INTRODUCTION

Lower extremity revascularization is being offered to an increasing number of patients. This is due in part to the aging of our population, but the population is also increasingly active and aware of the effects of peripheral arterial disease on lifestyle and mobility. Advances in open and endovascular therapies have allowed an increasingly aggressive approach to revascularization for a patient population that is becoming increasingly older and often sicker. These factors continue to increase the number of prospective patients seeking revascularization to increase mobility and avoid amputation. Although the advent of sophisticated endovascular techniques continues to push the limits of catheter-based revascularization, open bypass will continue to play a major role in the revascularization of the critically ischemic lower extremity. This may prove especially true for those patients who are in need of pulsatile flow directly to a specific angiosome to prevent tissue loss.

The classic indications for revascularization are incapacitating claudication, rest pain, and tissue loss including gangrene and nonhealing ulcerations.¹ Patient selection is important in determining the optimal mode of therapy because pain relief and maintenance of function are the goals of revascularization and not the cure of atherosclerosis. Claudication is rarely a limb-threatening situation, and a failed intervention can result in a more complicated revascularization and conversion to the threat of limb loss. Whereas 25% of claudicants have progressive symptoms, fewer than 20% require revascularization for limb salvage after 10 years.² The majority of infrapopliteal revascularization procedures should be performed for patients in a limb-threatening situation with symptoms manifesting as pain at rest or tissue loss. In these patients, both an aggressive approach to revascularization and proper wound care are essential to maintain limb length and the ambulatory status of the patient. This affects both life and limb.

The history and physical examination remain an important tool in management of the vascular patient. The history provides information about the indication for vascular intervention as well as concurrent risk factors in other arterial beds. The physical examination (pulses, skin envelope) provides an assessment of the extent of vascular involvement. The hand-held Doppler is widely used in the evaluation of ischemia. An experienced examiner can differentiate an acoustically normal from an abnormal Doppler signal. The presence of a Doppler signal indicates that there is blood flow in the examined artery; however, it does not indicate whether this flow is adequate. The severity of ischemic disease should be documented by noninvasive vascular laboratory testing prior to any intervention. These studies confirm the degree of ischemia and serve as a baseline for future postprocedure follow-up.

The noninvasive vascular laboratory uses Doppler ultrasound to measure the ankle/brachial index (ABI), segmental pressures, and waveform analysis and to generate duplex images. Other important tests include pulse volume recordings (PVR), transcutaneous oxygen tension (tcPO₂) and photoplethysmography (PPG). The ABI is measured as the ankle pressure divided by the brachial pressure, with a normal value of 1.0. In intermittent claudication, an ABI of 0.5 to 0.9 is usually obtained, whereas in severe ischemia, the ABI is usually less than 0.5. Noncompressible arteries lead to falsely high ankle pressures in more than 30% of diabetic patients ³; therefore, other noninvasive studies should be added to determine the adequacy of blood flow in diabetics with ischemia.⁴ Segmental pressures and waveforms can help localize vascular occlusive disease. The tcPO₂ measures the partial pressure of oxygen that diffuses through heated skin.⁵ A tcPO₂ can be accurate in predicting healing. Healing is likely if tcPO₂ is above 35 to 40 mm Hg, and unlikely if it is below 20 to 26 mm Hg. A tcPO₂ regional index can be used to account for changes in systemic arterial oxygen tension.⁶ To obtain the regional index, the tcPO₂ of the leg is divided by the tcPO₂ measured at a reference point (chest). Wounds with a tcPO₂ index below 0.4 are unlikely to heal, and those with tcPO₂ above 0.6 are likely to heal.⁷

After it has been determined that revascularization is indicated, an imaging study is needed to plan the appropriate procedure. Arteriography remains the most common method for arterial imaging in order to plan revascularization. However, new modalities such as duplex ultrasound, magnetic resonance angiography, and computed tomographic (CT) angiography are being used with increasing frequency. These new modalities avoid the complications of arterial puncture and possible renal dysfunction associated with arteriography. However, these newer, noninvasive imaging modalities are still being refined and require the involvement of physicians dedicated to obtaining precise images. The chosen method must allow the surgeon to identify the inflow and outflow arteries as well as the adequacy of the runoff—all key factors for a successful bypass.

A successful bypass depends on careful preoperative planning and meticulous attention to detail during the operation. Preoperative decisions include choice of inflow artery, recipient artery, and the conduit for bypass. Error in judgment in any of these decisions is a technical error leading to graft failure. Meticulous dissection, conduit preparation, and suturing of the anastomosis are crucial in preventing intraoperative technical errors leading to early graft failure. There is little margin for error in suturing anastomoses, especially to those small diseased arteries below the knee.

