title: Comparison of Thrombelastography-Derived Fibrinogen Values at Rewarming and Following Cardiopulmonary Bypass in Cardiac Surgery Patients.
abstract: The inflated costs and documented deleterious effects of excess perioperative transfusion have led to the investigation of targeted coagulation factor replacement strategies. One particular coagulation factor of interest is factor I (fibrinogen). Hypofibrinogenemia is typically tested for using time-consuming standard laboratory assays. The thrombelastography (TEG)-based functional fibrinogen level (FLEV) provides an assessment of whole blood clot under platelet inhibition to report calculated fibrinogen levels in significantly less time. If FLEV values obtained on cardiopulmonary bypass (CPB) during rewarming are similar to values obtained immediately after the discontinuation of CPB, then rewarming values could be used for preemptive ordering of appropriate blood product therapy.
  
  
  
  Fifty-one cardiac surgery patients were enrolled into this prospective nonrandomized study to compare rewarming fibrinogen values with postbypass values using TEG FLEV assays. Baseline, rewarming, and postbypass fibrinogen values were recorded for all patients using both standard laboratory assay (Clauss method) and FLEV. Mixed-effects regression models were used to examine the change in TEG FLEV values over time. Bland-Altman analysis was used to examine bias and the limits of agreement (LOA) between the standard laboratory assay and FLEVs.
  
  
  
  Forty-nine patients were included in the analysis. The mean FLEV value during rewarming was 333.9 mg/dL compared with 332.8 mg/dL after protamine, corresponding to an estimated difference of -1.1 mg/dL (95% confidence interval [CI], -25.8 to 23.6; P = 0.917). Rewarming values were available on average 47 minutes before postprotamine values. Bland-Altman analysis showed poor agreement between FLEV and standard assays: mean difference at baseline was 92.5 mg/dL (95% CI, 71.1 to 114.9), with a lower LOA of -56.5 mg/dL (95% CI, -94.4 to -18.6) and upper LOA of 242.4 mg/dL (95% CI, 204.5 to 280.3). The difference between assays increased after CPB and persisted after protamine administration.
  
  
  
  Our results revealed negligible change in FLEV values from the rewarming to postbypass periods, with a CI that does not include clinically meaningful differences. These findings suggest that rewarming samples could be utilized for ordering fibrinogen-specific therapies before discontinuation of CPB. Mean FLEV values were consistently higher than the reference standard at each time point. Moreover, bias was highly heterogeneous among samples, implying a large range of potential differences between assays for any 1 patient.
authors.affiliation: From the *Department of Anesthesiology, University of Miami, Miami, Florida; †Department of Anesthesiology and Critical Care, University of Pennsylvania, Philadelphia, Pennsylvania; and ‡Department of Biostatistics and Epidemiology, Center for Pharmacoepidemiology Research and Training, Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Michael
authors.initials: M
authors.lastname: Fabbro
authors.forename: Jacob T
authors.initials: JT
authors.lastname: Gutsche
authors.forename: Todd A
authors.initials: TA
authors.lastname: Miano
authors.forename: John G
authors.initials: JG
authors.lastname: Augoustides
authors.forename: Prakash A
authors.initials: PA
authors.lastname: Patel
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002315:Cardiopulmonary Bypass / Q000379:methods* / Q000639:trends; D005260:Female; D005340:Fibrinogen / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D017694:Rewarming / Q000379:methods* / Q000639:trends; D013916:Thrombelastography / Q000379:methods* / Q000639:trends; D055815:Young Adult
chemical_list: D005340:Fibrinogen