Global Activation of Coagulation Is the Initiating Event of Acute Coagulopathy of Trauma As Modeled By Hemorrhage and Lower Body Negative Pressure in Baboons

Up to 50% of preventable trauma deaths are due to truncal hemorrhage resulting in cardiovascular collapse. Lower body negative pressure (LBNP) causes central hypovolemia in humans, resulting in coagulation changes, platelet activation, and fibrinolysis. The model allows investigators to study impending hemorrhagic shock in a minimally invasive human model, but correlations to changes in clotting and lysis due to hemorrhage are not fully described. Published human data to date has not discriminated between altered coagulation due to the LBNP method versus changes attributable to incipient hemorrhagic shock. We measured multiple coagulation parameters in 16 baboons undergoing hemorrhage followed by LBNP and hypothesized that this model elicits early changes associated with acute coagulopathy due to hemorrhage.

Baboons underwent incremental hemorrhage (HEM) under an ACURO-approved protocol, followed by LBNP 2-4 weeks later. Blood was sampled at baseline (T0) and after approximately 18.75% (T1), and 25% (T2) blood loss (or until presyncope), and at recovery (T3). LBNP levels were determined by matching the pulse and central venous pressures elicited by hemorrhage. Measurements included: complete blood count; blood chemistries; and coagulations tests. Parameters measured by thromboelastography (TEG) included: R-time, K-time, angle, maximum amplitude (MA), and lysis at 30 and 60 minutes (LY30, LY60). Coagulation factors were quantified over time during both experiments (STA-R Evolution, STAGO).Platelet count was measured and response to agonists (ADP, collagen, TRAP) assessed with impedance aggregometry (Multiplate, Roche Diagnostics). Markers of platelet activation were evaluated under flow cytometry (P-selectin, PAC-1, and leukocyte-platelet aggregates (CD45:CD41)).

LBNP and hemorrhage caused activation of the coagulation system over time as measured by TEG R-time (HEM: T0=5.8±0.3 s; T2=4.7±0.3 s; LBNP: T0=6.5±0.3 s; T2=5.1±0.3 s; p<0.001), an increase in velocity of clot formation as measured by angle (HEM: T0=67±1°; T2=71±2°; LBNP: T0=67±1°; T3=70±1°; p=0.013), and clot strength as measured by MA (HEM: T0=60±2 mm; T2=66±2 mm; LBNP: T0=66±2 mm; T3=69±2 mm; p<0.003). R-time and angle differences between experiments were not significant (p≥0.05), whereas clot strength (MA) was higher in the LBNP experiment (p=0.015). Fibrinolysis at 30 and 60 minutes decreased over time with both study treatments (HEM LY30: T0=3.6±0.8%; T3=0.3±0.8%; LBNP LY30: T0=4.2±0.8%; T3=0.8±0.8%; HEM LY60: T0=7.2±1.3%; T3=1.8±1.4%; LBNP LY60: T0=7.3±1.3%; T3=2.9±1.3%; p<0.001), but effects between experiments were not significant (p≥0.05). D-Dimer measurements were not consistent with TEG lysis data, but rather increased over time during both experiments (HEM: T0=0.43±0.16 µg/ml; T3=0.96±0.16 µg/ml; LBNP: T0=0.58±0.16 µg/ml; T2=0.93±0.16 µg/ml; p<0.001). The coagulations factors V (FV), and VIII (VIII) changed over time; however effects were opposite, decreasing during hemorrhage and increasing during LBNP (HEM FV: T0=85±4%; T3=79±4%; LBNP FV: T0=88±4%; T3=102±4%; HEM FVIII: T0=122±7%; T3=117±7%; LBNP FVIII: T0=126±7%; T3=135±7%; p<0.001 for both factors). In contrast, Protein C (PC) levels decreased during both experiments, although baseline levels differed (HEM PC: T0=99±4%; T3=79±4%; LBNP PC: T0=113±4%; T3=99±4%; p<0.001). Fibrinogen decreased during recovery, but only during the HEM experiment (HEM: T0=211±20 mg/dl; T3=157±21 mg/dl, p<0.001; LBNP: T0=217±20 mg/dl; T3=216±20 mg/dl; p≥0.05). Platelet count did not change significantly over time during either experiment, but differences between HEM and LBNP were significant largely due to baseline effects (HEM: T0=199±12x10⁹/mm³; LBNP: T0=234±12x109/mm3; p<0.001). Platelet aggregation (U) did not change over time or between groups (p≥0.05).

LBNP-induced central hypovolemia and hemorrhage in the absence of tissue damage caused activation of the coagulation system in baboons, as well as increased clot formation velocity and strength. TEG and and Protein C results matched most closely between experiments and can be used with LBNP to study pre-hospital changes due blood loss. Lysis data, in contrast to human data, was contradictory. Central hypovolemia due to severe hemorrhage and LBNP caused global activation of coagulation function, indicating that this is the initiating event in acute coagulopathy of trauma.