Histone deacetylase-6 modulates the effects of 4°C platelets on vascular endothelial permeability.

Platelets (PLTs) stored at 4°C exhibit equivalent or superior hemostatic function compared with 22°C PLTs, but have shorter circulation times and a decreased ability to modulate vascular permeability. These differences may be due to morphological changes and storage-induced activation. Using a proteomics-based approach, we found that 4°C-stored PLTs express decreased α-tubulin, a key PLT structural protein. PLT activation is characterized by α-tubulin deacetylation, which is regulated by histone deacetylase-6 (HDAC-6). We hypothesized that inhibition of HDAC-6 in stored PLTs will improve their ability to regulate vascular permeability through reduced activation and α-tubulin deacetylation. In an in vivo model of vascular permeability, treatment of 4°C PLTs with the HDAC-6 inhibitor tubacin enhanced the vasculoprotective properties of untreated 4°C PLTs. 4°C PLT circulation, however, was unchanged by tubacin treatment, suggesting that circulation time may not be a critical factor in determining the vasculoprotective effects of PLTs. Assessing the factor content of stored PLTs revealed that angiopoietin-1 (Ang-1) increased in 4°C PLTs over time, which was further enhanced by tubacin treatment. In addition, angiopoietin-2, an inducer of vascular leak and antagonist of Ang-1, inhibited PLT barrier protection, suggesting involvement of the Tie-2 pathway. This study demonstrates that HDAC-6 inhibition with tubacin attenuates the diminished vasculo-protective properties of 4°C PLTs, and these properties may be independent of PLT circulation time.

Life-Threatening Bleeding in Children: A Prospective Observational Study.

OBJECTIVES: The purpose of our study was to describe children with life-threatening bleeding. DESIGN: We conducted a prospective observational study of children with life-threatening bleeding events. SETTING: Twenty-four childrens hospitals in the United States, Canada, and Italy participated. SUBJECTS: Children 0-17 years old who received greater than 40 mL/kg total blood products over 6 hours or were transfused under massive transfusion protocol were included. INTERVENTIONS: Children were compared according bleeding etiology: trauma, operative, or medical. MEASUREMENTS AND MAIN RESULTS: Patient characteristics, therapies administered, and clinical outcomes were analyzed. Among 449 enrolled children, 55.0% were male, and the median age was 7.3 years. Bleeding etiology was 46.1% trauma, 34.1% operative, and 19.8% medical. Prior to the life-threatening bleeding event, most had age-adjusted hypotension (61.2%), and 25% were hypothermic. Children with medical bleeding had higher median Pediatric Risk of Mortality scores (18) compared with children with trauma (11) and operative bleeding (12). Median Glasgow Coma Scale scores were lower for children with trauma (3) compared with operative (14) or medical bleeding (10.5). Median time from bleeding onset to first transfusion was 8 minutes for RBCs, 34 minutes for plasma, and 42 minutes for platelets. Postevent acute respiratory distress syndrome (20.3%) and acute kidney injury (18.5%) were common. Twenty-eight-day mortality was 37.5% and higher among children with medical bleeding (65.2%) compared with trauma (36.1%) and operative (23.8%). There were 82 hemorrhage deaths; 65.8% occurred by 6 hours and 86.5% by 24 hours. CONCLUSIONS: Patient characteristics and outcomes among children with life-threatening bleeding varied by cause of bleeding. Mortality was high, and death from hemorrhage in this population occurred rapidly.

The effects of human prothrombin complex concentrate on hemorrhagic shock-induced lung injury in rats: Implications for testing human blood products in rodents.

