Abstract
Objective: To study the correlation between high-level free fat acids（FFA）and red blood cell (RBC) injury and to explore the pathological mechanism of hidden blood loss (HBL) after total knee arthroplasty (TKA).Methods: Perioperative blood indexes were tested in 120 patients underwent unilateral total knee replacement for end-stage knee osteoarthritis. Venous blood samples were collected before operation and 24h, 48h, 72h and 120 h after operations. The changes of FFA, hemoglobin (Hb) and red blood cell number in the blood samples were detected by automatic hematology analyzer. The activity of glutathion peroxidase (GSH-Px), total superoxide dismutase (T-SOD) and hydrogen peroxide (H2O2) levels in the blood were measured. Measurement of reactive oxygen species（ROS）was performed by flow cytometry. Meanwhile, the morphological changes of RBC were analyzed under microscope. Results: Significant hidden blood loss was observed for all patients. The Hb content, RBC and hematocrit（Hct）decreased significantly 24 h after surgery (P <0.05)，while FFA concentration was significantly increased and heteromorphic red blood cells appeared under the microscope. The hemoglobin content decreased to the lowest level at 48 h after the operation (P < 0.01). The change of HBL was the most significant according to the Gross equation with the levels of FFA and ROS in the blood increased significantly and reached the peak at 48 h after operation (P <0.01). Meanwhile, GSH-PX activity, T-SOD activity and H2O2 levels significantly decreased compared with preoperative tested samples (P <0.01). Microscopically, erythrocyte atypia increased significantly with cellular rupture and necrosis identified. After 72 h of operation, ROS concentration began to decline along with FFA concentration. However, the Hb and RBC began to rise. Also, GSH-Px activity, T-SOD activity and H2O2 levels increased as well. All tested parameters tended to return to normal levels five days after surgery.Conclusion: High levels of FFA in blood can induce oxidative stress and damage RBCs, which in turns causes HBL after surgery.
Pathological mechanism of hidden blood loss after TKA: oxidative stress induced by free fatty acids