➢ The performance of operative procedures in an ambulatory surgery center has potential benefits to the patient, insurer, and surgeon.
➢ Factors associated with the patient’s preparedness for the operation as well as the operation itself need to be considered when deciding if a patient is a good candidate for spine surgery at an ambulatory surgery center.
➢ Anterior cervical discectomy and fusion is a commonly performed procedure at an ambulatory surgery center, and, while it is generally considered safe, potentially life-threatening complications have been reported.
➢ In properly selected patients, lumbar microdiscectomies and laminectomies can be safely performed at an ambulatory surgery center.
➢ While all ambulatory surgery centers are required to have an established transfer plan to a hospital, it is important, especially in cases of spine surgery, that the hospital has the ability to take care of a neurologic complication. Furthermore, the ability to transfer the patient in a timely manner is critical.
The first ambulatory surgery center was established in 1970 in Phoenix, Arizona by two surgeons with a vision of providing more convenient surgical services to their community. Twelve years later, Medicare approved the first payments to ambulatory surgery centers, sparking an era of substantial growth. By 1988, there were 1000 ambulatory surgery centers in the United States, and today more than 23 million procedures are performed yearly at 5300 ambulatory surgery centers1.
Because ambulatory surgery centers are delivering health care to patients, they require accreditation similar to traditional hospitals; however, while they can be accredited by The Joint Commission (http://www.jointcommission.org/) or the Healthcare Facilities Accreditation Program (HFAP) (http://www.hfap.org/) as can traditional hospitals, they also may be accredited by ambulatory surgery center-specific firms such as the American Association for Accreditation of Ambulatory Surgery Facilities (AAAASF) (http://www.aaaasf.org/) or the Accreditation Association for Ambulatory Health Care (AAAHC) (http://www.aaahc.org/). Additionally, all ambulatory surgery centers are required to have a hospital transportation plan in case a medical need arises that exceeds the capabilities of the ambulatory surgery center.
Ambulatory surgery centers initially were designed for outpatient procedures, including therapeutic procedures (e.g., knee arthroscopy), diagnostic procedures (e.g., colonoscopy), and injections requiring imaging or some level of sedation. While patients undergoing simple knee arthroscopies and epidural steroid injections invariably go home the same day, ambulatory surgery centers are accredited to perform any outpatient procedure, which is defined by the Centers for Medicare & Medicaid Services (CMS) as any procedure requiring a stay of less than twenty-four hours after admission2. Similarly, the definition of outpatient procedures3 as stated in the Medicare Benefit Policy Manual is:
When patients with known diagnoses enter a hospital for a specific minor surgical procedure or other treatment that is expected to keep them in the hospital for only a few hours (less than 24), they are considered outpatients for coverage purposes regardless of the hour they came to the hospital, whether they used a bed, and whether they remained in the hospital past midnight.
Because this definition clearly allows for operations that require an overnight admission to be performed in an ambulatory surgery center, there is an increasing trend for traditional inpatient operations such as anterior cervical discectomy and fusions4 and total hip arthroplasties5 to be performed at ambulatory surgery centers. The goal of this review is to evaluate the rationale for and safety of this trend.
The benefits of ambulatory surgery centers for the patient, insurer, and surgeon are well documented. The most obvious benefit of an ambulatory surgery center over a hospital is the convenience for patients. Rather than traveling to a large tertiary care hospital, patients can go to an ambulatory surgery center, which is often more easily accessible. The overall convenience, friendly staff, minimal wait times, efficiency, and ease of parking allow for ambulatory surgery centers to have an overall patient satisfaction rate of 92%6. Furthermore, the benefits are not limited to the patient as moving procedures out of hospitals and into ambulatory surgery centers has led to $2.6 billion in annual cost savings to Medicare alone6. Last, the efficiency and focus on quality in ambulatory surgery centers has led to high rates of surgeon satisfaction.
