Coagulation test changes associated with acute normovolemic hemodilution in cardiac surgery

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.

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).

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.

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.