Traumatic brain injury and aeromedical evacuation: when is the brain fit to fly?

When Is Air Travel Safe after Mild Traumatic Brain Injury/Sports-Related Concussion?

ABSTRACT

While the literature regarding return to play and recovery protocols from mild traumatic brain injury (mTBI) and sports-related concussions (SRC) is growing, there continues to be a paucity of data regarding when air travel is safe for athletes after sustaining certain brain injuries, such as mTBI and SRC. Although it is known hypoxia can negatively affect severe TBI patients, it is unclear whether mild hypoxia, which may be experienced during commercial air travel, is clinically significant for athletes who have recently sustained mTBI injuries. Further research is required to provide more standardized recommendations on when air travel is safe. With the current available literature, clinicians still need to weigh the evidence, consider how it applies to each individual patient, and engage in shared decision making to ultimately decide what is best for the patient.

Effects of sequential aeromedical evacuations following traumatic brain injury in swine

INTRODUCTION

Traumatic brain injuries (TBI) represent a significant percentage of critical injuries in military conflicts. Following injury, wounded warfighters are often subjected to multiple aeromedical evacuations (AE) and associated hypobaria, yet the impact in TBI patients remains to be characterized. This study evaluated the impact of two consecutive simulated AEs in a fluid-percussion TBI model in swine to characterize these effects.

METHODS

Following instrumentation, anesthetized Yorkshire swine underwent a frontal TBI via fluid-percussion. A hypobaric chamber was then used to simulate AE at simulated cabin pressure equivalent to 8000ft (hypobaria) in a 6 h initial flight on day 3, followed by a 9 h flight on day 6, and were monitored for 14 days. Animals in the normobaria group were subjected to the same steps at sea level while Sham animals in both groups were instrumented but not injured. Parameters measured included physiologic response, intracranial pressure (ICP), hematology, chemistry, and serum cytokines. Histopathology of brain, lung, intestine, and kidney was performed, as well as fluorojade staining to evaluate neurodegeneration. All animals were divided into sub-groups by block randomization utilizing a 2-way ANOVA to analyze independent variables.

RESULTS

Survival was 100% in all groups. Physiologic parameters were largely similar across groups as well during both 6 and 9 h AE. Animals exposed to hypobaria in both the TBI and Sham groups had elevated heart rate (HR) during the 6 h flight (p<0.05). Three animals in the TBI hypo group demonstrated leukocytosis with histologic evidence of meningeal inflammatory response. Expression of serum cytokines was low across all groups. No significant neuronal degeneration was identified in areas away from the site of injury.

CONCLUSION

Aeromedical evacuation in swine was not associated with significant differences in physiologic measures, cytokine expression or levels of neuronal degeneration. Histological examination revealed higher risk of meningeal inflammatory response and leucocytosis in swine exposed to hypobaria.

Chemical characteristics of Rhodiola Crenulata and its mechanism in acute mountain sickness using UHPLC-Q-TOF-MS/MS combined with network pharmacology analysis

ETHNOPHARMACOLOGICAL RELEVANCE

Rhodiola crenulata (Hook.f. & Thomson) H.Ohba has a long history of clinical application for the prevention and treatment of acute mountain sickness (AMS) in traditional Chinese medicine. However, gaps in knowledge still exist in understanding the underlying mechanisms of Rhodiola crenulata against AMS.

AIMS

To address this problem, a comprehensive method was established by combining UHPLC-Q-TOF-MS/MS analysis and network pharmacology.

MATERIALS AND METHODS

The ingredients of Rhodiola crenulata were comprehensively analyzed using UHPLC-Q-TOF-MS/MS method. On this basis, a network pharmacology method incorporated target prediction, protein-protein interaction network, gene enrichment analysis and components-targets-pathways network was performed. Finally, the possible mechanisms were verified through molecular docking, in vitro and in vivo experiments.