In spite of the quantifiable benefits reported to patients, insurers, and physicians, the growth of ambulatory surgery centers has drawn criticism. Sixty-five percent of ambulatory surgery centers are wholly owned by physicians, and >90% have some level of physician ownership7. This ownership stake creates a conflict of interest for surgeons. Physicians have the ability to preferentially allocate cases for their surgery center by directing healthier patients with higher-reimbursing insurance policies to their surgery centers while directing medically complex patients who will require increased health-care costs and patients with lower-reimbursing insurance to the hospital8. This situation potentially puts the burden of caring for patients who will require more expensive care or who have lower-reimbursing insurance on the hospitals. Bekelis et al., in a report on approximately 150,000 patients who underwent a microdiscectomy between 2005 and 2008, found that patients with private insurance and those with a lower Charlson Comorbidity Index9 were more likely to undergo surgery at an ambulatory surgery center, whereas older patients and patients with Medicaid were more likely to undergo inpatient surgery8. However, whether these findings were the result of surgeons preferentially allocating cases or surgeons carefully choosing patients in whom it would be safe to perform surgery at an ambulatory surgery center is unclear.
Additionally, because of the financial interests of surgeons, procedures that would be more suitable for a hospital operating room might be performed at an ambulatory surgery center, thereby putting patients at unnecessary risk. In a recent survey, Baird et al. reported a nonsignificant trend for higher-risk spine operations at ambulatory surgery centers to be performed by surgeons who have a financial investment in the ambulatory center as compared with those who do not10.
In the United States, the ambulatory surgery center industry has annual revenues in excess of $24 billion, with nearly 5% annual growth11. As a result, many large corporations have begun focusing on developing, owning, and operating ambulatory surgery centers (Table I). With the aforementioned benefits to health-care participants and the influx of corporate spending, ambulatory surgery centers have had a steady rise in the market share of some of the most commonly performed procedures (cataracts, arthroscopy, endoscopy, and colonoscopy) over the past ten years11.
When the costs of procedures performed at ambulatory surgery centers are compared with the costs of procedures performed in hospital outpatient departments, the differences are dramatic. In 2003, reimbursement for a procedure performed at an ambulatory surgery center was only slightly less than that for the same procedure performed in a hospital. Today, however, Medicare reimbursement for a procedure performed at an ambulatory surgery center is 42% less than that for the same procedure performed in a hospital (Table II)12. Importantly, this difference applies not only to what the facility and surgeon are paid but also to the patient’s out-of-pocket expenses. While this decline in reimbursement benefits patients and insurers, it is also a cause of the overall slowdown in the growth of ambulatory surgery centers over the last five years.
In spite of the decreasing speed with which ambulatory surgery centers are expanding, the overall number of procedures performed at ambulatory surgery centers in all surgical fields continues to increase13. As one would expect, this trend has occurred in spine surgery as well4,8. Spine surgery is particularly appealing to ambulatory surgery centers as it represents an area of remarkable growth and profit. In the inpatient setting, spine procedures often represent 20% to 25% of orthopaedic procedures but contribute >50% of profits14. Similarly, in ambulatory surgery centers, spine procedures have the highest contribution margin per operating room minute of all surgical cases ($48); in comparison, pain-management procedures have a $28 margin per operating room minute and ophthalmology procedures have only a $4 margin per operating room minute14. As a result, the average spine procedure generates between $10,000 and $20,000 of net revenue. Considering that a high-volume spine surgeon can easily perform four or more procedures a day, a successful spine program offers a high return on investment for ambulatory surgery centers, even with approximately $400,000 to $500,000 needed in initial capital expenditure14.
