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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

Bovonratwet, Patawut BS*; Webb, Matthew L. MD, MHS; Ondeck, Nathaniel T. BS*; Gala, Raj J. MD*; Nelson, Stephen J. MD*; McLynn, Ryan P. BS*; Cui, Jonathan J. BS*; Grauer, Jonathan N. MD*

doi: 10.1097/BSD.0000000000000615

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 “outpatientlumbar discectomy patients, 8968 had LOS=0, whereas 6198 had LOS>0. Of the 12,705 “inpatientlumbar 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.

Level of Evidence: Level 3.

*Department of Orthopaedics and Rehabilitation, Yale School of Medicine, New Haven, CT

Department of Orthopaedic Surgery, Hospital of the University of Pennsylvania, Philadelphia, PA

This study received approval from our institution’s Human Investigations Committee.

The authors declare no conflict of interest.

Reprints: Jonathan N. Grauer, MD, Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, 47 College Street, New Haven, CT 06520 (e-mail:

Received May 24, 2017

Accepted December 28, 2017

© 2018 by Lippincott Williams & Wilkins, Inc.