Redefining Clinically Significant Blood Loss in Complex Adult Spine Deformity Surgery.

Study design: Retrospective analysis of prospectively collected data.

Objective: This study aims to define clinically relevant blood loss in adult spinal deformity (ASD) surgery.

Background: Current definitions of excessive blood loss after spine surgery are highly variable and may be suboptimal in predicting adverse events (AEs).

Materials and methods: Adults undergoing complex ASD surgery were included. Estimated blood loss (EBL) was extracted for investigation, and estimated blood volume loss (EBVL) was calculated by dividing EBL by the preoperative blood volume utilizing Nadler's formula. "Least Absolute Shrinkage and Selection Operator" regression was performed to identify 5 variables from demographic and perioperative parameters. Logistic regression was subsequently performed to generate a receiver operating characteristic curve and estimate an optimal threshold for EBL and EBVL. Finally, the proportion of patients with AE was plotted against EBL and EBVL to confirm the identified thresholds.

Results: In total, 552 patients were included with a mean age of 60.7 ± 15.1 years, 68% females, mean Charlson Comorbidity Index was 1.0 ± 1.6, and 22% experienced AEs. Least Absolute Shrinkage and Selection Operator regression identified the American Society of Anesthesiologists score, baseline hypertension, preoperative albumin, and use of intraoperative crystalloids as the top predictors of an AE, in addition to EBL/EBVL. Logistic regression resulted in the receiver operating characteristic curve, which was used to identify a cutoff of 2.3 L of EBL and 42% for EBVL. Patients exceeding these thresholds had AE rates of 36% (odds ratio: 2.1, 95% CI: 1.2-3.6) and 31% (odds ratio: 1.7, 95% CI: 1.1-2.8), compared with 21% for those below the thresholds of EBL and EBVL, respectively.

Conclusion: In complex ASD surgery, intraoperative EBL of 2.3 L and an EBVL of 42% are associated with clinically significant AEs. These thresholds may be useful in guiding preoperative-patient-counseling, health care system quality initiatives, and clinical perioperative blood loss management strategies in patients undergoing complex spine surgery. In addition, a similar methodology could be performed in other specialties to establish procedure-specific clinically relevant blood loss thresholds.