KEY DECISION POINTS

• Bypass anatomy: inflow artery, recipient artery

• Conduit: vein, prosthetic, composite

INDICATIONS

• Severe disabling claudication

• Rest pain

• Tissue loss or gangrene

OPERATIVE STEPS

Step 1 Proximal artery exposure

Step 2 Distal artery exposure

Step 3 Preparation of conduit

Step 4 Tunneling of conduit

Step 5 Intraoperative anticoagulation

Step 6 Proximal anastomosis

Step 7 Distal anastomosis

Step 8 Evaluation of bypass

Step 9 Wound closure

OPERATIVE PROCEDURE

Proximal Artery Exposure

Proximal arterial exposure involves proper choice of the inflow artery for bypass. Several methods exist to aid this choice. Presence of a strong, palpable pulse and preoperative imaging should be considered. Any doubt requires measurement of an arterial pressure, which can be performed at the time of surgery.⁸ Careful dissection with minimal tissue manipulation and respect for anatomic tissue planes can avoid the complications associated with this portion of the procedure. There is some support for the use of a transverse groin incision as opposed to a vertical incision in order to avoid lymphoceles and seromas (Fig. 60-1). This decision should not compromise appropriate arterial exposure.

Figure 60-1 Transverse versus groin incision.

Improper Choice of Inflow Artery

Femoral Nerve Injury (Fig. 60-2)

• Consequence

Weakness in the extensor muscles of the thigh and paresthesias of the anterior thigh. Chronic pain can be observed in up to 15% of patients.⁹

Grade 1 complication

Figure 60-2 Proximal arterial exposure shows the proximity of the femoral nerve to the inflow artery.

• Repair

Direct repair by peripheral nerve specialist.

• Prevention

Nerve injuries occur approximately 4% of the time ¹⁰ and can be prevented with meticulous surgical technique and an understanding of the injury’s medial position to the femoral artery. The femoral sheath should be opened longitudinally to expose the femoral artery. Care must be taken to avoid transverse dissection because femoral nerve injury may occur at the lateral aspect of the dissection.

Distal Artery Exposure

Venous Injury (Fig. 60-4)

• Repair

A careful repair of the venous injury with fine suture must be performed with extra care given to control of bleeding during the repair. Often, the repair must be performed without formal vascular control through the use of digital pressure and judicious use of fine-tipped suction. Care should also be taken to avoid occlusion of the vein owing to the repair. This can create local venous hypertension and make the remaining venous circulation more difficult to handle.

• Prevention

Careful dissection of the outflow artery from its corresponding veins, with exposure limited to that minimal portion of the artery necessary for vascular control and the construction of the anastomosis. Consideration can also be given to the use of a proximal external pressure cuff for vascular control. This allows a more minimal dissection of the outflow artery, thereby minimizing the chance of venous injury and clamp injury to the artery.

Preparation of Conduit

Preparation of the conduit is obviously most important if autogenous vein is available to use for the bypass. Sources for venous conduit include the greater saphenous, lesser saphenous, and arm veins. If vein is not available, prosthetic materials can be used prior to the choice of primary amputation. However, every effort should be made to use an autogenous reconstruction. In this case, the avoidance of venous spasm and injury demands meticulous dissection and gentle vein handling. This is a crucial part of the operation and not one that should be left to the most junior member of the operating team (Fig. 60-5).

Saphenous Nerve Injury (Fig. 60-6)

• Prevention

Saphenous nerve injuries can be prevented with an understanding of its anatomy and relation to the saphenous vein. The saphenous nerve is a cutaneous branch of the femoral nerve. It travels with the superficial femoral artery through the adductor canal and then exits distal to the hiatus between the sartorius and the gracilis muscles to join the course of the greater saphenous vein. It may also be injured during medial exposure of the above-knee popliteal artery.

Preoperative vein mapping with duplex ultrasound can provide detailed information regarding the quality of a potential vein graft. It can detect constriction of veins secondary to sclerosis, previous manipulation, or thrombophlebitis. It can also assess length and diameter of the vein. These can be particularly important when performing a tibial bypass for which a long segment is necessary. Diameters greater than 3 mm for reverse ¹¹ and 2 mm for in situ¹² saphenous vein grafts have been recommended to obtain adequate long-term patency; however, judgment is required because the vein may be suitable with intraoperative preparation. Intraoperative preparation involves distal vein exposure with the instillation of premixed vein solution prior to more proximal dissection. This solution should be instilled under enough pressure to gently dilate the vein, but not to overdistend the vein, leading to endothelial injury. Endothelial ischemic time should also be minimized by allowing the vein to remain in place as long as possible whether it is used in a reversed, translocated, or in situ configuration.