Pathologic mechanism of hidden blood loss after total knee arthroplasty: oxidative stress induced by free fatty acids

Background: Hidden blood loss (HBL) often occurs after joint replacement; however, the mechanism of HBL is not clear. We conducted a prospective study to analyze the correlation between high-level free fatty acids (FFA) and erythrocyte injury, and explore the pathologic mechanism of hidden blood loss (HBL) after total knee arthroplasty (TKA). Methods: Perioperative blood indexes were tested in 120 patients who underwent unilateral total knee replacement for end-stage knee osteoarthritis. The changes in FFA, reactive oxygen species (ROS), hemoglobin (Hb), and red blood cells (RBC) in the blood samples were detected. The activity of glutathione peroxidase (GSH-Px), total superoxide dismutase (T-SOD) and hydrogen peroxide (H(2)O(2)) levels were measured. Morphologic changes of blood cells were analyzed under a microscope. Results: HBL occurred in all patients after TKA. The Hb and RBC decreased significantly 24 h after surgery (P