RESULTS

A total of 106 constituents of Rhodiola crenulata were charactered via UHPLC-Q-TOF-MS/MS. The 98 potentially active compounds out of 106 were screened and corresponded to 53 anti-AMS targets. Gene enrichment analysis revealed that hypoxia and inflammation related genes may be the central factors for Rhodiola crenulata to modulate AMS. Molecular docking revealed that TNF, VEGFA and HIF-1α had high affinities to Rhodiola crenulata compounds. Subsequently, Rhodiola crenulata extract was indicated to inhibit the protein expression level of TNF in hypoxia induced H9c2 cells. Lastly, Rhodiola crenulata extract was further verified to ameliorate heart injury and decreased the heart levels of TNF, VEGFA and HIF-1α in acute hypoxia-induced rats.

CONCLUSIONS

This study used UHPLC-Q-TOF-MS/MS analysis and a network pharmacology to provide an important reference for revealing the potential mechanism of Rhodiola crenulata in the prevention and treatment of AMS.

Combined traumatic brain injury and hemorrhagic shock in ferrets leads to structural, neurochemical, and functional impairments

Aeromedical evacuation-relevant hypobaria after traumatic brain injury (TBI) leads to increased neurologic injury and mortality in rats relative to those maintained under normobaria. However, applicability of rodent brain injury research to humans may be limited by differences in neuroanatomy. Therefore, we developed a model in which ferrets are exposed to polytrauma consisting of controlled cortical impact TBI and hemorrhagic shock subjected 24 h later to 6 h of hypobaria or normobaria. Our objective was to determine if the deleterious effects of hypobaria observed in rats, with lissencephalic brains, are also present in a species with a human-like gyrencephalic brain. While no mortality was observed, magnetic resonance spectroscopy (MRS) results obtained 2 days post-injury indicated reduced cortical creatine, N-acetylaspartate, GABA, myo-inositol, and glutamate which was not affected by hypobaria. T2-weighted magnetic resonance imaging (MRI) quantification revealed increased hyperintensity volume representing cortical edema at the site of impact following polytrauma. Hypobaria did not exacerbate this focal edema but did lead to overall reductions in total cortical volume. Both normobaric and hypobaric ferrets exhibited impaired spatial memory 6 days post-injury on the Object Location Test, but no differences were noted between groups. Finally, cortical lesion volume was not exacerbated by hypobaria exposure on day 7 post-injury. Results suggest that air travel 24 h after polytrauma is associated with structural changes in the ferret brain. Future studies should investigate secondary injury from hypobaria following polytrauma in greater detail including alternative outcome measures, timepoints, and exposure to multiple flights.

Clinical Value of Bilateral Balanced Frontotemporoparietal Decompressive Craniectomy in Severe Diffuse Traumatic Brain Injury

OBJECTIVE

To explore the clinical value of bilateral balanced frontotemporoparietal decompressive craniectomy (bbDC) in severe diffuse traumatic brain injury by comparison to the unilateral frontotemporoparietal decompressive craniectomy (uDC).

MATERIALS AND METHODS

Twenty three patients with severe diffuse traumatic brain injury from April 2015 to December 2019 were selected, including 10 cases underwent bbDC (bilateral group) and 13 cases underwent uDC (unilateral group). Compared with the postsurgical intracranial pressure (ICP), cerebral perfusion pressure, cerebral blood flow volume, postsurgical imaging score, the occurrence of complications as well as the 6 month outcome (Glasgow Outcome Scale, GOS) of two groups.

RESULTS

1. The postsurgical ICP was lower in the bbDC group than in the uDC group, while the postsurgical CCP and cerebral blood flow volume were higher in the bbDC group than in the uDC group. 2. Postsurgical imaging scores of the bbDC group were lower, indicating that the decompression effect of bbDC was more exhaustive than that of the uDC group. 3. The incidence of intraoperative acute cerebral bulging was lower in bbDC group than in uDC group. 4. The bbDC could effectively reduce the proportion of patients with the worst prognosis (dead+vegetative state).

CONCLUSION

For patients with severe, diffuse traumatic brain injury combined with bilateral or unilateral pupil dilation, bilateral balanced decompression craniotomy is an effective method, which should be performed as soon as possible. As compared to unilateral decompression, the decompression effect on the brainstem is more thorough; the incidence of acute cerebral bulging, postoperative incisional hernia, and postoperative cerebral infarction involving a large area are reduced. ICP can be better controlled, cerebral perfusion pressure and cerebral blood flow increases, improving the patient's survival rate, quality of life, and prognosis.

