Discrepancies in the Definition of Outpatient Surgeries and Their Effect on Study Outcomes Related to ACDF and Lumbar Discectomy Procedures A Retrospective Analysis of 45,204 Cases

Study Design: This is a retrospective study. Objective: To study the differences in definition of inpatient and outpatient [stated status vs. actual length of stay (LOS)], and the effect of defining populations based on the different definitions, for anterior cervical discectomy and fusion (ACDF) and lumbar discectomy procedures in the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database. Summary of Background Data: There has been an overall trend toward performing ACDF and lumbar discectomy in the outpatient setting. However, with the possibility of patients who underwent outpatient surgery staying overnight or longer at the hospital under observation status, the distinction of inpatient and outpatient is not clear. Materials and Methods: Patients who underwent ACDF or lumbar discectomy in the 2005-2014 ACS-NSQIP database were identified. Outpatient procedures were defined in 1 of 2 ways: either as being termed outpatient or hospital LOS=0. Differences in definitions were studied. Further, to evaluate the effect of the different definitions, 30-day outcomes were compared between inpatient and outpatient and between LOS>0 and LOS=0 for ACDF patients. Results: Of the 4123 outpatient ACDF patients, 919 had LOS=0, whereas 3204 had LOS>0. Of the 13,210 inpatient ACDF patients, 337 had LOS=0, whereas 12,873 had LOS>0. Of the 15,166 outpatient lumbar discectomy patients, 8968 had LOS=0, whereas 6198 had LOS>0. Of the 12,705 inpatient lumbar discectomy patients, 814 had LOS=0, whereas 11,891 had LOS>0. On multivariate analysis of ACDF patients, when comparing inpatient with outpatient and LOS>0 with LOS=0 there were differences in risks for adverse outcomes based on the definition of outpatient status. Conclusions: When evaluating the ACS-NSQIP population, ACDF and lumbar discectomy procedures recorded as outpatient can be misleading and often did not correlate with same day discharge. These findings have significant impact on the interpretation of existing studies and define an area that needs clarification for future studies.