title: Hidden blood loss during posterior spine fusion surgery.
abstract: BACKGROUND
  Posterior spine fusion is associated with significant intra- and postoperative blood losses. When referring to the total blood loss during spine surgery, the standard is to measure the intraoperative bleeding plus the postoperative drainage. This ignores the "hidden" blood loss that was found to be significant in other fields of surgery.
  
  
  OBJECTIVE
  The purpose of this study was to examine whether posterior spine fusion carries a substantial hidden blood loss.
  
  
  METHODS
  A prospective study.
  
  
  METHODS
  We prospectively studied 114 patients undergoing instrumented posterior spinal fusion at one center between January 2011 and April 2011.
  
  
  METHODS
  Total blood loss, visible blood loss, and hidden blood loss.
  
  
  METHODS
  For each patient, the hidden blood loss was calculated by deducting the observed perioperative blood loss from the calculated total blood loss based on the hematocrit changes. We compared the percentage of the hidden blood loss out of the total blood loss for primary versus revision posterior spine fusion.
  
  
  RESULTS
  Primary decompression and posterior fusion patients had a mean total true loss of 1,439 mL. Their calculated hidden loss was 600 mL, 42% of the total loss. After revision posterior spinal fusion surgery, the mean total blood loss was 1,606 mL. The mean visible loss was 975 mL, and the mean hidden loss was 631 mL, 39% of the total loss. Thus, there was no statistical difference in the hidden blood loss between primary and revision posterior spinal fusion surgeries (p>.05). We did not find a significant difference in the percentage of the hidden blood loss between patients who underwent one, two, or three or more levels of surgery.
  
  
  CONCLUSIONS
  After posterior spinal fusion, there may be a large amount of the hidden blood loss.
authors.affiliation: Department of Orthopedic Surgery, William Beaumont Hospital, 3535 W. 13 Mile Rd, Royal Oak, MI 48073, USA. noam_yossi@yahoo.com
authors.forename: Yossi
authors.initials: Y
authors.lastname: Smorgick
authors.forename: Kevin C
authors.initials: KC
authors.lastname: Baker
authors.forename: Casey C
authors.initials: CC
authors.lastname: Bachison
authors.forename: Harry N
authors.initials: HN
authors.lastname: Herkowitz
authors.forename: David M
authors.initials: DM
authors.lastname: Montgomery
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Fischgrund
mesh_terms: D000368:Aged; D016063:Blood Loss, Surgical; D019299:Decompression, Surgical / Q000009:adverse effects* / Q000379:methods; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011184:Postoperative Period; D011446:Prospective Studies; D012086:Reoperation; D013123:Spinal Fusion / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods; D013904:Thoracic Vertebrae / Q000601:surgery*
keywords: Hidden blood loss; Posterior spinal fusion; Total blood loss