Sickle cell disease (SCD) is characterized by oxidative stress, erythrocyte dehydration, and endothelial activation, promoting vaso-occlusion through expression of adhesion molecules, including von Willebrand factor (VWF), and the presence of rigid erythrocytes. N-acetylcysteine (NAC), a thiol-containing reducing agent, can decrease VWF multimer size and oxidative stress, which may reduce vaso-occlusive complications in SCD. We report Part 1 of a two-part phase I/II pilot study (NCT01800526) examining the safety and tolerability of high-dose intravenous NAC and, as a primary outcome, its effects on plasma VWF parameters (multimer distribution, VWF antigen, ADAMTS13 activity), and, as secondary parameters, on systemic redox status (plasma and whole blood thiol species), and RBC function (dense cell fraction and erythrocyte hydration) in SCD at baseline. We enrolled five adults [four with SCD (HbSS or HbSβ0) and one with sickle trait]. Each received two intravenous NAC infusions—150 mg/kg and 300 mg/kg—separated by four weeks. After mild adverse events (pruritus, headache, nausea, and vomiting) in the first two subjects during bolus dosing, the protocol was changed to continuous infusion; subsequent subjects had no adverse events. NAC reduced high-molecular-weight VWF multimers, reduced oxidized plasma thiol species, and produced rapid, sustained decreases in dense, dehydrated erythrocytes lasting up to 72 hours. VWF antigen levels and ADAMTS13 activity did not change significantly. Continuous intravenous NAC infusion is safe and well tolerated in adults with SCD and improves erythrocyte hydration and systemic redox balance, supporting further evaluation as an adjunctive therapy in SCD.

Trauma-induced coagulopathy (TIC) induces anticoagulation and increases bleeding mortality. Inflammation and oxidative stress play an unknown role in TIC. We examined plasma from injured human trauma patients presenting to the Emergency Department compared to healthy controls to elucidate the contribution of inflammation and oxidative stress to anticoagulation during TIC. Trauma patients demonstrated coagulopathy by prolongation of clotting time assays and decreased thrombin generation in addition to increased pro-inflammatory cytokines and increased markers of oxidative stress. Clotting factors seven (FVII), ten (FX), and twelve (FXII) were oxidatively modified without quantitative changes, displaying decreased activity after trauma. Factor five (FV) was decreased in concentration and retained normal activity. Factor eight (FVIII) concentration and activity were increased after trauma. Clotting factor oxidation after exposure to activated human leukocytes in vitro also impaired thrombin generation and reproduced the oxidative and functional changes seen in trauma patients. Both antioxidant and anti-inflammatory treatments prevented clotting factor oxidation and TIC after trauma in vivo using a rodent TIC model. These results suggest that inflammation and oxidative stress contribute directly to anticoagulation during TIC by direct and selective oxidation of clotting factors. FXII may make a novel contribution to the pathophysiology of TIC by its oxidation.

Background: After severe injury, optical measures of microvascular blood flow (MBF) decrease and do not normalize with resuscitation to normal blood pressure. These changes are associated with organ dysfunction, coagulopathy, and death. However, the pathophysiology is not well understood. Several possible pathways could also contribute to the development of trauma-induced coagulopathy (TIC). A small-animal model of trauma-related MBF derangement that persists after resuscitation and includes TIC would facilitate further study. Parametric contrast-enhanced ultrasound (CEUS) is particularly advantageous in this setting, because it noninvasively assesses MBF in large, deep vascular beds. We sought to develop such a model, measuring MBF with CEUS. Methods: Sixteen male Sprague-Dawley rats were anesthetized, ventilated, and cannulated. Rats were subjected to either no injury (sham group) or a standardized polytrauma and pressure-targeted arterial catheter hemorrhage with subsequent whole blood resuscitation (trauma group). At prespecified time points, CEUS measurements of uninjured quadriceps muscle, viscoelastic blood clot strength, and complete blood counts were taken. Results: After resuscitation, blood pressure normalized, but MBF decreased and remained low for the rest of the protocol. This was primarily driven by a decrease in blood volume with a relative sparing of blood velocity. Viscoelastic blood clot strength and platelet count also decreased and remained low throughout the protocol. Conclusion: We present a rat model of MBF derangement in uninjured skeletal muscle and coagulopathy after polytrauma that persists after resuscitation with whole blood to normal macrohemodynamics. Parametric CEUS analysis shows that this change is primarily due to microvascular obstruction. This platform can be used to develop a deeper understanding of this important process.

