CHAPTER 26 Femoropopliteal Bypass
INDICATIONS FOR FEMOROPOPLITEAL BYPASS
I. Disabling or refractory claudication is the most common indication for surgical revascularization of the lower extremity. Patients with claudication symptoms that significantly limit their lifestyle or compromise their ability to work or perform activities of daily living are candidates for lower extremity bypass. Claudication is deemed refractory when lifestyle modification (e.g., smoking cessation, exercise therapy, cholesterol reduction, blood pressure control, blood sugar control) and pharmacologic therapy (e.g., anticoagulation, antiplatelet therapy, arterial vasodilation) do not reduce symptoms or halt the progression of atherosclerotic disease. The primary reason to intervene in the patient with claudication is to improve lifestyle; the likelihood of a severe decline in cardiovascular status (<20%) or progression to major limb amputation (<5%) over a 5-year period is low, especially with lifestyle modification and appropriate medical therapy.
II. Limb Salvage in the Presence of Critical Limb Ischemia: Critical ischemia is defined as ischemic rest pain or tissue loss (e.g., ulceration or gangrene). A significant number of patients with critical ischemia eventually require vascular bypass or major limb amputation during the course of treatment.
III. Other Indications: Less common indications for lower extremity bypass include trauma (e.g., popliteal artery injury from posterior knee dislocation), popliteal entrapment syndrome, and femoropopliteal arterial aneurysmal disease.
PREOPERATIVE EVALUATION
I. Physical examination of the patient with exercise-induced leg pain should aim to confirm the diagnosis of IC and determine the level of occlusive disease. Palpation of the aortic, bilateral femoral, popliteal, posterior tibial, and dorsalis pedis pulses is essential. Patients with aortoiliac disease will have dampened or absent femoral pulses. Occlusive disease of the superficial femoral artery presents with normal femoral pulses and absent or reduced popliteal and pedal pulses. Palpable femoral and popliteal pulses in the setting of absent pedal pulses suggest infrapopliteal disease.
II. Noninvasive Diagnostic Evaluation
A. The ankle–brachial index (ABI) is the primary noninvasive study used in the diagnosis of PAD. If occlusive disease is suspected, based on presentation, but the resting ABI is normal, the ratio should be recalculated after a period of exercise. Any decrease in ABI with exercise is considered abnormal. The ABI may be falsely elevated and unreliable in patients with extensive arterial calcification as a result of noncompressibility of lower extremity vessels (Fig. 26-1).
B. Segmental limb pressures are obtained with a blood pressure cuff and Doppler probe, comparing brachial artery pressures and pressures at various arterial levels in the bilateral lower extremities. ABI and segmental limb pressure recordings are commonly used in conjunction with pulse volume recordings (PVR) of arterial waveforms to further delineate the anatomy of the occlusive disease. A normal PVR resembles an arterial waveform, with a sharp systolic spike and a diastolic downstroke. A change in contour, typically observed as a dampened waveform, indicates proximal occlusive disease. The extent of this change correlates with the severity of disease.
C. Arterial duplex ultrasonography can confirm the diagnosis of PAD, identify the level of disease, and differentiate between stenotic and occlusive lesions. Lower extremity examination begins at the common femoral artery and proceeds distally. Arterial stenosis is localized with color Doppler imaging and assessed by measuring Doppler velocities at several arterial levels.