Several refinements were made to the NASS sampling design in 2019:

• The 2019 NASS is based on data selected from both the HCUP State Ambulatory Surgery and Services Databases (SASD) and the State Emergency Department Databses (SEDD) in order to capture both planned and emergent major ambulatory surgeries.
• The hospital-owned facility universe for the 2019 NASS was expanded to include more than general acute care and children's service types of facilities. Consistent with all other HCUP nationwide database, the 2019 NASS now includes specialty hospitals such as surgical, cancer, heart, and orthopedic facilities owned by community hospitals that performed in-scope major ambulatory surgeries.
• Consistent with all other HCUP nationwide databases, the hospital-owned facility universe for the 2019 NASS was limited to hospitals included in the American Hospital Association (AHA) Annual Survey of Hospitals that reported performing outpatient surgeries. In prior years, the Centers for Medicare and Medicaid Services (CMS) Provider of Services (POS) data were also used to augment the information on hospital-owned facilities.
• The list of in-scope procedures was expanded to include heart value procedures, destruction of lesion or retina and choroid, excision of skin lesion, suture of skin and subcutaneous tissue, and other operations on ovary. Two in-scope procedures from the 2018 NASS were excluded: varicose vein stripping and other diagnostic procedures of female organs.
• These changes will cause some discontinuity in estimates from before and after data year 2019.

See the Introduction to the NASS on the NASS Database Documentation page on HCUP-US for more information about the impact of these design changes.