Inhalational Gases for Neuroprotection in Traumatic Brain Injury

Despite multiple prior pharmacological trials in traumatic brain injury (TBI), the search for an effective, safe, and practical treatment of these patients remains ongoing. Given the ease of delivery and rapid absorption into the systemic circulation, inhalational gases that have neuroprotective properties will be an invaluable resource in the clinical management of TBI patients. In this review, we perform a systematic review of both pre-clinical and clinical reports describing inhalational gas therapy in the setting of TBI. Hyperbaric oxygen, which has been investigated for many years, and some of the newest developments are reviewed. Also, promising new therapies such as hydrogen gas, hydrogen sulfide gas, and nitric oxide are discussed. Moreover, novel therapies such as xenon and argon gases and delivery methods using microbubbles are explored.

Postinjury treatments to make early tactical aeromedical evacuation practical for the brain after TBI

BACKGROUND

Traumatic brain injury (TBI) is common in civilians and military personnel. No potential therapeutics have been evaluated to prevent secondary injury induced by the hypobaric hypoxia (HH) environment integral to postinjury aeromedical evacuation (AE). We examined the role of allopurinol, propranolol, adenosine/lidocaine/magnesium (ALM), or amitriptyline administration prior to simulated flight following murine TBI.

METHODS

Mice underwent TBI and were given allopurinol, propranolol, amitriptyline, or ALM prior to simulated AE or normobaric normoxia (NN) control. Heart rate (HR), respiratory rate, and oxygen saturation (Spo2) were recorded throughout simulated AE. Mice were sacrificed at 24 hours, 7 days, or 30 days. Serum and cerebral cytokines were assessed by enzyme-linked immunosorbent assay. Motor function testing was performed with Rotarod ambulation. Immunohistochemistry was conducted to examine phosphorylated tau (p-tau) accumulation in the hippocampus at 30 days.

RESULTS

While all treatments improved oxygen saturation, propranolol, amitriptyline, and allopurinol improved AE-induced tachycardia. At 24 hours, both propranolol and amitriptyline reduced tumor necrosis factor alpha levels while allopurinol and ALM reduced tumor necrosis factor alpha levels only in NN mice. Propranolol, amitriptyline, and ALM demonstrated lower serum monocyte chemoattractant protein-1 7 days after AE. Both amitriptyline and allopurinol improved Rotarod times for AE mice while only allopurinol improved Rotarod times for NN mice. Propranolol was able to reduce p-tau accumulation under both HH and NN conditions while ALM only reduced p-tau in hypobaric hypoxic conditions.

CONCLUSION

Propranolol lowered post-TBI HR with reduced proinflammatory effects, including p-tau reduction. Amitriptyline-induced lower post-TBI HR and improved functional outcomes without affecting inflammatory response. Allopurinol did not affect vital signs but improved late post-TBI systemic inflammation and functional outcomes. Adenosine/lidocaine/magnesium provided no short-term improvements but reduced p-tau accumulation at 30 days in the HH cohort. Allopurinol may be the best of the four treatments to help prevent short-term functional deficits while propranolol may address long-term effects.

LEVEL OF EVIDENCE

Basic science article.

Influence of Time to Transport to a Higher Level Facility on the Clinical Outcomes of US Combat Casualties with TBI: A Multicenter 7-Year Study

INTRODUCTION

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide and is associated with mortality rates as high as 30%. Patients with TBI are at high risk for secondary injury and need to be transported to definitive care expeditiously. However, the physiologic effects of aeromedical evacuation are not well understood and may compound these risks. Combat TBI patients may benefit from delayed aeromedical evacuation. The goal of this study was to evaluate the impact of transport timing out of theater via Critical Care Air Transport Teams (CCATT) to a higher level facility on the clinical outcomes of combat casualties with TBI.