BACKGROUND: Hemorrhagic shock (HS) and trauma can result in an endotheliopathy of trauma, characterized by endothelial compromise, inflammation, and aberrant coagulation. Kcentra, a prothrombin concentrate, has been demonstrated to mitigate pulmonary vascular leak in a murine model of HS. We investigated the effects of Kcentra in a rat model of HS, to achieve physiologic endpoints of relevance. METHODS: Rats subjected to a grade intravenous splenic injury and controlled hemorrhage for 60 minutes were resuscitated with shed volumes of (1) Lactated Ringer's (LR) solution, (2) LR + 20 IU/kg Kcentra, (3) LR + 50 IU/kg Kcentra, (4) rat fresh frozen plasma (RFFP), or (5) human fresh frozen plasma (HFFP). Blood was harvested for monitoring metabolic and coagulation function. Rat lungs were evaluated for lung injury and permeability. RESULTS: Animals resuscitated with LR displayed a significant increase in pulmonary vascular permeability (sham, 407.9 ± 122.4; shock + LR, 2040 ± 1462). Resuscitation with RFFP (606.5 ± 169.3) reduced leak; however, treatment with Kcentra (HS + Kcentra [20 IU/kg]: 1792 ± 903.4, HS + Kcentra [50 IU/kg]: 1876 ± 1103), and HFFP (1450 ± 533.2) had no significant effect on permeability. Kcentra modestly altered clotting parameters. Metabolic measures, such as lactate, pH, and base deficit, were restored to baseline levels by both RFFP and HFFP, but not Kcentra or LR. CONCLUSION: Kcentra did not alter pulmonary vascular permeability, but modestly increased clotting potential in injured rats. This suggests that there may be a xenogenic reaction of human products in rats and that the effects of Kcentra on vascular stability may be distinct from its ability to modulate clotting. Our data indicate that the species chosen and utilized for in vivo preclinical testing of human derived blood products is of critical importance in determining their efficacy in animal models and is the primary impetus to communicate these results.

Characterization of organ dysfunction and mortality in pediatric patients with trauma with acute traumatic coagulopathy.

BACKGROUND: Traumatic injuries are a leading cause of mortality and morbidity in pediatric patients and abnormalities in hemostasis play an important role in these poor outcomes. One such abnormality, acute traumatic coagulopathy (ATC), is a near immediate endogenous response to injury and has recently been described in the pediatric population. This study aims to evaluate the epidemiology of pediatric ATC, specifically its association with organ dysfunction. METHODS: All patients with trauma presenting to the University of California, Benioff Children's Hospital Oakland between 2006 and 2015 with coagulation testing drawn at presentation were included. Patients were excluded if they (1) were >18 years of age, (2) were admitted with a non-mechanical mechanism of injury, (3) were on anticoagulation medications, or (4) had coagulation testing >4 hours after injury. ATC was defined as an international normalized ratio (INR) ≥1.3. The primary outcome was new or progressive multiple organ dysfunction syndrome (MODS) and secondary outcomes included in-hospital mortality and other morbidities. RESULTS: Of the 7382 patients that presented in the 10-year study period, 545 patients met criteria for analysis and 88 patients (16%) presented with ATC. Patients with ATC were more likely to develop MODS than those without ATC (68.4% vs 7.7%, p<0.001) and had higher in-hospital mortality (26.1% vs 0.4%, p<0.001) than those without ATC. Along with arterial hypotension and an Injury Severity Score ≥30, ATC was independent predictor of MODS and in-hospital mortality. An isolated elevated INR was associated with MODS and in-hospital mortality while an isolated elevated partial thromboplastin time was not. CONCLUSIONS: Pediatric ATC was associated with organ dysfunction, mortality, and other morbidities. ATC along with arterial hypotension and high injury severity were independent predictors of organ dysfunction and mortality. Pediatric ATC may be biologically distinct from adult ATC and further studies are needed. LEVEL OF EVIDENCE: IV, epidemiologic.

Clinical Characteristics, Major Morbidity, and Mortality in Trauma-Related Pediatric Acute Respiratory Distress Syndrome.

OBJECTIVES: To determine the presence, central characteristics, and impact on major morbidity and mortality of trauma-related pediatric acute respiratory distress syndrome. DESIGN: Retrospective review of a prospective trauma database. SETTING: American College of Surgeons verified level 1 trauma center in an urban setting. PATIENTS: Trauma patients age 0 to 18 years old inclusive. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Of the 7,382 patients presenting within the 10-year study period, 646 met study criteria for inclusion in the analysis. Trauma-related pediatric acute respiratory distress syndrome was present in 9% of the analyzed cohort. On univariate analysis and compared with those without, trauma-related pediatric acute respiratory distress syndrome occurred more commonly among those with traumatic brain injury (77.2% vs 45.5%; p < 0.001), non-accidental trauma (28.8% vs 10.2%; p < 0.001), and an injury severity score greater than 30 (27.1% vs 3.8%; p 0.001). New or progressive multiple organ dysfunction syndrome was significantly higher in trauma-related pediatric acute respiratory distress syndrome patients (86.7% vs 10.4%; p < 0.001) as was mortality (18.3% vs 3.1%; p < 0.001) than in those without. The presence of trauma-related pediatric acute respiratory distress syndrome (odds ratio, 6.98; 95% CI, 2.95-16.5; p < 0.001), younger age (odds ratio, 0.93; 95% CI, 0.87-0.99; p = 0.038), and worse injury severity (odds ratio, 1.19; 95% CI, 1.14-1.24; p < 0.001) were all independent statistical predictors of new or progressive multiple organ dysfunction syndrome in this retrospective cohort. Mortality in patients without trauma-related pediatric acute respiratory distress syndrome increased with increasing injury severity, whereas mortality in patients with trauma-related pediatric acute respiratory distress syndrome was the same regardless of injury severity. On multivariable regression analysis, while age and injury severity were independent statistical predictors of mortality, trauma-related pediatric acute respiratory distress syndrome was not (odds ratio, 2.35; 95% CI, 0.88-6.28; p = 0.087). CONCLUSIONS: Pediatric acute respiratory distress syndrome is present in the pediatric trauma population. Trauma-related pediatric acute respiratory distress syndrome is associated with eight times the organ dysfunction and five times the mortality compared with patients without trauma-related pediatric acute respiratory distress syndrome, yet research in this area is lacking. Further prospective, mechanistic evaluations are essential to understand why these patients are at risk and how to effectively intervene to improve outcomes.

