Hyperthermia following traumatic brain injury: a critical evaluation

Temperature Control in Acute Brain Injury: An Update

Temperature control in severe acute brain injury (SABI) is a key component of acute management. This manuscript delves into the complex role of temperature management in SABI, encompassing conditions like traumatic brain injury (TBI), acute ischemic stroke (AIS), intracerebral hemorrhage (ICH), aneurysmal subarachnoid hemorrhage (aSAH), and hypoxemic/ischemic brain injury following cardiac arrest. Fever is a common complication in SABI and is linked to worse neurological outcomes due to increased inflammatory responses and intracranial pressure (ICP). Temperature management, particularly hypothermic temperature control (HTC), appears to mitigate these adverse effects primarily by reducing cerebral metabolic demand and dampening inflammatory pathways. However, the effectiveness of HTC varies across different SABI conditions. In the context of post-cardiac arrest, the impact of HTC on neurological outcomes has shown inconsistent results. In cases of TBI, HTC seems promising for reducing ICP, but its influence on long-term outcomes remains uncertain. For AIS, clinical trials have yet to conclusively demonstrate the benefits of HTC, despite encouraging preclinical evidence. This variability in efficacy is also observed in ICH, aSAH, bacterial meningitis, and status epilepticus. In pediatric and neonatal populations, while HTC shows significant benefits in hypoxic-ischemic encephalopathy, its effectiveness in other brain injuries is mixed. Although the theoretical basis for employing temperature control, especially HTC, is strong, the clinical outcomes differ among various SABI subtypes. The current consensus indicates that fever prevention is beneficial across the board, but the application and effectiveness of HTC are more nuanced, underscoring the need for further research to establish optimal temperature management strategies. Here we provide an overview of the clinical evidence surrounding the use of temperature control in various types of SABI.

Brain Temperature as an Indicator of Cognitive Function in Traumatic Brain Injury Patients

Whether brain temperature noninvasively extracted by magnetic resonance imaging has a role in identifying brain changes in the later phases of mild to moderate traumatic brain injury (TBI) is not known. This prospective study aimed to evaluate if TBI patients in subacute and chronic phases had altered brain temperature measured by whole-brain magnetic resonance spectroscopic imaging (WB-MRSI) and if the measurable brain temperature had any relationship with cognitive function scores. WB-MRSI was performed on eight TBI patients and fifteen age- and sex-matched control subjects. Brain temperature (T) was extracted from the brain's major metabolites and compared between the two groups. The T of the patients was tested for correlation with cognitive function test scores. The results showed significantly lower brain temperature in the TBI patients (p < 0.05). Brain temperature derived from N-acetylaspartate (TNAA) strongly correlated with the 2 s paced auditory serial addition test (PASAT-2s) score (p < 0.05). The observation of lower brain temperature in TBI patients may be due to decreased metabolic activity resulting from glucose and oxygen depletion. The correlation of brain temperature with PASAT-2s may imply that noninvasive brain temperature may become a noninvasive index reflecting cognitive performance.

Traumatic brain injury extending to the striatum alters autonomic thermoregulation and hypothalamic monoamines in recovering rats

The brain cortex is the structure that is typically injured in traumatic brain injury (TBI) and is anatomically connected with other brain regions, including the striatum and hypothalamus, which are associated in part with motor function and the regulation of body temperature, respectively. We investigated whether a TBI extending to the striatum could affect peripheral and core temperatures as an indicator of autonomic thermoregulatory function. Moreover, it is unknown whether thermal modulation is accompanied by hypothalamic and cortical monoamine changes in rats with motor function recovery. The animals were allocated into three groups: the sham group (sham), a TBI group with a cortical contusion alone (TBI alone), and a TBI group with an injury extending to the dorsal striatum (TBI + striatal injury). Body temperature and motor deficits were evaluated for 20 days post-injury. On the 3rd and 20th days, rats were euthanized to measure the serotonin (5-HT), noradrenaline (NA), and dopamine (DA) levels using high-performance liquid chromatography (HPLC). We observed that TBI with an injury extending to the dorsal striatum increased core and peripheral temperatures. These changes were accompanied by a sustained motor deficit lasting for 14 days. Furthermore, there were notable increases in NA and 5-HT levels in the brain cortex and hypothalamus both 3 and 20 days after injury. In contrast, rats with TBI alone showed no changes in peripheral temperatures and achieved motor function recovery by the 7th day post-injury. In conclusion, our results suggest that TBI with an injury extending to the dorsal striatum elevates both core and peripheral temperatures, causing a delay in functional recovery and increasing hypothalamic monoamine levels. The aftereffects can be attributed to the injury site and changes to the autonomic thermoregulatory functions.

Adverse Effect of Neurogenic, Infective, and Inflammatory Fever on Acutely Injured Human Spinal Cord

This study aims to determine the effect of neurogenic, inflammatory, and infective fevers on acutely injured human spinal cord. In 86 patients with acute, severe traumatic spinal cord injuries (TSCIs; American Spinal Injury Association Impairment Scale (AIS), grades A-C) we monitored (starting within 72 h of injury, for up to 1 week) axillary temperature as well as injury site cord pressure, microdialysis (MD), and oxygen. High fever (temperature ≥38°C) was classified as neurogenic, infective, or inflammatory. The effect of these three fever types on injury-site physiology, metabolism, and inflammation was studied by analyzing 2864 h of intraspinal pressure (ISP), 1887 h of MD, and 840 h of tissue oxygen data. High fever occurred in 76.7% of the patients. The data show that temperature was higher in neurogenic than non-neurogenic fever. Neurogenic fever only occurred with injuries rostral to vertebral level T4. Compared with normothermia, fever was associated with reduced tissue glucose (all fevers), increased tissue lactate to pyruvate ratio (all fevers), reduced tissue oxygen (neurogenic + infective fevers), and elevated levels of pro-inflammatory cytokines/chemokines (infective fever). Spinal cord metabolic derangement preceded the onset of infective but not neurogenic or inflammatory fever. By considering five clinical characteristics (level of injury, axillary temperature, leukocyte count, C-reactive protein [CRP], and serum procalcitonin [PCT]), it was possible to confidently distinguish neurogenic from non-neurogenic high fever in 59.3% of cases. We conclude that neurogenic, infective, and inflammatory fevers occur commonly after acute, severe TSCI and are detrimental to the injured spinal cord with infective fever being the most injurious. Further studies are required to determine whether treating fever improves outcome. Accurately diagnosing neurogenic fever, as described, may reduce unnecessary septic screens and overuse of antibiotics in these patients.

