Applied Radiology

The Site-Rite II device (Dymax Corporation, Pittsburgh, PA) is a dedicated vascular access ultrasound that is battery powered and has interchangeable 7.5 and 9.5 MHz transducers (figure 1). At 7.5 MHz, the device has a maximum visualized depth of 4 cm. The transducers are lightweight, fit easily into a small sterile field, and have an attachment to which any of three disposable needle guides can be attached over a sterile drape (figure 2). The guides are configured with slightly different angles so that the depth at which the needle crosses the visual field can be selected by choosing the appropriate guide. Three color-coded guides are provided in a single-use prep kit which additionally contains a sterile sleeve and sterile coupling gel. The monitor also is quite small and can easily be placed next to a procedure table. The display includes a depth indicator, measured in 5 mm increments, which is aligned along the center of the visualized field. When the depth marker is activated, it provides an indication of the path that the needle will follow. We initially used the device for central venous access in the placement of tunnelled catheters, vena cava filters, TIPS, and similar procedures. More recently, we have found it useful for directing antegrade access to the superficial femoral artery (SFA).

After routine consent and sterile preparation, the femoral vasculature is delineated with a draped Site-Rite II ultrasound transducer. The femoral bifurcation is identified in the transverse plane, and the distal common femoral artery (CFA) depth is determined using the distance scale on the image display (figure 3). Using this measurement, the appropriate needle guide is placed on the transducer. With the transducer and attached needle guide angled caudally, a micropuncture needle is directed into the distal CFA under direct visualization (figure 4). When blood return is noted, contrast is injected through the needle, and a roadmap image is generated (figure 5). The micropuncture wire is then advanced though the needle, using the roadmap and fluoroscopic guidance to direct the wire into the SFA. The needle is then exchanged for the micropuncture sheath/dilator assembly, after which an 0.038" guidewire can be introduced and the micropuncture set exchanged for a standard vascular access sheath.

In some cases, initial ultrasound evaluation will show the femoral bifurcation to be above, or very close to, the inguinal ligament. In these situations, we may elect to gain antegrade access by direct micropuncture of the SFA. The profunda femoris artery (PFA) can be avoided by using the Site-Rite for direct visualization. After blood return and prior to placing a vascular sheath, we obtain a roadmap image to verify that the PFA has not been entered in error. Direct SFA puncture requires careful consideration, as discussed in the following section.

Ultrasound guidance with the Site-Rite device is our standard approach to antegrade access and has been used in 16 consecutive patients at our institution. In 14 of these cases, the CFA was entered first, followed by placement of a sheath into the SFA. The other 2 patients underwent direct puncture of the SFA. We were successful in establishing antegrade access to the SFA in all 16 cases, usually on the first attempt. No complications related to the antegrade access have occurred.

Discussion

Antegrade access facilitates lower extremity interventional procedures in several ways. The need for "up-and-over" catheterization of the aortic bifurcation is eliminated. As a result, the distance to a given lesion is reduced by some 60 cm, allowing the use of shorter catheters, wires, and other devices. Manipulation of endovascular devices is enhanced both by their shorter length and the mechanical advantage of a straighter course. In addition, the operator is spared having to reach across the image field.

Gaining antegrade access to the SFA is difficult because reliable radiographic landmarks are absent. The usual technique is to enter the ipsilateral common femoral artery (CFA) and subsequently advance a wire into the SFA under fluoroscopic observation. If the entry site is too high, intraperitoneal or retroperitoneal hemorrhage can occur; an entry site that is too low can cause femoral pseudoaneurysms and arteriovenous fistulae.1,2 In either situation, the injury can be difficult to diagnose, and even more difficult to treat, without surgical intervention. Furthermore, successful entry into the CFA does not guarantee success in advancing a guidewire into the SFA. Rather, the wire may preferentially enter the profunda femoris, with possible injury to a significant collateral bed.

Several techniques for direct puncture of the SFA have been described. If diagnostic angiography has been performed from the contralateral approach, a "target" wire or contrast injection through the catheter can be used to localize the CFA or SFA for puncture under direct fluoroscopic control.3 A similar approach may be possible if the vessels are sufficiently calcified to allow clear visualization without additional contrast. Other procedures are required when no catheter is in place and calcification is absent or insufficient for fluoroscopic identification. Kikkawa,4 Saddekni,5 and Saltzman6 all have used specially designed entry needles or catheters, while Bishop7 has used a variable stiffness guidewire. Blais described direct antegrade puncture of the SFA using palpation alone.8 In his series, 25 consecutive antegrade punctures were carried out, with only two minor complications. No comment was made regarding the amount of time or number of passes required to gain access. Still, his results demonstrate that selective catheterization of the SFA may be safe. While each of these techniques has been shown to be successful, they all require a significant amount of manipulation, additional puncture sites, or specialized equipment. The device that we describe, while specialized for vascular access, can be used in any superficial vessel.

