This was a retrospective study of clinical data from patients who underwent surgery for OVF using MIS techniques between June 1, 2020, and November 30, 2021. Only cases in which a control blood analysis was performed 24–48 hours after surgery were included. All surgeries were performed by the same specialized surgeon in our unit. The most appropriate surgical technique was decided according to the computer tomography fracture morphology based on the AO Spine—Spine Section of the German Society for Orthopaedics and Trauma (DGOU) Osteoporotic Fracture Classification System : vertebroplasty, percutaneous fixation one level above and one level below (1L-1L) cemented or uncemented, percutaneous fixation two levels above and two levels below (2L-2L) cemented or uncemented, and combinations of these techniques.
We excluded all patients with pathological fractures, using anticoagulant or antiplatelet therapy (only 100 mg acetylsalicylic acid was accepted, a drug that was withdrawn before surgery), with severe anemia (considered hemoglobin [Hb] <9 g/dL), who had received a transfusion before surgery, or with hematological disorders such as thrombopenia and coagulation abnormalities.
Data were collected regarding sex, age, body mass index (BMI), cardiovascular risk factors (CVRF, considered dyslipidemia, arterial hypertension, or diabetes mellitus), American Society of Anesthesiologists (ASA) anesthetic risk classification , type of surgery, days of hospital stay (considering the day of discharge when the patient resumed independent ambulation), and postoperative evolution (a torpid evolution was defined as delayed ambulation due to issues such as pain, poor general condition, nausea, desaturation, sustained arterial hypotension, orthostatic dizziness, or loss of appetite). Total blood volume (TBV), total bleeding (TB), HBL, and Hb drop were calculated according to the following equations.
The formulas used in earlier studies were applied for the calculation of HBL :
HBL (mL) = TB (mL) – measured blood loss (mL)
Since the surgical aspirator used measures a minimum of 100 mL, accurately recording intraoperative measured bleeding was not possible, given that for a high percentage of patients, it did not achieve that level. For this reason, to carry out the necessary calculations and homogenize the results, we assumed that the intraoperative measured bleeding reached 100 mL for all patients, considering that bleeding is also collected in compresses.
TB was estimated using Gross et al.’s method , based on hematocrit levels before and after surgery (24–48 hours):
The method described by Nadler et al.  was used to calculate the patient’s TBV.
TBV (L): = k1 × height(m)3 + k2 × weight (kg) + k3
where k1 = 0.3669, k2 = 0.03219, and k3 = 0.6041 for men, and k1 = 0.3561, k2 = 0.03308, and k3 = 0.1833 for women.
The preoperative and postoperative Hb (after 24 or 48 hours, taking as reference the lowest value) were used to calculate the Hb drop, according to the equation used by Chen et al. :
Hb drop (g/L) = preoperative Hb (g/L) – postoperative Hb (g/L)
A descriptive analysis of the results was performed using IBM SPSS version 25 statistics software, expressing the results as mean ± standard deviation for quantitative variables, and absolute values and percentages for qualitative variables. A comparative analysis was performed between the calculated HBL (<500 mL vs. ≥500 mL) and the variables of hospital stay (days) and postoperative evolution (torpid vs. favorable). Student’s t-test was used for the comparative analysis between hospital stay and HBL, and Pearson’s Chi-square test was used to compare post-surgical evolution and HBL. A statistical significance value of 0.05 was assumed.