Dysregulation of the actin scavenging system and inhibition of DNase activity following severe thermal injury.

BACKGROUND: Circulating cell-free DNA (cfDNA) is not found in healthy subjects, but is readily detected after thermal injury and may contribute to the risk of multiple organ failure. The hypothesis was that a postburn reduction in DNase protein/enzyme activity could contribute to the increase in cfDNA following thermal injury. METHODS: Patients with severe burns covering at least 15 per cent of total body surface area were recruited to a prospective cohort study within 24 h of injury. Blood samples were collected from the day of injury for 12 months. RESULTS: Analysis of blood samples from 64 patients revealed a significant reduction in DNase activity on days 1-28 after injury, compared with healthy controls. DNase protein levels were not affected, suggesting the presence of an enzyme inhibitor. Further analysis revealed that actin (an inhibitor of DNase) was present in serum samples from patients but not those from controls, and concentrations of the actin scavenging proteins gelsolin and vitamin D-binding protein were significantly reduced after burn injury. In a pilot study of ten military patients with polytrauma, administration of blood products resulted in an increase in DNase activity and gelsolin levels. CONCLUSION: The results of this study suggest a novel biological mechanism for the accumulation of cfDNA following thermal injury by which high levels of actin released by damaged tissue cause a reduction in DNase activity. Restoration of the actin scavenging system could therefore restore DNase activity, and reduce the risk of cfDNA-induced host tissue damage and thrombosis.

ANTECEDENTES: El ADN libre de las células circulantes (circulating cell-free DNA, cfDNA) no se encuentra en sujetos sanos, pero se detecta fácilmente después de una lesión térmica y puede contribuir al riesgo de fallo multiorgánico. La hipótesis fue que una disminución en la actividad de la proteína/enzima ADNasa tras la lesión térmica podría contribuir a la elevación del cfDNA que ocurre tras la misma. MÉTODOS: Los pacientes con quemaduras graves con una extensión ≥ 15% del área de superficie corporal total (total body surface area, TBSA) se incluyeron en un estudio prospectivo de cohortes durante las primeras 24 horas posteriores a la lesión. Se recogieron muestras de sangre desde el día de la lesión hasta los 12 meses posteriores a la misma. RESULTADOS: El análisis de muestras de sangre de 64 pacientes reveló una reducción significativa de la actividad de la ADNasa en los días 1 a 28 después de la lesión, en comparación con los controles sanos. Los niveles de proteína ADNasa no se vieron afectados, lo que sugiere la presencia de un inhibidor enzimático. Un análisis adicional reveló que la actina (un inhibidor de la ADNasa) estaba presente en las muestras de suero de los pacientes, pero no en los controles, y las concentraciones de la gelsolina, proteína que causa la disociación de la actina, y la proteína de unión a la vitamina D se redujeron significativamente después de la lesión térmica. En un estudio piloto de 10 pacientes con politrauma por lesiones militares, la administración de hemoderivados produjo un aumento en la actividad de la ADNasa y de los niveles de gelsolina. CONCLUSIÓN: Este estudio sugiere un nuevo mecanismo biológico para la acumulación de cfDNA después de una lesión térmica, por el cual los altos niveles de actina liberada por el tejido dañado causarían una reducción en la actividad de la ADNasa. La restauración del sistema eliminador de actina podría, por lo tanto, restaurar la actividad de la ADNasa y reducir el riesgo de daño tisular y trombosis en el huésped inducido por el cfDNA.

Guidelines for using animal models in blast injury research.

Blast injury is a very complex phenomenon and frequently results in multiple injuries. One method to investigate the consequences of blast injuries is with the use of living systems (animal models). The use of animals allows the examination and evaluation of injury mechanisms in a more controlled manner, allowing variables such as primary or secondary blast injury for example, to be isolated and manipulated as required. To ensure a degree of standardisation across the blast research community a set of guidelines which helps researchers navigate challenges of modelling blast injuries in animals is required. This paper describes the guidelines for Using Animal Models in Blast Injury Research developed by the NATO Health Factors and Medicine (HFM) Research Task Group 234.