MATERIALS AND METHODS

We performed a retrospective review of patients with TBI who were evacuated out of theater by CCATT from January 2007 to May 2014. Data abstractors collected flight information, vital signs, procedures, in-flight assessments, and outcomes. Time to transport was defined as the time from injury to CCATT evacuation out of combat theater. We calculated descriptive statistics and constructed regression models to determine the association between time to transport and clinical outcomes. This study was approved by the U.S. Air Force 59th Medical Wing Institutional Review Board.

RESULTS

We analyzed the records of 438 patients evacuated out of theater via CCATT and categorized them into three groups: patients who were transported in one day or less (n = 165), two days (n = 163), and three or more days (n = 110). We used logistic regression models to compare outcomes among patients who were evacuated in two days or three or more days to those who were transported within one day while adjusting for demographics, injury severity, and injury type. Patients who were evacuated in two days or three or more days had 50% lower odds of being discharged on a ventilator and were twice as likely to return to duty or be discharged home than those who were evacuated within one day. Additionally, patients transported in three or more days were 70% less likely to be ventilated at discharge with a GCS of 8 or lower and had 30% lower odds of mortality than those transported within one day.

CONCLUSIONS

In patients with moderate to severe TBI, a delay in aeromedical evacuation out of the combat theater was associated with improved mortality rates and a higher likelihood of discharge to home and return to duty dispositions. This study is correlational in nature and focused on CCATT transports from Role III to Role IV facilities; as such, care must be taken in interpreting our findings and future studies are needed to establish a causal link between delayed evacuation and improved discharge disposition. Our study suggests that delaying aeromedical evacuation of TBI patients when feasible may confer benefit.

An Endovascular Surgery Experience in Far-Forward Military Healthcare-A Case Series

SUMMARY

INTRODUCTION

The advancement of interventional neuroradiology has drastically altered the treatment of stroke and trauma patients. These advancements in first-world hospitals, however, have rarely reached far forward military hospitals due to limitations in expertise and equipment. In an established role III military hospital though, these life-saving procedures can become an important tool in trauma care.

MATERIALS AND METHODS

We report a retrospective series of far-forward endovascular cases performed by 2 deployed dual-trained neurosurgeons at the role III hospital in Kandahar, Afghanistan during 2013 and 2017 as part of Operations Resolute Support and Enduring Freedom.

RESULTS

A total of 15 patients were identified with ages ranging from 5 to 42 years old. Cases included 13 diagnostic cerebral angiograms, 2 extremity angiograms and interventions, 1 aortogram and pelvic angiogram, 1 bilateral embolization of internal iliac arteries, 1 lingual artery embolization, 1 administration of intra-arterial thrombolytic, and 2 mechanical thrombectomies for acute ischemic stroke. There were no complications from the procedures. Both embolizations resulted in hemorrhage control, and 1 of 2 stroke interventions resulted in the improvement of the NIH stroke scale.

CONCLUSIONS

Interventional neuroradiology can fill an important role in military far forward care as these providers can treat both traumatic and atraumatic cerebral and extracranial vascular injuries. In addition, knowledge and skill with vascular access and general interventional radiology principles can be used to aid in other lifesaving interventions. As interventional equipment becomes more available and portable, this relatively young specialty can alter the treatment for servicemen and women who are injured downrange.

Flying After Concussion and Symptom Recovery in College Athletes and Military Cadets

IMPORTANCE

Concussions are a common occurrence in young athletes. Hypobaric hypoxemia, such as that experienced during airplane travel, can potentially cause alterations to cerebral blood flow and increased neuroinflammatory response. It remains unknown whether flying early after a concussion may influence the clinical course of injury.

OBJECTIVE

To determine whether there is an association between concussion recovery and airplane travel in collegiate athletes and military cadets.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study was conducted by the National Collegiate Athletic Association and US Department of Defense Concussion Assessment, Research, and Education Consortium from August 3, 2014, to September 13, 2018. Participant groups were categorized by those who flew within 72 hours of injury and those who did not fly. All participants included in the final analyses had complete data of interest and only 1 injury during the study. Data analysis was performed from September 2018 to March 2020.

