placebo.

Methods

A multicentre, randomised, blind, placebo-controlled clinical trial in adult patients with traumatic brain injury (TBI). Patients were randomised to receive an intravenous infusion of either 1g of paracetamol or 0.9% sodium chloride (saline) every 4 hours for 72 hours. The primary outcome was the mean difference in core temperature during the study intervention period.

Results

Forty-one patients were included in this study: 21 were allocated to paracetamol and 20 to saline. The median (interquartile range) number of doses of study drug was 18 (17–18) in the paracetamol group and 18 (16–18) in the saline group (P = 0.85). From randomisation until 4 hours after the last dose of study treatment, there were 2798 temperature measurements (median 73 [67–76] per patient). The mean ± standard deviation temperature was 37.4±0.5°C in the paracetamol group and 37.7±0.4°C in the saline group (absolute difference -0.3°C; 95% confidence interval -0.6 to 0.0; P = 0.09). There were no significant differences in the use of physical cooling, or episodes of hypotension or hepatic abnormalities, between the two groups.

Conclusion

The routine administration of 6g/day of intravenous paracetamol did not significantly reduce core body temperature in patients with TBI.

Trial Registration

Australian New Zealand Clinical Trials Registry ACTRN12609000444280

Early temperature and mortality in critically ill patients with acute neurological diseases: trauma and stroke differ from infection

BACKGROUND

Fever suppression may be beneficial for patients with traumatic brain injury (TBI) and stroke, but for patients with meningitis or encephalitis [central nervous system (CNS) infection], the febrile response may be advantageous.

OBJECTIVE

To evaluate the relationship between peak temperature in the first 24 h of intensive care unit (ICU) admission and all-cause hospital mortality for acute neurological diseases.

DESIGN, SETTING AND PARTICIPANTS

Retrospective cohort design from 2005 to 2013, including 934,159 admissions to 148 ICUs in Australia and New Zealand (ANZ) and 908,775 admissions to 236 ICUs in the UK.

RESULTS

There were 53,942 (5.8 %) patients in ANZ and 56,696 (6.2 %) patients in the UK with a diagnosis of TBI, stroke or CNS infection. For both the ANZ (P = 0.02) and UK (P < 0.0001) cohorts there was a significant interaction between early peak temperature and CNS infection, indicating that the nature of the relationship between in-hospital mortality and peak temperature differed between TBI/stroke and CNS infection. For patients with CNS infection, elevated peak temperature was not associated with an increased risk of death, relative to the risk at 37-37.4 °C (normothermia). For patients with stroke and TBI, peak temperature below 37 °C and above 39 °C was associated with an increased risk of death, compared to normothermia.

CONCLUSIONS

The relationship between peak temperature in the first 24 h after ICU admission and in-hospital mortality differs for TBI/stroke compared to CNS infection. For CNS infection, increased temperature is not associated with increased risk of death.

Targeted temperature management processes and outcomes after out-of-hospital cardiac arrest: an observational cohort study*

OBJECTIVES

Targeted temperature management has been shown to improve survival with good neurological outcome in patients after out-of-hospital cardiac arrest. The optimal approach to inducing and maintaining targeted temperature management, however, remains uncertain. The objective of this study was to evaluate these processes of care with survival and neurological function in patients after out-of-hospital cardiac arrest.

DESIGN

An observational cohort study evaluating the association of targeted temperature management processes with survival and neurological function using bivariate and generalized estimating equation analyses.

SETTING

Thirty-two tertiary and community hospitals in eight urban and rural regions of southern Ontario, Canada.

PATIENTS

Consecutive adult (≥ 18 yr) patients admitted between November 1, 2007, and January 31, 2012, and who were treated with targeted temperature management following nontraumatic out-of-hospital cardiac arrest.

INTERVENTIONS

Evaluate the association of targeted temperature management processes with survival and neurologic function using bivariate and generalized estimating equation analyses.

MEASUREMENTS AND MAIN RESULTS

There were 5,770 consecutive out-of-hospital cardiac arrest patients, of whom 747 (12.9%) were eligible and received targeted temperature management. Among patients with available outcome data, 365 of 738 (49.5%) survived to hospital discharge and 241 of 675 (35.7%) had good neurological outcomes. After adjusting for the Utstein variables, a higher temperature prior to initiation of targeted temperature management was associated with improved neurological outcomes (odds ratio, 1.27 per °C; 95% CI, 1.08-1.50; p = 0.004) and survival (odds ratio, 1.26 per °C; 95% CI, 1.09-1.46; p = 0.002). A slower rate of cooling was associated with improved neurological outcomes (odds ratio, 0.74 per °C/hr; 95% CI, 0.57-0.97; p = 0.03) and survival (odds ratio, 0.73 per °C/hr; 95% CI, 0.54-1.00; p = 0.049).