Guidelines for conducting epidemiological studies of blast injury.

Blast injuries are often caused by more than one mechanism, do not occur in isolation, and typically elicit a secondary multi-system response. Research efforts often do not separate blast injuries caused by blast waves from those caused by blunt force trauma and other mechanisms. 15 experts from nine different NATO nations developed in the HFM Research Task Group (RTG; HFM-234 (RTG)) 'Environmental Toxicology of Blast Exposures: Injury Metrics, Modelling, Methods and Standards' Guidelines for Conducting Epidemiological Studies of Blast Injury. This paper describes these guidelines, which are intended to provide blast injury researchers and clinicians with a basic set of recommendations for blast injury epidemiological study design and data collection that need to be considered and described when conducting prospective longitudinal studies of blast injury.

Nebulised recombinant activated factor VII (rFVIIa) does not attenuate the haemorrhagic effects of blast lung injury.

INTRODUCTION: Primary blast lung injury causes intrapulmonary haemorrhage. A number of case reports have suggested the efficacy of recombinant activated factor VII (rFVIIa) in the treatment of diffuse alveolar haemorrhage from a range of medical causes, but its efficacy in blast lung is unknown. The aim of this study was to investigate whether nebulised rFVIIa attenuates the haemorrhagic effects of blast lung injury in an animal model. METHODS: Terminally anaesthetised rabbits subjected to blast lung injury were randomised to receive either rFVIIa or placebo via a nebuliser. The primary outcome was the level of blood iron-transferrin complex, a marker of the extent of blast lung injury, analysed using low temperature electron paramagnetic resonance spectroscopy. RESULTS: Blast exposure led to a significant fall in iron-bound transferrin in both groups of animals (p<0.001), which remained depressed during the study. There were no significant differences in iron-transferrin between the rFVIIa and placebo treatment groups over the duration of the study (p=0.081), and there was no trend towards elevated iron-transferrin in the rFVIIa-treated group once drug treatment had started. There was suggestive evidence of systemic absorption of rFVIIa given via the inhaled route. CONCLUSION: A single dose of nebulised rFVIIa did not attenuate pulmonary haemorrhage in a rabbit model of blast lung injury. As there was some evidence of systemic absorption, the inhaled route does not avoid the concern about potential thromboembolic complications from administration of rFVIIa.

Primary blast lung injury - a review.

Bomb or explosion-blast injuries are likely to be increasingly encountered as terrorist activity increases and pre-hospital medical care improves. We therefore reviewed the epidemiology, pathophysiology and treatment of primary blast lung injury. In addition to contemporary military publications and expert recommendation, an EMBASE and MEDLINE search of English speaking journals was undertaken using the medical subject headings (MeSHs) 'blast injury' and 'lung injury'. Review articles, retrospective case series, and controlled animal modelling studies published since 2000 were evaluated. 6-11% of military casualties in recent conflicts have suffered primary blast lung injury but the incidence increases to more than 90% in terrorist attacks occurring in enclosed spaces such as trains. The majority of victims require mechanical ventilation and intensive care management. Specific therapies do not exist and treatment is supportive utilizing current best practice. Understanding the consequences and supportive therapies available to treat primary blast lung injury are important for anaesthetists.

Modelling primary blast lung injury: current capability and future direction.

Primary blast lung injury frequently complicates military conflict and terrorist attacks on civilian populations. The fact that it occurs in areas of conflict or unpredictable mass casualty events makes clinical study in human casualties implausible. Research in this field is therefore reliant on the use of some form of biological or non-biological surrogate model. This article briefly reviews the modelling work undertaken in this field until now and describes the rationale behind the generation of an in silico physiological model.

