Nathan J. White

Trauma hemostasis and oxygenation research position paper on remote damage control resuscitation: definitions, current practice, and knowledge gaps.

ABSTRACT The Trauma Hemostasis and Oxygenation Research Network held its third annual Remote Damage Control Resuscitation Symposium in June 2013 in Bergen, Norway. The Trauma Hemostasis and Oxygenation Research Network is a multidisciplinary group of investigators with a common interest in improving outcomes and safety in patients with severe traumatic injury. The network’s mission is to reduce the risk of morbidity and mortality from traumatic hemorrhagic shock, in the prehospital phase of resuscitation through research, education, and training. The concept of remote damage control resuscitation is in its infancy, and there is a significant amount of work that needs to be done to improve outcomes for patients with life-threatening bleeding secondary to injury. The prehospital phase of resuscitation is critical in these patients. If shock and coagulopathy can be rapidly identified and minimized before hospital admission, this will very likely reduce morbidity and mortality. This position statement begins to standardize the terms used, provides an acceptable range of therapeutic options, and identifies the major knowledge gaps in the field.

Self-propelled particles that transport cargo through flowing blood and halt hemorrhage

Simple, water-reactive particles can carry enzymes upstream through aqueous solutions and into wounds to halt severe bleeding. Delivering therapeutics deep into damaged tissue during bleeding is challenging because of the outward flow of blood. When coagulants cannot reach and clot blood at its source, uncontrolled bleeding can occur and increase surgical complications and fatalities. Self-propelling particles have been proposed as a strategy for transporting agents upstream through blood. Many nanoparticle and microparticle systems exhibiting autonomous or collective movement have been developed, but propulsion has not been used successfully in blood or used in vivo to transport therapeutics. We show that simple gas-generating microparticles consisting of carbonate and tranexamic acid traveled through aqueous solutions at velocities of up to 1.5 cm/s and delivered therapeutics millimeters into the vasculature of wounds. The particles transported themselves through a combination of lateral propulsion, buoyant rise, and convection. When loaded with active thrombin, these particles worked effectively as a hemostatic agent and halted severe hemorrhage in multiple animal models of intraoperative and traumatic bleeding. Many medical applications have been suggested for self-propelling particles, and the findings of this study show that the active self-fueled transport of particles can function in vivo to enhance drug delivery.

Fibrin Clot Structure and Mechanics Associated with Specific Oxidation of Methionine Residues in Fibrinogen

Using a combination of structural and mechanical characterization, we examine the effect of fibrinogen oxidation on the formation of fibrin clots. We find that treatment with hypochlorous acid preferentially oxidizes specific methionine residues on the α, β, and γ chains of fibrinogen. Oxidation is associated with the formation of a dense network of thin fibers after activation by thrombin. Additionally, both the linear and nonlinear mechanical properties of oxidized fibrin gels are found to be altered with oxidation. Finally, the structural modifications induced by oxidation are associated with delayed fibrin lysis via plasminogen and tissue plasminogen activator. Based on these results, we speculate that methionine oxidation of specific residues may be related to hindered lateral aggregation of protofibrils in fibrin gels.

A synthetic fibrin cross-linking polymer for modulating clot properties and inducing hemostasis

By cross-linking fibrin, intravenously injected factor XIII–inspired hemostatic polymers stabilize clots and reduce bleeding in a rat model of trauma and fluid resuscitation. Bioinspired polymers fortify blood clots Major blood loss is a leading cause of death after trauma, and currently available intravenously delivered clotting agents are expensive, require special storage, have limited shelf life, and carry risk of immunogenicity. In this issue, Chan et al. describe an off-the-shelf, synthetic, bioinspired polymer called PolySTAT that stops the bleeding after trauma and restores hemostasis. In healthy animals, the polymer flows throughout the body, harmless and passive. Upon encountering a blood clot at a site of vascular injury, PolySTAT cross-links the fledgling fibrin matrix much like the transglutaminase factor XIII, strengthening the clot and fortifying it against degrading enzymes that are overactive in trauma. In a rat model of femoral artery injury and fluid resuscitation, PolySTAT or control therapies were injected immediately after the onset of bleeding. All animals treated with PolySTAT survived, whereas only 4 of the remaining 20 animals in various control groups survived. Additionally, none of the PolySTAT-treated animals experienced rebleeding, suggesting that the clots formed were strong, despite increased blood pressure from the infusions. This polymer-based solution to clotting could be a welcomed addition in critical care medicine, because its specificity minimizes risk of distant thrombosis (for example, in the heart or lungs) and has scalable manufacturing properties as well as favorable biodistribution and pharmacokinetics. Further preclinical studies will be needed in larger animal models to evaluate not only clotting function but also the extent of organ injury in surviving animals. Clotting factor replacement is the standard management of acute bleeding in congenital and acquired bleeding disorders. We present a synthetic approach to hemostasis using an engineered hemostatic polymer (PolySTAT) that circulates innocuously in the blood, identifies sites of vascular injury, and promotes clot formation to stop bleeding. PolySTAT induces hemostasis by cross-linking the fibrin matrix within clots, mimicking the function of the transglutaminase factor XIII. Furthermore, synthetic PolySTAT binds specifically to fibrin monomers and is uniformly integrated into fibrin fibers during fibrin polymerization, resulting in a fortified, hybrid polymer network with enhanced resistance to enzymatic degradation. In vivo hemostatic activity was confirmed in a rat model of trauma and fluid resuscitation in which intravenous administration of PolySTAT improved survival by reducing blood loss and resuscitation fluid requirements. PolySTAT-induced fibrin cross-linking is a novel approach to hemostasis using synthetic polymers for noninvasive modulation of clot architecture with potentially wide-ranging therapeutic applications.