Anesthesia at an Ambulatory Surgery Center
There are mounting data focusing on ambulatory surgery centers and outpatient surgery in the anesthesia literature. The Society for Ambulatory Anesthesia (SAMBA), whose goal is to provide guidance for the use of anesthesia in an ambulatory setting, was founded in 1985 and has >1500 active members. The Society has established practice guidelines on some of the important treatment decisions regarding patients undergoing anesthesia in an ambulatory setting15. In an effort to safely minimize postoperative nausea, SAMBA recommends avoiding general anesthesia when possible, using propofol for induction and maintenance, avoiding nitrous oxide and other volatile anesthetics, minimizing opioids, and maintaining adequate hydration15. While avoiding general anesthesia is difficult in most procedures involving the spine, this recommendation is appropriate for many other orthopaedic procedures. Similarly, in an effort to provide the safest and most efficacious perioperative pain relief for patients with sleep apnea, SAMBA recommends the use of non-opioid medications to prevent excessive respiratory depression. Last, SAMBA attempted to establish a consensus of how perioperative diabetes mellitus should be treated at an ambulatory surgery center. Although the society was not able to establish clear guidelines, it does recommend that all diabetic patients undergoing surgery at an ambulatory surgery center should have a hemoglobin A1C of <7%15.
While anesthesiologists have identified ways to improve safety for patients undergoing surgery at an ambulatory surgery center, patient-related factors also play a critical role. In 2013, Mathis et al. identified seven risk factors for early adverse events (defined as those occurring less than seventy-two hours postoperatively) for patients undergoing ambulatory surgery. Using the American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) database, they reviewed 244,297 outpatient procedures from 2005 to 2010 and reported 232 events (prevalence, 0.1%). After controlling for surgical complexity, the independent risk factors for an early adverse event following ambulatory surgery were prolonged operative time (defined as a surgical time greater than the Current Procedural Terminology [CPT] code-specific 75th percentile for each surgical procedure), overweight body mass index (BMI) (>25), obese BMI (>30), chronic obstructive pulmonary disease, history of transient ischemic attack or stroke, hypertension, and previous cardiac surgery16.
Similarly, Whippey et al. performed a historical case-control study to determine the rate of and risk factors for unanticipated admission after ambulatory surgery17. With use of data from Hamilton Health Sciences hospitals, 20,657 ambulatory surgical procedures were identified, and the rate of unanticipated admission was 2.67%. The reasons for admission were variable, with surgical and anesthesia concerns accounting for 40% and 20% of readmissions, respectively. Risk factors for hospital admission were similar to those reported by Mathis et al. and included a BMI of >30, an age of more than eighty years, an American Society of Anesthesiologists (ASA) score of ≥3 (a surrogate for medical comorbidities), and an operative time of longer than one hour17. An evidence-based list of patient-related and surgical risk factors that may make surgery at an ambulatory surgery center inappropriate is provided in Table III. However, it is also important to consider social factors when deciding if a patient is appropriate for surgery at an ambulatory surgery center. Although a patient may have none of the listed risk factors, a tenuous social situation may increase the risk that the patient will return to the emergency room for care.
Spine Surgery at an Ambulatory Surgery Center
Cost Savings in Spine Surgery at an Ambulatory Surgery Center
Pettine reported on safety, outcome, and cost in a series of 710 consecutive spine procedures that were performed at an ambulatory surgery center18. The procedures included 108 one-level, eighty-two two-level, and three three-level anterior cervical discectomy and fusion procedures; fifty-seven cervical disc replacements; eighty-three lumbar disc replacements; and 377 lumbar decompressions. Overall, there was an improvement in patient-reported outcomes in all groups, and the rate of patient satisfaction was 97%. A cost analysis identified a 60% cost reduction in association with operations that were performed at ambulatory surgery centers rather than hospitals18. However, it is likely that patient-related factors played an important role in this cost reduction. Walid et al. performed a retrospective review in which ninety-seven outpatient spine procedures were compared with 578 inpatient procedures19. While the authors reported an average cost decrease of $3000 to $6000 per procedure, they also reported that the patients who underwent outpatient spine surgery were younger and had significantly (p < 0.05) decreased rates of congestive heart failure, diabetes mellitus, and depression. It is likely that these healthier patients also would have had a lower cost per operation if they had been managed in the hospital.
