Fibrinolysis shutdown phenotype masks changes in rodent coagulation in tissue injury versus hemorrhagic shock

Abstract

Introduction: Systemic hyperfibrinolysis (accelerated clot degradation) and fibrinolysis shutdown (impaired clot degradation) are associated with increased mortality compared with physiologic fibrinolysis after trauma. Animal models have not reproduced these changes. We hypothesize rodents have a shutdown phenotype that require an exogenous profibrinolytic to differentiate mechanisms that promote or inhibit fibrinolysis.

Methods: Fibrinolysis resistance was assessed by thrombelastography (TEG) using exogenous tissue plasminogen activator (tPA) titrations in whole blood. There were 3 experimental groups: (1) tissue injury (laparotomy/bowel crush), (2) shock (hemorrhage to mean arterial pressure of 20 mmHg), and (3) control (arterial cannulation and tracheostomy). Baseline and 30-minute postintervention blood samples were collected, and assayed with TEG challenged with taurocholic acid (TUCA).

Results: Rats were resistant to exogenous tPA; the percent clot remaining 30 minutes after maximum amplitude (CL30) at 150 ng/mL (P = .511) and 300 ng/mL (P = .931) was similar to baseline, whereas 600 ng/mL (P = .046) provoked fibrinolysis. Using the TUCA challenge, the percent change in CL30 from baseline was increased in tissue injury compared with control (P = .048.), whereas CL30 decreased in shock versus control (P = .048). tPA increased in the shock group compared with tissue injury (P = .009) and control (P = .012).

Conclusion: Rats have an innate fibrinolysis shutdown phenotype. The TEG TUCA challenge is capable of differentiating changes in clot stability with rats undergoing different procedures. Tissue injury inhibits fibrinolysis, whereas shock promotes tPA-mediated fibrinolysis.

Figure 1. Physiologic Response to Interventions

Error bars =95% confidence intervals Y axis represents the mean arterial pressure in mmHg. X axis represents time points at which blood pressure was measured. Animals in all experimental arms experienced a decrease in blood pressure after first blood samples. Those animals not in the hemorrhagic shock recovered from this transient blood loss over the following 30 minutes of observation.

Figure 2. Rodent Whole Blood is Resistant to TPA Mediated Fibrinolysis

*= P<0.05 compared to whole blood Y axis represents the CL30 (percent of remaining clot strength 30 minutes after reaching maximum amplitude). On the X axis represents increasing concentrations of tissue plasminogen activator to exogenously mixed to non shocked rat whole blood.

Figure 3. Native TEG does not Discriminate Tissue Injury from Shock

The Y axis represents the percent change in CL30 from baseline to post procedure. The X axis represents different experimental arms. The control group by the end of the experiment had stage II shock and mild tissue injury, the shock group by the end of the experiment had stage IV shock and mild tissue injury, and the tissue injury group had major tissue injury and stage II shock.

Figure 4. TUCA Challenge TEG Discriminates Tissue Injury from Shock

*=P<0.05 compared to control **=P<0.05 compared to shock The Y axis represents the percent change in CL30 from baseline to post procedure. The X axis represents different experimental arms. The control group by the end of the experiment had stage II shock and mild tissue injury, the shock group by the end of the experiment had stage IV shock and mild tissue injury, and the tissue injury group had major tissue injury and stage II shock.

Figure 5. tPA Levels Increase After Shock not Tissue Injury

*=P<0.05 compared to control **=P<0.05 compared to shock The Y axis represents the percent change in tissue plasminogen activator from baseline to post procedure. The X axis represents different experimental arms. The control group by the end of the experiment had stage II shock and mild tissue injury, the shock group by the end of the experiment had stage IV shock and mild tissue injury, and the tissue injury group had major tissue injury and stage II shock.