Overview of Hypothermia, Its Role in Neuroprotection, and the Application of Prophylactic Hypothermia in Traumatic Brain Injury

The current standard of practice is to maintain normothermia in traumatic brain injury (TBI) patients despite the theoretical benefits of hypothermia and numerous animal studies with promising results. While targeted temperature management or induced hypothermia to support neurological function is recommended for a select patient population postcardiac arrest, similar guidelines have not been instituted for TBI. In this review, we will examine the pathophysiology of TBI and discuss the benefits and risks of induced hypothermia in this patient population. In addition, we provide an overview of the largest randomized controlled trials testing-induced hypothermia. Our literature review on hypothermia returned a myriad of studies and trials, many of which have inconclusive results. The aim of this review was to recognize the effects of hypothermia, summarize the latest trials, address the inconsistencies, and discuss future directions for the study of hypothermia in TBI.

Antipyretic Efficacy of Bromocriptine in Central Fever: an Exploratory Analysis

BACKGROUND

'Central' fevers are thought to result from disruption of hypothalamic thermoregulatory pathways following severe brain injuries. Bromocriptine, due to its central dopamine receptor agonism, has been hypothesized to have antipyretic effect in this setting. However, clinical evidence for this off-label use is limited to a few case reports. In this retrospective cohort study, we analyzed the effect of bromocriptine administration on body temperature in acute brain injury patients with suspected central fever.

METHODS

We screened a cohort of adult patients that received bromocriptine in the neurologic-intensive care unit of a tertiary care hospital between January 2018 and December 2021. Indication of central fever was ascertained by review of clinical documentation. A generalized additive mixed model (GAMM) was used to model temperature as a function of time relative to bromocriptine initiation. We adjusted for potential confounding due to the following covariates: temperature recording method (invasive vs surface), concurrent antipyretic administration within 8 h, and surface cooling device use within 4 h of temperature measurement. Temperature-time function was modeled using a cubic spline with k = 10 knots.

RESULTS

A total of 33 patients were included in the analysis (14 women; mean age: 50 y, standard deviation 14 y). Median dose of bromocriptine was 7.5 mg (range 2.5-40) for a median of 13 d (range 5-160). Age and sex did not impact the function of temperature over time. Predicted temperatures were significantly (p < 0.05) higher by 0.4 °C with invasive compared to surface recording methods, lower by 0.2 °C in the presence of cooling device use and lower by 0.1 °C with concurrent antipyretic use. On adjusted analysis with the GAMM, there was decline (p < 0.05) in temperature following bromocriptine initiation by - 0.3 °C at 24 h, - 0.5 °C at 48 h, and - 0.7 °C at 72 h.

CONCLUSIONS

Bromocriptine use was associated with modest but statistically significant decline in temperature, with nadir at 72 h post initiation. The findings provide a data driven basis for prospective evaluation.

Use of baclofen and propranolol for treatment of neurogenic fever in a patient with pontine hemorrhage: A case report

Key Clinical Message

Neurogenic fever (NF) is a potentially life-threatening complication commonly seen in patients with pontine hemorrhage. This case report highlights the successful use of oral baclofen and propranolol as an effective treatment strategy to manage NF.

Abstract

Neurogenic fever (NF) is a common complication following pontine hemorrhage and poses significant challenges for clinicians in terms of diagnosis, management, and patient outcomes. This study delves into the efficacy of treatment methods involving baclofen and propranolol for neurogenic fever in patients with pontine hemorrhage. The results demonstrated a significant reduction in the duration and intensity of fever. Moreover, the treatment modality was well-tolerated and devoid of any adverse effects. These findings suggest that the use of oral baclofen and propranolol may be a promising therapeutic option for managing neurogenic fever in patients with pontine hemorrhage.

Systemic Inflammation after Aneurysmal Subarachnoid Hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is one of the most severe neurological disorders, with a high mortality rate and severe disabling functional sequelae. Systemic inflammation following hemorrhagic stroke may play an important role in mediating intracranial and extracranial tissue damage. Previous studies showed that various systemic inflammatory biomarkers might be useful in predicting clinical outcomes. Anti-inflammatory treatment might be a promising therapeutic approach for improving the prognosis of patients with aSAH. This review summarizes the complicated interactions between the nervous system and the immune system.

Diclofenac Sodium for Fever Control in Neurocritical Care: A Systematic Review

BACKGROUND

Fever is extremely common in neurocritical care patients and is independently associated with a worse outcome. Non-steroidal anti-inflammatory drugs (NSAIDs) lower the hypothalamic set point temperature through the inhibition of prostaglandin E2 synthesis, and they constitute a second line of pharmacological treatment for temperature control. This systematic review aims to evaluate the effectiveness of DCF in reducing body temperature and its effects on brain parameters.

METHODS

A comprehensive search of several databases was run in November 2022 in Ovid EBM (Evidence Based Medicine) Reviews, Cochrane library, Ovid Medline and Scopus (1980 onward). The outcome of interest included DCF control of body temperature and its impact on cerebral parameters.

RESULTS

A total of 113 titles were identified as potentially relevant. Six articles met eligible criteria and were reviewed. DCF induce a reduction in body temperature (MD, 1.10 [0.72, 1.49], p < 0.00001), a slight decrease in ICP (MD, 2.22 [-0.25, 4.68] IC 95%; p < 0.08) as well as in CPP and MAP (MD, 5.58 [0.43, 10.74] IC 95%; p < 0.03). The significant heterogeneity and possibility of publication bias reduces the strength of the available evidence.

