CHAPTER 12 Bypass surgery consists of a thousand tiny moves, and it takes just one bad move to ruin the bypass. Errors are often unrecognized at the time of commission, whether it is a bad bite, a through stitch, a tear in the wall, or a rough grasp. After the last knot in the anastomosis is tied, the moment arrives to check patency. There is an urge that goes beyond confirming that the bypass is open; it is the urge to know whether an error was made in one of those thousand tiny moves. A throbbing bypass is sweet victory, an affirmation of the surgeon’s skill and a fulfillment of the patient’s hopes and expectations. However, a limp bypass is an agonizing defeat, an embarrassment for the surgeon, and a complication for the patient with devastating consequences. That moment of truth arrives after the last knot in the anastomosis is tied and the temporary clips come off, after delaying gratification throughout the entire case: was your performance good enough? The temporary clip on the distal recipient artery is removed first, which allows retrograde flow to back-fill the anastomosis under low pressure (Fig. 12.1). Stagnant coagulation factors and platelets react to the suture line without a flowing bloodstream, during which tufts of absorbable hemostatic agent are applied along both suture lines at leak points with some pressure from the sucker (Fibrillar Surgicel®, Ethicon/Johnson & Johnson, Somerville, NJ). Complete hemostasis before removing the temporary clip on the proximal recipient artery would be ideal, but the ischemia time would be prolonged and this clip is removed once the Fibrillar Surgicel is on the seams. The proximal temporary clip is removed after the distal clip; otherwise, the anastomosis might be disrupted by exposure to full arterial pressure with no outflow. Anastomotic bleeding is expected, even with the most perfectly snug suture lines. With long arteriotomies, 20 bites in the walls, gaps between stitches, and needle punctures only partially filled with suture, it is surprising that more bleeding does not occur. Bleeding is a sign that blood is flowing through the anastomosis, whereas no bleeding is a sign that the bypass may be occluded. In most cases, suture-line bleeding stops after 2 minutes of patience and gentle pressure—the “2-minute rule.” Extra measures like additional stitches or detailed inspections are not needed unless brisk bleeding persists beyond 2 minutes. If it does persist, an interrupted or “figure-of-8” stitch may be needed at a gap between stitches, with or without replacing temporary clips on the proximal and distal recipient artery. Temporary clips on the donor artery are not removed until the anastomosis has settled and complete hemostasis is established, initiating flow in the bypass. Look, listen, and feel to assess the patency (Table 12.1). Inspection of the recipient artery distal to the anastomosis reveals two types of bypass pulsations: expansile and axial. During the cardiac cycle, expansile pulsations enlarge an artery circumferentially (perpendicular to its long axis) and indicate an open bypass with bounding boluses of flow. However, axial pulsations lengthen an artery (parallel to its long axis) and indicate a partially or completely occluded bypass with the bloodstream pushing and rebounding against an obstruction. A finger on the donor assesses patency, especially with EC-IC bypasses using scalp arteries and grafts that are easily palpated. Acland’s test is more definitive, milking the recipient artery with a forceps to empty and refill it with bypass flow (Fig. 12.2). Two microforceps squeeze the artery distal to the anastomosis and close together. The artery is stroked by sliding the distal forceps further distally to produce a blood-free segment several millimeters long. The proximal forceps is then opened and blood refills the distal vessel through a patent anastomosis. Blood does not flow through an occluded anastomosis and the distal vessel does not refill. Acland’s test requires rough tissue handling and is performed only when patency is in doubt, not routinely. A less traumatic assessment of patency is the “flicker” test, which requires thin, translucent arterial walls that allow blood flow through the anastomosis to be visualized under the microscope. The vessel is narrowed by upward pressure from microforceps underneath the anastomosis, and the thinned column of red blood cells blanches the artery (Fig. 12.3). With a patent anastomosis, blood flows across the narrowed segment over the forceps, synchronous with the pulse; with an occluded anastomosis, no blood will flow. Only slight pressure is exerted on the vessels, with no endothelial damage. Videoangiography with fluorescent dyes is the best visual confirmation of bypass patency. It is fast, easy, safe, and accurate, which makes it more practical and economical in a busy operating room’s workflow than catheter angiography. Fluorescent videoangiography requires a near-infrared laser light source on the operating microscope, ICG dye injected as an intravenous bolus (25 mg in 10 cc of saline), and a nearinfrared video camera (IR800, Carl Zeiss, Inc., Dublin, CA). ICG binds to globulins in the blood and remains intravascular in the bloodstream. The bolus is seen filling the donor, coursing through the anastomosis, and then filling the recipient artery and its branches. The run is displayed as a black and white video with clear depiction of flow and patency, but the fluorescence is not visible directly in the field and the video must be viewed on a monitor outside of the field. Intravascular binding of the dye produces a bolus that shines brightly even through thick-walled arteries and grafts. With moyamoya disease, demand on the bypass is immediate and flow in the extracranial donor artery precedes that in the intracranial arteries. With aneurysms, initial bypass flow may be minimal or absent, mimicking a bypass occlusion until demand on the bypass is elicited by aneurysm trapping, after which brisk flow is observed. The ICG is not metabolized but excreted in the liver with a half-life of 3 to 4 minutes, which keeps it in the circulation for 15 to 20 minutes. Therefore, ICG videoangiography cannot be repeated immediately and should be saved for fluorescing final flow patterns after the aneurysm has been clip occluded. Doppler ultrasonography can also check the patency of a bypass or other arteries