BACKGROUND:Our objective was to optimize a novel damage control resuscitation (DCR) cocktail composed of hydroxyethyl starch, vasopressin, and fibrinogen concentrate for the polytraumatized casualty. We hypothesized that slow intravenous infusion of the DCR cocktail in a pig polytrauma model would decrease internal hemorrhage and improve survival compared with bolus administration. METHODS:We induced polytrauma, including traumatic brain injury (TBI), femoral fracture, hemorrhagic shock, and free bleeding from aortic tear injury, in 18 farm pigs. The DCR cocktail consisted of 6% hydroxyethyl starch in Ringer's lactate solution (14mL/kg), vasopressin (0.8U/kg), and fibrinogen concentrate (100mg/kg) in a total fluid volume of 20mL/kg that was either divided in half and given as two boluses separated by 30 minutes as control or given as a continuous slow infusion over 60 minutes. Nine animals were studied per group and monitored for up to 3 hours. Outcomes included internal blood loss, survival, hemodynamics, lactate concentration, and organ blood flow obtained by colored microsphere injection. RESULTS:Mean internal blood loss was significantly decreased by 11.1mL/kg with infusion compared with the bolus group (p = .038). Survival to 3 hours was 80% with infusion and 40% with bolus, which was not statistically different (Kaplan Meier log-rank test, p = .17). Overall blood pressure was increased (p < .001), and blood lactate concentration was decreased (p < .001) with infusion compared with bolus. There were no differences in organ blood flow (p > .09). CONCLUSION:Controlled infusion of a novel DCR cocktail decreased hemorrhage and improved resuscitation in this polytrauma model compared with bolus. The rate of infusion of intravenous fluids should be considered as an important aspect of DCR.

Immune cell inflammation is implicated in the pathophysiology of acute trauma-induced coagulopathy (TIC). We hypothesized that leukocyte inflammation contributes to TIC through the oxidation and proteolysis of fibrinogen. To test this hypothesis, antioxidants and a novel anti-inflammatory melanocortin fusion protein (AQB-565) were used to study the effects of interleukin-6 (IL-6)-stimulated human leukocytes on fibrinogen using single-cell imaging flow cytometry and multiplex fluorescent western blotting. We also studied the effects of AQB-565 on fibrinogen using an in vivo rat trauma model of native TIC. IL-6 induced cellular inflammation and mitochondrial superoxide production in human monocytes, causing fibrinogen oxidation and degradation in vitro. Antioxidants suppressing mitochondrial superoxide reduced oxidative stress and inflammation and protected fibrinogen. AQB-565 decreased inflammation, inhibited mitochondrial superoxide, and protected fibrinogen in vitro. Trauma with hemorrhagic shock increased IL-6 and other proinflammatory cytokines and chemokines, selectively oxidized and degraded fibrinogen, and induced TIC in rats in vivo. AQB-565, given at the onset of hemorrhage, blocked inflammation, protected fibrinogen from oxidation and degradation, and prevented TIC. Leukocyte activation contributes to TIC through the oxidation and degradation of fibrinogen, which involves mitochondrial superoxide and cellular inflammation. Suppression of inflammation by activation of melanocortin pathways may be a novel approach for the prevention and treatment of TIC.

