Endogenous heparin decreases the thrombotic response to hemorrhagic shock in rabbits

Effects of profound hypoxemia on coagulation & fibrinolysis in normal individuals

Hypoxia has been proposed to enhance, diminish, or have no effect on laboratory measures of coagulation or clinical thrombosis. Further, there usually are significant pathological or environmental factors concurrently present with hypoxia. Thus, the goal of the present investigation was to determine whether whole blood or plasmatic coagulation and fibrinolytic kinetics would change in response to progressive hypoxia to a systemic oxygenation (SpO2) of 70%. Healthy, conscious volunteers (n = 9) breathing a hypoxic mixture of gases during an in-vivo validation of noninvasive cerebral oximetry had blood samples collected and assessed with thrombelastography at normoxia and after SpO2 of 70%. A mild release of endogenous heparin-like activity occurred that diminished plasmatic coagulation, and a mild increase in clot lysis time also was noted. Further investigation to determine whether these phenomena occur in more chronic, less hypoxic states as sources of hypocoagulation or thrombophilia is needed.

A novel heparin-dependent inhibitor of activated protein C that potentiates consumptive coagulopathy in Russell's viper envenomation

The activation of coagulation factors V and X by Russell's viper venom (RVV) has been implicated in the development of consumptive coagulopathies in severely envenomed patients. However, factor Va is prone to inactivation by activated protein C (APC), an important serine protease that negatively regulates blood coagulation. It is therefore hypothesized that APC may be down-regulated by some of the venom components. In this study, we managed to isolate a potent Kunitz-type APC inhibitor, named DrKIn-I. Using chromogenic substrate, DrKIn-I dose-dependently inhibited the activity of APC. Heparin potentiated the inhibition and reduced the IC(50) of DrKIn-I by 25-fold. DrKIn-I, together with heparin, also protected factor Va from APC-mediated inactivation. Using surface plasmon resonance, DrKIn-I exhibited fast binding kinetics with APC (association rate constant = 1.7 × 10(7) M(-1) s(-1)). Direct binding assays and kinetic studies revealed that this inhibition (K(i) = 53 pM) is due to the tight binding interactions of DrKIn-I with both heparin and APC. DrKIn-I also effectively reversed the anticoagulant activity of APC and completely restored the thrombin generation in APC-containing plasma. Furthermore, although the injection of either DrKIn-I or RVV-X (the venom factor X-activator) into ICR mice did not significantly deplete the plasma fibrinogen concentration, co-administration of DrKIn-I with RVV-X resulted in complete fibrinogen consumption and the deposition of fibrin thrombi in the glomerular capillaries. Our results provide new insights into the pathogenesis of RVV-induced coagulopathies and indicate that DrKIn-I is a novel APC inhibitor that is associated with potentially fatal thrombotic complications in Russell's viper envenomation.

Is damage control orthopedics essential for the management of bilateral femoral fractures associated or complicated with shock? An animal study

BACKGROUND

The maximum score of a single anatomic system, the Injury Severity Score, may not reflect the overall damage inflicted by bilateral femoral fractures and justify the strategy of damage control orthopedics (DCO). It is necessary to investigate effects of various therapeutic procedures on such fractures with or without shock to facilitate correct decision making on DCO.

METHODS

A model of bilateral femoral fractures was made in 36 of 48 male New Zealand White rabbits. A model of bilateral femoral shaft fractures associated with shock was made. After resuscitation, a reamed intramedullary nailing fixation was performed in the first group (IM group), and an external fixation device applied in the second group (EF group), and the fractures in the third group (control group) were supported with splints only. They were divided into four groups: shock with IM nailing (shock-IM), shock with external fixation (shock-EF), shock with conservative method (shock-Cons), and intramedullary nailing without shock (nonshock-IM). Vital signs and inflammatory reactions were recorded. Thirty-six hours after the therapeutic procedures in four groups, the animals were killed for histologic evaluation.