after an initial ICG run, when the dye remains in the circulation within the time window of ICG’s half-life. Sodium fluorescein is another fluorescent dye with similar applications. Fluorescein is a salt with an accepted safety profile and FDA approval for ophthalmologic applications. It uses a blue laser light source on the operating microscope, fluorescein dye (1.0 mg/kg) injected as an intravenous bolus, and a video camera with a 560-nm filter (YE560). Fluorescein does not bind to globulins in the blood and therefore distributes beyond the intravascular space. It produces a brilliant yellow bolus of fluorescence initially that demonstrates bypass patency, but gets drowned out as the agent quickly leaks into surrounding tissues. Unlike ICG, fluorescein is visible through the microscope without looking away at a monitor, but its fluorescence does not always shine through thick vessels and grafts. Fluorescein videoangiography is an excellent adjunct when a second videoangiogram is needed after an initial ICG run, when it remains in the circulation within ICG’s half-life. Doppler ultrasonography confirms patency of the anastomosis by listening to the bypass. I prefer a percutaneous Doppler used for gaining vascular access because it has a fine probe that mounts on a tuberculin syringe and reaches deep targets easily (Smart Needle and Percutaneous Doppler Access, Vascular Solutions, Inc., Minneapolis, MN). This ultrasonography provides only qualitative confirmation of bypass flow, whereas quantitative ultrasonography measures flow velocities (Charbel micro-flow probes, Transonic, Ithaca, NY). Its large probe tip has a body and a reflector that are bulky, and it must be applied around the artery circumferentially, which is difficult with deep bypasses. Quantitative Doppler analysis allows for the measurement of the CFI, which is the ratio of blood flow in a completed bypass to the free flow from the cut end of the donor artery before the bypass is performed. This initial cut flow represents the maximum carrying capacity of the bypass with zero impedance, and CFIs greater than or equal to 50% have greater than 90% bypass patency postoperatively. In contrast, a CFI less than 50% is associated with a 50% bypass patency rate and suggests a problem in need of revision. Although intraoperative angiography in bypass surgery has been supplanted by fluorescent videoangiography, some indications for intraoperative DSA remain in aneurysm surgery because it demonstrates unexpected aneurysm remnants and arterial occlusions after clipping, enabling clip readjustments and preventing strokes. Proximal ICA aneurysms (such as cavernous, paraclinoidal, OphA, and SHA aneurysms), giant aneurysms, and those in deep surgical corridors (such as posterior circulation aneurysms) have high revision rates and might benefit from intraoperative angiography, but it is not necessary for confirming bypass patency. Bypass patency is simple information that does not justify the additional operating room time, anesthesia, heparin use, radiation exposure, and angiography risks of DSA, particularly when complications can include stroke, dissection, groin hematomas, femoral artery thrombosis, and pseudoaneurysms. Intraoperative fluorescence is faster, easier, safer, and highly accurate. Bypass occlusion is unmistakable: the donor artery looks lifeless and feels flaccid, the Doppler is silent, the videoangiography is dark, and the bypass fails the Acland and flicker tests. The opportunity to salvage an occluded bypass must be seized immediately (Table 12.2). An imperfect anastomosis will sometimes attract platelets that adhere to the suture line and form a “white” plug visible through the anastomosis walls. This pale clump of platelets slows blood flow through the anastomosis and might trap stagnant blood. White plugs can be broken down by gently squeezing the arterial walls with microforceps and dispersing the plug downstream (Fig. 12.4). This simple maneuver can reopen an occluding bypass before it fully occludes. A reopened anastomosis must be watched for a while to be sure that it remains open, because squeezing actions can injure endothelium and lead to reocclusion. More than an aggregation of platelets, a “red” plug activates the coagulation cascade and forms a thrombus at the anastomosis site, in addition to attracting platelets. This plug is also seen through arterial walls, but is darker in color and cannot be dispersed easily. Whereas white plugs are granular and weakly adhesive, red plugs are tenacious and strongly cohesive, requiring disassembly of the anastomosis and extraction of thrombus with one of three techniques: suture-line thrombectomy, donor arteriotomy and thrombectomy, or complete reanastomosis (Fig. 12.5). Suture-line thrombectomy opens the anastomosis by cutting the suture in the middle of the suture line and unraveling the spiral toward each anchoring knot, but not disrupting the knots and destabilizing the other suture line (Fig. 12.6). Thrombus is extracted through this opening and technical errors can sometimes be fixed. Successful suture-line thrombectomy salvages the anastomosis with only one suture line needing re-sewing. This technique is used when the thrombus appears to be lodged in the anastomotic lumen and recipient artery. Table 12.2 Salvage Maneuvers for an Occluded Bypass
Bypass Patency
One Thousand Moves
Hemostasis First
Assessment of Bypass Patency
Salvaging an Occluded Bypass
Problem | Description | Maneuver |
White plug | Adherent platelet plug | Squeeze and disperse with microforceps |
Red plug | Adherent thrombus and platelets | Suture line thrombectomy (unravel one suture line, extract thrombus, resuture) |
|
| Thrombectomy through donor arteriotomy (incise donor, extract thrombus, resuture) |
|
| Complete reanastomosis |
Proximal graft occlusion | Proximal anastomosis occluded | Mid-graft arteriotomy with retrograde bleeding only; Fogarty catheter thrombectomy or revision |
Distal graft occlusion | Distal anastomosis occluded | Mid-graft arteriotomy with anterograde bleeding only; Fogarty catheter thrombectomy or revision |
Mid-graft occlusion | Twist, kink, or compression | Unkink or untwist graft |
Unsalvageable bypass | Failed revisions | Alternative bypass or temporalis muscle onlay graft |
Delayed ischemia | False-negative BTO or unexpected arterial sacrifice | Rescue bypass (new EC-IC interpositional bypass) |