CONCLUSIONS

A higher baseline temperature prior to initiation of targeted temperature management and a slower rate of cooling were associated with improved survival and neurological outcomes. This may reflect a complex relationship between the approach to targeted temperature management and the extent of underlying brain injury causing impaired thermoregulation in out-of-hospital cardiac arrest patients.

Multi-parameter brain tissue microsensor and interface systems: calibration, reliability and user experiences of pressure and temperature sensors in the setting of neurointensive care

The objective was to investigate sensor measurement uncertainty for intracerebral probes inserted during neurosurgery and remaining in situ during neurocritical care. This describes a prospective observational study of two sensor types and including performance of the complete sensor-bedside monitoring and readout system. Sensors from 16 patients with severe traumatic brain injury (TBI) were obtained at the time of removal from the brain. When tested, 40% of sensors achieved the manufacturer temperature specification of 0.1 °C. Pressure sensors calibration differed from the manufacturers at all test pressures in 8/20 sensors. The largest pressure measurement error was in the intraparenchymal triple sensor. Measurement uncertainty is not influenced by duration in situ. User experiences reveal problems with sensor 'handling', alarms and firmware. Rigorous investigation of the performance of intracerebral sensors in the laboratory and at the bedside has established measurement uncertainty in the 'real world' setting of neurocritical care.

The epidemiology of spontaneous fever and hypothermia on admission of brain injury patients to intensive care units: a multicenter cohort study

OBJECTIVES

Fever and hypothermia (dysthermia) are associated with poor outcomes in patients with brain injuries. The authors sought to study the epidemiology of dysthermia on admission to the intensive care unit (ICU) and the effect on in-hospital case fatality in a mixed cohort of patients with brain injuries.

METHODS

The authors conducted a multicenter retrospective cohort study in 94 ICUs in the United States. Critically ill patients with neurological injuries, including acute ischemic stroke (AIS), aneurysmal subarachnoid hemorrhage (aSAH), intracerebral hemorrhage (ICH), and traumatic brain injury (TBI), who were older than 17 years and consecutively admitted to the ICU from 2003 to 2008 were selected for analysis.

RESULTS

In total, 13,587 patients were included in this study; AIS was diagnosed in 2973 patients (22%), ICH in 4192 (31%), aSAH in 2346 (17%), and TBI in 4076 (30%). On admission to the ICU, fever was more common among TBI and aSAH patients, and hypothermia was more common among ICH patients. In-hospital case fatality was more common among patients with hypothermia (OR 12.7, 95% CI 8.4-19.4) than among those with fever (OR 1.9, 95% CI 1.7-2.1). Compared with patients with ICH (OR 2.0, 95% CI 1.8-2.3), TBI (OR 1.5, 95% CI 1.3-1.8), and aSAH (OR 1.4, 95% CI 1.2-1.7), patients with AIS who developed fever had the highest risk of death (OR 3.1, 95% CI 2.5-3.7). Although all hypothermic patients had an increased mortality rate, this increase was not significantly different across subgroups. In a multivariable analysis, when adjusted for all other confounders, exposure to fever (adjusted OR 1.3, 95% CI 1.1-1.5) or hypothermia (adjusted OR 7.8, 95% CI 3.9-15.4) on admission to the ICU was found to be significantly associated with in-hospital case fatality.

CONCLUSIONS

Fever is frequently encountered in the acute phase of brain injury, and a small proportion of patients with brain injuries may also develop spontaneous hypothermia. The effect of fever on mortality rates differed by neurological diagnosis. Both early spontaneous fever and hypothermia conferred a higher risk of in-hospital death after brain injury.

Brain-systemic temperature gradient is temperature-dependent in children with severe traumatic brain injury

OBJECTIVES

To understand the gradient between rectal and brain temperature in children after severe traumatic brain injury. We hypothesized that the rectal temperature and brain temperature gradient will be influenced by the child's body surface area and that this relationship will persist over physiologic temperature ranges.

DESIGN

Retrospective review of a prospectively collected pediatric neurotrauma registry.

SETTING

Academic, university-based pediatric neurotrauma program.

