Ambulatory surgery is any planned surgical procedure where you go home the same day, without an overnight hospital stay. It’s also called outpatient surgery, same-day surgery, or day surgery. The defining feature is simple: you’re admitted and discharged within 24 hours. As of 2005, about 63 percent of all surgeries in the United States were performed on an outpatient basis, up from just 16 percent in 1980. That share has only continued to grow as surgical techniques and anesthesia have improved.
Where Ambulatory Surgery Takes Place
There are two main types of facilities that perform outpatient surgery. The first is a hospital outpatient department (HOPD), which is owned by and usually attached to a hospital. The second is an ambulatory surgery center (ASC), a standalone facility dedicated to same-day procedures. The distinction between the two is largely regulatory and financial rather than clinical. A freestanding surgery center can still be classified as an HOPD if it’s within 35 miles of a hospital and operates under the same financial and administrative contracts. Conversely, a hospital-operated facility can hold ASC status if it maintains its own independent finances and Medicare agreement.
ASCs tend to focus on a narrower range of procedures, which allows for more specialized care, smaller teams, and scheduling tailored to specific surgical specialties. Some ASCs are partially owned by the surgeons who operate there, which can translate into more direct accountability over quality. HOPDs, on the other hand, operate under hospital regulations and have access to the broader resources of a full hospital system, which matters if a complication arises during surgery.
Most Common Outpatient Procedures
The range of surgeries performed in ambulatory settings is wide and spans multiple specialties. In 2019, the single most common ambulatory surgery in hospital-owned facilities was cataract and lens procedures, accounting for about 1.24 million operations and 8 percent of all major outpatient surgeries. These were especially common among patients 65 and older.
Orthopedic procedures dominated the top 20 list. Seven of the top 20 ambulatory surgery categories involved the musculoskeletal system, including muscle and tendon repairs, joint procedures, knee meniscus removal, knee replacements, and spinal disc procedures. Together, these made up 22 percent of all major outpatient surgeries.
Gastrointestinal and general surgery procedures also featured prominently. Gallbladder removal ranked third overall with about 643,000 procedures. Groin hernia repair, other hernia repairs, and appendectomies combined for 12 percent of major ambulatory surgeries. Even procedures that once required several nights in the hospital, like knee replacements and spinal disc surgery, are now routinely done on a same-day basis.
What the Day Looks Like
A typical ambulatory surgery visit follows a predictable sequence: check-in, pre-operative preparation, the procedure itself, recovery, and discharge. You’ll arrive at the facility, complete administrative paperwork, and be brought to a pre-operative area where nurses check your vital signs, place an IV, and prepare you for anesthesia. The surgical team and anesthesiologist usually meet with you briefly before the procedure begins.
After surgery, you’re moved to a recovery area sometimes called the PACU (post-anesthesia care unit). Staff monitor your breathing, blood pressure, alertness, and pain level as the anesthesia wears off. The scoring systems used to evaluate your readiness for discharge assess things like your ability to walk, tolerate fluids, manage pain, and whether any surgical bleeding or nausea is under control. Once you meet those benchmarks, you’re cleared to go home. The total time at the facility varies by procedure but generally ranges from a few hours to most of the day.
Preparing for Your Procedure
Most facilities require you to stop eating and drinking after midnight the night before surgery. This fasting rule reduces the risk of complications from anesthesia. You’ll also need to arrange for a responsible adult, 18 or older, to drive you home. Because anesthesia impairs your judgment and reflexes, you typically can’t drive for at least 24 hours after the procedure. Many facilities ask your driver to stay at the facility for the duration of your surgery so they’re available as soon as you’re discharged.
Your surgical team will give you specific instructions about which medications to take or skip on the morning of surgery, what to wear, and what to leave at home. Following these instructions closely helps prevent delays or cancellations on the day of your procedure.
Cost Differences Between Settings
One of the driving forces behind the growth of ambulatory surgery is cost. Outpatient procedures avoid the expense of an overnight hospital bed, staffing, and extended monitoring. When comparing ASCs to hospital outpatient departments, the cost picture is more nuanced than many people expect. A study of spinal fusion procedures found that ASC reimbursements were about 9.8 percent higher than those at hospital outpatient departments, and patients paid roughly 17 percent more out of pocket at ASCs. However, both settings were significantly cheaper than having the same surgery as an inpatient, where average out-of-pocket costs were roughly double those of the outpatient alternatives.
The cost difference between ASCs and HOPDs varies by procedure and insurance plan, so it’s worth checking with your insurer before choosing a facility.
Safety and Infection Risk
Ambulatory surgery is broadly considered safe for appropriately selected patients. Infection rates for common outpatient procedures are comparable to those seen in inpatient settings. One surveillance study found surgical site infection rates of 0.4 percent for pacemaker placement, 0.5 percent for gallbladder removal, 1.3 percent for hernia repair, and 3.2 percent for appendectomy, numbers that closely mirror inpatient data for the same operations.
One important caveat: infections after outpatient surgery are harder to track because they typically develop after you’ve already gone home. More than half of confirmed surgical site infections in one study were managed entirely in an outpatient setting, meaning they never showed up in hospital records. This suggests that traditional hospital-based tracking methods likely undercount infections following ambulatory procedures. Knowing the signs of infection (increasing redness, warmth, swelling, drainage, or fever in the days after surgery) matters, since you’ll be recovering at home rather than under continuous medical observation.
Who Is a Good Candidate
Not every patient or every procedure is appropriate for ambulatory surgery. Facilities evaluate candidates based on overall health status, the complexity of the planned procedure, and the likelihood of needing extended monitoring or overnight care. Generally, patients with well-controlled chronic conditions like high blood pressure or diabetes are good candidates. Those with severe, unstable medical problems or procedures that carry a high risk of significant blood loss or airway complications are typically directed to an inpatient setting.
Your home situation matters too. You need a safe environment for recovery, a reliable adult who can stay with you for at least the first night, and the ability to get back to a medical facility quickly if something goes wrong. Surgeons and anesthesiologists weigh all of these factors when deciding whether an outpatient approach is appropriate for your specific case.