An evaluation of the normal range of StO2measurements at rest and following a mixed exercise protocol.

BACKGROUND: Assessment of local tissue oxygenation (StO2) using near infrared spectroscopy is an emerging technique in medical practice with applications in trauma/sepsis management, diagnosis of acute compartment syndrome and assessment of tissue viability. Despite this, there have been little published data on the range of StO2values in normal subjects. METHODS: StO2measurements were recorded in 105 infantry soldiers using an INVOS System Monitor (Somanetics) from both deltoids, the anterior compartment of the leg and the frontal lobe of the brain. Measurements were taken at rest and following completion of a mixed exercise protocol, consisting of overarm pull-ups, sit-ups and a 3-mile run. RESULTS: StO2values at rest were found to have a wide normal range with a skew left distribution. Mean StO2was similar between the deltoids (left deltoid 80%, right deltoid 79%), but significantly different between other anatomical sites (leg 68%, brain 73%). However, all sites demonstrated a similar lower range cut-off at approximately 40%. Following exercise, there was a significant increase in StO2values at all sites (left deltoid by 3.1 ± 2.0%, right deltoid by 2.6 ± 2.3%, leg by 8.0 ± 2.3% and brain by 8.6 ± 1.9%), which persisted for at least 10 min. CONCLUSIONS: There were statistically significant differences in mean StO2values recorded at different anatomical sites, although the reference ranges were wide and substantially overlapped. StO2increased at all sites after exercise with the effect persisting for at least 10 min. The interaction between exercise and pathological phenomena remains unknown and is an area for further study.

Haemodynamic changes in trauma.

Trauma is the leading cause of death during the first four decades of life in the developed countries. Its haemodynamic response underpins the patient's initial ability to survive, and the response to treatment and subsequent morbidity and resolution. Trauma causes a number of insults including haemorrhage, tissue injury (nociception) and, predominantly, in military casualties, blast from explosions. This article discusses aspects of the haemodynamic responses to these insults and subsequent treatment. 'Simple' haemorrhage (blood loss without significant volume of tissue damage) causes a biphasic response: mean arterial blood pressure (MBP) is initially maintained by the baroreflex (tachycardia and increased vascular resistance, Phase 1), followed by a sudden decrease in MAP initiated by a second reflex (decrease in vascular resistance and bradycardia, Phase 2). Phase 2 may be protective. The response to tissue injury attenuates Phase 2 and may cause a deleterious haemodynamic redistribution that compromises blood flow to some vital organs. In contrast, thoracic blast exposure augments Phase 2 of the response to haemorrhage. However, hypoxaemia from lung injury limits the effectiveness of hypotensive resuscitation by augmenting the attendant shock state. An alternative strategy ('hybrid resuscitation') whereby tissue perfusion is increased after the first hour of hypotensive resuscitation by adopting a revised normotensive target may ameliorate these problems. Finally, morphine also attenuates Phase 2 of the response to haemorrhage in some, but not all, species and this is associated with poor outcome. The impact on human patients is currently unknown and is the subject of a current physiological investigation.

Deployed research.

The Role 3 Medical Treatment Facility (Field Hospital) in Camp Bastion (R3 Bastion) is acknowledged to be one of the busiest dedicated trauma facilities in the world. Casualties typically present with severe injuries and in physiological extremis. These casualties form a unique cohort representing the most relevant population to evaluate the effectiveness of treating battlefield injuries as academic clinicians and scientists interested in trauma seek to improve outcomes for such patients in the future. This article describes four separate but related research projects that have been undertaken in Camp Bastion, Afghanistan, over the last year. They traverse the spectrum of clinical research, ranging from data collection to a randomised control trial. The aim is to discuss some of the problems encountered and the solutions that made it possible to undertake research in a theatre of operations, thereby providing a starting point for others who may wish to initiate research in a similar environment.

Modelling the blast environment and relating this to clinical injury: experience from the 7/7 inquest.

