To analyze the correlation of hemolysis with hidden blood loss after primary TKA.

A total of 93 patients with primary total knee arthroplasty were retrospectively analyzed from the July 2015 to December 2015 in West China Hospital of Sichuan University. The inclusion criteria were patients with severe osteoarthritis of the knee, normal blood sedimentation and C-reactive protein values, and total fluid volume not exceeding 2 000 ml in 24 h. Patients with non-knee osteoarthritis, hematologic and autoimmune diseases, infection, deep vein thrombosis, pulmonary embolism and incomplete medical records were excluded. There were 43 males and 50 were females with an average age of(67±9)years (range, 58-79 years). Hemoglobin (Hb), hematocrit (HCT), haptoglobin, direct bilirubin, indirect bilirubin, peripheral blood picture, the upper and lower knee circumferences were compared respectively on the preoperative and postoperative day 1 and day 3. The perioperative blood loss according to the Gross equation was calculated. Based on the results of a double venous ultrasound performed on postoperative day 5, the incidences of deep vein thrombosis and calf muscular venous thrombosis were evaluated. The postoperative drainage and the incidence of subcutaneous ecchymosis were also measured, and using the microscope to observe changes in preoperative and postoperative peripheral blood pictures (Wright staining). The differences between the two groups were compared by paired t-test. The categorical variables were compared using chi-square test.

All the patients were followed up for one to three months, and the average follow-up time was (1.6±0.8) months. Values of Hb and HCT on postoperative day 1 and day 3 were significantly higher than the preoperative ones (t=2.384, 2.681, 0.305, 0.429, all P<0.05). Postoperative haptoglobin level compared with preoperative one showed a rising trend, and the difference between the data of postoperative day 3 and the preoperative period was statistically significant(t=9.284, P<0.05). The direct bilirubin on postoperative day 1 and day 3 were significantly higher than the preoperative period (t=1.357, 2.316, all P<0.05), but there was no statistically significant difference in indirect bilirubin (t=2.449, 2.514, all P>0.05). The upper and lower knee circumferences on postoperative day 1 and day 3 were significantly higher than the preoperative ones (t=1.882, 1.937, 2.362, 2.294, all P<0.05). The total blood loss and drainage respectively were (979±192) ml and (165±41) ml. There was no obvious difference in the red blood cell morphology, size nor broken red blood cells was observed in the postoperative peripheral blood erythrocyte compared with the preoperative period. There were 17 cases of postoperative subcutaneous ecchymosis, eight cases of calf muscular venous thrombosis, and no deep vein thrombosis occurred.

The reasons for hidden blood loss mainly relate to a large number of perioperative blood gathered in the tissue space and joint cavity, and the effect of hemolysis is small.