The use of ultrasound guidance for invasive procedures, including vascular access, is well known. However, the "freehand" technique most commonly employed can be cumbersome and time consuming. Visualization of the needle tip frequently is poor, especially when the target is superficial and near-field artifact degrades image quality. By combining an integral needle guide with depth and course indicators, the Site-Rite device eliminates the need for continuous sonographic visualization of the needle as it advances toward the vessel. The operator is able to align the depth guide with the center of the vessel, and can simply advance the needle tip until it appears as a bright echo within the relatively hypoechoic vessel lumen. We have not recorded the actual time required to gain vascular access using this technique, but we believe it to be significantly less than that required for either the freehand ultrasound technique or a puncture directed by palpation alone.

During the process that we described, it is useful to carefully evaluate the vascular anatomy prior to attempts at needle placement (figure 3). The femoral vein is medial to the artery and can be compressed with manual pressure on the transducer. However, the arteries are not as easily compressible. The SFA is anterior to the profunda, and the two vessels can be followed caudally from the bifurcation. The ideal entry site is distal to the inguinal ligament and proximal to the bifurcation. We generally select a site roughly 5 mm cranial to the point at which the SFA and PFA are first seen as distinct structures. One should avoid an entry site distal to the femoral head, however, as postprocedure hemostasis is more easily achieved when the puncture site can be compressed against the femoral head. As stated earlier, direct puncture into the SFA may be safe when it is necessary to avoid the inguinal ligament. This technique should not be considered the standard approach, however, as the smaller diameter of the SFA may increase the risk of vascular injury or of occlusion of the vessel by the large catheters required for stent placement. Furthermore, direct access to the SFA may limit the operator's ability to treat very proximal SFA lesions.

During needle placement, the bevel should be pointing anteriorly and the transducer should be angled caudally (figure 4). This assures that the angle of entry will be shallow, reducing the risk of posterior wall injury during guidewire placement and enhancing the opportunity for selective SFA access. The needle guides are designed for an 18 gauge needle. This occasionally causes some difficulty when a micropuncture technique is used, as slight lateral deviations of the 20 gauge needle within the guide can cause it to miss a small vessel. If desired, one can use an 18 gauge needle followed by an 0.035" wire. We prefer micropuncture technique, however, for the following reasons: l) the micropuncture wire is highly torqueable, allowing subsequent selection of the SFA; 2) the needle is relatively atraumatic, but is large enough to allow a digital roadmap to be produced; 3) single-wall technique can be used; and 4) there is no need for a dermotomy until stable access has been achieved.

Regardless of the needle used to gain access, a roadmap should always be generated prior to placement of a large catheter or sheath. Despite direct visualization, it is possible that aberrant anatomy or operator error could result in the profunda femoris being entered instead of the CFA or SFA. In addition, a roadmap image reduces the risk of dissection if the entry site is immediately adjacent to an occult plaque or stenosis.

In summary, the technique that we describe provides quick, simple antegrade access to the SFA while minimizing the risk of complication. It has become our standard practice. The Site-Rite II device, although expensive to purchase initially, also can be used for numerous other types of peripheral and central vascular access. AR

References

1. Rapoport S, Sniderman KW, Morse SS, et al: Pseudoaneurysm: A complication of faulty technique in femoral arterial puncture. Radiology 154:529-530, 1985.

2. Lampmann LE, Leenen L: Hemorrhage due to laceration of an aberrant inferior epigastric artery during femoropopliteal PTA in an obese patient; a rare complication of a high antegrade femoral puncture. Vasa 24(4):382-384, 1995.

3. Berman HL, Katz SG, Tihansky DP: Guided direct antegrade puncture of the superficial femoral artery. AJR 147:632-634, 1986.

4. Kikkawa K: A new antegrade femoral artery catheter needle set. Radiology 151:798, 1984.

5. Saddekni S, Srur M, Cohn DJ, et al: Antegrade catheterization of the superficial femoral artery. Radiology 157:531-532, 1985.

6. Saltzman J. Probst P: A new puncture technique (Seldinger technique) for easy antegrade catheterization of the superficial femoral artery. Eur J Radiol 7:54-55, 1987.

7. Bishop AF, Berkman WA, Palagalla GL: Antegrade selective catheterization of the superficial femoral artery using a movable-core guidewire. Radiology 157:548, 1985.

8. Blais C: Antegrade puncture of the superficial femoral artery: a pilot project. Can Assoc Radiol J 44(4):253-256, 1993.

Dr. Andrews and Dr. Osterman are with the Division of Interventional Radiology at Johns Hopkins Medical Institutions in Baltimore, MD. Dr. Andrews is currently with the Dotter Interventional Institute at Oregon Health Sciences University in Portland, OR.