von Willebrand factor (VWF) mediates primary hemostasis and thrombosis in response to hydrodynamic forces. We previously showed that high shear promoted self-association of VWF into hyperadhesive strands, which can be attenuated by high-density lipoprotein (HDL) and apolipoprotein A-I. In this study, we show that low-density lipoprotein (LDL) binds VWF under shear and enhances self-association. Vortexing VWF in tubes resulted in its loss from the solution and deposition onto tube surfaces, which was prevented by HDL. At a stabilizing HDL concentration of 1.2 mg/mL, increasing concentrations of LDL progressively increased VWF loss, the effect correlating with the LDL-to-HDL ratio and not the absolute concentration of the lipoproteins. Similarly, HDL diminished deposition of VWF in a post-in-channel microfluidic device, whereas LDL increased both the rate and extent of strand deposition, with both purified VWF and plasma. Hypercholesterolemic human plasma also displayed accelerated VWF accumulation in the microfluidic device. The initial rate of accumulation correlated linearly with the LDL-to-HDL ratio. In Adamts13-/- and Adamts13-/-LDLR-/- mice, high LDL levels enhanced VWF and platelet adhesion to the myocardial microvasculature, reducing cardiac perfusion, impairing systolic function, and producing early signs of cardiomyopathy. In wild-type mice, high plasma LDL concentrations also increased the size and persistence of VWF-platelet thrombi in ionophore-treated mesenteric microvessels, exceeding the accumulation seen in similarly treated ADAMTS13-deficient mice that did not receive LDL infusion. We propose that targeting the interaction of VWF with itself and with LDL may improve the course of thrombotic microangiopathies, atherosclerosis, and other disorders with defective microvascular circulation.

Critical illness leads to rapid fibrinogen consumption, hyperfibrinolysis, and coagulopathy that exacerbates bleeding and increases mortality. Immune cell activation and inflammation are associated with coagulopathy after injury but play an undetermined role. We performed high dimensional immunophenotyping and single-cell imaging flow cytometry to investigate for a pathophysiological mechanism governing the effects of leukocyte-associated inflammation on fibrinogen function. Fibrinogen was oxidized early, followed by its degradation after 3 hours of lipopolysaccharides (LPS)-induced sterile inflammation in a rat model in vivo. Fibrinogen incubated with human leukocytes activated by TNFα was similarly oxidized, and later proteolyzed after 3 hours in vitro. TNFα induced mitochondrial superoxide generation from neutrophils and monocytes, myeloperoxidase (MPO)-derived reactive oxygen species (ROS) from neutrophils, and nitric oxide from lymphocytes and monocytes. Inhibition of mitochondrial superoxide prevented oxidative modification and proteolysis of fibrinogen, whereas inhibition of MPO attenuated only fibrinogen proteolysis. Quenching of both mitochondrial superoxide and MPO-derived ROS prevented coagulopathy better than tranexamic acid. Collectively, these findings indicate that neutrophil and monocyte mitochondrial superoxide generation can rapidly oxidize fibrinogen as a priming step for fibrinogen proteolysis and coagulopathy during inflammation.

Cardiac dysfunction is common in the days after severe traumatic brain injury (TBI) and may contribute to hypotension episodes, leading to worse outcomes. Little is known about cardiac function in the minutes and hours immediately following TBI. By using fluid percussion TBI in a swine model, we aimed to characterize the immediate post injury cardiac function. Intubated, anesthetized immature (25.8 ± 1.5 kg) female swine were subjected to severe fluid percussion TBI (4.2 ± 0.2 atm). Beginning at 45 min, simulating hospital arrival, all animals were resuscitated with normal saline (NS), mannitol, and phenylephrine as needed to maintain a cerebral perfusion pressure more than 60 mm Hg and intracranial pressure (ICP) less than 20 mm Hg. Primary outcomes of cardiac function were cardiac output measured by thermodilution and transesophageal echo measurements of cardiac function recorded at prespecified time points and tested for trends over time using linear regression with spline at the time of resuscitation onset. Secondary outcomes included hemodynamic measurements, ICP, and cerebral perfusion pressure. Eighteen animals were included. Post-TBI hemodynamic changes demonstrated an early decrease in mean arterial pressure and cerebral perfusion pressure with a corresponding increase in heart rate and ICP. Immediately after injury, there was a significant decrease in both left atrial area and tissue Doppler imaging e′ of the LV lateral wall. In addition, there was a simultaneous increase in LV end diastolic diameter and increase in E/e′ ratio of the lateral mitral annulus. All other transesophageal echo measurements demonstrated no significant changes throughout the duration of the experiment. Traumatic brain injury is associated with cardiac dysfunction and increased mortality, however there is still a limited understanding of the hemodynamic and echocardiographic response associated with TBI. In this study we demonstrate the hemodynamic and echocardiographic changes in the early stages of TBI in swine. The authors hope that these results may help better understanding on the management of patients with severe head injury.