Mechanisms of trauma-induced coagulopathy

The identification and management of coagulopathy is a critical component of caring for the severely injured patient. Notions of the mechanisms of coagulopathy in trauma patients have been supplanted by new insights resulting from close examination of the biochemical and cellular changes associated with acute tissue injury and hemorrhagic shock. Acute intrinsic coagulopathy arising in severely injured trauma patients is now termed trauma-induced coagulopathy (TIC) and is an emergent property of tissue injury combined with hypoperfusion. Mechanisms contributing to TIC include anticoagulation, consumption, platelet dysfunction, and hyperfibrinolysis. This review discusses current understanding of TIC mechanisms and their relative contributions to coagulopathy in the face of increasingly severe injury and highlights how they interact to produce coagulation system dysfunction.

PolySTAT-modified chitosan gauzes for improved hemostasis in external hemorrhage.

UNLABELLED Positively-charged chitosan gauzes stop bleeding from wounds by electrostatically interacting with negatively-charged cell membranes of erythrocytes to cause erythrocyte agglutination and by sealing wounds through tissue adhesion. In the following work, nonwoven chitosan gauze was impregnated with PolySTAT, a synthetic polymer that enhances coagulation by cross-linking fibrin, to generate PolySTAT/chitosan gauzes with improved hemostatic efficacy. When comparing nonwoven chitosan and PolySTAT/chitosan to a commercially-available chitosan-containing gauze (Celox® Rapid), no appreciable differences were observed in fiber size, morphology, and pore size. However, PolySTAT/chitosan demonstrated more rapid blood absorption compared to Celox® Rapid. In a rat model of femoral artery injury, PolySTAT/chitosan gauzes reduced blood loss and improved survival rate compared to non-hemostatic controls and Celox® Rapid. While Celox® Rapid had stronger adherence to tissues compared to PolySTAT/chitosan gauzes, blood loss was greater due to hematoma formation under the Celox® dressing. Animals treated with PolySTAT/chitosan gauzes required less saline infusion to restore and maintain blood pressure above the target blood pressure (60mmHg) while other treatment groups required more saline due to continued bleeding from the wound. These results suggest that PolySTAT/chitosan gauzes are able to improve blood clotting and withstand increasing arterial pressure with the addition of a fibrin cross-linking hemostatic mechanism. STATEMENT OF SIGNIFICANCE Blood loss remains one of the leading causes of death after traumatic injury in civilian populations and on the battlefield. Advanced biomaterials that interact with blood components and/or accelerate the clotting process to form a hemostatic plug are necessary to staunch bleeding after injury. Chitosan-based gauzes, which stop bleeding by causing red blood cell aggregation, are currently used on the battlefield and have shown variable performance under high pressure arterial blood flow in animal studies, suggesting that red blood cell aggregates require further mechanical stabilization for more reliable performance. In this work, we investigate the binding and cross-linking of fibrin, a major component in blood clots, on chitosan gauze fiber surfaces to structurally reinforce red blood cell aggregates.

Variability of ICU Use in Adult Patients With Minor Traumatic Intracranial Hemorrhage