CONCLUSIONS

Diclofenac sodium is effective in reducing body temperature in patients with brain injury, but data in the literature are scarce and further studies are needed to evaluate the benefits of DCF.

Lactate shuttling as an allostatic means of thermoregulation in the brain

Lactate, the redox-balanced end product of glycolysis, travels within and between cells to fulfill an array of physiologic functions. While evidence for the centrality of this lactate shuttling in mammalian metabolism continues to mount, its application to physical bioenergetics remains underexplored. Lactate represents a metabolic "cul-de-sac," as it can only re-enter metabolism by first being converted back to pyruvate by lactate dehydrogenase (LDH). Given the differential distribution of lactate producing/consuming tissues during metabolic stresses (e.g., exercise), we hypothesize that lactate shuttling vis-à-vis the exchange of extracellular lactate between tissues serves a thermoregulatory function, i.e., an allostatic strategy to mitigate the consequences of elevated metabolic heat. To explore this idea, the rates of heat and respiratory oxygen consumption in saponin-permeabilized rat cortical brain samples fed lactate or pyruvate were measured. Heat and respiratory oxygen consumption rates, and calorespirometric ratios were lower during lactate vs. pyruvate-linked respiration. These results support the hypothesis of allostatic thermoregulation in the brain with lactate.

Cerebral Oxygen Delivery and Consumption in Brain-Injured Patients

Organism survival depends on oxygen delivery and utilization to maintain the balance of energy and toxic oxidants production. This regulation is crucial to the brain, especially after acute injuries. Secondary insults after brain damage may include impaired cerebral metabolism, ischemia, intracranial hypertension and oxygen concentration disturbances such as hypoxia or hyperoxia. Recent data highlight the important role of clinical protocols in improving oxygen delivery and resulting in lower mortality in brain-injured patients. Clinical protocols guide the rules for oxygen supplementation based on physiological processes such as elevation of oxygen supply (by mean arterial pressure (MAP) and intracranial pressure (ICP) modulation, cerebral vasoreactivity, oxygen capacity) and reduction of oxygen demand (by pharmacological sedation and coma or hypothermia). The aim of this review is to discuss oxygen metabolism in the brain under different conditions.

Temperature-dependent structural plasticity of hippocampal synapses

The function of the central nervous system (CNS) is strongly affected by temperature. However, the underlying processes remain poorly understood. Here, we show that hypothermia and hyperthermia trigger bidirectional re-organization of presynaptic architecture in hippocampal neurons, resulting in synaptic strengthening, and weakening, respectively. Furthermore, hypothermia remodels inhibitory postsynaptic scaffold into enlarged, sparse synapses enriched in GABAA receptors. This process does not require protein translation, and instead is regulated by actin dynamics. Induction of hypothermia in vivo enhances inhibitory synapses in the hippocampus, but not in the cortex. This is confirmed by the proteomic analysis of cortical synapses, which reveals few temperature-dependent changes in synaptic content. Our results reveal a region-specific form of environmental synaptic plasticity with a mechanism distinct from the classic temperature shock response, which may underlie functional response of CNS to temperature.

The utility of therapeutic hypothermia on cerebral autoregulation

Cerebral autoregulation (CA) dysfunction is a strong predictor of clinical outcome in patients with acute brain injury (ABI). CA dysfunction is a potential pathologic defect that may lead to secondary injury and worse functional outcomes. Early therapeutic hypothermia (TH) in patients with ABI is controversial. Many factors, including patient selection, timing, treatment depth, duration, and rewarming strategy, impact its clinical efficacy. Therefore, optimizing the benefit of TH is an important issue. This paper reviews the state of current research on the impact of TH on CA function, which may provide the basis and direction for CA-oriented target temperature management.

Fever management in acute brain injury

PURPOSE OF REVIEW

Fever is common after acute brain injury and is associated with poor prognosis in this setting.

RECENT FINDINGS

Achieving normothermia is feasible in patients with ischemic or hemorrhagic stroke, subarachnoid hemorrhage and traumatic brain injury. Pharmacological strategies (i.e. paracetamol or nonsteroidal anti-inflammatory drugs) are frequently ineffective and physical (i.e. cooling devices) therapies are often required. There are no good quality data supporting any benefit from therapeutic strategies aiming at normothermia in all brain injured patients when compared with standard of care, where mild-to-moderate fever is tolerated. However, recent guidelines recommended fever control in this setting.

SUMMARY

As fever is considered a clinically relevant secondary brain damage, we have provided an individualized therapeutic approach to treat it in brain injured patients, which deserved further validation in the clinical setting.

A hypothalamomedullary network for physiological responses to environmental stresses

Various environmental stressors, such as extreme temperatures (hot and cold), pathogens, predators and insufficient food, can threaten life. Remarkable progress has recently been made in understanding the central circuit mechanisms of physiological responses to such stressors. A hypothalamomedullary neural pathway from the dorsomedial hypothalamus (DMH) to the rostral medullary raphe region (rMR) regulates sympathetic outflows to effector organs for homeostasis. Thermal and infection stress inputs to the preoptic area dynamically alter the DMH → rMR transmission to elicit thermoregulatory, febrile and cardiovascular responses. Psychological stress signalling from a ventromedial prefrontal cortical area to the DMH drives sympathetic and behavioural responses for stress coping, representing a psychosomatic connection from the corticolimbic emotion circuit to the autonomic and somatic motor systems. Under starvation stress, medullary reticular neurons activated by hunger signalling from the hypothalamus suppress thermogenic drive from the rMR for energy saving and prime mastication to promote food intake. This Perspective presents a combined neural network for environmental stress responses, providing insights into the central circuit mechanism for the integrative regulation of systemic organs.

Neurogenic fever due to injury of the hypothalamus in a stroke patient: Case report

RATIONALE

Neurogenic fever is a non-infectious source of fever in a patient with brain injury, especially hypothalamic injury. We report on a stroke patient with neurogenic fever due to injury of hypothalamus, demonstrated by using diffusion tensor imaging (DTI).