MAIN OUTCOMES AND MEASURES

Recovery outcome measures were defined as time (in days) from injury to return to activity, school, and baseline symptoms. Symptom and headache severity scores were derived from the Sports Concussion Assessment Tool-Third Edition. Scores for both groups were taken at baseline and a median of 2 days after injury.

RESULTS

A total of 92 participants who flew (mean [SD] age, 19.1 [1.2] years; 55 male [59.8%]) and 1383 participants who did not fly (mean [SD] age, 18.9 [1.3] years; 809 male [58.5%]) were included in the analysis of symptom recovery outcomes (analysis 1). Similarly, 100 participants who flew (mean [SD] age, 19.2 [1.2] years; 63 male [63.0%]) and 1577 participants who did not fly (mean [SD] age, 18.9 [1.3] years; 916 male [58.1%]) were included in the analysis of symptom severity outcomes (analysis 2). No significant group differences were found regarding recovery outcome measures. Likewise, there were no group differences in symptom (estimated mean difference, 0.029; 95% CI, -0.083 to 0.144; P = .67) or headache (estimated mean difference, -0.007; 95% CI, -0.094 to 0.081; P = .91) severity scores.

CONCLUSIONS AND RELEVANCE

Airplane travel early after concussion was not associated with recovery or severity of concussion symptoms. These findings may help guide future recommendations on flight travel after concussion in athletes.

Hypobaria during aeromedical evacuation exacerbates histopathological injury and modifies inflammatory response in rats exposed to blast overpressure injury

BACKGROUND

Aeromedical evacuation (AE) is often used as a rapid and effective way to evacuate patients. However, little is known about the possible effects of AE on patients with blast and traumatic brain injury. In the current study, we used blast overpressure (BOP) as a method to introduce traumatic brain injury in rats and investigated the effects of hypobaria during AE on histology and inflammatory response.

METHODS

Animals were exposed to a 12-hour flight 2 days after BOP and euthanized 48 hours after flight. Control animals were kept at normobaria.

RESULTS

Overall, BOP animals exposed to flight demonstrated higher histopathologic injury scores as compared to control animals in lungs, brain, kidney, heart, and intestine. The BOP animals exposed to normobaria exhibited a proinflammatory response compared to those that were not blasted, an observation that was not seen in BOP animals exposed to hypobaria.

CONCLUSION

These data suggest that AE 48 hours post blast may lead to impairment in the inflammatory process and worsening of long-term outcomes.

LEVEL OF EVIDENCE

Animal research, level II.

Neurosurgery and Medical Management of Severe Head Injury

Management of the patient with moderate to severe brain injury in any environment can be time consuming and resource intensive. In the austere or hostile environment, the challenges to deliver care to this patient population are magnified. These guidelines have been developed by acknowledging commonly recognized recommendations for neurosurgical and neuro-critical care patients and augmenting those evaluations and interventions based on the experience of neurosurgeons, trauma surgeons, and intensivists who have delivered care during recent coalition conflicts.

Aeromedical evacuation-relevant hypobaria worsens axonal and neurologic injury in rats after underbody blast-induced hyperacceleration

BACKGROUND

Occupants of military vehicles targeted by explosive devices often suffer from traumatic brain injury (TBI) and are typically transported by the aeromedical evacuation (AE) system to a military medical center within a few days. This study tested the hypothesis that exposure of rats to AE-relevant hypobaria worsens cerebral axonal injury and neurologic impairment caused by underbody blasts.

METHODS

Anesthetized adult male rats were secured within cylinders attached to a metal plate, simulating the hull of an armored vehicle. An explosive located under the plate was detonated, resulting in a peak vertical acceleration force on the plate and occupant rats of 100G. Rats remained under normobaria or were exposed to hypobaria equal to 8,000 feet in an altitude chamber for 6 hours, starting at 6 hours to 6 days after blast. At 7 days, rats were tested for vestibulomotor function using the balance beam walking task and euthanized by perfusion. The brains were then analyzed for axonal fiber injury.

