Risk Factors of Hidden Blood Loss in Unilateral Biportal Endoscopic Surgery for Patients with Lumbar Spinal Stenosis

Objective Unilateral biportal endoscopic (UBE) surgery has recently been used as a minimally invasive procedure for the treatment of lumbar spinal stenosis and is associated with less perioperative blood loss. However, perioperative hidden blood loss (HBL) may be neglected during UBE. This study aimed to examine the volume of HBL and discuss the influential risk factors for HBL during unilateral biportal endoscopic surgery. Methods From January 2022 to August 2022, 51 patients underwent percutaneous unilateral biportal endoscopic surgery for lumbar spinal stenosis at the Department of Spinal Surgery of the Affiliated Traditional Chinese Medicine Hospital of Southwest Medical University and were enrolled in this study. The data included general indicators (age, sex and body mass index [BMI]), underlying disease (hypertension and diabetes), laboratory test results (prothrombin time [PT], activated partial thromboplastin time [APTT], fibrinogen [Fbg]), and preoperative and postoperative hematocrit and hemoglobin), related imaging parameters (severity of intervertebral disc [IVD] degeneration and soft tissue thickness of the interlaminar approach), number of operated vertebrae and operation time. Total blood loss (TBL) and HBL during surgical procedures were measured via the Gross formula. Influential factors were further analyzed by multivariate linear regression analysis and t ‐tests. Results The mean HBL was 257.89 ± 190.66 mL for single‐operation patients and 296.58 ± 269.75 mL for two‐operation patients. Patients with lower PT ( p = 0.044), deeper tissue thickness ( p = 0.047), and diabetes mellitus were determined to have more HBL during UBE. The operation time might also be an important factor ( p = 0.047). However, sex ( p = 0.265), age ( p = 0.771/0.624), BMI ( p = 0.655/0.664), APTT ( p = 0.545/0.751), degree of degenerated IVD ( p = 0.932/0.477), and hypertension ( p = 0.356/0.896) were not related to HBL. Conclusion This study determined the different influential factors of HBL during UBE. PT, tissue thickness, and diabetes mellitus are the independent risk factors that affect HBL incidence. Long PT may decrease the volume of HBL within a certain range. Tissue thickness and diabetes mellitus can lead to an increased volume of HBL.