title: Hidden blood loss in anterior lumbar interbody fusion (ALIF) surgery.
abstract: BACKGROUND
  A retrospective study was performed to determine the factors affecting the total perioperative blood loss during anterior lumbar interbody fusion (ALIF). Measurements of intraoperative blood loss underestimate the true blood loss during surgery. Our research project was to examine the hidden blood loss in lumbar spine surgery. Hidden blood loss in elective knee and hip replacement surgeries range between 100% and 30%. Hidden blood loss was about 40% in posterior spine surgery.
  
  
  METHODS
  The factors analyzed included gender, body mass index (BMI), duration of surgery, type of surgery, aspiration, and number of fusion levels. Estimated blood loss (EBL) was obtained from the clinical records of patients as the blood collected from suctioning and the cumulative weight of the saturated sponges. Actual blood loss (ABL) was calculated from the estimated blood volume and hemoglobin level of patients. Hidden blood loss was calculated as the difference between ABL and EBL.
  
  
  RESULTS
  Seventy-eight consecutive patients who underwent ALIF were reviewed. The average values (mean±SD) for EBL and ABL were 700.1±562.3mL and 1150.6±770.0mL, respectively (P=0.001, Student's t-test). The hidden blood loss averaged 39.2% of the ABL. According to linear regression analysis, surgical duration, type of surgery, and the inclusion of the L4/5 level were independent factors contributing to the ABL (P<0.05), whereas BMI and gender did not correlate with ABL or EBL.
  
  
  CONCLUSIONS
  ALIF is associated with substantial perioperative hidden blood loss. Length of surgery, type of surgery, and the inclusion of L4/5 in the procedure are significant risk factors for increased blood loss.
  
  
  METHODS
  Level IV: retrospective or historical series.
authors.affiliation: Department of Orthopedics, Guangzhou First Municipal People's Hospital, Guangzhou, Guangdong, China; Department of Orthopedics and Rehabilitation, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97201, United States. Electronic address: bin7810@126.com.
authors.forename: H
authors.initials: H
authors.lastname: Ju
authors.affiliation: Department of Orthopedics and Rehabilitation, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97201, United States. Electronic address: hartro@ohsu.edu.
authors.forename: R A
authors.initials: RA
authors.lastname: Hart
mesh_terms: D000328:Adult; D000368:Aged; D016063:Blood Loss, Surgical / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012307:Risk Factors; D013122:Spinal Diseases / Q000601:surgery*; D013123:Spinal Fusion / Q000009:adverse effects*; D016896:Treatment Outcome
keywords: Complications; Estimated blood loss; Hidden blood loss; Lumbar spine; Spine surgery