Hemostatic Testing in Critically Ill Infants and Children.

Children with critical illness frequently manifest imbalances in hemostasis with risk of consequent bleeding or pathologic thrombosis. Traditionally, plasma-based tests measuring clot formation by time to fibrin clot generation have been the "gold standard" in hemostasis testing. However, these tests are not sensitive to abnormalities in fibrinolysis or in conditions of enhanced clot formation that may lead to thrombosis. Additionally, they do not measure the critical roles played by platelets and endothelial cells. An added factor in the evaluation of these plasma-based tests is that in infants and young children plasma levels of many procoagulant and anticoagulant proteins are lower than in older children and adults resulting in prolonged clot generation times in spite of maintaining a normal hemostatic "balance." Consequently, newer assays directly measuring thrombin generation in plasma and others assessing the stages hemostasis including clot initiation, propagation, and fibrinolysis in whole blood by viscoelastic methods are now available and may allow for a global measurement of the hemostatic system. In this manuscript, we will review the processes by which clots are formed and by which hemostasis is regulated, and the rationale and limitations for the more commonly utilized tests. We will also discuss selected newer tests available for the assessment of hemostasis, their "pros" and "cons," and how they compare to the traditional tests of coagulation in the assessment and management of critically ill children.

Pathophysiology and Management of Acute Respiratory Distress Syndrome in Children.

Acute respiratory distress syndrome (ARDS) is a syndrome of noncardiogenic pulmonary edema and hypoxia that accompanies up to 30% of deaths in pediatric intensive care units. Pediatric ARDS (PARDS) is diagnosed by the presence of hypoxia, defined by oxygenation index or Pao2/Fio2 ratio cutoffs, and new chest infiltrate occurring within 7 days of a known insult. Hallmarks of ARDS include hypoxemia and decreased lung compliance, increased work of breathing, and impaired gas exchange. Mortality is often accompanied by multiple organ failure. Although many modalities to treat PARDS have been investigated, supportive therapies and lung protective ventilator support remain the mainstay.

Venovenous Extracorporeal Life Support in Single-Ventricle Patients with Acute Respiratory Distress Syndrome.

There is new and growing experience with venovenous extracorporeal life support (VV ECLS) for neonatal and pediatric patients with single-ventricle physiology and acute respiratory distress syndrome (ARDS). Outcomes in this population have been defined but could be improved; survival rates in single-ventricle patients on VV ECLS for respiratory failure are slightly higher than those in single-ventricle patients on venoarterial ECLS for cardiac failure (48 vs. 32-43%), but are lower than in patients with biventricular anatomy (58-74%). To that end, special consideration is necessary for patients with single-ventricle physiology who require VV ECLS for ARDS. Specifically, ARDS disrupts the balance between pulmonary and systemic blood flow through dynamic alterations in cardiopulmonary mechanics. This complexity impacts how to run the VV ECLS circuit and the transition back to conventional support. Furthermore, these patients have a complicated coagulation profile. Both venous and arterial thrombi carry marked risk in single-ventricle patients due to the vulnerability of the pulmonary, coronary, and cerebral circulations. Finally, single-ventricle palliation requires the preservation of low resistance across the pulmonary circulation, unobstructed venous return, and optimal cardiac performance including valve function. As such, the proper timing as well as the particular conduct of ECLS might differ between this population and patients without single-ventricle physiology. The goal of this review is to summarize the current state of knowledge of VV ECLS in the single-ventricle population in the context of these special considerations.