PATIENT CONCERNS

A 28-year-old male patient was admitted to the rehabilitation department of university hospital at 30 months after onset. Brain MRI showed leukomalactic lesions in hypothalamus, bilateral medial temporal lobe, and bilateral basal ganglia. He showed intermittent high body temperature (maximum:39.5°C, range:38.5-39.2°C), but did not show any infection signs upon physical examination or after assessing his white blood cell count and inflammatory enzyme levels such as erythrocyte sedimentation rate and C-reactive protein. In addition, 8 age-matched normal (control) subjects (4 male, mean age: 26.6 years, range: 21-29years) were enrolled in the study.

DIAGNOSIS

Intraventricular hemorrhage and intracerebral hemorrhage in the left basal ganglia.

INTERVENTIONS

He underwent extraventricular drainage and ventriculoperitoneal shunting for hydrocephalus.

OUTCOMES

DTI was performed at 30 months after onset, fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values were obtained for hypothalamus. The FA and ADC values of patient were lower and higher, respectively, by more than two standard deviations from control values. Injury of hypothalamus was demonstrated in a stroke patient with neurogenic fever.

LESSIONS

Our results suggest that evaluation of hypothalamus using DTI would be helpful in patients show unexplained fever following brain injury.

An Exploratory Report on Electrographic Changes in the Cerebral Cortex Following Mild Traumatic Brain Injury with Hyperthermia in the Rat

Traumatic brain injury (TBI) has the potential to perturb perception by disrupting electrical propagation within and between the thalamus and cerebral cortex. Moderate and severe TBI may result in posttraumatic epilepsy, a condition characterized by convulsive tonic-clonic seizures. Spike/wave discharges (SWDs) of generalized nonconvulsive seizures, also called absence seizures, may also occur as a consequence of brain trauma. As mild hyperthermia has been reported to exacerbate histopathological and behavioral outcomes, we used an unbiased algorithm to detect periodic increases in power across different frequency bands following single or double closed head injury (CHI) under normothermia and hyperthermia conditions. We demonstrated that mild TBI did not significantly alter the occurrence of events containing increases in power between the delta (0.5-4 Hz), theta (4-8 Hz), alpha (8-12 Hz), and beta1 (12-20 Hz) frequency bands in the Sprague Dawley rat 12 weeks after injury. However, when hyperthermia (39°C) was induced before and after CHI, electrographic events containing a similar waveform and harmonic frequency to SWDs were observed in a subset of animals. Further experiments utilizing chronic recordings will need to be performed to determine if these trends lead to absence seizures.

Negligible influence of moderate to severe hyperthermia on blood-brain barrier permeability and neuronal parenchymal integrity in healthy men

With growing use for hyperthermia as a cardiovascular therapeutic, there is surprisingly little information regarding the acute effects it may have on the integrity of the neurovascular unit (NVU). Indeed, relying on animal data would suggest hyperthermia comparable to levels attained in thermal therapy will disrupt the blood-brain barrier (BBB) and damage the cerebral parenchymal cells. We sought to address the hypothesis that controlled passive hyperthermia is not sufficient to damage the NVU in healthy humans. Young men (n = 11) underwent acute passive heating until +2°C or absolute esophageal temperature of 39.5°C. The presence of BBB opening was determined by trans-cerebral exchange kinetics (radial-arterial and jugular venous cannulation) of S100B. Neuronal parenchymal damage was determined by the trans-cerebral exchange of tau protein, neuron-specific enolase (NSE), and neurofilament-light protein (NF-L). Cerebral blood flow to calculate exchange kinetics was measured by duplex ultrasound of the right internal carotid and left vertebral artery. Passive heating was performed via a warm-water perfused suit. In hyperthermia, there was no increase in the cerebral exchange of S100B (P = 0.327), tau protein (P = 0.626), NF-L (P = 0.447), or NSE (P = 0.908) suggesting the +2°C core temperature is not sufficient to acutely stress the NVU in healthy men. However, there was a significant condition effect (P = 0.028) of NSE, corresponding to a significant increase in arterial (P = 0.023) but not venous (P = 0.173) concentrations in hyperthermia, potentially indicating extra-cerebral release of NSE. Collectively, results from the present study support the notion that in young men there is little concern for NVU damage with acute hyperthermia of +2 °C.NEW & NOTEWORTHY The acute effects of passive whole-body hyperthermia on the integrity of the neurovascular unit (NVU) in humans have remained unclear. We demonstrate that passive heating for ∼1 h until an increase of +2°C esophageal temperature in healthy men does not increase the cerebral release of neuronal parenchymal stress biomarkers, suggesting the NVU integrity is maintained. This preliminary study indicates passive heating is safe for the brain, at least in young healthy men.

Ultrastructural investigation of synaptic alterations in the rat hippocampus after irradiation and hyperthermia

This study aimed to investigate ultrastructural synaptic alterations in rat hippocampus after in utero exposure to irradiation (IR) and postnatal exposure to hyperthermia (HT). There were four groups in each of the time points (3^rd and 6^th months). IR group: Pregnant rats were exposed to radiation on the 17^th gestational day. HT group: Hyperthermia was applied to the rat pups on the 10th day after their birth. IR+HT group: Both IR and HT were applied at the same time periods. Control group: No IR or HT was applied. Rat pups were sacrificed after 3 and 6 months. Thin sections from the dentate gyrus (DG) and the CA3 of hippocampus were evaluated for synapse numbers by electron microscopy. Synapses were counted, and statistical analysis was performed. Abnormalities in myelin sheath, mossy terminals and neuropil were observed in the CA3 and DG of all groups. The synapses in the CA3 region were significantly increased in the IR-3^rd month, IR-6^th month, and IR+HT-3^rd month groups vs control group. Synapses were significantly increased in the DG of HT-3^rd month group. A trend for an increase in synapse numbers was seen in the CA3 and DG. Increased number of synapses in the rat hippocampus may be due to mossy fiber sprouting, possibly caused by in utero irradiation and/or postnatal hyperthermia.

