How Much Blood Loss Is Appropriate for a 2- to 3-Level Posterior Lumbar Fusion?

Background: Despite the known association between higher estimated blood loss (EBL) and suboptimal outcomes, the threshold of EBL that negatively impacts outcomes following elective spine surgery remains unknown. In an open 2-and 3 -level posterolateral lumbar fusion, we sought to find a threshold of surgeon-reported EBL associated with length of stay (LOS), 30 -day complications, and patient-reported outcomes (PROs).Methods: A single-center, retrospective cohort study was performed for 2-and 3 -level open posterolateral lumbar fusions between October 2010 and April 2021. Surgeon-reported EBL (milliliters) was the primary independent variable for predicting LOS (days). Secondary outcomes included 30 -day complications and PROs as the minimal clinically important difference (MCID). Multivariable regression and receiver operating characteristic curve with Youden's Index were calculated.Results: 2-Level Fusion: A total of 557 patients underwent 2 -level fusions. Multivariable regression found EBL to be a significant risk factor for prolonged LOS. A threshold of 375 mL was associated with LOS beyond postoperative day 2 (POD2) (area under the curve [AUC] = 0.64, 95% CI 0.58-0.70, P < 0.001). 3-Level Fusion: A total of 287 patients underwent 3 -level fusions. Similarly, EBL was a significant risk factor for prolonged LOS, with a threshold of 675 mL to predict LOS beyond POD2 (AUC = 0.63, 95% CI 0.54-0.73, P = 0.012). EBL was associated with increased odds of 30 -day complications, with a threshold of 538 mL (AUC = 0.63, 95% CI 0.51-0.76, P < 0.001). For both 2-and 3 -level fusions, EBL was not significantly associated with MCID for any of the PROs.Conclusions: In patients undergoing open, posterolateral lumbar fusions, surgeon-reported EBL thresholds at 375 mL for 2 -level fusions and 675 mL for 3 -level fusions were moderately associated with LOS beyond POD2. In 3 -level lumbar fusions, EBL above 538 mL showed a potential association with an increased odds of 30 -day complications.Clinical Relevance: Surgeons should improve their ability to manage blood loss and implement methods to keep EBL below the provided thresholds to decrease LOS and minimize the risk of complications.Level of Evidence: 3.