RESULTS

The changes of vital signs were most significant in shock-IM group (p < 0.05). The exaggerated levels of interleukin-6, Interleukin-10, and tumor necrosis factor alpha concentrations demonstrated a significant difference between all the groups-shock-IM and other groups (p < 0.05). As to histologic appearances, the statistical difference varies from organ to organ. There is highly significant difference when the IM group is compared with the other two groups as far as lungs are concerned. As to the liver, there is only significant difference between the IM group and the control group. In terms of kidney and heart, there is no significant difference cross the groups. As to histologic appearances, there is highly significant difference in lungs between shock-IM group and other three groups. There is significant difference in liver between the shock-IM group and the shock-Cons group (p < 0.05). Kidneys and heart were less affected cross the groups.

CONCLUSIONS

In this study, an early reamed intramedullary nailing fixation procedure resulted in more adverse effects on system stress, inflammatory response, and multiple organs. The injuries also cause histologic damages to lungs and liver. Therefore, early reamed intramedullary nailing fixation may pose a potential risk of developing complications and adopting the DCO strategy may be more preferable. Shock and IM combined cause most severe damages, followed by IM without shock, shock plus EF, and shock plus conservative procedure in that order. If IM must be used for some reasons, it is desirable be delayed until shock has been fully controlled and vasculorespiratory stability restored.

Usefulness of soluble Fms-like tyrosine kinase-1 as a biomarker of acute severe heart failure in patients with acute myocardial infarction

Placental growth factor and vascular endothelial growth factor increase angiogenesis and promote healing after acute myocardial infarction (MI), but the significance of soluble Fms-like tyrosine kinase-1 (sFlt-1), an antagonist of placental growth factor and vascular endothelial growth factor, in the setting of acute MI has not been elucidated. The development of acute heart failure in the immediate period after MI is a dreaded complication, but there are no useful biomarkers that identify patients at risk of acute heart failure. We wished to investigate the clinical significance of circulating sFlt-1 during acute MI. We enrolled 174 patients with acute MI, and arterial blood sampling was performed. Plasma levels of sFlt-1 were measured by enzyme-linked immunosorbent assay and their relation to clinical parameters was analyzed. Circulating levels of sFlt-1 on admission were significantly increased in patients with acute MI compared to controls (528.1 +/- 290.9 vs 355.7 +/- 205.0 pg/ml, p <0.001). Circulating levels of sFlt-1 on admission were significantly higher in patients who developed severe acute heart failure requiring mechanical circulatory support devices compared to those with stable hemodynamics (611.4 +/- 373.6 vs 494.6 +/- 243.9 pg/ml, p = 0.016). Moreover, circulating levels of sFlt-1 on admission were directly related to duration of hospitalization. Multivariate logistic analysis showed that hemodynamic instability was predicted by sFlt-1 on admission and left ventricular systolic pressure. In conclusion, the circulating level of sFlt-1 is increased in patients with acute MI, and the sFlt-1 level on admission is a promising biomarker for the development of severe acute heart failure after MI.

Hemodilution with lactated Ringer's solution causes hypocoagulability in rabbits

Hemodilution (HD) has been associated with hypercoagulability. It was hypothesized that HD with lactated Ringer's solution (LR) would result in hypercoagulability in rabbits. Sedated rabbits (n = 12) underwent HD with LR (40% estimated blood volume replaced with five volumes of LR) via ear vessels. Key procoagulants and anticoagulant activities were assessed prior to and 3 h after HD. Hemostatic function was assessed with the activated coagulation time and platelet-inhibited thrombelastography. Circulating tissue factor activity was much more diluted (-67.2% from baseline) than tissue factor pathway inhibitor (-45.2%) or antithrombin (-9.5%) activities after HD. HD significantly decreased factor VIII complex activity (-31.5%) more than protein C activity (-5.9%), and factor X activity (-29.2%) was more diluted than antithrombin activity. The activated coagulation time and thrombelastography demonstrated a significant decrease in hemostatic function after HD. Hemodilution with LR caused hypocoagulability in the rabbit. A greater decrease in circulating procoagulant activity than anticoagulant activity appears to be the mechanism underlying HD-mediated decreases in hemostasis.