Dag Winstedt

Fibrinogen measurement in cardiac surgery with cardiopulmonary bypass: Analysis of repeatability and agreement of Clauss method within and between six different laboratories

Plasma fibrinogen concentration is important for coagulopathy assessment, and is most commonly measured using the Clauss method. Several factors, including device type and reagent, have been shown to affect results. The study objective was to evaluate performance and repeatability of the Clauss method and to assess differences between measurements performed during and after cardiopulmonary bypass (CPB), by testing plasma samples from patients undergoing cardiac surgery with CPB. Samples were collected from 30 patients before surgery, approximately 20 minutes before weaning from CPB, and 5 minutes after CPB and protamine. Fibrinogen concentration was determined using the Clauss method at six quality-controlled specialised laboratories, according to accredited standard operating procedures. Regarding within-centre agreement for Clauss measurement, mean differences between duplicate measurements were between 0.00 g/l and 0.15 g/l, with intervals for 95% limits of agreement for mean Bland-Altman differences up to 1.3 g/l. Regarding between-centre agreement, some mean differences between pairs of centres were above 0.5 g/l. Differences of up to ~2 g/l were observed with individual samples. Increased variability was observed between centres, with inter-class correlation values below 0.5 suggesting only fair agreement. There were no significant differences in fibrinogen concentration before weaning from CPB and after CPB for most centres and methods. In conclusion, considerable differences exist between Clauss-based plasma fibrinogen measured using different detection methods. Nevertheless, the similarity between measurements shortly before weaning from CPB and after CPB within centres suggests that on-pump measurements could provide an early estimation of fibrinogen deficit after CPB and thus guidance for haemostatic therapy.

Free oscillation rheometry monitoring of haemodilution and hypothermia and correction with fibrinogen and factor XIII concentrates.

BackgroundHaemodilution and hypothermia induce coagulopathy separately, but their combined effect on coagulation has not been widely studied. Fibrinogen concentrate can correct dilutional coagulopathy and has an additional effect when combined with factor XIII concentrate. However, their effect on dilutional coagulopathy concomitant with hypothermia has not been studied previously. Free oscillation rheometry – FOR (Reorox®) – is a novel viscoelastic haemostatic assay that has not been studied in this context before.MethodsBlood from 10 healthy volunteers was diluted by 33% with hydroxyethyl starch or Ringer’s acetate solutions. Effects of fibrinogen added in vitro with and without factor XIII were studied at 33°C and 37°C. Coagulation velocity (coagulation time) and clot strength (elasticity) were assessed with FOR. Coagulation was initiated in vitro with thromboplastin alone, or thromboplastin plus a platelet inhibitor.ResultsHydroxyethyl starch increased the coagulation time and decreased clot strength significantly more than Ringer’s acetate solution, both in the presence and absence of a platelet inhibitor. There was a significant interaction between haemodilution with hydroxyethyl starch and hypothermia, resulting in increased coagulation time. After addition of fibrinogen, coagulation time shortened and elasticity increased, with the exception of fibrinogen-dependent clot strength (i.e., elasticity in the presence of a platelet inhibitor) after hydroxyethyl starch haemodilution. Factor XIII had an additional effect with fibrinogen on fibrinogen-dependent clot strength in blood diluted with Ringer’s acetate solution. Hypothermia did not influence any of the coagulation factor effects.ConclusionsBoth haemodilution and mild hypothermia impaired coagulation. Coagulopathy was more pronounced after haemodilution with hydroxyethyl starch than with Ringer’s acetate. Addition of fibrinogen with factor XIII was unable to reverse hydroxyethyl starch induced clot instability, but improved coagulation in blood diluted with Ringer’s acetate solution. Fibrinogen improved coagulation irrespective of hypothermia.

Fibrinogen and FXIII dose response effects on albumin-induced coagulopathy.

Abstract Objectives. Natural colloid albumin induces a lesser degree of dilutional coagulopathy than synthetic colloids. Fibrinogen concentrate has emerged as a promising strategy to treat coagulopathy, and factor XIII (FXIII) works synergistically with fibrinogen to correct coagulopathy following haemodilution with crystalloids. Our objectives were to examine the ability of fibrinogen and FXIII concentrates to reverse albumin-induced dilutional coagulopathy. Methods. High and low concentrations of both fibrinogen and FXIII were used to reverse coagulopathy induced by 1:1 dilution in vitro with 5% albumin of blood samples from healthy volunteers, monitored by rotational thromboelastometry (ROTEM®). Results. Haemodilution with albumin significantly attenuated EXTEM maximum clot firmness (MCF), alpha angle (AA), clotting time (CT) and clot formation time (CFT), and FIBTEM MCF (p < 0.001). Following haemodilution, both doses of fibrinogen significantly corrected all ROTEM parameters (p ≤ 0.02), except the lower dose did not correct AA. Compared to the lower dose, the higher dose of fibrinogen significantly improved FIBTEM MCF and EXTEM MCF, AA and CFT (p < 0.001). The lower dose of FXIII did not significantly correct any of the ROTEM parameters, and the high dose only improved EXTEM CT (p = 0.004). All combinations of high/low concentrations of fibrinogen/FXIII significantly improved all ROTEM parameters examined (p ≤ 0.001). Fibrinogen concentration generally had a greater effect on each parameter than did FXIII concentration; the best correction of ROTEM parameters was achieved with high-dose fibrinogen concentrate and either low- or high-dose FXIII. Conclusions. Fibrinogen concentrate successfully corrected initiation, propagation and clot firmness deficits induced by haemodilution with albumin, and FXIII synergistically improved fibrin-based clot strength.

Intraoperative Hydroxyethyl Starch and its Effects on Different Fibrinogen Measurements

Background: Intravenous fluids with synthetic colloids such as hydroxyethyl starch (HES) are known to interfere with plasma fibrinogen concentration measurements. The aim of this study was to evaluate the effects of an HES solution on fibrinogen measurements in a clinical setting. Methods: The study was performed in patients who received at least 1 L of HES during intracranial tumor resection surgery. Blood samples were drawn before the start of surgery (baseline), after infusion of 1 L of HES, and at later time points. The fibrinogen concentration was measured using 3 different methods: (a) enzyme-linked immunosorbent assay (ELISA), (b) Clauss method with a photometric readout, and (c) Clauss method with an electromechanical readout. In addition, the fibrin-based clot quality was evaluated with the thromboelastometric FIBTEM test. Results: Forty patients were enrolled, and 25 patients were included in the analysis. The fibrinogen concentrations at baseline were 2.2, 2.3, and 2.6 g/L and after 1 L of HES 1.6, 1.7, and 1.9 g/L as measured by ELISA, the photometric test, and the electromechanical test, respectively. The electromechanical Clauss test measured significantly higher concentrations at these time points. The relative decrease, however, was comparable between methods (31%, 29%, and 25%, respectively) but significantly lower than the 44% relative decrease with FIBTEM maximum clot firmness. Conclusion: Despite providing different fibrinogen concentration values at baseline, the relative decrease in fibrinogen concentration after HES infusion was comparable among the 3 tests. In contrast, fibrin-based clot quality was more affected than fibrinogen concentration tests by HES infusion.

Viscoelastic haemostatic assays and fibrinogen concentration tests during haemodilution.

The efficacy of concentrates of fibrinogen and factor XIII in hypothermia and haemodilution has not yet been completely investigated. Clauss fibrinogen measurement may overestimate fibrinogen concentrations during in vitro haemodilution with hydroxyethyl starch (HES).