Elevated fibrinogen, von Willebrand factor, and Factor VIII confer resistance to dilutional coagulopathy and activated protein C in normal pregnant women.

BACKGROUND: Gestational changes in coagulation factor concentrations include elevations in fibrinogen, Factor VIII, and von Willebrand factor (vWF). We hypothesised that blood samples from term pregnant (TP) subjects are less prone to coagulation disturbances from haemodilution compared with those from non-pregnant (NP) females. METHODS: Blood samples were collected from 15 NP and 15 TP subjects. In vitro haemodilution with normal saline was assessed by modified Clauss fibrinogen assay, factor activity, flow-chamber assay, and thromboelastometry. The impact of human fibrinogen concentrate (hFC), cryoprecipitate, and vWF/Factor VIII (FVIII) concentrate replacement in diluted TP and NP blood was compared. Thrombin generation and activated protein C sensitivity were assessed. RESULTS: TP blood contained twice the concentrations of fibrinogen, FVIII, and vWF relative to NP blood (P<0.0001). Platelet thrombus formation (PTF) under flow was reduced by 99.2% and 69.2% in diluted NP and TP blood, respectively. Platelet thrombus formation was partially restored by adding vWF/FVIII, but not hFC or cryoprecipitate. Fibrin clot firmness approached the threshold of 10 mm in diluted NP blood, and clot firmness was effectively restored by hFC, but not by vWF/FVIII. In the presence of thrombomodulin, peak thrombin generation was decreased by 86.7% in NP plasma, but by 31.8% in TP plasma (P<0.0001 vs NP plasma), indicating reduced activated protein C sensitivity in TP plasma. Both elevated FVIII and haemodilution contributed to activated protein C insensitivity. CONCLUSIONS: Our in vitro model showed relative resistance of TP blood to dilutional coagulation changes with respect to platelet adhesion, fibrin polymerisation, and thrombin generation. Careful therapeutic monitoring for different pro-haemostatic agents in pregnant women is warranted.

Factor IX from prothrombin complex concentrate augments low dose tissue factor-triggered thrombin generation in vitro.

BACKGROUND: Prothrombin complex concentrate (PCC) is increasingly used to correct acquired coagulopathy in trauma and surgery. Dosing of PCC is guided by the prothrombin time, which only reflects the onset of thrombin generation, but does not account for variations in intrinsic pathway coagulation factors, including factor IX (FIX). We hypothesised that FIX contained in PCC could strongly influence thrombin generation patterns. METHODS: Pooled normal, FIX-deficient, and warfarinised plasma were used to analyse the effects of FIX contained in PCC. PCC was evaluated at final concentrations of 0.2 and 0.4 IU ml-1 in FIX-deficient and normal plasma, and at 0.6 IU ml-1 in warfarinised plasma with elevated FVIII (1.5 IU ml-1), 40% dilution with saline, or both. The effects on thrombin generation were assessed by measuring both procoagulant and inhibitory segments. RESULTS: FIX-deficient plasma had lower peak thrombin generation [30.6 (20.5-35.8) nM vs 130.2 (107-168) nM] and endogenous thrombin potential [472 (391-532) nM vs 1096 (958-1190) nM] than normal plasma. PCC addition resulted in significant increases of peak thrombin generation [81.8 (37.3-98.3) nM] and endogenous thrombin potential [808 (472-842) nM] in FIX-deficient plasma. The combination of FVIII and PCC resulted in greater increases relative to each agent alone, restoring normal thrombin generation. After 40% dilution, adding PCC, FVIII, or both, to FIX-deficient plasma increased peak thrombin generation, and prolonged the inhibitory phase of the endogenous thrombin potential. CONCLUSIONS: FIX derived from PCC strongly enhances tissue factor-triggered thrombin generation in the presence of elevated FVIII activity. Haemodilution further enhances procoagulant effects of FIX and FVIII by slowing down inhibition of procoagulant enzymes. Dosing of PCC per prothrombin time may underestimate PCC's procoagulant potential because it does not account for intrinsic tenase or antithrombin activity.

Comparison between thrombelastography and thromboelastometry in hyperfibrinolysis detection during adult liver transplantation.

BACKGROUND: Hyperfibrinolysis is one of the main causes of non-surgical bleeding during liver transplantation (LT). Viscoelastic haemostatic assays, including thromboelastometry (ROTEM(®)) and thrombelastography (TEG(®)), can detect hyperfibrinolysis at the bedside. No study has yet demonstrated which device or assay is more suitable for detecting hyperfibrinolysis. METHODS: This prospective observational study compared ROTEM(®) and TEG(®) in isolated adult LT. ROTEM(®) (EXTEM(®) [tissue factor activation], FIBTEM(®) [tissue factor activation with platelet inhibition], and APTEM(®) [tissue factor activation with tranexamic acid/aprotinin]) and TEG(®) (kaolin-TEG(®)) were simultaneously performed using arterial blood samples at eight time-points during LT: induction of general anaesthesia, 60 min after skin incision, 10 and 45 min after portal vein clamp, 15 min before graft reperfusion, and five, 30, and 90 min after graft reperfusion. Hyperfibrinolysis was identified per the manufacturers' definitions (maximum lysis >15% in ROTEM(®) or Lysis30>8% in TEG(®)) and confirmed with APTEM(®); incidence was compared between assays McNemar's test. RESULTS: Among 296 possible measurement points from 376 consecutive LT recipients, 250 underwent final analysis: 46 measurement points were excluded because of missing assays or flat line. Hyperfibrinolysis was confirmed at 89 (36%) of 250 measurement points: FIBTEM(®), EXTEM(®), and kaolin-TEG(®) detected 84 (94%), 41 (46%), and 21 (24%) hyperfibrinolysis, respectively. These hyperfibrinolysis detection rates significantly differed from each other (P<0.001). CONCLUSIONS: Tissue factor-triggered ROTEM(®) tests were more sensitive than contact-activated k-TEG(®) in identifying hyperfibrinolysis in LT patients. Inhibition of platelet-fibrin interaction in FIBTEM(®) enhanced sensitivity to hyperfibrinolysis detection compared with EXTEM(®).