RESULTS

The number of internal capsule silver-stained axonal fibers was greater in animals exposed to 100G blast than in shams. Animals exposed to hypobaria starting at 6 hours to 6 days after blast exhibited more silver-stained fibers than those not exposed to hypobaria. Rats exposed to 100% oxygen (O2) during hypobaria at 24 hours postblast displayed greater silver staining and more balance beam foot-faults, in comparison with rats exposed to hypobaria under 21% O2.

CONCLUSION

Exposure of rats to blast-induced acceleration of 100G increases cerebral axonal injury, which is significantly exacerbated by exposure to hypobaria as early as 6 hours and as late as 6 days postblast. Rats exposed to underbody blasts and then to hypobaria under 100% O2 exhibit increased axonal damage and impaired motor function compared to those subjected to blast and hypobaria under 21% O2. These findings raise concern about the effects of AE-related hypobaria on TBI victims, the timing of AE after TBI, and whether these effects can be mitigated by supplemental oxygen.

Decompressive Craniectomy in Traumatic Brain Injury: A Review Article

The importance of treating traumatic brain injury (TBI) is well known worldwide. Although many studies have been conducted in this topic, there is still much uncertainty about the effectiveness of surgical treatment in TBI. Recently, good randomized controlled trial (RCT) papers about the effectiveness of decompressive craniectomy (DC) in TBI has been published. In this article, we will review the overall contents of the DC (historical base, surgical technic, rationale, complications) and the results of the recently published RCT paper.

Interleukin 6 mediates neuroinflammation and motor coordination deficits after mild traumatic brain injury and brief hypoxia in mice

Traumatic brain injury (TBI) is a leading cause of mortality and disability. Acute postinjury insults after TBI, such as hypoxia, contribute to secondary brain injury and worse clinical outcomes. The functional and neuroinflammatory effects of brief episodes of hypoxia experienced following TBI have not been evaluated. Our previous studies have identified interleukin 6 (IL-6) as a potential mediator of mild TBI-induced pathology. In the present study, we sought to determine the effects of brief hypoxia on mild TBI and whether IL-6 played a role in the neuroinflammatory and functional deficits after injury. A murine model of mild TBI was induced by a weight drop (500 g from 1.5 cm). After injury, mice were exposed to immediate hypoxia (FIO2 = 15.1%) or normoxia (FIO2 = 21%) for 30 min. Serum and brain samples were analyzed for inflammatory cytokines 24 h after TBI. Neuron-specific enolase was measured as a serum biomarker of brain injury. Evaluation of motor coordination was performed for 5 days after TBI using a rotarod device. In some animals, anti-IL-6 was administered following TBI and hypoxia to neutralize systemic IL-6. Mice undergoing TBI had significant increases in brain injury. Exposure to brief hypoxia after TBI resulted in a more than 5-fold increase in serum neuron-specific enolase. This increase was associated with increases in serum and brain cytokine expression, suggesting that brief hypoxia exacerbates systemic and brain inflammation. Neutralization of IL-6 suppressed postinjury neuroinflammation and neuronal injury. In addition, TBI and hypoxia induced significant motor coordination deficits that were completely abrogated by IL-6 blockade. Exposure to hypoxia after TBI induces neuroinflammation and brain injury. These changes can be mitigated by neutralization of systemic IL-6. Interleukin 6 blockade also corrected the TBI-induced deficit in motor coordination. These data suggest that systemic IL-6 modulates the degree of neuroinflammation and contributes to reduced motor coordination after mild TBI.

A murine model of mild traumatic brain injury exhibiting cognitive and motor deficits

BACKGROUND

Mild traumatic brain injury (TBI) is a serious public health concern affecting more than 1.7 million people in the United States annually. Mild TBI is difficult to diagnose and is clinically associated with impaired motor coordination and cognition.

METHODS

We subjected mice to a mild TBI (mTBI-1 or mTBI-2) induced by a weight drop model. We assessed brain injury histologically and biochemically, the latter by serum neuron-specific enolase and glial fibrillary acidic protein. Systemic and brain inflammation were measured by cytokine array. We determined blood-brain barrier integrity by cerebral vascular leakage of micromolecular and macromolecular fluorescent molecules. We evaluated mice using a rotarod device and novel object recognition to measure motor coordination and cognition, respectively.

