Differing Definitions of "Outpatient" Surgery Can Influence Study Outcomes Related to Lumbar Fusion.

Study design: Retrospective cohort study.

Objective: To evaluate whether different methods of defining "outpatient" surgery influence postoperative outcomes following lumbar fusion.

Summary of background data: Lumbar spinal fusion is increasingly performed in outpatient settings due to advancements in techniques and patient selection. However, inconsistencies in the definition of "outpatient" surgery can complicate outcome comparisons with patients categorized as outpatient by the hospital may unexpectedly require inpatient admission postoperatively.

Methods: ACS-NSQIP was queried for patients undergoing primary elective lumbar fusion from 2012 to 2022. Those with revision surgeries, infection, malignancy, and nonelective cases were excluded. Two definitions of "outpatient" surgery were evaluated: hospital-defined outpatient (HDO) and same-day discharge (SDD). Propensity score matching was used to compare HDO and SDD cohorts to their respective inpatient counterparts. Primary outcomes analyzed included 30-day readmission, reoperation, and postoperative complications. Univariate analyses were performed to compare the risks of complications for HDO and SDD cohorts compared with their inpatient counterparts.

Results: Of the 131,113 patients included, 9623 (7.3%) were HDO and 2019 (1.5%) were SDD. In propensity matched cohorts, inpatient lumbar fusion was associated with greater risk of 30-day readmission [odds ratio (OR) 1.148, P<0.001], reoperation (OR: 1.243, P<0.001), mortality (OR: 2.339, P<0.001), pulmonary embolism (OR: 1.790, P=0.002), urinary tract infection (OR: 1.359, P<0.001), and myocardial infarction (OR: 1.773, P=0.003). Compared with the propensity matched SDD cohort, inpatient lumbar fusion was significantly associated with greater rates of readmission (OR: 1.279, P=0.005), reoperation (OR: 1.429, P=0.006), and urinary tract infection (OR: 2.520, P<0.001).

Conclusion: Discrepancies in outcomes between inpatient and outpatient lumbar fusion were more pronounced with the hospital-defined outpatient definition compared with in the same-day discharge cohort.