This paper addresses the computational modelling of a series of specific blast-related incidents and the relationships of clinical and engineering interpretations. The Royal Centre for Defence Medicine and the Defence Science and Technology Laboratory were tasked in 2010 by the UK Ministry of Defence to assist the Coroner's inquests into the 7 July 2005 London bombings. A three phase approach was taken. The first phase included an engineering expert in blast effects on structures reviewing photographs of the damaged carriages and bus to give a view on the likely physical effects on people close to the explosions. The second phase was a clinical review of the evidence by military clinicians to assess blast injury in the casualties. The third phase was to model the blast environment by structural dynamics experts to assess likely blast loading on victims to evaluate the potential blast loading on individuals. This loading information was then assessed by physiology experts. Once all teams (engineering, clinical and modelling/physiological) had separately arrived at their conclusions, the information streams were integrated to arrive at a consensus. The aim of this paper is to describe the methodology used as a potential model for others to consider if faced with a similar investigation, and to show the benefit of the transition of military knowledge to a civilian environment.

Utility of interim ROTEM(®) values of clot strength, A5 and A10, in predicting final assessment of coagulation status in severely injured battle patients.

BACKGROUND: Proactive management of trauma-related coagulopathy requires early identification and rapid assessment in order to allow targeted resuscitation. This study determined whether early (interim) ROTEM(®) (TEM International GmbH, Munich, Germany) values could predict hypocoagulopathy in seriously injured military patients. METHODS: Normal ranges for ROTEM(®) values were obtained from 50 volunteers. 108 samples were collected during the early phase of clinical management from 48 severe trauma patients. The blood was subject to EXTEM analysis and compared to the 95% tolerance limits from the volunteers. Coagulopathy (was deemed to be present if EXTEM MCF was below 40 mm, which is in the range indicating clinical concern defined by the ROTEM(®) Expert Working Group. RESULTS: The normal range data was broadly similar to ROTEM(®) published data. Admission samples were available from 31 battlefield casualties, and 39% of these were coagulopathic 51% of the samples from all 48 patients were coagulopathic (EXTEM MCF<40 mm) and interim EXTEM values of these at 5 and 10 min (A5 and A10) predicted coagulopathy with sensitivities/specificities of 0.96/0.58 (A5) and 1.00/0.70 (A10). In addition, statistical comparison of clotting domains between normal volunteers and trauma patients suggests a difference in clot strengths due to a difference in platelet function rather than platelet number (mean 142 × 10(9)l(-1)). CONCLUSIONS: The A10 value of ROTEM(®) provides an early sensitive and specific assessment of coagulopathy after military trauma and may be of utility in guiding bespoke resuscitation. We found some speculative evidence that in major trauma platelet function is particularly affected.

Temporal changes in ROTEM®-measured coagulability of citrated blood samples from coagulopathic trauma patients.

BACKGROUND: Rotational thromboelastometry (ROTEM(®)) relies on citrated blood samples, which are regarded as biologically stable for up to 4 h after venepuncture. However, this recommendation is based on data from normal volunteers. The aim of this study was to evaluate possible temporal changes in the coagulability of blood samples from coagulopathic trauma patients. PATIENTS AND METHODS: This is a prospective series of 10 coagulopathic (maximum clot firmness, MCF<40 mm) trauma patients. ROTEM(®) EXTEM (tissue factor activated) and FIBTEM (tissue factor activated, cytochalasin D inhibited) analyses were performed on samples obtained on admission, and after approximately 60 min of storage in an incubator, at 37°C. RESULTS: There were statistically significant differences between the median EXTEM MCF (22 mm vs 54 mm, p<0.001) and α angle (30.5 vs 59.5°, p=0.004) of the analyses performed immediately after sampling, and 51 min (median) subsequently, but not coagulation time (CT, p=0.133), clot formation time (p=0.0625) or maximum lysis (ML, p=0.154). There were also no differences in median FIBTEM MCF (p=1.00) or CT (p=0.877) between the immediate and delayed analyses. CONCLUSIONS: Repeated ROTEM(®) EXTEM analysis of citrated samples from coagulopathic trauma patients shows a spontaneous improvement in coagulability with time. The absence of parallel changes on FIBTEM analysis suggests that this effect may be due to a change in platelet function.