Systemic Hyperthermia in Traumatic Brain Injury-Relation to Intracranial Pressure Dynamics, Cerebral Energy Metabolism, and Clinical Outcome

BACKGROUND

Systemic hyperthermia is common after traumatic brain injury (TBI) and may induce secondary brain injury, although the pathophysiology is not fully understood. In this study, our aim was to determine the incidence and temporal course of hyperthermia after TBI and its relation to intracranial pressure dynamics, cerebral metabolism, and clinical outcomes.

MATERIALS AND METHODS

This retrospective study included 115 TBI patients. Data from systemic physiology (body temperature, blood pressure, and arterial glucose), intracranial pressure dynamics (intracranial pressure, cerebral perfusion pressure, compliance, and pressure reactivity), and cerebral microdialysis (glucose, pyruvate, lactate, glycerol, glutamate, and urea) were analyzed during the first 10 days after injury.

RESULTS

Overall, 6% of patients did not have hyperthermia (T>38°C) during the first 10 days after injury, whereas 20% had hyperthermia for >50% of the time. Hyperthermia increased from 21% (±27%) of monitoring time on day 1 to 36% (±29%) on days 6 to 10 after injury. In univariate analyses, higher body temperature was not associated with higher intracranial pressure nor lower cerebral perfusion pressure, but was associated with lower cerebral glucose concentration (P=0.001) and higher percentage of lactate-pyruvate ratio>25 (P=0.02) on days 6 to 10 after injury. Higher body temperature and lower arterial glucose concentration were associated with lower cerebral glucose in a multiple linear regression analysis (P=0.02 for both). There was no association between hyperthermia and worse clinical outcomes.

CONCLUSION

Hyperthermia was most common between days 6 and 10 following TBI, and associated with disturbances in cerebral energy metabolism but not worse clinical outcome.

Cerebral metabolism, oxidation and inflammation in severe passive hyperthermia with and without respiratory alkalosis

KEY POINTS

It was unknown whether respiratory alkalosis impacts the global cerebral metabolic response as well as the cerebral pro-oxidation and inflammatory response in passive hyperthermia. This study demonstrated that the cerebral metabolic rate was increased by ∼20% with passive hyperthermia of up to +2°C oesophageal temperature, and this response was unaffected by respiratory alkalosis. Additionally, the increase in cerebral metabolism did not significantly impact the net cerebral release of oxidative and inflammatory markers. These data indicate that passive heating of up to +2°C core temperature in healthy young men is not enough to confer a major oxidative and inflammatory burden on the brain, but it does markedly increase the cerebral metabolic rate, independently of P aC O 2 .

ABSTRACT

There is limited information concerning the impact of arterial P C O 2 /pH on heat-induced alteration in cerebral metabolism, as well as on the cerebral oxidative/inflammatory burden of hyperthermia. Accordingly, we sought to address two hypotheses: (1) passive hyperthermia will increase the cerebral metabolic rate of oxygen (CMRO₂ ) consistent with a combined influence of Q10 and respiratory alkalosis; and (2) the net cerebral release of pro-oxidative and pro-inflammatory markers will be elevated in hyperthermia, particularly in poikilocapnic hyperthermia. Healthy young men (n = 6) underwent passive heating until an oesophageal temperature of 2°C above resting was reached. At 0.5°C increments in core temperature, CMRO₂ was calculated from the product of cerebral blood flow (ultrasound) and the radial artery-jugular venous oxygen content difference (cannulation). Net cerebral glucose/lactate exchange, and biomarkers of oxidative and inflammatory stress were also measured. At +2.0°C oesophageal temperature, arterial P C O 2 was restored to normothermic values using end-tidal forcing. The primary findings were: (1) while CMRO₂ was increased (P < 0.05) by ∼20% with hyperthermia of +1.5-2.0°C, this was not influenced by respiratory alkalosis, and (2) although biomarkers of pro-oxidation and pro-inflammation were systemically elevated in hyperthermia (P < 0.05), there were no differences in the trans-cerebral exchange kinetics. These novel data indicate that passive heating of up to +2°C core temperature in healthy young men is not enough to confer a major oxidative and inflammatory burden on the brain, despite it markedly increasing CMRO₂ , irrespective of arterial pH.

Can Therapeutic Hypothermia Diminish the Impact of Traumatic Brain Injury in Drosophila melanogaster?

Background/main objectives:

No effective strategy exists to treat the well-recognized, devastating impact of traumatic brain injury (TBI) and chronic traumatic encephalopathy (CTE), which is the brain degeneration likely caused by repeated head trauma. The goals of this project were (1) to study the effects of single and recurrent TBI (rTBI) on Drosophila melanogaster’s (a) life span, (b) response to sedatives, and (c) behavioral responses to light and gravity and (2) to determine whether therapeutic hypothermia can mitigate the deleterious effects of TBI.

Methods:

Five experimental groups were created: (1) control, (2) single TBI or concussion; (3) concussion + hypothermia, (4) rTBI, and (5) rTBI + hypothermia. A “high-impact trauma” (HIT) device was built, which used a spring-based mechanism to propel flies against the wall of a vial, causing mechanical damage to the brain. Hypothermia groups were cooled to 15°C for 3 minutes. Group differences were analyzed with chi-square tests for the categorical variables and with ANOVA tests for the continuous variables.

Results:

Survival curve analysis showed that rTBI can decrease Drosophila lifespan and hypothermia diminished this impact. Average sedation time for control vs concussion vs concussion + hypothermia was 78 vs 52 vs 61 seconds (P < .0001). Similarly, rTBI vs rTBI/hypothermia groups took 43 vs 59 seconds (P < .0001). Concussed flies preferred dark environments compared with control flies (risk ratio 3.3, P < .01) while flies who were concussed and cooled had a risk ratio of 2.7 (P < .01). Flies with rTBI were almost 4 times likely to prefer the dark environment but only 3 times as likely if they were cooled, compared with controls. Geotaxis was significantly affected by rTBI only and yet less so if rTBI flies were cooled.

Conclusions:

Hypothermia successfully mitigated many deleterious effects of single TBI and rTBI in Drosophila and may represent a promising breakthrough in the treatment of human TBI.

