Hidden blood loss during posterior spine fusion surgery

Background contextPosterior 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.PurposeThe purpose of this study was to examine whether posterior spine fusion carries a substantial hidden blood loss.Study design/settingA prospective study.Patient sampleWe prospectively studied 114 patients undergoing instrumented posterior spinal fusion at one center between January 2011 and April 2011.Outcome measuresTotal blood loss, visible blood loss, and hidden blood loss.MethodsFor 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.ResultsPrimary 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.ConclusionsAfter posterior spinal fusion, there may be a large amount of the hidden blood loss.