Hidden blood loss during perioperative period and the influential factors after surgery of thoracolumbar burst fracture: A retrospective case series.

Surgical therapy is vital for thoracolumbar burst fracture in restoring vertebral height, correcting kyphosis, decompressing nervous, and maintaining stability. Patients have unexpectedly lower hemoglobin levels postoperatively, which is remarkably inconsistent with the measured blood loss. However, hidden blood loss (HBL) is often neglected.To investigate HBL during perioperative period and determine its influential factors after surgery.A total of 68 patients who underwent surgery in our institution between January 2015 and January 2017 were included in the study. The demographic information, including the patients' age, gender, weight, height, duration of symptoms, surgery approach, time of operation, volume of drainage, classification of fracture, percentage of vertebral height loss and restoration, was collected. HBL was calculated according to the Gross formula. Influential factors were further analyzed using multivariate linear regression analysis.The mean HBL was 303.5 (range 18.4-803.5) mL, accounting for 67.5% of total blood loss. It indicated that the amount of HBL was much higher than we expected. Multiple and stepwise regression analysis revealed that blood loss, preoperative activated partial prothrombin time (APPT), percentage of anterior and medium vertebral height restoration were positively correlated with HBL. The association between HBL and the influential factors was analyzed based on the regression model equation: HBL = [1 + e [216.737 + 0.627*blood loss + 10.817*APTT + 207.549*anterior height restoration + 20.002*medium height restoration]]-1.HBL during perioperative period accounted for a substantial portion of the total blood loss and was much larger than what we thought. The blood loss, preoperative APPT, percentage of anterior and medium vertebral height restoration were positively correlated with HBL. Therefore, more attention needs to be paid to HBL to ensure patients' safety.