How Accurate is Estimated Blood Loss? A Comparison Between Open and Minimally Invasive Craniosynostosis Surgery

INTRODUCTION: Accurate quantification of intraoperative blood loss is critical for guiding resuscitation. Although estimated blood loss (EBL) is known to be inaccurate, its reliability compared with calculated blood loss (CBL) across surgical techniques remains underexplored. This study examined discrepancies between EBL and CBL in the repair of open versus minimally invasive craniosynostosis. METHODS: A single institution retrospective review included 186 open and 79 minimally invasive craniosynostosis repairs. EBL was obtained from intraoperative documentation. Weight-adjusted CBL was calculated using pre- and postoperative hematocrit values. Absolute and relative differences between EBL and CBL were compared with paired t tests. Threshold analyses assessed the proportion of cases in which EBL underestimated CBL by >50%, >70%, or >80% using the χ2 tests. RESULTS: EBL consistently underestimated CBL in both techniques. In open repairs, the mean EBL was 173 mL versus a CBL of 474 mL, a mean underestimation of 301 mL (P<0.0001). Open repairs showed greater absolute underestimation than minimally invasive repairs (301 versus 228 mL, P=0.0019). However, minimally invasive repairs demonstrated greater proportional underestimation (75% versus 57% P=0.0003) and were more likely to exceed the 50%, 70%, and 80% discrepancy cutoffs (all P<0.01). CONCLUSION: Craniosynostosis repair carries substantial transfusion risk, and even modest blood loss can significantly affect infants. EBL markedly underestimated CBL in both craniosynostosis techniques, with disproportionately greater relative underestimation in minimally invasive cases. These findings highlight the need for more reliable intraoperative blood loss assessment, especially in minimally invasive cases, as deceptively low EBL values may underestimate resuscitation needs and compromise patient safety.