The morphology and other phenotypic characteristics of erythrocytes in sickle cell disease (SCD) have been analyzed for decades in patient evaluation. This involves a variety of techniques, including microscopic analysis of stained blood films, flow cytometry, and cell counting. Here, we analyzed SCD blood using imaging flow cytometry (IFC), a technology that combines flow cytometry and microscopy to enable simultaneous rapid-throughput analysis of cellular morphology and cell-surface markers. With IFC, we were able to automate quantification of poikilocytes from SCD blood. An important subpopulation of poikilocytes represented dense cells, although these could not be distinguished from other poikilocytes without first centrifuging the blood through density gradients. In addition, CD71-positive RBCs from SCD patients had two subpopulations: one with high CD71 expression and a puckered morphology and another with lower CD71 expression and biconcave morphology and presumably representing a later stage of differentiation. Some RBCs with puckered morphologies that were strongly positive for DAPI and CD49d were in fact nucleated RBCs. IFC identified more phosphatidylserine-expressing red cells in SCD than did conventional flow cytometry and these could also be divided into two subpopulations. One population had diffuse PS expression and appeared to be composed primarily of RBC ghosts; the other had lower overall PS expression present in intense, punctate dots overlying Howell-Jolly bodies. This study demonstrates that IFC can rapidly reveal and quantify RBC features in SCD that require numerous tedious methods to identify conventionally. Thus, IFC is likely to be a useful technique for evaluating and monitoring SCD.

Self-association of VWF on the surface of activated endothelium provides an efficient surface for the capture of platelets and is at least partially responsible for the microvascular dysfunction seen in several diseases, including diabetes, coronary heart disease, malaria, sepsis, ischemia/reperfusion injury, and the thrombotic microangiopathies, including thrombotic thrombocytopenic purpura. We showed previously that high density lipoprotein (HDL) can prevent VWF self-association (PMID: 26552698) and decided to explore whether other lipoproteins affected the phenomenon. Of all the lower density lipoproteins (chylomicrons, VLDL, and LDL) only LDL affected VWF self-association, having the opposite effect as HDL. Vortexing a solution of recombinant VWF (5 μg/ml) for 90 min resulted in complete loss of VWF from the solution by deposition on the wall of the tube. Addition of HDL at increasing concentrations progressively protected VWF in solution, with no VWF lost at 1.3 mg/ml of HDL. At an HDL concentration of 1.2 mg/ml, the addition of LDL at increasing concentrations progressively increased VWF loss, the effect being related to the ratio of LDL to HDL and not the absolute concentration of the lipoprotein particles. Similarly, HDL diminished deposition of VWF in a post-in-channel microfluidic device, whereas LDL markedly potentiated deposition, increasing both the rate and extent of VWF strand formation, demonstrated with a solution of purified VWF and with plasma. The effects of the lipoproteins appeared to be from direct interactions with VWF, as shown by the association of fluorescently labeled HDL and LDL with VWF strands. Plasma from hypercholesterolemic patients with elevated LDL but equivalent levels of HDL also displayed accelerated VWF accumulation on the microfluidic device, the initial rate of deposition correlating linearly with the LDL level in the plasma. We evaluated the physiological consequences of the LDL/VWF interaction in mice with molecular imaging ultrasound and contrast enhanced ultrasound. In mice deficient in ADAMTS13 and the LDL receptor fed a high-fat diet for two weeks, the high LDL levels enhanced VWF and platelet adhesion to the myocardial microvasculature, reducing myocardial microvascular perfusion, impairing systolic function, and producing early signs of cardiomyopathy. Finally, by intravital microscopy of the mesenteric microvasculature of wild-type C57Bl6 stimulated by calcium ionophore to activate endothelial secretion of VWF, preinjection of LDL markedly enhanced the formation of microvascular thrombosis. The intensity of thrombosis exceeded even that seen in similarly treated ADAMTS13-deficient mice that did not receive an LDL infusion, with a greater number of large thrombi being formed and a prolonged time to thrombus resolution (> 20 min in LDL-treated WT mice vs 10 min in ADAMTS13-deficient mice). In summary, we show that LDL, in addition to its role in cholesterol delivery and atherosclerosis, interacts with the hemostatic system, increasing the efficiency of VWF self-association. Regulation of VWF self-association and therefore platelet adhesion by lipoproteins has some obvious clinical implications. Long term, one would expect that the counterbalancing effects of HDL and LDL on VWF self-association would contribute to the well-known effects of these lipoproteins on the genesis and progression of atherosclerosis, largely a disease of large blood vessels. But the balance between the two lipoproteins is also likely to influence the course of acute and chronic diseases affecting the microcirculation, including the thrombotic microangiopathies.

