Ambulatory Surgical Centers Deemed Safe, But Mortality Varies by Procedure

By Michael Vlessides

Originally published by our sister publication, Anesthesiology News

San Diego—One of the first studies of its kind has established an important reference point for national death rates associated with common ambulatory surgical procedures.

The investigation found that these procedures are exceedingly safe, although they show marked variation by procedure type. The study was presented at the 2021 annual meeting of the American Society of Anesthesiologists (abstract A1005).

“In 2019 and 2020, the Healthcare Cost and Utilization Project [HCUP] released a national ambulatory surgery database for the years 2016 through 2018,” said Atul Gupta, MD, MPH, an assistant professor of anesthesia and critical care at the University of Chicago. “Since we really don’t know what happens to patients who come for ambulatory surgery on a national level, we saw this as an opportunity to analyze national-level data on death rates in ambulatory surgery, which would not only give us a baseline of the safety of these various procedures but also allow us to trend possible changes over time. In doing so, we would create foundational data that we’ve never had before.”

The Nationwide Ambulatory Surgery Sample (NAss) database is maintained by HCUP and is the largest all-payor ambulatory surgery database in the United States, providing national estimates of major ambulatory surgery encounters that are performed in hospital-owned facilities. Unweighted, the NAss comprises approximately 9 million annual ambulatory surgery encounters and approximately 11.8 million ambulatory surgery procedures. Weighted, the database estimates 11.9 million ambulatory surgery encounters and 15.7 million ambulatory surgery procedures.

“The sample only includes patients from hospital-owned ambulatory surgical centers [ASCs],” Dr. Gupta said. “It does not include any freestanding surgical centers.”

Overall Safety of Ambulatory Surgery Confirmed

For purposes of the analysis, Dr. Gupta and his colleagues included a population of adult patients (age >17 years) who had a verifiable death, were not actively considered to be “do not resuscitate” (DNR) status, and underwent a primary procedure (considered a major therapeutic procedure by HCUP) in one of 14 categories. According to HCUP definition, a major procedure is one that requires the use of an operating room; penetrates or breaks the skin; and involves regional anesthesia, general anesthesia or sedation to control pain.

“We limited the analysis to what we call select procedures, those that were deemed to be ‘in-scope’ by HCUP for the entire study period,” Dr. Gupta explained. “Among other things, in-scope procedures must be primarily performed in hospital-based ASCs in each year of the analysis.

“For example, coronary angioplasty was reliably reported until 2017,” he said. “In 2018, however, hospitals stopped reporting it reliably as an ambulatory procedure, so it was dropped from the list.”

Overall, the 2016-2018 data sets contained 31,889,894 records. Of these, 10,744,035 were from patients over 17 years of age who underwent a primary procedure in one of the selected categories. The final study cohort comprised 9,931,417 records of patients with discharge disposition and no DNR status.

According to Dr. Gupta, death was noted in a total of 773 patient records, yielding an unadjusted mortality rate of 7.8 per 100,000 records (95% CI, 7.0-8.6/100,000). After adjustment for several potential confounding variables, the mortality rate was 6.8 per 100,000 records (95% CI, 6.2-7.6/100,000).

However, mortality rates varied widely according to the type of procedure performed (Table).

“I was actually surprised at the wide variability in mortality rates that our analysis revealed,” Dr. Gupta said. “We knew that lens replacement was going to be associated with very low risk. However, I was surprised that colorectal resection [mortality] was so high, even when compared with something like pacemaker procedures.”

Nevertheless, the study’s overall death rate demonstrates the safety of ambulatory surgery in the country, he said.

“Of course, there may be a selection bias among patients who are chosen for ambulatory surgery, but at least in the ambulatory surgery centers included in this analysis, mortality remains exceedingly low,” Dr. Gupta explained.

The investigators hope to expand the analysis when 2019 data become available. “I’m also hopeful that there may be a way in the coming years to link these data with inpatient data, which would give us a better comparative picture of mortality,” he added.

Inclusion of High-Risk Procedures Questioned

For Girish P. Joshi, MD, greater granularity is required from the research if it is to modify practice patterns. “In addition, I am not sure how procedures such as colorectal surgery and limb amputation got included in the database,” commented Dr. Joshi, a professor of anesthesiology and pain medicine at The University of Texas Southwestern Medical Center, in Dallas. “These are inpatient procedures and have a high mortality rate relative to the outpatient procedures, such as laparoscopic cholecystectomy.

“Controlling for comorbid conditions helps to compare procedures, but identifying which comorbid conditions increases patients’ risk of mortality is also important,” he added.