Hidden blood loss in adolescent idiopathic scoliosis surgery

Introduction: Posterior spinal fusions (PSF) for adolescent idiopathic scoliosis (AIS) have higher blood loss than other pediatric orthopedic surgeries. There is a paucity of literature estimating the hidden blood loss (HBL) in patients with AIS undergoing PSF. The purpose of this study was to compare intraoperative and postoperative estimated blood loss (EBL) in patients undergoing PSF for AIS to determine HBL. Hypothesis: With contemporary blood loss prevention strategies, HBL will be higher than intraoperative EBL. Material and methods: Over a 3-year period, 67 patients with preoperative and postoperative hemoglobin (Hgb) measurements undergoing PSF for AIS were evaluated. Intraoperative EBL was estimated using a volumetric method and recorded by a perfusionist managing a cell saver machine. Total perioperative EBL was estimated using the validated formula: EBL = weight (kg) × age sex factor × (preoperative Hgb−postoperative Hgb)/preoperative Hgb. HBL was calculated as the total perioperative EBL minus the intraoperative EBL. Results: Calculated total EBL was higher than intraoperative EBL (771 ± 256 mL vs. 110 ± 115 mL, p < 0.001). Mean HBL after wound closure was 660 ± 400 mL. Patients 14 years or greater (p = 0.03), with a BMI ≥ 25 kg/m² (p = 0.02) and with surgical times over 3.5 hours (p = 0.05) had increased HBL. Multivariate analysis determined BMI ≥ 25 kg/m² (OR 9.91; CI, 1.01–104.26; p = 0.05) was associated with increased HBL. Allogenic blood transfusion was rare (4 %) and associated with increased HBL (897 ± 112 mL vs. 540 ± 402 mL, p = 0.05). Discussion: For patients undergoing PSF for AIS there is more HBL after wound closure than intraoperative blood loss. This HBL is higher in older patients who undergo longer operations and have a BMI ≥ 25 kg/m². Level of evidence: IV; retrospective cohort study.