Safety in Cervical Spine Surgery at an Ambulatory Surgery Center
Multiple cervical spine operations have been reported to be done safely at ambulatory surgery centers, including anterior cervical discectomy and fusion procedures, cervical disc replacements, and posterior laminoforaminotomies20-24; however, we are not aware of any studies on the safety of posterior cervical decompression and fusion procedures or laminoplasties performed at ambulatory surgery centers. The safety of performing anterior cervical discectomy and fusion procedures in an ambulatory surgery center was first evaluated by Stieber et al.21 in 2005, and, since that time, anterior cervical discectomy and fusion has become one of the primary spine procedures being done in ambulatory surgery centers4,21. Stieber et al. retrospectively reviewed thirty patients who underwent an anterior cervical discectomy and fusion procedure at an ambulatory surgery center21. Patients in that study were meticulously selected such that all were subjected to a primary one or two-level operation between C4 and C7. In addition, patients were excluded if they were myelopathic, if they had a concerning discharge environment, or if the operation lasted longer than two hours. In that highly controlled population, the authors reported that three patients (10%) had dysphagia but no other complications. The authors concluded that anterior cervical discectomy and fusion can be performed safely in an ambulatory surgery center in properly selected patients21.
Over the last nine years, many other studies have demonstrated the safety of performing anterior cervical discectomy and fusion at an ambulatory surgery center20,23. Villavicencio et al. performed a retrospective review of a nonconsecutive series of 103 patients who underwent an anterior cervical discectomy and fusion procedure on an outpatient basis23. Ninety-nine patients who underwent a one or two-level procedure went home an average of eight hours after the operation, and the four patients who had a three-level procedure were observed overnight but were discharged within twenty-three hours after admission. Only one patient required readmission to the hospital after the development of severe dehydration. Similar to Stieber et al., the authors concluded that anterior cervical discectomy and fusion can be performed safely in an ambulatory surgery center with use of meticulous surgical technique in properly selected patients.
Garringer and Sasso reported the results of the largest series to date on the safety of performing anterior cervical discectomy and fusion as an outpatient procedure20. The authors retrospectively reviewed the rate of acute complications (complications occurring less than forty-eight hours postoperatively) in a study of 645 consecutive patients who underwent a single-level anterior cervical discectomy and fusion. Prior to discharge, all patients were observed for four hours after completion of the operation. The authors reported a 6% rate of unanticipated hospital admission, and two patients developed epidural hematomas, one of which required an emergent decompression. Both hematomas occurred within an hour after the end of the operation; thus, in spite of these two possible life-threatening complications, the authors still asserted that a single-level anterior cervical discectomy and fusion can be performed safely as an outpatient procedure, provided that the patient is observed for an appropriate time after the operation.
Wohns reported the results of a small retrospective study of twenty-six consecutive patients with cervical radiculopathy who underwent cervical disc arthroplasty in either an ambulatory center (fourteen patients) or in a hospital (twelve patients)24. All patients were observed for a minimum of three hours postoperatively, and none developed a complication. However, a cost saving was associated with performing the procedure in an ambulatory surgery center ($11,000 compared with $68,000).
Similarly, there is minimal literature on the safety and efficacy of performing a posterior laminoforaminotomy in an ambulatory surgery center. However, on the basis of the available literature, this procedure does appear to be safe. Tomaras et al. reported on 183 patients with minimal comorbidities who underwent a posterior laminoforaminotomy on an outpatient basis22. All patients were observed for a minimum of four hours after surgery and were required to void, tolerate oral intake, and walk without assistance prior to discharge. The main complaint postoperatively was nausea and vomiting (three patients; 1.6%), and the overall results were very favorable, with 93% of patients reporting an excellent or good result.
