Critical Limb Ischemia (CLI) or chronic limb-threatening ischemia (CLTI) represents the end stage of peripheral artery disease (PAD) where arterial flow is compromised to the lower extremities and risk of limb loss may become imminent. Revascularization of lower extremities is one of the cornerstones of limb salvage and amputation prevention. Data associated with major lower extremity amputation (MALE) shows the grim outcomes for these patients.1, 2, 3, 4 Establishing centers of high quality CLI therapy requires creating different foundational pillars in order to be successful. This article discusses CLI center creation from the perspective of CLI therapists working in an outpatient setting.

Evaluation and workup of the CLI patient includes a detailed history and physical examination, with emphasis on identifying factors that may impact procedural risk and durability, short-and long-term recovery, wound healing potential, and overall survival. Vascular risk factors that need specific attention include diabetes, dyslipidemia, hypertension, and smoking. Appropriate glycemic control in diabetics has significant impact on wound healing potential. Statin therapy has been shown in some studies to improve patency and reduce restenosis rates, although the data is conflicting. Current hypertension management guidelines suggest tighter control can decrease overall cardiovascular risk. Smoking cessation, perhaps the most difficult risk factor to manage successfully, is associated with improved overall survival. It is estimated that only one-third of CLI patients receive optimal medical therapy (OMT).5, 6, 7, 8 The recently concluded BEST-CLI trial showed that only 25% of 1830 enrolled patients were on guideline-directed OMT at the time of randomization.9 An outpatient CLI center should offer these services or have a system in place to manage this important aspect of clinical care of the CLI patient.

A complete CLI center should be able to offer physiologic evaluation as well as an anatomic assessment of an individual patient's arterial disease. The usual physiologic assessment tools for the PAD patient with claudication (ankle-brachial index (ABI) & segmental pressures can be misleading in the CLI patient due to frequently non-compressible outflow vessels. The classic teaching is that the ABI may be falsely elevated in patients with heavily calcified vessels. Perhaps more important however, is the fact that pressure measurements have historically been used to help predict wound healing capacity. The unreliability and non-reproducibility of ankle/toe pressures has led to numerous other potential options to evaluate this such as TCPO2, which has its own limitations.10 Regardless of choice of physiologic tools, imaging of the affected limb can be helpful to plan potential interventions including access selection (single or multiple sites), lesion characterization (length, occlusion versus stenosis, degree of calcification, cap configuration), and exit strategy. Like physiologic assessment, noninvasive imaging modalities have some limitations. Duplex ultrasound (DUS) is widely available, noninvasive and painless however, resolution may be limited especially in smaller vessels below the knee. Heavy calcification can be a challenge to adequate imaging due to acoustic shadowing; a well-trained vascular sonographer is invaluable! CT angiography (CTA) has much better spatial resolution than DUS or MR angiography (MRA) but involves use of typically 100cc of iodinated contrast or more to ensure image quality. This may be an issue for CLI patients, a significant number of whom have chronic renal insufficiency. If these patients go on to angiography with intervention, this increases contrast exposure again. Further, heavy and/or concentric calcification in small vessels can produce significant beam hardening, so-called “bloom artifact,” precluding accurate luminal assessment. MRA avoids the iodinated contrast use (and radiation) of CTA but has poorer spatial resolution, which can hinder distal vessel evaluation.11 Angiography can play an important diagnostic role in the CLI patient. Sadly and of particular note, is that in a recent claims-based assessment of Medicare beneficiaries who underwent MALE, 63% did not receive any revascularization attempt prior to the amputation and did not undergo angiography.12 Many interventionalists believe angiography remains the gold standard for anatomic evaluation of the CLI patient and provides the opportunity for treatment at the same time13. In this population, the more information obtained on the front end, the better. The trade-off of an invasive procedure for a complete and reliable roadmap of arterial disease is well worth it. This needs to be explained in detail to patients who may think that the operator is just going to “fix everything” at the time of angiography.

