Recombinant tissue-type plasminogen activator-evoked hyperfibrinolysis is enhanced by acidosis and inhibited by hypothermia but still can be blocked by tranexamic acid.

BACKGROUND: Hypothermia and acidosis have been suggested as key initiators of trauma-induced coagulopathy, and severe bleeding caused by hyperfibrinolysis (HF) predicts mortality. We tested in vitro (1) whether clinically relevant grades of hypothermia, acidosis, and their combination impact on recombinant tissue-type plasminogen activator (r-tPA)-evoked HF and assessed (2) the efficacy of tranexamic acid (TA) in inhibiting fibrinolysis under such conditions.
METHODS: To assess the effects of r-tPA-evoked HF, venous blood (3,000 μL) from healthy volunteers was incubated with r-tPA (final concentration, 100 ng/mL) or saline (control) for 30 minutes at the final measurement temperature. Before thromboelastometric measurements, samples were acidified (addition of 40 μL of 0.5 or 1N hydrochloric acid, respectively) to achieve a pH (alpha-stat) of approximately 7.1 or 6.9, respectively. To assess effects of hypothermia, tests were performed at blood/thromboelastometer temperatures of 33°C and 37°C, respectively. Coagulation was analyzed using rotational thromboelastometry (ROTEM), particularly assessing the Clot Lysis Index (CLI) after 45 minutes (CLI45) in extrinsically activated assays (EXTEM).
RESULTS: Addition of r-tPA evoked fibrinolysis (CLI45: median, 64; 25th/75th percentile, 48/80) compared with saline controls (CLI45: median, 93; 25th/75th percentile, 91/96). Moderate acidosis (pH [mean ± SD], 7.12 ± 0.03) did not affect r-tPA-induced fibrinolysis. However, severe acidosis (pH, 6.91 ± 0.02) significantly aggravated r-tPA-induced fibrinolysis (CLI45: median, 49; 25th/75th percentile, 26/71; p = 0.0039) compared with fibrinolysis with normal pH and normothermia (median, 77; 25th/75th percentile, 65.5/83). In contrast, hypothermia (33°C) at normal pH (median ± SD, 7.37 ± 0.02) markedly mitigated fibrinolysis (CLI45: median, 94; 25th/75th percentile, 88/96; p = 0.0156) compared with normothermia (CLI45: median, 64; 25th/75th percentile, 48/80). TA (final concentration, 0.33 mg/mL) abolished r-tPA-evoked fibrinolysis even during severe acidosis (CLI45: median, 92; 25th/75th percentile, 86.5/94; p = 0.0039).
CONCLUSION: Severe acidosis significantly increases r-tPA-evoked fibrinolysis, whereas hypothermia markedly mitigates HF. The latter finding may imply that rapid rewarming of trauma patients might aggravate fibrinolysis. TA reliably abolished fibrinolysis also under these conditions, supporting its role in trauma-induced coagulopathy.