While the safety of performing cervical surgery in an ambulatory surgery center has been reported, the surgeon and the patient must be aware of the possibility of rare complications and how these complications can be handled at an ambulatory surgery center. Some rare complications, such as epidural hematoma, are life-threatening events, but successful and safe treatment can be provided by the orthopaedic surgeon without assistance from another subspecialty. Furthermore, performing the procedure at an ambulatory surgery center does not prevent the surgeon from placing a surgical drain and keeping the patient for observation overnight. However, other rare complications, such as a vertebral artery injury or an esophageal injury, often require an intraoperative consultation with another surgical subspecialty (e.g., vascular surgery or otolaryngology) that may not be available in an ambulatory surgery center.
Vertebral artery injuries are rare events, occurring in association with approximately 0.3% to 0.5% of all anterior subaxial cervical procedures25,26. While this complication most commonly occurs in association with complex procedures, such as corpectomies for the treatment of infection or tumor, it has been reported in association with primary one and two-level anterior cervical discectomy and fusion procedures25-27. Curylo et al., in a well-known cadaveric study, reported a 2.7% incidence of an aberrant vertebral artery28; thus, preoperative assessment of the location of the artery on cross-sectional imaging is paramount. Damage to this artery can present with a wide variety of clinical sequelae, ranging from minimal symptoms to lateral medullary (Wallenberg) syndrome, quadriparesis, and death25-27,29.
If a vertebral artery injury occurs, the surgeon must achieve control of the hemorrhage and decide if a direct repair, a bypass, or sacrifice of the vessel is appropriate. In a hospital, this decision often is made and treatment is performed in conjunction with a vascular surgeon; however, in an ambulatory surgery center, the orthopaedic surgeon may be forced to either directly repair the vessel with 7-0 or 8-0 Prolene (Ethicon, Somerville, New Jersey) or sacrifice the vessel, even though the neurologic complication rate has been reported to be as high as 43% if the vessel is sacrificed26,30,31.
Esophageal injuries are even more rare, with the rate of such injuries during elective anterior cervical procedures ranging from 0.1% to 0.3%32-34. These injuries are usually the result of misplaced retractor blades or sharp surgical dissection35. While these injuries most commonly are identified in a delayed manner36,37, multiple techniques, such as intraesophageal dye injection and direct visualization via endoscopy, have been described to aid in the identification of possible iatrogenic injuries38. If the injury is identified intraoperatively, the esophagus may be able to be repaired primarily32 and the patient should be placed on broad-spectrum antibiotics and fed via a nasogastric tube for ten days. While the mortality rate associated with a cervical esophageal tear may be as high as 16% if the tear is identified postoperatively37, the mortality rate may be drastically reduced if the injury is recognized intraoperatively and proper postoperative management is performed39,40. An otolaryngologist is often consulted in a hospital to help assess and treat a suspected esophageal injury; however, this may not be possible at an ambulatory surgery center, leaving the orthopaedic surgeon solely responsible for identifying and treating the injury.
Although many reports have supported the safety of performing cervical spine surgery at an ambulatory surgery center20-24, the risks of rare but serious complications need to be considered. Currently, the senior author (A.R.V.) will only perform cervical spine surgery at locations where it is possible for patients to be observed for twelve to twenty-four hours as the majority of complications occur within the first several hours after cervical spine surgery.
Lumbar Spine Surgery at an Ambulatory Surgery Center
The spinal procedure that is most commonly performed on an outpatient basis is a single-level lumbar decompression41-45. Several reports have supported the safety of performing this procedure on an outpatient basis (Table IV). In 1994, Zahrawi retrospectively reviewed the records for 103 patients who underwent an outpatient lumbar microdiscectomy45. Three patients were admitted because of urinary retention and postoperative nausea, but no serious complications were reported. Similarly, in a prospective case series, An et al. reported that fifty-seven of sixty-one patients were able to go home after a microdiscectomy41. One patient was admitted to the hospital for pain control, and another was admitted because of urinary retention. The remaining patients who were hospitalized were admitted only because of a lack of social support. The largest prospective series of outpatient lumbar microdiscectomies was described by Asch et al. in 200242. Two hundred and twelve patients underwent a microdiscectomy; however, the exact number of patients who were able to go home the same day is unclear. Still, the authors concluded that outpatient microdiscectomy is safe and effective.