The resuscitation of polytrauma with hemorrhagic shock and traumatic brain injury (TBI) is a balance between permissive hypotension and maintaining vital organ perfusion. There is no current optimal solution. This study tested whether a multifunctional resuscitation cocktail supporting hemostasis and perfusion could mitigate blood loss while improving vital organ blood flow during prolonged limited resuscitation. Anesthetized Yorkshire swine were subjected to fluid percussion TBI, femur fracture, catheter hemorrhage, and aortic tear. Fluid resuscitation was started when lactate concentration reached 3–4 mmol/L. Animals were randomized to one of five groups. All groups received hydroxyethyl starch solution and vasopressin. Low- and high-dose fibrinogen (FBG) groups additionally received 100 and 200 mg/kg FBG, respectively. A third group received TXA and low-dose FBG. Two control groups received albumin, with one also including TXA. Animals were monitored for up to 6 h. Blood loss was decreased and vital organ blood flow was improved with low- and high-dose fibrinogen compared to albumin controls, but survival was not improved. There was no additional benefit of high- vs. low-dose FBG on blood loss or survival. TXA alone decreased blood loss but had no effect on survival, and combining TXA with FBG provided no additional benefit. Pooled analysis of all groups containing fibrinogen vs. albumin controls found improved survival, decreased blood loss, and improved vital organ blood flow with fibrinogen delivery. In conclusion, a low-volume resuscitation cocktail consisting of hydroxyethyl starch, vasopressin, and fibrinogen concentrate improved outcomes compare to controls during limited resuscitation of polytrauma.