Blast injury research models.

Blast injuries are an increasing problem in both military and civilian practice. Primary blast injury to the lungs (blast lung) is found in a clinically significant proportion of casualties from explosions even in an open environment, and in a high proportion of severely injured casualties following explosions in confined spaces. Blast casualties also commonly suffer secondary and tertiary blast injuries resulting in significant blood loss. The presence of hypoxaemia owing to blast lung complicates the process of fluid resuscitation. Consequently, prolonged hypotensive resuscitation was found to be incompatible with survival after combined blast lung and haemorrhage. This article describes studies addressing new forward resuscitation strategies involving a hybrid blood pressure profile (initially hypotensive followed later by normotensive resuscitation) and the use of supplemental oxygen to increase survival and reduce physiological deterioration during prolonged resuscitation. Surprisingly, hypertonic saline dextran was found to be inferior to normal saline after combined blast injury and haemorrhage. New strategies have therefore been developed to address the needs of blast-injured casualties and are likely to be particularly useful under circumstances of enforced delayed evacuation to surgical care.

Characterization of the response to primary blast injury.

Lung injuries, predominantly arising from blast exposure, are a clinical problem in a significant minority of current military casualties. This special feature consists of a series of articles on lung injury. This first article examines the mechanism of the response to blast lung (primary blast injury to the lung). Subsequent articles examine the incidence of blast lung, clinical consequences and current concepts of treatment, computer (in silico) modelling of lung injury and finally chemical injuries to the lungs. Blast lung is caused by a shock wave generated by an explosion causing widespread damage in the lungs, leading to intrapulmonary haemorrhage. This, and the ensuing inflammatory response in the lung, leads to a compromise in pulmonary gas exchange and hypoxia that can worsen over several hours. There is also a characteristic cardio-respiratory effect mediated via an autonomic reflex causing apnoea (or rapid shallow breathing), bradycardia and hypotension (the latter possibly also due to the release of nitric oxide). An understanding of this response, and the way it modifies other reflexes, can help the development of new treatment strategies for this condition and for the way it influences the patient's response to concomitant injuries.

Development of a large animal model for investigating resuscitation after blast and hemorrhage.

BACKGROUND: Blast injuries are an increasing problem owing to the widespread terrorist threat, but hemorrhage remains the second leading cause of civilian trauma death. Against this background, increasing numbers of prehospital and military trauma organizations are advocating a hypotensive approach to resuscitation of the hypovolemic casualty, deliberately aiming not to achieve a normal blood pressure so as not to disturb any newly formed blood clots at the site of a vascular injury. METHODS: There are no data available to guide clinicians as to how best to resuscitate the blast-injured casualty who has also suffered a hemorrhagic injury. A large-scale program was initiated to examine this question and to offer clinical guidance on the optimal resuscitation strategy in such circumstances in terms of volume, type of fluid, speed of resuscitation, and appropriate endpoints. Before such experiments could be undertaken, a novel large animal model of blast and hemorrhage had to be devised and validated. This study outlines the derivation of such a large animal model utilizing terminally anesthetized Large White pigs exposed to a standardized primary blast wave followed by a controlled hemorrhage of 30% of the total blood volume. RESULTS AND CONCLUSION: The preliminary results confirm the reliability and reproducibility of this model.

Damage control resuscitation.

Damage Control Resuscitation (DCR) is a novel concept that draws together a series of technical and organisational advances in combat casualty care. It is consistent with and encapsulates the established concept of damage control surgery (DCS).