The role of proper patient selection is paramount as not all patients are ideal candidates for a lumbar decompression at an ambulatory surgery center. Best and Sasso reported that thirty (11.4%) of 263 patients over the age of sixty-five years who had a single-level microdiscectomy or laminectomy required hospital admission43, and comorbidities such as obesity, chronic obstructive pulmonary disease, and a history of a stroke increase the risk of needing hospitalization16. Furthermore, the likelihood of specific complications should be considered before performing a lumbar decompression at an ambulatory surgery center. While dural tears have been repeatedly shown not to affect long-term results46,47, they do have an impact on postoperative management46,48,49. The overall rate of dural tears in lumbar spine surgery has been reported to be approximately 2.9%48; however, this rate is increased in older patients, patients undergoing a decompression for the treatment of a facet cyst, and patients undergoing a revision decompression49-51. Special consideration is required before performing a lumbar decompression at an ambulatory surgery center for a patient who is at high risk for a dural tear. Recent literature has suggested that there may not be a benefit to flat bed rest for more than twenty-four hours52,53. However, in clinical practice, many surgeons are still managing patients with flat bed rest for twenty-four hours or more, and such treatment may not be possible at an ambulatory surgery center.
More recently, there has been a push to perform single-level lumbar fusion as an outpatient procedure; however, there is a paucity of literature on the safety of doing so. In the study by Villavicencio et al., twenty-seven patients who underwent a transforaminal lumbar interbody fusion in an ambulatory surgery center were compared with twenty-five patients who underwent the procedure in a hospital54. Patients who had the procedure in an ambulatory surgery center were discharged an average of 4.4 hours after surgery, whereas those who had the procedure in a hospital were discharged an average of twenty-one hours after surgery. Four patients (15%) who underwent surgery at the ambulatory surgery center were readmitted or visited the emergency department in the first week after surgery, compared with only one patient (4%) who underwent surgery in the hospital. On the basis of the results of their study, the authors were cautiously optimistic that lumbar fusion could be performed on an outpatient basis.
While there is little published information to guide the discussion on performing lumbar fusion at an ambulatory surgery center, we have concerns. Recently, there has been a push to perform more spine procedures with a minimally invasive technique in the hope of getting patients out of the hospital faster. While minimally invasive spine surgery can be done effectively, this technique has a steep learning curve55, and the decrease in morbidity is often accompanied by an increase in radiation exposure to the patient and the operating room staff56,57. While the merits of minimally invasive spine surgery are beyond the scope of this article, it is important to emphasize that basic principles should not be deviated from in order to perform surgery in a minimally invasive manner. In the aforementioned study by Villavicencio et al., unilateral pedicle screws were used in twenty patients54. While this technique inherently will save time, decrease blood loss, and possibly reduce pain—making it an attractive option for patients undergoing surgery at an ambulatory surgery center—it has been repeatedly demonstrated to be biomechanically inferior to bilateral pedicle screw fixation58,59. We are not aware of any high-level studies comparing the fusion rates of unilateral and bilateral fixation; however, previous studies have clearly indicated that an increase in stability leads to an increase in fusion rates and an improvement in long-term clinical results60.
Spine surgery in ambulatory surgery centers is becoming increasingly common, and, when done in carefully selected patients, it can be safe and effective. However, its use is not without controversy20,23,24,41,42,54. Catastrophic complications such as epidural hematoma after anterior cervical discectomy and fusion have been reported, and the ability to treat rare complications such as vertebral artery injuries and esophageal tears may be compromised20. In addition, elderly patients and patients with multiple comorbidities may be better managed at a hospital as they are at an increased risk of requiring admission17,43.
Source of Funding: No funding was received for this work.
Investigation performed at the Rothman Institute at Thomas Jefferson University, Philadelphia, Pennsylvania
Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. One or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.
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