RESULTS

Mice undergoing mTBI-1 or mTBI-2 had significant deficits in motor coordination and cognition for several days after injury compared with controls. Furthermore, both mTBI-1 and mTBI-2 caused micromolecular leakage in the blood-brain barrier, whereas only mTBI-2 caused macromolecular leakage. Serum neuron-specific enolase and glial fibrillary acidic protein were elevated acutely and corresponded to the degree of injury, but returned to baseline within 24 h. Serum cytokines interleukin-6 and keratinocyte-derived chemokine were significantly increased within 90 min of TBI. Interleukin-6 levels correlated with the degree of injury.

CONCLUSIONS

The current study provides a reproducible model of mild TBI in mice that exhibits pathologic features of mild TBI in humans. Furthermore, our data suggest that serum cytokines, such as IL-6, may be effective biomarkers for severity of head injury.

Decompressive Craniectomy and Traumatic Brain Injury: A Review

Intracranial hypertension is the largest cause of death in young patients with severe traumatic brain injury. Decompressive craniectomy is part of the second level measures for the management of increased intracranial pressure refractory to medical management as moderate hypothermia and barbiturate coma. The literature lack of concepts is their indications. We present a review on the state of the art.

Long-range critical care evacuation and reoperative surgery

Long-range critical care aeromedical evacuation has significantly contributed to the unprecedented survival during recent military operations. With advances in critical care, patients with increased injury severity and overall complexity are routinely evacuated while resuscitation is ongoing. Additional specialty teams now provide advanced pulmonary rescue therapies for the most critically ill patients. As part of the continuum of trauma care, an overseas fixed facility provides follow-on emergency surgical critical care to optimize patient outcomes before final evacuation to the continental United States.

Use of serum biomarkers to predict cerebral hypoxia after severe traumatic brain injury

The management of severe traumatic brain injury (TBI) focuses on prevention and treatment of secondary insults such as cerebral hypoxia (CH). There are a number of biomarkers that are thought to play a part in secondary injury following severe TBI. This study evaluates the association between S100β, neuron-specific enolase (NSE), and glial fibrillary acidic protein (GFAP), detected in the serum of severe TBI patients and CH as measured by brain tissue oxygen partial pressure (Pbo(2)). Patients with severe TBI were prospectively enrolled. Pressure times time (PTD; mm Hg*h), measuring the depth and duration of CH, was calculated for 12-h periods for episodes of moderate (Pbo(2) < 20 mm Hg) and severe (Pbo(2) < 15 mm Hg) CH, and compared to serum levels of S100β, NSE, and GFAP drawn prior to periods of monitoring. An adjusted mixed model analysis was applied as was receiver operating characteristic (ROC) curve analysis. Of 76 patients enrolled, 24 had Pbo(2) monitoring. One hundred and thirty serum samples were matched with 12-h periods of monitoring. Significant associations were found in adjusted analyses between increasing serum levels of S100β (coefficient=0.57, 0.56; p<0.001), NSE (coefficient=0.48, 0.52; p<0.001), and GFAP (coefficient=0.29, 0.30; p=0.003 and 0.002), and increasing PTD of moderate (Pbo(2)<20 mm Hg) and severe (Pbo(2)<15 mm Hg) CH. AUCs for the prediction of moderate and severe CH were 0.62 and 0.66 for S100β, 0.55 and 0.71 for NSE, and 0.50 and 0.62 for GFAP, respectively. Specificities were between 76% and 90% for S100β and NSE. S100β, NSE, and GFAP demonstrate promise as candidate serum markers of impending CH. The fact that these biomarker elevations occur prior to the onset of clinical manifestations suggests that we may be able to predict imminent events following TBI. Given the morbidity of CH, early intervention and prevention may have a significant impact on outcomes and help guide decisions about the timing of interventions.

Association of CSF biomarkers and secondary insults following severe traumatic brain injury

BACKGROUND

Management of severe traumatic brain injury (TBI) focuses on mitigating secondary insults. There are a number of biomarkers that are thought to play a part in secondary injury following severe TBI. Two of these, S100β and neuron-specific enolase (NSE), have been extensively studied in the setting of neurological injury. This pilot study was undertaken to investigate the relationship of S100β and NSE to clinical markers of severity and poor outcome: intracranial hypertension (ICH), and cerebral hypoperfusion (CH).

