Decision Tree-based Modelling for Identification of Predictors of Blood Loss and Transfusion Requirement After Adult Spinal Deformity Surgery

Abstract

Background: Multilevel fusions and complex osteotomies to restore global alignment in adult spinal deformity (ASD) surgery can lead to increased operative time and blood loss. In this regard, we assessed factors predictive of perioperative blood product transfusion in patients undergoing long posterior spinal fusion for ASD.

Methods: A single-institution retrospective review was conducted on 909 patients with ASD, age > 18 years, who underwent surgery for ASD with greater than 4 levels fused. Using conditional inference tree analysis, a machine learning methodology, we sought to predict the combination of variables that best predicted increased risk for intraoperative percent blood volume lost and perioperative blood product transfusion.

Results: Among the 909 patients included in the study, 377 (41.5%) received red blood cell (RBC) transfusion. The conditional inference tree analysis identified greater than 13 levels fused, American Society of Anesthesiologists (ASA) score > 1, a history of hypertension, 3-column osteotomy, pelvic fixation, and operative time > 8 hours, as significant risk factors for perioperative RBC transfusion. The best predictors for the subgroup with the highest risk for intraoperative percent blood volume lost (subgroup mean: 53.1% ± 42.9%) were greater than 13 levels fused, ASA score > 1, preoperative hemoglobin < 13.6 g/dL, 3-column osteotomy, posterior column osteotomy, and pelvic fixation. Patients who underwent major blood transfusion intraoperatively had significantly longer length of stay (8.5 days) versus those who did not (6.1 days) (P < .0001). The overall 90-day complication rate in patients who underwent major blood transfusion intraoperatively was 49%, compared with 19% in those who did not (P < .0001). By multivariate regression analysis, patients with a preoperative hemoglobin > 13.0 were less likely to require major blood transfusion (odds ratio: 0.52, P = .046).

Conclusions: Using a supervised learning technique, this study demonstrates that greater than 13 levels fused, ASA score > 1, 3-column osteotomy, and pelvic fixation are consistent risk factors for increased intraoperative percent blood volume lost and perioperative RBC transfusion. The addition of having a preoperative hemoglobin < 13.6 g/dL or undergoing a posterior column osteotomy conferred the highest risk for intraoperative blood loss. This information can assist spinal deformity surgeons in identifying at-risk individuals and allocating healthcare resources.

Level of evidence: 3.

Keywords: blood product transfusion; complex spine surgery; perioperative blood loss.

Figure 1

Classification and decision tree model for intraoperative percent blood volume (BV) lost in different risk groups of patients who underwent surgery for ASD. Performance measures: ≤ 6 levels: R^2-Adj = 0.58; 6 to 13 levels: R^2-Adj = 0.51; > 13 levels: R^2-Adj = 0.64.

Figure 2

Classification and decision tree model for intraoperative RBCs transfused in different risk groups of patients who underwent surgery for ASD. Performance measures: ≤ 13 levels: R^2-Adj = 0.43; > 13 levels: R^2-Adj = 0.59.

Figure 3

Classification and decision tree model for units of postoperative RBCs transfused in different risk groups of patients who underwent surgery for ASD. Performance measures: ≤ 13 levels: R^2-Adj = 0.41; > 13 levels: R^2-Adj = 0.45.