Background. Coagulopathic bleeding is a major cause of mortality after trauma, and platelet dysfunction contributes to this problem. The causes of platelet dysfunction are unknown, but a great deal can be learned from the plasma environment after injury, which may directly alter platelet function. Studying the changes in plasma using untargeted proteomics would provide unbiased insight into the presence of possible inhibitors of platelet function, changes to their major ligands, or other previously unknown pathways affecting platelet function. Methods. Citrated blood was collected from severely injured trauma patients at the time of their arrival to the Emergency Department. Platelet testing was performed immediately, and plasma was frozen for analysis. Samples were collected from 110 patients, and a subset of 24 patients was identified by a preserved (n=12) or severely impaired (n=12) platelet aggregation response to five different agonists (adenosine diphosphate, arachidonic acid, collagen, thrombin receptor-activating peptide, and ristocetin). Untargeted proteomics was performed by nanoflow liquid chromatography tandem mass spectrometry to determine the plasma protein profile associated with platelet dysfunction. Protein abundance levels for each patient were normalized to total protein concentration to control for hemodilution by crystalloid fluid infusion prior to blood draw. Results were compared by Wilcoxon rank-sum test, and a two-tailed p value less than 0.05 was considered significant. No adjustment was made for multiple comparisons, as the risk of a type II error was felt to outweigh that of a type I error in this exploratory analysis. Results. Patients with platelet dysfunction were more severely injured (median Injury Severity Score 29.5 vs. 13.5, p=0.002) but otherwise demographically similar to those with retained platelet function. Of 232 proteins identified, twelve were significantly different in the low- vs. high-platelet function groups: gelsolin (median peak intensity 9.70E+6 vs. 1.48 E+7, p=0.002), transketolase (2.86E+4 vs. 9.36E+3, p=0.003), protein S100-A8 (4.60E+4 vs. 2.64E+4, p=0.006) and -A9 (5.83E+4 vs. 4.07E+4, p=0.012), histone H4 (5.72E+4 vs. 8.47E+6, p=0.007), histidine-rich glycoprotein (HRG) (5.00E+6 vs. 8.30E+6, p=0.008), factor XIII B chain (1.09E+6 vs. 1.61E+6, p=0.020), apolipoprotein A-IV (2.30E+7 vs. 3.28E+7, p=0.024), alpha-enolase (1.02E+5 vs. 4.15E+4, p=0.024), heat shock protein 90-alpha (1.41E+4 vs. 4.08E+3, p=0.045), alpha-2-HS-glycoprotein (2.83E+7 vs. 3.68E+7, p=0.045), and neutrophil gelatinase-associated lipocalin (3.44E+4 vs. 1.36E+4, p=0.045). These results are summarized in the figure, which shows one group of proteins that decreased in abundance (on the left side of the volcano plot) and another that increased (on the right side) in the patients with low platelet function. The twelve proteins that changed the most fall into several categories related to platelet function. Low gelsolin and high histone levels are each associated with microvascular obstruction by release of intracellular material that accumulates in small vessels and activates platelets. Low HRG and high damage-associated molecular pattern (DAMP) protein levels are consistent with massive innate immune activation, which can impair platelet function in many ways. Conclusion. This study provides an unbiased description of the change in proteomic profile associated with platelet dysfunction after trauma and identifies twelve proteins with the most profound changes. The pathways involving these proteins are salient targets for immediate investigation to better understand platelet dysfunction after trauma and identify targets for intervention. Figure Legend. Volcano plot depicting fold-change and statistical significance of individual proteins in patients with low vs. high platelet function. Dotted horizontal line represents p = 0.05. Twelve proteins showed a statistically significant p value. Figure Disclosures No relevant conflicts of interest to declare.

Trauma induces a change in nearly every observable aspect of hemostasis, generally tipping the balance toward trauma-induced coagulopathy (TIC) and bleeding in the critical early stages. Two particularly important aspects of TIC are platelets and fibrinogen, which are the primary determinants of clot formation and hemostasis. Their loss and dysfunction represent important transition points between coagulopathy phenotypes, highlighting their mechanistic roles in TIC as well as unveiling new potential avenues toward important diagnostic and therapeutic interventions. This review synthesizes current knowledge of platelets and fibrinogen during TIC, with a focus on emerging concepts related to their dysfunction and development of new therapeutic approaches.

The adhesion of blood clots to wounds is necessary to seal injured vasculature and achieve hemostasis. However, it has not been specifically tested if adhesive failure of clots is a major contributor to rebleeding and what mechanisms prevent clot delamination. Here, we quantified the contribution of adhesive and cohesive failure to rebleeding in a rat model of femoral artery injury, and identified mechanisms that contribute to the adhesive strength of bulk clots in a lap-shear test in vitro. In the rat bleeding model, the frequency of clot failures correlated positively with blood loss (R = 0.81, p = 0.014) and negatively with survival time (R = − 0.89, p = 0.0030), with adhesive failures accounting for 51 ± 14% of rebleeds. In vitro, adhesion depended on fibrinogen and coagulation factor XIII (FXIII), and supraphysiological FXIII improved adhesive strength. Furthermore, when exogenous FXIII was topically applied into the wound pocket of rats, eleven adhesive failures occurred between eight rats, compared to seventeen adhesive failures between eight untreated rats, whereas the number of cohesive failures remained the same at sixteen in both groups. In conclusion, rebleeding from both adhesive and cohesive failure of clots decreases survival from hemorrhage in vivo. Both endogenous and exogenous FXIII improves the adhesive strength of clots.