Patient selection for any CLI intervention involves many factors, some of which are technical, and others which are related to overall patient risk. The technical considerations are few. Complicated interventions can be and are performed safely and effectively in an outpatient setting. Establishing a CLI center requires a highly skilled team of operators supported by a highly trained revascularization team. The team involves skilled nurses, radiologic technologists and experienced sonographers. Patient-specific factors to consider might include significant renal insufficiency that may require pre and post procedure hydration, patients at risk for conscious sedation (high ASA) or who may need deep/general anesthesia (uncooperative patients or patients with dementia who may not be able to hold still for often long procedures). Multiple facilities employ certified nurse anesthetists that can aid in moderate sedation. Some procedural risks can certainly be mitigated (use of carbon dioxide DSA to minimize risk to renal insufficiency patients), but the point is that complex CLI intervention can be done in the non-hospital setting with a high degree of technical success and patient safety. The use of non-radiation modalities also can decrease the risk of complications and increase success rate. Access to high quality imaging enhances the operator's ability to properly diagnose and treat complex CLI cases. The use of extravascular US (EVUS) and intravascular US (IVUS) increases safety, improves the success rate of chronic total occlusion crossing, and can adequately assess of revascularization in complex PAD and CLI patients14,15. Recent data from Secemsky, et al shows that clinical outcomes are indeed better when utilizing IVUS guidance during peripheral arterial intervention.16 Additionally, the operator must have a wide range of revascularization tools available including wires, catheters, atherectomy devices, stents, specialty balloons, drug-coated balloons and closure devices.

Developing a CLI Center is no small undertaking, but once the team and platform have been created, it is time to get to work. CLI therapy is as rewarding as it is complex. Advanced endovascular skills are required, and the willingness to go that extra mile is essential. The first step to success and potential complication management is to prep the whole leg, so it can be accessed throughout the evolving case. Complex CTOs of the pedal, tibial, popliteal, and femoral arteries are expected and often require antegrade and retrograde access17. We have experienced a progression of thought and technique for tibial-pedal access from micropuncture access only to standard or thin-walled sheaths. For known distal tibial and pedal occlusive disease for Rutherford 5/6 patients, an antegrade approach is preferred by many physicians. An antegrade SFA approach is often preferred (finished with closure), which allows access to the anterior and posterior circulation of the foot utilizing advanced techniques such as dual tibial wire access, or plantar-pedal loop intervention. Remember, the immediate goal must be to have inline flow from the heart to the pedal arch to be successful for R5/R6 patients.

Complication management is an important aspect of patient management. Identifying patients at high risk of bleeding is important. Factors such as extreme body weight, renal insufficiency and older age increase the risk of bleeding. Access site complications are the most common post procedural event and well trained, experienced staff members that can identify bleeding/hematoma may allow the physician to intervene immediately if indicated. Treatment options for hematoma formation range from manual compression to urgent angiography from contralateral femoral access and endovascular balloon tamponade or placement of a covered stent.

The operator should never leave the procedure room or allow a patient to be discharged from the center with poor perfusion. Assessing perfusion post procedure and prior to discharge is important to recognize and treat prior to leaving the center. Another option to minimize access site complications is to avoid large vessel access all together with radial or tibial/pedal access. Manual closure is simple and optimal in many cases. Multiple outpatient CLI centers have established access protocols using interventional sonographers to assess the compressibility of the access vessel and evaluate access site hemostasis at the end of the procedure. This is an extra layer of safety beyond the simple palpation strategy.

An outpatient CLI center affords providers the freedom to choose tools, staff and the process that works best for the patients. In other words, the CLI center is truly built around the patient needs. While hospital-based programs can be successful, they need to accommodate a variety of needs and a wide range of patient cohorts. For example, the needs of coronary or structural heart disease patients are certainly different from CLI patients. A busy interventional radiology (IR) department frequently needs to be available for emergency procedures. Hospital-based CLI centers therefore (and rightly) have many priorities that may “compete” for staff and resources. However, a well-trained staff that focuses solely on treatment of the CLI population understands the complexity of these patients and procedures. With current advances, a thorough understanding of the extensive toolbox of equipment used allows streamlined procedures. Rigorous staff training is focused on complex devices and reduces the risk of human mistakes.

Participating in quality initiatives and tracking outcomes is an essential part of any clinical practice. The Outpatient Endovascular & Interventional Society (OEIS) has a national quality clinical data registry (QCDR) with more than 40,000 procedures entered.18 The information gathered and publications from this robust data set has been a testament to the safety and success of providing care within the outpatient environment.