Coagulation test changes associated with acute normovolemic hemodilution in cardiac surgery.

BACKGROUND: Patients undergoing cardiac surgery requiring cardiopulmonary bypass (CPB) are at risk for coagulopathy and bleeding requiring blood product transfusion. Acute normovolemic hemodilution (ANH) is a blood conservation technique shown to reduce transfusion and bleeding associated with cardiac surgery. Despite numerous advantages, little is known about the effect of ANH on coagulation testing. METHODS: Prospective observational study, 80 patients (40 controls, 40 ANH) undergoing cardiac surgery requiring CPB. Blood for coagulation testing (hemoglobin, platelet count, prothrombin time/International Normalized Ratio [PT/INR], activated partial thromboplastin time [aPTT], fibrinogen, and kaolin thromboelastography [TEG]) was collected 5 minutes after protamine (Time 1), and following ANH reinfusion (or 30 minutes after Time 1) in controls (Time 2). RESULTS: Patients undergoing ANH had a significantly lower aPTT (-1.4 seconds 95% CI [-2.7, 0.0]; P = .044) and higher fibrinogen (+13 mg/dL [+1, +26]; P = .040) between Time 1 and Time 2 compared to controls. Additionally, the change in hemoglobin between Time 1 and Time 2 was significantly increased in the ANH group (+0.4 [+0.1, +0.8]; P = .024). The study also demonstrated a normalization of the platelet count, PT/INR, aPTT, and TEG values between Time 1 and Time 2 in control patients. CONCLUSIONS: In patients undergoing cardiac surgery requiring CPB, ANH results in significant improvements of aPTT, fibrinogen and hemoglobin values; however, the true clinical significance is questionable. In the absence of ongoing surgical bleeding, there appears to be normalization of coagulation tests (excluding fibrinogen) following CPB.