PATIENTS

Consecutive children (n = 40) with severe traumatic brain injury (Glasgow coma scale of <8) who underwent brain temperature monitoring (July 2003 to December 2008) were studied after informed consent was obtained. A subset of children (n = 24) were concurrently enrolled in a randomized, controlled clinical trial of early-moderate hypothermia for neuroprotection.

INTERVENTIONS

Data extraction of multiple clinical variables, including demographic data, body surface area, and rectal and brain temperature at recorded at hourly intervals.

MEASUREMENTS AND MAIN RESULTS

Paired brain and rectal temperature measurements (in degrees Celsius, n = 4369) were collected hourly and compared by using Pearson correlations. Patients were stratified according to body surface area (<1.0 m, 1.0-1.99 m, 2.0-2.99 m, and >3.0 m) and based on brain temperature (≤34.0, 34.1-36.0; 36.1-38, ≥38.1). Body surface area and brain temperature were compared between groups by using Pearson correlations with correction for repeated measures. Mean brain temperature-rectal temperature difference was calculated for stratified brain temperature ranges. Overall, brain and rectal temperatures were highly correlated (r = .86, p < .001). During brain hyperthermia, brain temperature-rectal temperature was similar to that reported in previous studies with brain temperature higher than rectal temperature (1.75 ± 0.4; r = .54). Surprisingly, this relationship was reversed during brain hypothermia (brain temperature-rectal temperature = -1.87 ± 0.8; r = .37), indicating a reversal of the brain-systemic temperature gradient. When stratified for body surface area, the correlation between rectal temperature and brain temperature remained strong (r = .78, 0.91, 0.79 and 0.95, respectively, p < .001). However, the correlation between brain temperature and rectal temperature was substantially decreased when stratified for brain temperature (r = .37, 0.58, 0.48, 0.54, p < .001). In particular, during moderate brain hypothermia (brain temperature ≤34), the correlation between brain temperature and rectal temperature was weakest, indicating the greatest variability during this condition which is often targeted for therapeutic trials.

CONCLUSIONS

Brain temperature and rectal temperature are generally well-correlated in children with traumatic brain injury. This relationship is different at the extremes of the physiologic temperature range, with the temperature gradient reversed during brain hypothermia and hyperthermia. Given that studies showing neuroprotection from hypothermia in animal models of brain injury generally target brain temperature, our data suggest the possibility that, if brain temperature were the therapeutic target in clinical trials, this would result in somewhat higher systemic temperature and potentially fewer side effects. This relationship may be exploited in future clinical trials to maintain brain hypothermia (for neurologic protection) at slightly higher systemic temperatures (and potentially fewer systemic side effects).

Report of a consensus meeting on human brain temperature after severe traumatic brain injury: its measurement and management during pyrexia

Temperature disturbances are common in patients with severe traumatic brain injury. The possibility of an adaptive, potentially beneficial role for fever in patients with severe brain trauma has been dismissed, but without good justification. Fever might, in some patients, confer benefit. A cadre of clinicians and scientists met to debate the clinically relevant, but often controversial issue about whether raised brain temperature after human traumatic brain injury (TBI) should be regarded as "good or bad" for outcome. The objective was to produce a consensus document of views about current temperature measurement and pyrexia treatment. Lectures were delivered by invited speakers with National and International publication track records in thermoregulation, neuroscience, epidemiology, measurement standards and neurocritical care. Summaries of the lectures and workshop discussions were produced from transcriptions of the lectures and workshop discussions. At the close of meeting, there was agreement on four key issues relevant to modern temperature measurement and management and for undergirding of an evidence-based practice, culminating in a consensus statement. There is no robust scientific data to support the use of hypothermia in patients whose intracranial pressure is controllable using standard therapy. A randomized clinical trial is justified to establish if body cooling for control of pyrexia (to normothermia) vs moderate pyrexia leads to a better patient outcome for TBI patients.

A systematic performance evaluation of brain and body temperature sensors using ultra-stable temperature references

The impact of a rise in the temperature of the human brain in patients who have suffered cerebral damage is not completely understood. Current studies are ambiguous; some show that a high brain temperature, and others a low brain temperature, is an indicator of poor prognosis. The reported effect is often very subtle, at the <0.5 degrees C level, and this may be due to the performance, or even the location of the temperature sensor. This study investigates the first of these issues, i.e. the performance of the sensor. Here performance validation is undertaken for three commonly used temperature sensors for brain and body temperature measurement, using ultra-stable temperature references. At body temperature all three sensor types performed within manufacturer's specifications. Given that only a small number of temperature sensors were tested, the indication is that, provided the sensors are located correctly, the small observed differences in temperature are real - though the issue of clinical significance is still to be addressed.

