Procedural volume is linearly associated with malignant brain tumor resection outcomes across most institutions

Introduction: Improved outcomes have been reported in patients undergoing malignant brain tumor resection at high-volume centers. Studies have arbitrarily chosen cutoffs (e.g.,90%) to dichotomously define high-volume. However, such models do not evaluate continuous volume-outcome associations at specific institutional volumes (other than 90%). We establish the continuous association of volume with patient outcomes, and identify procedural volume cutoffs significantly associated with mortality, major complications, and readmissions. We hypothesized that a linear volume-outcome relationship adjusting for risk factors in multivariate analysis can estimate likelihood of adverse outcomes when comparing any two institutional volumes.

Methods: The cohort was identified retrospectively with ICD-10 coding in the Nationwide Readmissions Database(NRD). Patient and hospital characteristics were obtained from standard NRD collected variables. The association of hospital volume and mortality, major complications, and 30-/90-day readmissions were evaluated in multivariate analyses. Hospital volume was used as a continuous variable with two or three-piece splines, with various knot positions to reflect the best model performance, based on the Quasi Information Criterion(QIC).

Results: From 2016-2018, 34,486 patients with malignant brain tumors underwent resection. A majority underwent resection at hospitals with at least 17 cases/year (top 75th percentile). When volume was analyzed as a continuous variable, risk of mortality decreased at a steady rate of OR 0.988 (95%CI:0.982-0.993,p < 0.0001) per 1 procedure increase for hospitals with a procedure volume of 1-65 cases/year. After this cutoff (66-349 cases/year), decrease in risk was not statistically significant (OR=0.999, 95%CI:0.997-1.002,p=0.54). Risk of major complications decreased from 1-41 cases/year (OR=0.983,95%CI:0.979-0.988,p < 0.0001), 30-day readmissions from 1-24 cases/year (OR=0.987,95%CI:0.979-0.995,p=0.001) and 90-day readmissions from 1-23 cases/year (OR:0.989,95%CI:0.983-0.995,p=0.0003) and 24-349 cases/year (OR=0.9994,95%CI:0.999-1,p=0.01).

Conclusion : When adjusting for covariates, institutional procedural volume remains linearly associated with mortality, major complications, and 30-/90-day readmission up to a specific volume. The resulting linear association can be used to calculate relative likelihood of adverse outcomes between any two procedural volumes.