METHODS

Patients at the R Adams Cowley Shock Trauma Center were prospectively enrolled over an 18-month period. Inclusion criteria were: age > 18, admission within the first 6 h after injury, Glasgow Coma Scale (GCS) < 9 on admission, isolated TBI, and placement of an intraventricular catheter (IVC). Patients were managed according to an institutional protocol based on the Brain Trauma Foundation Guidelines. CSF was collected from the IVC on admission and twice daily for 7 days. S100β and NSE levels were analyzed by ELISA. CSF levels drawn before (PRE) and after (POST) 12-h time periods were compared to percentage time intracranial pressure (ICP) > 20 mmHg (% ICP(20)) and cerebral perfusion pressure (CPP) < 60 mmHg (% CPP(60)), and cumulative "Pressure times Time Dose" (PTD) for episodes of ICP > 20 mmHg (PTD ICP(20)) and CPP < 60 mmHg (PTD CPP(60)). Statistical analysis was performed using the Student's t test to compare means and non-parametric Wilcoxon statistic to compare ranked data. Linear regression methods were applied to compare levels of S100β and NSE with ICP and CPP(.)

RESULTS

Twenty-three patients were enrolled. The cohort of patients was severely injured and neurologically compromised on admission (admission GCS = 5.6 ± 3.1, Injury Severity Score (ISS) = 31.9 ± 10.6, head Abbreviated Injury Scale (AIS) = 4.4 ± 0.7, Marshall score = 2.6 ± 0.9). Elevated levels of S100β and NSE were found in all 223 CSF samples analyzed. ICH was found to be associated with PRE and POST S100β levels when measured as % ICP(20) (r = 0.20 and r = 0.23, P < 0.01) and PTD ICP(20) (r = 0.35 and r = 0.26, P < 0.001). POST increasing NSE levels were weakly correlated with increasing PTD ICP(20) (r = 0.17, P = 0.01). PRE S100β levels were associated with episodes of CH as measured by % CPP(60) (r = 0.20, P = 0.002) and both PRE and POST S100β levels were associated with PTD CPP(60) (r = 0.24 and r = 0.23, P < 0.001). PRE and POST NSE levels were also associated with episodes of CH as measured by % CPP(60) (r = 0.22 and r = 0.18, P < 0.01) and PTD CPP(60) (r = 0.20 and r = 0.21, P < 0.01).

CONCLUSIONS

In this preliminary analysis, S100β levels were associated with ICH and CH over a full week of ICP monitoring. We also found associations between CH and NSE levels in CSF of patients with severe TBI. Our results suggest that there is an association between levels of ICH and CH and these biomarkers when measured before episodes of clinically significant secondary insults. These markers of neuronal cell death demonstrate promise as both indicators of impending clinical deterioration and targets of future therapeutic interventions.

Traumatic brain injury

There is an increasing incidence of military traumatic brain injury (TBI), and similar injuries are seen in civilians in war zones or terrorist incidents. Indeed, blast-induced mild TBI has been referred to as the signature injury of the conflicts in Iraq and Afghanistan. Assessment involves schemes that are common in civilian practice but, in common with civilian TBI, takes little account of information available from modern imaging (particularly diffusion tensor magnetic resonance imaging) and emerging biomarkers. The efficient logistics of clinical care delivery in the field may have a role in optimizing outcome. Clinical care has much in common with civilian TBI, but intracranial pressure monitoring is not always available, and protocols need to be modified to take account of this. In addition, severe early oedema has led to increasing use of decompressive craniectomy, and blast TBI may be associated with a higher incidence of vasospasm and pseudoaneurysm formation. Visual and/or auditory deficits are common, and there is a significant risk of post-traumatic epilepsy. TBI is rarely an isolated finding in this setting, and persistent post-concussive symptoms are commonly associated with post-traumatic stress disorder and chronic pain, a constellation of findings that has been called the polytrauma clinical triad.