Hidden blood loss and its risk factors after hip hemiarthroplasty for displaced femoral neck fractures: a cross-sectional study.

Purpose: Several authors have reported the degree of total blood loss (TBL) following hemiarthroplasty for displaced femoral neck fracture; however, the research specifically investigating on hidden blood loss (HBL) after hip hemiarthroplasty is still lacking. The purpose of this study is to evaluate the HBL in patients who underwent hip hemiarthroplasty for displaced femoral neck fractures and to analyze its risk factors.

Patients And Methods: From January 2015 to December 2016, 212 patients (57 males and 155 females) with displaced femoral neck fracture undergoing hip hemiarthroplasty were included in this study. The demographic and relevant clinical information of the patients were collected. According to the Gross's formula, each patient's height, weight, and preoperative and postoperative hematocrit were recorded and used for calculating the total perioperative blood loss and HBL. Risk factors were further analyzed by multivariate linear regression.

Results: The HBL was 525±217 mL, with 61.0%±13.6% in the total perioperative blood loss (859±289 mL), and the perioperative hemoglobin (Hb) loss was 23.8±7.4 g/L. Multivariate linear regression analysis revealed that HBL was positively associated with higher American Society of Anesthesiologists (ASA) classification (regression coefficient=62.169, 95% CI=15.616-108.722; =0.009), perioperative gastrointestinal bleeding/ulcer (regression coefficient=155.589, 95% CI=38.095-273.083; =0.010), and transfusion (regression coefficient=192.118, 95% CI=135.578-248.659; <0.001). Compared with females, males had a risk of increased HBL (regression coefficient=87.414, 95% CI=28.547-146.280; =0.004), and general anesthesia had an increased HBL compared with spinal anesthesia (regression coefficient=68.920, 95% CI=11.707-126.134; =0.018).

Conclusion: HBL should not be ignored in patients who underwent hip hemiarthroplasty for displaced femoral neck fractures in the perioperative period, because it is a significant portion of TBL. Female patients, patients with higher ASA classification and perioperative gastrointestinal bleeding/ulcer, patients who were administered general anesthesia, or patients who underwent transfusion had a greater amount of HBL after hip hemiarthroplasty was performed. Having a correct understanding of HBL may help surgeons improve clinical assessment capabilities and ensure patients' safety.