The Correlation Of Tirofiban-modified Thromboelastography With Fibrinogen Level In Patients Undergoing Cardiopulmonary Bypass

Background: Although complications trom cardiopulmonary bypass(CPB) have decreased, excessive perioperative bleeding is still common.Cardiac surgical procedures still consume 10%～20% of the nation'ssupply of allogeneic blood products in U.S.A. Abnormal massivehemorrhage after cardiac surgery remain a clinical problem. Transfusiontherapy during cardiac surgery remains largely empiric and aimlessbecause the turnaround times of conventional laboratory tests ofhemostatic system are too long to facilitate targeted blood componenttherapy. Thrombelastography (TEG) has been used to predictperioperation hemastatic disturbances and Point-of-care coagulationmonitoring using TEG has resulted in fewer transfusions in thepostoperative period. The maximum amplitude (MA) of TEG measuresthe maximum clot strength, which is dependent on both fibrinogen leveland platelet function. Standard TEG traceing fails in measuring theimpact of a single element on MA accurately. Inhibition of platelet function with tirofiban in TEG measurements may allow discriminationbetween platelet dysfunction or decreased fibrinogen levels.Objective: To investigation the correlation of tirofiban-modifiedthromboelastography's MA with plasma fibrinogen level duringcardiopulmonary bypass.Methods Fifty consecutive patients scheduled for selective valvereplacement under CPB were investigated. Blood samples wereexclusively obtained from a centre venous catheter at three points:directlyafter th induction of anesthesia(T₁), during CPB after rewarming(T₂), and15 min after protamine administration(T₃). Samples of 4 ml were collectedin glass tubes, containing 0.5 ml of 0.129 M buffered sodium citrate orEDTAK₂, and were used for the measurement of platelet count andfibrinogen level with Routine blood analyzer and Coagulation analyzer inClinical Testing Center.TEG was performed with 360μl native wholeblood. TEG tracings were performed on samples with and withoutaddition of addition of 10μl of 2 mg/ml Tirofiban. TEG analysiscontaining heparinase at T₂ and T₃. Linear regression analysis wasperformed to determine the correlation of plasma fibrinogen level withstandard MA or Tirofiban-modified MA, and of platelet count withstandard MA,â–³MA andâ–³GMA[â–³MA=standard MA—Tirofiban MA;â–³GMA=(5,000 standard MA)/(100—standardMA)—(5,000 TirofibanMA)/(100—Tirofiban MA)]. Results The correlation between plasma fibrinogen levels and standardMA was significant (r²=0.5, p＜0.01). Correlation between plasmafibrinogen levels and tirofiban-modified MA was significant(r²=0.8, p＜0.01). Correlation ofâ–³MA with platelet count was notsignificant when calculated in millimeters (r²=0.05, p=0.74). However,whenâ–³MA was calculated with the difference of elastic shear modulus(â–³GMA), it correlated significantly with platelet count (r²=0.52, p＜0.01).Conclusion The correlation between standard MA and plasmafibrinogen levels was similar to that between tirofiban-modified MA andplasma fibrinogen levels. However, tirofian-modified MA showed moreprecision in the evaluation of fibrinogen levels. The difference of themost elastic shear modulus between standard MA and its correspondingtirofiban-modified MA correlates with platelet number.