Timely diagnosis and accurate recognition of the etiology of decreased limb perfusion is essential for successful treatment of ALI. History should be focused on determining the onset of symptoms and symptoms are most commonly due to pain. Duration, location, and severity can provide important clues about the source of the ischemia and institution of an appropriate treatment plan. In addition, past and recent medical history is important to establish as this may suggest an etiology and the urgency of intervention. If a patient has a history of claudication or previous vascular surgery, collaterals may have developed and result in less severe presenting symptoms or even a delay in presentation. In contrast, if a patient has a history of atrial fibrillation or aneurysmal disease, an embolic source may be responsible. This patient will present with sudden and severe onset of ischemic symptoms that may be urgently and effectively treated with embolectomy.

Physical exam findings of ALI have traditionally correlated with six signs and symptoms referred to as the “six Ps.” These include pain, pallor, poikilothermia, pulselessness, paresthesia, and paralysis (Fig. 39.1). Careful physical exam allows identification of the level of occlusion, the viability of the limb, the urgency of revascularization efforts, and the decision to proceed with endovascular versus surgical modalities. For instance, a patient with complaints of bilateral lower-extremity pain, lack of femoral pulses, mottling to the proximal lower extremities, and complete lack of lower-extremity motor or sensory function is most likely suffering from an aortoiliac occlusion . This patient’s ischemic event should be urgently addressed and carries a high risk of morbidity and mortality. This presentation is contrast with a patient presenting with a palpable femoral pulse and a painful, pale foot that is numb but without motor dysfunction. In contrast to the first scenario, the less severe presentation may allow more detailed evaluation of the cause for acute limb ischemia. Additional diagnostic studies may be obtained prior to revascularization. The two previous clinical scenarios also highlight the importance of comparing both lower extremities during the physical exam. This comparison will help establish a baseline of the degree of peripheral vascular disease and assist with identifying if the acute ischemic event is secondary to an embolus or thrombosis .

Proper identification of the degree of acute ischemia is the cornerstone of management for this entity. Reporting standards approved by the Joint Council of the Society for Vascular Surgery and the North American Chapter of the International Society for Cardiovascular Surgery for acute limb ischemia were first proposed in 1986 and revised in 1997 [1]. Acute limb ischemia should be categorized according to the criteria illustrated in Table 39.1. These criteria are frequently referred to as the Rutherford classification. Categories are based on the presenting viability of a threatened limb, prognosis of intervention, and physical exam findings. These exam findings include evaluation of sensory function, motor function, and Doppler exam. This categorization tool will assist with developing a treatment algorithm. Category I refers to a viable limb that can be investigated with further diagnostic studies and does not require prompt revascularization. Category III refers to acutely ischemic limbs with loss of motor and sensory function along with tissue loss. Category III limbs are frequently managed with primary amputation as revascularization efforts may result in a painful, nonfunctional limb. Finally, category II can be subdivided into two levels of severity. Category IIa refers to a marginally threatened limb with retained motor function and minimal numbness restricted to the toes. Category IIb refers to an immediately threatened limb with more severe pain such as rest pain and most importantly, mild or moderate motor dysfunction. Patients in category IIa require prompt revascularization and those patients in category IIb require immediate revascularization. Therefore, patients categorized in either category I or III do not represent the management dilemma involved with correctly identifying and managing those patients in the subcategories of category II. Historically, patients categorized as IIb were not candidates for endovascular treatment due to the need for immediate revascularization. Due to advances in therapy, endovascular revascularization can now be performed concurrently with diagnostic studies. For instance, an arteriogram can be performed in the same setting as restoration of flow in an expedient manner with pharmacomechanical thrombolytic therapy. Therefore, revascularization efforts for category II patients should proceed regardless of endovascular versus surgical techniques according to the urgency dictated by the subcategorization into a marginally threatened IIa versus immediately threatened IIb limb.

After determining if a patient is a revascularization candidate, proper management is also dependent on identifying the underlying cause of the acute limb ischemia. Acute limb ischemia occurs typically in the setting of either an embolic or a thrombotic event. Thrombotic events are estimated to be responsible for 85 % of cases of ALI. Embolic events occur less commonly and make up roughly 15 % of events [2]. Proper identification of the responsible etiology will assist with the type of intervention performed and the durability of this intervention.

An embolic event involves lodging of material in a vessel with obstruction of distal limb perfusion. The majority of emboli are secondary to thrombus with a cardiac origin [3]. Cardiac emboli frequently result from arrhythmias, thrombus formation after myocardial infarction, valvular destruction, cardiac tumors, or paradoxical emboli . Thrombus from proximal aneurysmal disease and embolization of proximal atherosclerotic plaque may also be responsible. Finally, emboli secondary to an endovascular intervention may be due to dislodgement of thrombus by catheters and wires or thrombus formation with prolonged sheath placement.

The second type of event, thrombosis , should be suspected in patients with a history of peripheral vascular disease. Atherosclerotic plaque rupture may cause thrombosis of the vessel at this site and result in occlusion of the vessel with limited collateral flow. Other sources of thrombosis include arterial dissection causing distal occlusion of distal outflow, hypercoagulable states, trauma resulting in intimal damage or flap creation, low-flow states created by hypotension or vasoactive drugs, and compartment syndrome.

Once the diagnosis of acute limb ischemia is made and the viability of the affected limb has been categorized, patients should undergo systemic heparinization . The main goal of heparin administration is to prevent propagation of thrombus and thereby, prevent worsening of ischemia. Most often, intravenous, unfractionated heparin is utilized.

Electrocardiogram is routinely obtained and will help establish if a patient has a possible arrhythmia responsible for the ALI. In addition, a metabolic panel should be obtained and can help guide diagnostic studies and interventional methods based on a patient’s renal function. Finally a complete blood count, prothrombin time, and partial thromboplastin time should also be obtained. Other studies should be collected, such as a baseline fibrinogen level if thrombolytic therapy is being considered and a baseline creatine phosphokinase level if compartment syndrome following revascularization is a concern. The next step in management involves the decision to obtain imaging studies. The classification of ALI guides the need for emergent intervention versus the luxury of imaging to more specifically delineate the etiology and treatment for ALI. Imaging modalities include formal ultrasound studies, arteriography, computed tomographic angiography (CTA ), and magnetic resonance angiography (MRA ). Ultrasound can help identify the level of occlusion and status of distal outflow but is operator dependent. In addition, ultrasound does not routinely identify proximal sources accurately and may not be easily obtained during off-hours. Arteriography accurately diagnoses the level of obstruction and status of distal runoff. Also, patients that will be more effectively treated with percutaneous interventions versus surgery (embolectomy or bypass) can be identified. As previously stated, patients categorized as category IIb and requiring immediate revascularization were not traditionally candidates for formal arteriography performed in an interventional suite. The recent institution of hybrid operating room suites now makes postponing intervention for an arteriogram less of an issue as the study can be performed prior to surgical interventions with little delay. CTA may be performed relatively expediently but should not delay intervention in patients with category IIb ALI. In addition, those patients with renal insufficiency or those expected to need significant contrast administration for revascularization efforts may not be candidates for CTA . Finally, MRA is traditionally an imaging modality that is time consuming, may be contraindicated in those with metal implants or renal insufficiency, and is typically reserved for those patients not needing immediate revascularization.