BACKGROUND:Endogenous fibrinolytic activation contributes to coagulopathy and mortality after trauma. Administering tranexamic acid (TXA), an antifibrinolytic agent, is one strategy to reduce bleeding; however, it must be given soon after injury to be effective and minimize adverse effects. Administering TXA topically to a wound site would decrease the time to treatment and could enable both local and systemic delivery if a suitable formulation existed to deliver the drug deep into wounds adequately. OBJECTIVES:To determine whether self-propelling particles could increase the efficacy of TXA. METHODS:Using previously developed self-propelling particles, which consist of calcium carbonate and generate CO2 gas, TXA was formulated to disperse in blood and wounds. The antifibrinolytic properties were assessed in vitro and in a murine tail bleeding assay. Self-propelled TXA was also tested in a swine model of junctional hemorrhage consisting of femoral arteriotomy without compression. RESULTS:Self-propelled TXA was more effective than non-propelled formulations in stabilizing clots from lysis in vitro and reducing blood loss in mice. It was well tolerated when administered subcutaneously in mice up to 300 to 1000 mg/kg. When it was incorporated in gauze, four of six pigs treated after a femoral arteriotomy and without compression survived, and systemic concentrations of TXA reached approximately 6 mg/L within the first hour. CONCLUSIONS:A formulation of TXA that disperses the drug in blood and wounds was effective in several models. It may have several advantages, including supporting local clot stabilization, reducing blood loss from wounds, and providing systemic delivery of TXA. This approach could both improve and simplify prehospital trauma care for penetrating injury.

Platelets contract forcefully after their activation, contributing to the strength and stability of platelet aggregates and fibrin clots during blood coagulation. Viscoelastic approaches can be used to assess platelet-induced clot strengthening, but they require thrombin and fibrin generation and are unable to measure platelet forces directly. Here, we report a rapid, microfluidic approach for measuring the contractile force of platelet aggregates for the detection of platelet dysfunction. We find that platelet forces are significantly reduced when blood samples are treated with inhibitors of myosin, GPIb-IX-V, integrin α IIb β 3, P2Y 12 , or thromboxane generation. Clinically, we find that platelet forces are measurably lower in cardiology patients taking aspirin. We also find that measuring platelet forces can identify Emergency Department trauma patients who subsequently require blood transfusions. Together, these findings indicate that microfluidic quantification of platelet forces may be a rapid and useful approach for monitoring both antiplatelet therapy and traumatic bleeding risk.

Platelets in trauma-induced coagulopathy (TIC) are impaired, but the mechanism is not known. We performed comprehensive longitudinal platelet function testing in trauma patient samples. Platelets in TIC are widely impaired early after injury, but platelet activatability is intact. This suggests a mechanism of transient platelet cytoskeletal/integrin dysfunction during TIC. Summary Background Trauma-induced coagulopathy (TIC) is a common and deadly bleeding disorder. Platelet dysfunction is present during TIC, but its mechanisms remain unclear. Platelets are currently thought to become exhausted, a state in which they have released their granule contents and can no longer aggregate or contract. Methods This prospective observational cohort study tested the hypothesis that platelet exhaustion is present during TIC and characterized the early time course of platelet dysfunction. Blood was collected from 95 adult trauma patients at a Level I trauma center at time of Emergency Department arrival and several time points over 72 h. Platelet activation state and function were characterized using CD62P (P-selectin) and PAC-1 surface membrane staining, platelet function analyzer (PFA-100), aggregometry, viscoelastic platelet mapping, and, to test for exhaustion, their ability to express CD62P after ex vivo adenosine diphosphate (ADP) agonism. Platelet function was compared between patients with and without TIC, defined by prothrombin time 18 s. Results Platelets in TIC showed no initial increase in their level of surface activation markers or impairment of their capacity to express CD62P in response to ADP stimulation. However, TIC platelets were impaired in nearly all functional assays, spanning adhesion, aggregation, and contraction. These effects largely remained after controlling for platelet count and fibrinogen concentration and resolved after 8 h. Conclusion The TIC platelets exhibit early impairment of adhesion, aggregation, and contraction with retained alpha granule secretion ability, suggesting a specific mechanism of cytoskeletal or integrin dysfunction that is not a result of more general platelet exhaustion.