STUDY OBJECTIVE Patients with minor traumatic intracranial hemorrhage are frequently admitted to the ICU, although many never require critical care interventions. To describe ICU resource use in minor traumatic intracranial hemorrhage, we assess (1) the variability of ICU use in a cohort of patients with minor traumatic intracranial hemorrhage across multiple trauma centers, and (2) the proportion of adult patients with traumatic intracranial hemorrhage who are admitted to the ICU and never receive a critical care intervention during hospitalization. In addition, we evaluate the association between ICU admission and key independent variables. METHODS A structured, historical cohort study of adult patients (aged 18 years and older) with minor traumatic intracranial hemorrhage was conducted within a consortium of 8 Level I trauma centers in the western United States from January 2005 to June 2010. The study population included patients with minor traumatic intracranial hemorrhage, defined as an emergency department (ED) Glasgow Coma Scale (GCS) score of 15 (normal mental status) and an Injury Severity Score less than 16 (no other major organ injury). The primary outcome measure was initial ICU admission. The secondary outcome measure was a critical care intervention during hospitalization. Critical care interventions included mechanical ventilation, neurosurgical intervention, transfusion of blood products, vasopressor or inotrope administration, and invasive hemodynamic monitoring. ED disposition and the proportion of ICU patients not receiving a critical care intervention were compared across sites with descriptive statistics. The association between ICU admission and predetermined independent variables was analyzed with multivariable regression. RESULTS Among 11,240 adult patients with traumatic intracranial hemorrhage, 1,412 (13%) had minor traumatic intracranial hemorrhage and complete ED disposition data (mean age 48 years; SD 20 years). ICU use within this cohort across sites ranged from 50% to 97%. Overall, 847 of 888 patients (95%) with minor traumatic intracranial hemorrhage who were admitted to the ICU did not receive a critical care intervention during hospitalization (range between sites 80% to 100%). Three of 524 (0.6%) patients discharged home or admitted to the observation unit or ward received a critical care intervention. After controlling for severity of injury (age, blood pressure, and Injury Severity Score), study site was independently associated with ICU admission (odds ratios ranged from 1.5 to 30; overall effect P<.001). CONCLUSION Across a consortium of trauma centers in the western United States, there was wide variability in ICU use within a cohort of patients with minor traumatic intracranial hemorrhage. Moreover, a large proportion of patients admitted to the ICU never required a critical care intervention, indicating the potential to improve use of critical care resources in patients with minor traumatic intracranial hemorrhage.

Structural effects of methionine oxidation on isolated subdomains of human fibrin D and αC regions.

Oxidation of key methionine residues on fibrin leads to altered fibrin polymerization producing severely altered fibrin gel structure and function. This is important because fibrinogen and its modification by oxidative stress have been implicated as key contributors to both pathological thrombotic and hemorrhagic diseases ranging from cardiovascular thrombosis to the acute coagulopathy of trauma. However, how oxidation leads to altered fibrin polymerization remains poorly understood at the molecular level. We have applied a powerful and novel well-tempered ensemble parallel tempering (PT-WTE) technique along with conventional molecular dynamics (MD) simulation to investigate the molecular-level consequences of selective methionine oxidation of fibrinogen. We offer new insights into molecular mechanisms of oxidation-induced changes in fibrin polymerization, while focusing on the D region knob ‘B’ and hole ‘b’ interaction and αC-domain interactions, both of which are hypothesized to contribute to the lateral aggregation mechanism of fibrin fibrils. Methionine oxidation did not alter the native state or the stability of a bound knob ‘B’ surrogate when interacting with hole ‘b’ in the D region. However, applying PT-WTE simulation to a human homology model of the bovine N-terminal subdomain fragment from the αC-domain revealed that methionine oxidation altered the conformation of the hairpin-linking region to favor open rather than closed hairpin structures. We attribute this alteration to the disruption of the hairpin-linking regions conformation, with oxidation increasing the radius of gyration for this segment. This result is in agreement with experimental data demonstrating decreased fibrin protofibril lateral aggregation when methionine oxidation is present in the same αC-domain fragment. Therefore, single methionine oxidation within the αC-domain is a likely molecular mechanism.

Fluid resuscitation of uncontrolled hemorrhage using a hemoglobin-based oxygen carrier: effect of traumatic brain injury.

ABSTRACT Animal models of combined traumatic brain injury (TBI) and hemorrhagic shock (HS) suggest a benefit of hemoglobin-based oxygen carrier (HBOC)–based resuscitation, but their use remains controversial, and little is known of the specific effects of TBI and high-pressure (large arterial injury) bleeding on resuscitation. We examine the effect of TBI and aortic tear injury on low-volume HBOC resuscitation in a swine polytrauma model and hypothesize that HBOC-based resuscitation will improve survival in the setting of aortic tear regardless of the presence of TBI. Anesthetized swine subjected to HS with aortic tear with or without fluid percussion TBI underwent equivalent limited resuscitation with HBOC, lactated Ringer’s solution, or HBOC + nitroglycerine (vasoattenuated HBOC) and were observed for 6 h. There was no independent effect of TBI on survival time after adjustment for fluid type, and there was no interaction between TBI and resuscitation fluid type. However, total catheter hemorrhage volume required to reach target shock blood pressure was less with TBI (14.0 mL · kg−1 [confidence interval, 12.4–15.6 mL · kg−1]) versus HS only (21.0 mL · kg−1 [confidence interval, 19.5–22.5 mL · kg−1]), with equivalent lactate accumulation. Traumatic brain injury did not affect survival in this polytrauma model, but less hemorrhage was required in the presence of TBI to achieve an equivalent degree of shock suggesting globally impaired cardiovascular response to hemorrhage in the presence of TBI. There was also no benefit of HBOC-based fluid resuscitation over lactated Ringer’s solution, contrary to models using liver injury as the source of hemorrhage, considering wound location is of paramount importance when choosing resuscitation strategy.

Early hemostatic responses to trauma identified with hierarchical clustering analysis.

Trauma‐induced coagulopathy is a complex multifactorial hemostatic response that is poorly understood.