Neutrophils in traumatic brain injury (TBI): friend or foe?

Our knowledge of the pathophysiology about traumatic brain injury (TBI) is still limited. Neutrophils, as the most abundant leukocytes in circulation and the first-line transmigrated immune cells at the sites of injury, are highly involved in the initiation, development, and recovery of TBI. Nonetheless, our understanding about neutrophils in TBI is obsolete, and mounting evidences from recent studies have challenged the conventional views. This review summarizes what is known about the relationships between neutrophils and pathophysiology of TBI. In addition, discussions are made on the complex roles as well as the controversial views of neutrophils in TBI.

The course of intracranial pressure after antipyretic therapy in acute brain injury

BACKGROUND

The present study was performed to evaluate intracranial pressure (ICP) variations after antipyretic therapy and their relationship to ICP at baseline (ICPbas) in acute brain injury (ABI) patients.

METHODS

We completed a retrospective analysis on data derived from 2 previously published prospective observational studies. The first study involved 32 ABI patients and was performed to elucidate the cerebral and hemodynamic effects of intravenous (IV) paracetamol. The second study involved 30 ABI patients and was performed to investigate cerebral and hemodynamic effects of intramuscular IM diclofenac sodium (DCF). Overall patient population was divided into 2 groups: 1) Group A (G-A) when ICPbas was ≤ 15 mmHg and 2) Group B (G-B) when ICPbas was > 15 mmHg. The main objective was to evaluate if ICPbas affects the time course of ICP after antipyretics administration.

RESULTS

Data from 62 ABI patients were analyzed. We failed to observe a significant change in ICP after antipyretic treatment in the overall group of patients (P1 = 0.486). A significant difference, however, was found between the two groups (P2 < 0.001). We observed that in the G-A, ICP increased in response to antipyretic administration, whereas in the G-B, ICP decreased. These opposite responses are reflected in the statistically significant interaction (P3 < 0.001).

CONCLUSIONS

Variation in ICP after antipyretic therapy is influenced by ICPbas. Specifically, patients with ICPbas ≤ 15 mmHg showed a significant increase in ICP after antipyretic therapy, while a significant reduction in ICP was observed in patients with ICPbas > 15 mmHg.

Decoupling of Brain Temperature and Glutamate in Recent Onset of Schizophrenia: A 7T Proton Magnetic Resonance Spectroscopy Study

BACKGROUND

Converging evidence suggests that cerebral metabolic and cellular homeostasis is altered in patients with recent onset of schizophrenia. As a possible marker of metabolic changes that might link to altered neurotransmission, we used proton magnetic resonance spectroscopy to estimate brain temperature, and we evaluated its relationship to a relevant metabolite, glutamate, within this study population.

METHODS

Using proton magnetic resonance spectroscopy at 7T, 20 patients with recent onset (≤24 months after first psychotic symptoms) of schizophrenia and 20 healthy control subjects were studied. We measured levels of N-acetylaspartate and glutamate and estimated brain temperature in a noninvasive manner.

RESULTS

Healthy control subjects showed a significant negative correlation between glutamate and brain temperature in the anterior cingulate cortex. In contrast, the physiological correlation between glutamate and brain temperature was lost in patients with recent onset of schizophrenia.

CONCLUSIONS

This study supports the hypothesized disrupted relationship between brain metabolism and neurotransmission in patients with recent onset of schizophrenia. The findings include mechanistic implications that are to be followed up in both preclinical and clinical studies.

Thermoregulation in brain injury

Different mechanisms explain thermoregulatory dysfunction following ischemic stroke, hemorrhagic stroke, and traumatic brain injury. Temperature instability following brain injury likely involves hypothalamic injury, pathologic changes in cerebral blood flow, metabolic derangement, and a neurogenic inflammatory response. Although targeted temperature management (TTM) exerts pleiotropic effects, the heterogeneity of brain injury has hindered identification of patient subsets most likely to benefit from TTM. Early optimism about TTM's role in brain injury has been tempered by the failure of successive clinical trials to show improved patient outcomes. However, given the deleterious effects of fever, aggressive fever management is still warranted in the critically ill neurologic patient.

Early fever after trauma: Does it matter?

BACKGROUND

Fever is strongly associated with poor outcome after traumatic brain injury (TBI). We hypothesized that early fever is a direct result of brain injury and thus would be more common in TBI than in patients without brain injury and associated with inflammation.

METHODS

We prospectively enrolled patients with major trauma with and without TBI from a busy Level I trauma center intensive care unit (ICU). Patients were assigned to one of four groups based on their presenting Head Abbreviated Injury Severity Scale scores: multiple injuries: head Abbreviated Injury Scale (AIS) score greater than 2, one other region greater than 2; isolated head: head AIS score greater than 2, all other regions less than 3; isolated body: one region greater than 2, excluding head/face; minor injury: no region with AIS greater than 2. Early fever was defined as at least one recorded temperature greater than 38.3°C in the first 48 hours after admission. Outcome measures included neurologic deterioration, length of stay in the ICU, hospital mortality, discharge Glasgow Outcome Scale-Extended, and plasma levels of seven key cytokines at admission and 24 hours (exploratory).

RESULTS

Two hundred sixty-eight patients were enrolled, including subjects with multiple injuries (n = 59), isolated head (n = 97), isolated body (n = 100), and minor trauma (n = 12). The incidence of fever was similar in all groups irrespective of injury (11-24%). In all groups, there was a significant association between the presence of early fever and death in the hospital (6-18% vs. 0-3%), as well as longer median ICU stays (3-7 days vs. 2-3 days). Fever was significantly associated with elevated IL-6 at admission (50.7 pg/dL vs. 16.9 pg/dL, p = 0.0067) and at 24 hours (83.1 pg/dL vs. 17.1 pg/dL, p = 0.0025) in the isolated head injury group.

CONCLUSION

Contrary to our hypothesis, early fever was not more common in patients with brain injury, though fever was associated with longer ICU stays and death in all groups. Additionally, fever was associated with elevated IL-6 levels in isolated head injury.

