Association Between Postoperative Admission and Location of Hernia Surgery: A Matched Case-Control Study in the Veterans Administration | Health Care Safety | JAMA Surgery | JAMA Network
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Table 1.  Frequency of Patient, Procedure, and Facility Characteristics in 26 019 VA Hernia Procedures (FY 2012-2014)a
Frequency of Patient, Procedure, and Facility Characteristics in 26 019 VA Hernia Procedures (FY 2012-2014)a
Table 2.  Logistic Regression Results Predicting Postoperative Admissions in 26 019 VA Hernia Procedures (FY 2012-2014) in 109 VA Hospitals and 14 VA ASCsa
Logistic Regression Results Predicting Postoperative Admissions in 26 019 VA Hernia Procedures (FY 2012-2014) in 109 VA Hospitals and 14 VA ASCsa
Research Letter
Association of VA Surgeons
December 2016

Association Between Postoperative Admission and Location of Hernia Surgery: A Matched Case-Control Study in the Veterans Administration

Author Affiliations
  • 1Center for Healthcare Organization and Implementation Research, VA Boston Healthcare System, Boston, Massachusetts
  • 2Department of Surgery, Boston University School of Medicine, Boston, Massachusetts
  • 3Health Care Financing & Economics, Department of Veterans Affairs, Boston, Massachusetts
  • 4Northeastern University, Boston, Massachusetts
  • 5Department of Surgery, VA Boston Healthcare System, Boston, Massachusetts
  • 6Harvard Medical School, Boston, Massachusetts
JAMA Surg. 2016;151(12):1187-1190. doi:10.1001/jamasurg.2016.3113

Within the Veterans Administration (VA) system, ambulatory surgery centers (ASCs) are gradually replacing traditional hospitals for outpatient surgical care.1 The expansion of ASCs is expected to continue as outpatient surgery increases. Although private-sector studies have shown that patient outcomes are better in ASCs than hospital outpatient departments (HOPDs),2-4 these settings have different financial incentives and a generally healthier population than the VA health care system. We examined postoperative outcomes (ie, hospital admissions) after inguinal hernia surgery in VA ASCs vs HOPDs.


We used the VA Corporate Data Warehouse fiscal years 2012-2014 outpatient procedure file to identify surgical procedures with a Current Procedural Terminology code of 49505 for repair of initial inguinal hernia. We obtained patient demographics, comorbidities, distance to VA hospital, median income, hospital bed supply in area of residence, American Society of Anesthesiologists score, facility’s geographic region, and date (month and year) of the hernia surgery from the Corporate Data Warehouse and the Area Health Resource File as model predictors. Facilities were excluded if they performed fewer than 30 hernia surgical procedures in fiscal years 2012-2014; cases were excluded if the patient lived more than 120 miles from a VA hospital or the surgery was emergent. Our final sample included 109 HOPDs and 14 ASCs. The VA Boston Healthcare System’s institutional review board approved this study and waived informed consent.

Postoperative hospitalization was defined as an admission 1 to 14 days after outpatient surgery with length of stay longer than 24 hours or same-day admission with length of stay longer than 48 hours (to exclude observation stays). We performed a χ2 test of proportion and logistic regression predicting admission by ASC, adjusting for the predictors described here. To control for factors associated with having surgery in an ASC, we used the same set of predictors in a model estimating likelihood of ASC-based hernia surgery and obtained a propensity score for each patient. We matched ASC patients to those with surgery in a HOPD by propensity score and estimated a second logistic regression model using only ASC status to predict postoperative admission.5 Analyses were performed using SAS (SAS Institute).


Of 26 019 outpatient hernia surgical procedures, 6.9% (n = 1803) were performed in an ASC and 1.8% (n = 471) had an admission 0 to 14 days after the operation. There were significantly fewer admissions among ASC patients than HOPD patients (1.1% [n = 20] vs 1.9% [n = 451]; P = .02; Table 1). The initial logistic regression model measured no significant association between ASC surgery location and probability of admission (odds ratio, 0.9; 95% CI, 0.56-1.45; Table 2). The propensity score model included 1709 matched ASC and HOPD cases; ASC surgery location remained an insignificant factor in predicting admission (odds ratio, 0.76; 95% CI, 0.42-1.38).


Private-sector studies suggest ASCs are safer than hospitals for routine outpatient surgery, although these findings have been criticized for failing to consider a patient’s likelihood of using an ASC. After controlling for patient characteristics and facility factors in a propensity score–matched model, we found no evidence that risk of postoperative admission after hernia surgery differed between ASCs and HOPDs. Although this is a promising sign that VA ASCs represent a safe alternative setting for outpatient surgery, more research is needed to confirm our findings because we did not incorporate non-VA hospitalizations as outcomes. We may also be missing important predictors of having care in an ASC (eg, patient preference) and experiencing a postoperative admission (eg, clinician availability). Finally, despite its use in private-sector quality comparisons, postoperative admissions may be an inadequate marker of patient safety and quality differences between ASCs and HOPDs. Our results show that postoperative admissions after inguinal hernia surgery are rare events regardless of the location of the surgery. Future research should add other types of outpatient surgical procedures and examine additional outcomes such as postoperative emergency department visits and cost.

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Article Information

Corresponding Author: Hillary J. Mull, PhD, MPP, Center for Healthcare Organization and Implementation, VA Boston Healthcare System, 150 S Huntington Ave (152M), Boston, MA 02130 (

Published Online: September 28, 2016. doi:10.1001/jamasurg.2016.3113

Author Contributions: Dr Mull had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: All Authors.

Acquisition, analysis, or interpretation of data: Mull, Pizer, Itani.

Drafting of the manuscript: Mull.

Critical revision of the manuscript for important intellectual content: All Authors.

Statistical analysis: Mull, Rosen, Pizer.

Administrative, technical, or material support: Mull, Pizer.

Study supervision: All Authors.

Conflict of Interest Disclosures: None reported.

Funding/Support: This research was supported by grant CDA 13-270 from the VA Health Services Research and Development Service (Dr Mull).

Role of the Funder/Sponsor: The funder had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Previous Presentation: This study was presented at the 2016 Association of VA Surgeons Annual Meeting; April 12, 2016; Virginia Beach, Virginia.

Additional Contributions: We thank Qi Chen, MD, PhD, VA Boston, for initial methodological input. She did not receive compensation.

US Department of Veterans Affairs. VHA directive 2011-037: facility infrastructure requirements to perform invasive procedures in an ambulatory surgery Published October 14, 2011. Accessed April 3, 2013.
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