Peak body temperature predicts mortality in critically ill patients without cerebral damage

OBJECTIVES

We investigated whether mortality in intensive care unit (ICU) patients without cerebral damage is associated with fever manifestation and characteristics.

METHODS

Patients admitted to a medical-surgical ICU between October 2005 and July 2006 were prospectively studied. Exclusion criteria were acute brain injury, intracerebral/subarachnoid hemorrhage, ischemic stroke, and brain surgery. An ear-based or axillary thermometer was used to measure body temperature. The association between fever (ear-based temperature, >38.3 degrees C), fever characteristics, and ICU mortality was evaluated using univariate and multivariate analysis.

RESULTS

Two hundred and thirty-nine patients were enrolled. Fever was not associated with ICU mortality after adjustment for confounding patient factors. A significant dose-response increase of ICU mortality according to 1 degree C increments of peak body temperature was demonstrated, whereas peak body temperature was an independent predictor of ICU mortality.

CONCLUSION

These findings imply that, although fever is not generally associated with mortality in patients without cerebral damage, it can be harmful and should be suppressed when it becomes very high. Rigorous clinical trials are needed to help establish antipyretic therapy guidelines.

Reliability issues in human brain temperature measurement

Introduction

The influence of brain temperature on clinical outcome after severe brain trauma is currently poorly understood. When brain temperature is measured directly, different values between the inside and outside of the head can occur. It is not yet clear if these differences are 'real' or due to measurement error.

Methods

The aim of this study was to assess the performance and measurement uncertainty of body and brain temperature sensors currently in use in neurocritical care. Two organic fixed-point, ultra stable temperature sources were used as the temperature references. Two different types of brain sensor (brain type 1 and brain type 2) and one body type sensor were tested under rigorous laboratory conditions and at the bedside. Measurement uncertainty was calculated using internationally recognised methods.

Results

Average differences between the 26°C reference temperature source and the clinical temperature sensors were +0.11°C (brain type 1), +0.24°C (brain type 2) and -0.15°C (body type), respectively. For the 36°C temperature reference source, average differences between the reference source and clinical thermometers were -0.02°C, +0.09°C and -0.03°C for brain type 1, brain type 2 and body type sensor, respectively. Repeat calibrations the following day confirmed that these results were within the calculated uncertainties. The results of the immersion tests revealed that the reading of the body type sensor was sensitive to position, with differences in temperature of -0.5°C to -1.4°C observed on withdrawing the thermometer from the base of the isothermal environment by 4 cm and 8 cm, respectively. Taking into account all the factors tested during the calibration experiments, the measurement uncertainty of the clinical sensors against the (nominal) 26°C and 36°C temperature reference sources for the brain type 1, brain type 2 and body type sensors were ± 0.18°C, ± 0.10°C and ± 0.12°C respectively.

Conclusions

The results show that brain temperature sensors are fundamentally accurate and the measurements are precise to within 0.1 to 0.2°C. Subtle dissociation between brain and body temperature in excess of 0.1 to 0.2°C is likely to be real. Body temperature sensors need to be secured in position to ensure that measurements are reliable.

You are only coming through in waves: wakefulness variability and assessment in patients with impaired consciousness

The vegetative state (VS) is defined as a condition of wakefulness without awareness. Being awake and being asleep are two behavioral and physiological manifestations of the daily cycles of vigilance and metabolism. International guidelines for the diagnosis of VS propose that a patient fulfills criteria for wakefulness if he/she exhibits cycles of eye closure and eye opening giving the impression of a preserved sleep-wake cycle. We argue that these criteria are insufficient and we suggest guidelines to address wakefulness in a more comprehensive manner in this complex and heterogeneous group of patients. Four factors underlying wakefulness, as well as their interactions, are considered: arousal/responsiveness, circadian rhythms, sleep cycle, and homeostasis. The first refers to the arousability and capacity to, consciously or not, respond to external stimuli. The second deals with the circadian clock as a synchronizer of physiological functions to environmental cyclic changes. The third evaluates general sleep patterns, while homeostasis refers to the capacity of the body to regulate its internal state and maintain a stable condition. We present examples of reflex responses, activity rhythms, and electroencephalographic (EEG) measurements from patients with disorders of consciousness (DOC) to illustrate these factors of wakefulness. If properly assessed, they would help in the evaluation of consciousness by informing when and in which context the patient is likely to exhibit maximal responsiveness. This evaluation has the potential to improve diagnosis and treatment and may also add prognostic value to the multimodal assessment in DOC.