LEVEL OF EVIDENCE

Prognostic and Epidemiological study, level III.

Critical Evaluation of the Lund Concept for Treatment of Severe Traumatic Head Injury, 25 Years after Its Introduction

When introduced in 1992, the Lund concept (LC) was the first complete guideline for treatment of severe traumatic brain injury (s-TBI). It was a theoretical approach, based mainly on general physiological principles-i.e., of brain volume control and optimization of brain perfusion and oxygenation of the penumbra zone. The concept gave relatively strict outlines for cerebral perfusion pressure, fluid therapy, ventilation, sedation, nutrition, the use of vasopressors, and osmotherapy. The LC strives for treatment of the pathophysiological mechanisms behind symptoms rather than just treating the symptoms. The treatment is standardized, with less need for individualization. Alternative guidelines published a few years later (e.g., the Brain Trauma Foundation guidelines and European guidelines) were mainly based on meta-analytic approaches from clinical outcome studies and to some extent from systematic reviews. When introduced, they differed extensively from the LC. We still lack any large randomized outcome study comparing the whole concept of BTF guidelines with other guidelines including the LC. From that point of view, there is limited clinical evidence favoring any of the s-TBI guidelines used today. In principle, the LC has not been changed since its introduction. Some components of the alternative guidelines have approached those in the LC. In this review, I discuss some important principles of brain hemodynamics that have been lodestars during formulation of the LC. Aspects of ventilation, nutrition, and temperature control are also discussed. I critically evaluate the most important components of the LC 25 years after its introduction, based on hemodynamic principles and on the results of own an others experimental and human studies that have been published since then.

Body Temperature after EMS Transport: Association with Traumatic Brain Injury Outcomes

INTRODUCTION

Low body temperatures following prehospital transport are associated with poor outcomes in patients with traumatic brain injury (TBI). However, a minimal amount is known about potential associations across a range of temperatures obtained immediately after prehospital transport. Furthermore, a minimal amount is known about the influence of body temperature on non-mortality outcomes. The purpose of this study was to assess the correlation between temperatures obtained immediately following prehospital transport and TBI outcomes across the entire range of temperatures.

METHODS

This retrospective observational study included all moderate/severe TBI cases (CDC Barell Matrix Type 1) in the pre-implementation cohort of the Excellence in Prehospital Injury Care (EPIC) TBI Study (NIH/NINDS: 1R01NS071049). Cases were compared across four cohorts of initial trauma center temperature (ITCT): <35.0°C [Very Low Temperature (VLT)]; 35.0-35.9°C [Low Temperature (LT)]; 36.0-37.9°C [Normal Temperature (NT)]; and ≥38.0°C [Elevated Temperature (ET)]. Multivariable analysis was performed adjusting for injury severity score, age, sex, race, ethnicity, blunt/penetrating trauma, and payment source. Adjusted odds ratios (aORs) with 95% confidence intervals (CI) for mortality were calculated. To evaluate non-mortality outcomes, deaths were excluded and the adjusted median increase in hospital length of stay (LOS), ICU LOS and total hospital charges were calculated for each ITCT group and compared to the NT group.

RESULTS

22,925 cases were identified and cases with interfacility transfer (7361, 32%), no EMS transport (1213, 5%), missing ITCT (2083, 9%), or missing demographic data (391, 2%) were excluded. Within this study cohort the aORs for death (compared to the NT group) were 2.41 (CI: 1.83-3.17) for VLT, 1.62 (CI: 1.37-1.93) for LT, and 1.86 (CI: 1.52-3.00) for ET. Similarly, trauma center (TC) LOS, ICU LOS, and total TC charges increased in all temperature groups when compared to NT.

CONCLUSION

In this large, statewide study of major TBI, both ETs and LTs immediately following prehospital transport were independently associated with higher mortality and with increased TC LOS, ICU LOS, and total TC charges. Further study is needed to identify the causes of abnormal body temperature during the prehospital interval and if in-field measures to prevent temperature variations might improve outcomes.

Improving on Laboratory Traumatic Brain Injury Models to Achieve Better Results

Experimental modeling of traumatic brain injury (TBI) in animals has identified several potential means and interventions that might have beneficial applications for treating traumatic brain injury clinically. Several of these interventions have been applied and tried with humans that are at different phases of testing (completed, prematurely terminated and others in progress). The promising results achieved in the laboratory with animal models have not been replicated with human trails as expected. This review will highlight some insights and significance attained via laboratory animal modeling of TBI as well as factors that require incorporation into the experimental studies that could help in translating results from laboratory to the bedside. Major progress has been made due to laboratory studies; in explaining the mechanisms as well as pathophysiological features of brain damage after TBI. Attempts to intervene in the cascade of events occurring after TBI all rely heavily on the knowledge from basic laboratory investigations. In looking to discover treatment, this review will endeavor to sight and state some central discrepancies between laboratory models and clinical scenarios.

Clinical relevance of midline fluid percussion brain injury: Acute deficits, chronic morbidities and the utility of biomarkers

BACKGROUND

After 30 years of characterisation and implementation, fluid percussion injury (FPI) is firmly recognised as one of the best-characterised reproducible and clinically relevant models of TBI, encompassing concussion through diffuse axonal injury (DAI). Depending on the specific injury parameters (e.g. injury site, mechanical force), FPI can model diffuse TBI with or without a focal component and may be designated as mild-to-severe according to the chosen mechanical forces and resulting acute neurological responses. Among FPI models, midline FPI may best represent clinical diffuse TBI, because of the acute behavioural deficits, the transition to late-onset behavioural morbidities and the absence of gross histopathology.

REVIEW

The goal here was to review acute and chronic physiological and behavioural deficits and morbidities associated with diffuse TBI induced by midline FPI. In the absence of neurodegenerative sequelae associated with focal injury, there is a need for biomarkers in the diagnostic, prognostic, predictive and therapeutic approaches to evaluate outcomes from TBI.

CONCLUSIONS

The current literature suggests that midline FPI offers a clinically-relevant, validated model of diffuse TBI to investigators wishing to evaluate novel therapeutic strategies in the treatment of TBI and the utility of biomarkers in the delivery of healthcare to patients with brain injury.

Neurogenic Fever

Fever is a relatively common occurrence among patients in the intensive care setting. Although the most obvious and concerning etiology is sepsis, drug reactions, venous thromboembolism, and postsurgical fevers are all on the differential diagnosis. There is abundant evidence that fever is detrimental in acute neurologic injury. Worse outcomes are reported in acute stroke, subarachnoid hemorrhage, and traumatic brain injury. In addition to the various etiologies of fever in the intensive care setting, neurologic illness is a risk factor for neurogenic fevers. This primarily occurs in subarachnoid hemorrhage and traumatic brain injury, with hypothalamic injury being the proposed mechanism. Paroxysmal sympathetic hyperactivity is another source of hyperthermia commonly seen in the population with traumatic brain injury. This review focuses on the detrimental effects of fever on the neurologically injured as well as the risk factors and diagnosis of neurogenic fever.

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.

Fever and sickness behavior: Friend or foe?

Fever has been recognized as an important symptom of disease since ancient times. For many years, fever was treated as a putative life-threatening phenomenon. More recently, it has been recognized as an important part of the body's defense mechanisms; indeed at times it has even been used as a therapeutic agent. The knowledge of the functional role of the central nervous system in the genesis of fever has greatly improved over the last decade. It is clear that the febrile process, which develops in the sick individual, is just one of many brain-controlled sickness symptoms. Not only will the sick individual appear "feverish" but they may also display a range of behavioral changes, such as anorexia, fatigue, loss of interest in usual daily activities, social withdrawal, listlessness or malaise, hyperalgesia, sleep disturbances and cognitive dysfunction, collectively termed "sickness behavior". In this review we consider the issue of whether fever and sickness behaviors are friend or foe during: a critical illness, the common cold or influenza, in pregnancy and in the newborn. Deciding whether these sickness responses are beneficial or harmful will very much shape our approach to the use of antipyretics during illness.

Intracranial temperature and pressure measurement: in vitro temperature sensing characteristics of the dual sensing element

A pressure sensor has been used to measure temperature concurrently. We have designed, and characterized the measurement of temperature from the same sensor to allow simultaneous monitoring of intracranial temperature and pressure. The temperature measurement has a sensitivity of 85.08 mV/°C across the measurement range 20-45 °C. The time constant of the temperature sensor is 150 ms. We have evaluated the accuracy of the temperature measurement and the long term drift of 13 sensors over 28 days. The mean difference of the temperature measurements from the reference measurements was less than 0.2 °C.

Targeted Temperature Management in Pediatric Central Nervous System Disease

Acute central nervous system conditions due to hypoxic-ischemic encephalopathy, traumatic brain injury (TBI), status epilepticus, and central nervous system infection/inflammation, are a leading cause of death and disability in childhood. There is a critical need for effective neuroprotective therapies to improve outcome targeting distinct disease pathology. Fever, defined as patient temperature > 38°C, has been clearly shown to exacerbate brain injury. Therapeutic hypothermia (HT) is an intervention using targeted temperature management that has multiple mechanisms of action and robust evidence of efficacy in multiple experimental models of brain injury. Prospective clinical evidence for its neuroprotective efficacy exists in narrowly-defined populations with hypoxic-ischemic injury outside of the pediatric age range while trials comparing hypothermia to normothermia after TBI have failed to demonstrate a benefit on outcome but consistently demonstrate potential use in decreasing refractory intracranial pressure. Data in children from prospective, randomized controlled trials using different strategies of targeted temperature management for various outcomes are few but a large study examining HT versus controlled normothermia to improve neurological outcome in cardiac arrest is underway.

Critical Care for the Patient With Multiple Trauma

Trauma remains the leading cause of death worldwide and the leading cause of death in those less than 44 years old in the United States. Admission to a verified trauma center has been shown to decrease mortality following a major injury. This decrease in mortality has been a direct result of improvements in the initial evaluation and resuscitation from injury as well as continued advances in critical care. As such, it is vital that intensive care practitioners be familiar with various types of injuries and their associated treatment strategies as well as their potential complications in order to minimize the morbidity and mortality frequently seen in this patient population.

Exercise-associated hyponatremic encephalopathy and exertional heatstroke in a soldier: High rates of fluid intake during exercise caused rather than prevented a fatal outcome

Athletes are often advised to drink in order to "fully replace bodyweight losses" in order to prevent exertional heatstroke (EHS) during exercise in the heat. There is little evidence that "dehydration" in the range experienced by athletes adversely affects thermoregulation or is the exclusive cause of EHS. In contrast it is established that excess fluid intake can cause exercise-associated hyponatremia (EAH) sometimes associated with encephalopathy (EAHE). As part of a series of experiments to determine optimal fluid replacement during exercise in the heat, we studied a group of exceptionally well-conditioned and heat-adapted members of the South African National Defence Force. A 20 year old male started a time restricted 50 km route-march in a dry bulb temperature that reached 37.5°C (WBGT of 33.6°C, relative humidity of 85%). Pre-march plasma osmolality, serum [Na(+)] and total body water measures indicated euhydration. Fluid was available ad libitum and isotonic sports drinks at 5 km intervals. Fluid intake and core body temperature (Tc) were recorded throughout while he was tracked by a global positioning system measuring distance travelled, position and speed. Comparing the total fluid intake of the soldier (12930 mL) to the rest of the participants (mean intake of 9 038 mL) up to 40 km, it is evident that his intake was 3892 mL (approximately 300 mL h(-1)) more than the mean for group. At approximately 17h14 the soldier was found lying by himself at the side of the route, 2.24 km from the finish point. He passed away the next day in a medical care facility. This tragic event provides the valuable opportunity to present data on the pacing, temperature regulation and fluid consumption of an exceptional athlete during the development of a fatal case of combined EAHE and EHS. Pacing, fluid intake, Tc and environmental condition data are presented for 5 km intervals throughout the march. We propose a novel hypothesis on the possible contribution of EAHE to the development of EHS.