The importance of a good clinical examination cannot be overstated. In a patient with imminent risk of limb loss, a well-performed clinical examination may provide enough diagnostic information to bring the patient directly to the operating room without wasting time on unnecessary imaging studies.

Treatment decisions concerning an acutely threatened limb can be challenging for even the most experienced surgeons. Making the best treatment choice requires a basic understanding of the etiology, pathophysiology, and consequences of limb ischemia. Younger patients with acute limb ischemia are at risk for limb loss, whereas older patients have a high risk of mortality in addition to the threat of limb loss. Patients with acute myocardial infarction and poor cardiac output have substantially higher postoperative mortality, regardless of the type of operation performed [12, 13]. Therefore, performing a thorough history and physical examination and accurately placing the patient in the appropriate category of limb ischemia are crucial.

Anticoagulation should be initiated on all patients with acute limb ischemia. Blaisdell introduced the role of heparin in preventing proximal and distal propagation of thrombus in patients with acute limb ischemia [14]. Although heparin does not have thrombolytic properties, it stabilizes and prevents extension of the already formed thrombus while preserving the patency of the microcirculation. An initial heparin bolus of 80 units/kg should be followed by a continuous infusion of 18 units/kg/h. Most patients are dehydrated and benefit from large bore intravenous access and hydration. Contrast which is required for angiographic imaging may be harmful to kidney function, especially in dehydrated patients.

Patients with class I limb ischemia have viable limbs which allows more time to get investigational studies that will guide definitive treatment. Revascularization for this group of patients can be performed less emergently, and patients may benefit from anticoagulation in the interim period. In addition, high surgical risk patients occasionally are not revascularized if their residual perfusion is adequate and the addition of long-term anticoagulation is felt to prevent further ischemic events.

Patients with reversible ischemia (class II) require revascularization for limb salvage. The majority of patients with acute limb ischemia present as class II ischemia and benefit the most from revascularization efforts. Any sensory or motor deficit in this group of patients must be identified, as the presence of these deficits implies that the peripheral nerve cells are getting ischemic and will soon become anoxic. Nerve death is followed by muscle necrosis and limb loss. Patients with class IIa ischemia have marginally threatened limbs allowing the surgeon more time to decide on definitive treatment. All of these patients should be immediately anticoagulated and undergo an imaging study. Revascularization can involve endovascular or open surgical techniques, depending on the surgeon’s familiarity and comfort with the use of modern endovascular technology. The duration of symptoms can help guide treatment decisions. Patients who have less than 2 weeks duration of signs and symptoms benefit the most from endovascular treatment, while patients whose duration of symptoms is more than 2 weeks usually benefit more from open surgical procedures [15]. Intra-arterial thrombolytic therapy requires close clinical monitoring and interval angiography. If the patient cannot tolerate thrombolysis or develops worsening ischemia with motor loss, the treating surgeon must be prepared to perform an emergent open surgical revascularization to save the leg.

Patients with class IIb ischemia have acute critical ischemia and are at an extremely high risk for limb loss if emergent revascularization is not performed. Institutions with limited resources should consider transferring these patients to vascular centers of excellence which offer a full range of vascular and endovascular services. Evidence suggests that this strategy improves surgical outcomes in patients with acutely threatened limbs [3]. Historically, these patients had extremely high rates of limb loss. The advent of the embolectomy catheter by Fogarty in 1963 revolutionized the treatment of acutely threatened limbs [16]. Balloon catheter embolectomy became the gold standard surgical therapy for acute limb ischemia. Although low-dose intra-arterial thrombolytic treatment is effective for subcritical ischemia, the long treatment time required makes thrombolysis ill suited for threatened limbs requiring immediate reperfusion. Well-equipped endovascular centers can perform accelerated thrombolysis with high-dose, short-duration infusions [17] or pulse spray thrombolysis [18]. Use of these advanced techniques requires 24-h availability of angiography suites and a commitment to perform emergent open surgery if the limb status deteriorates during thrombolytic therapy. Patients with severe ischemia from a focal thrombus or embolus in a proximal vessel usually benefit more by proceeding directly to a definitive surgical thromboembolectomy.

Patients with class III acute limb ischemia have irreversible ischemia that cannot be treated with revascularization. In fact, revascularization attempts in this group of patients can be harmful by causing rhabdomyolysis and myoglobinuria. These patients are better served with limb amputation at the appropriate anatomic level.

The use of thrombolytic therapy for acute limb ischemia has evolved over the last several decades with many reports in the literature describing its benefit. Systemic infusion of thrombolytic therapy has given way to catheter-directed thrombolysis (i.e., percutaneous placement of a catheter directly into the intra-arterial thrombus). Tissue plasminogen activator (TPA) has largely replaced streptokinase and urokinase and is infused in a variety of doses and infusion times. Although randomized trials have been performed, they failed to provide a clear-cut answer to the treatment dilemma of thrombolysis versus surgical revascularization. Meta-analyses have found similar mortality and amputation rates for both percutaneous thrombolysis and open surgery. Thrombolysis reduces the need for open major surgery at a cost of causing more bleeding and distal embolization [19, 20].

Patients who present with limb ischemia less than 14 days duration with intact motor and sensory function may benefit from intra-arterial catheter-directed thrombolysis followed by correction of the causative lesion. Treatment options for patients with an acutely occluded bypass graft include surgical graft thrombectomy, thrombolysis with correction of the causative lesion, or creation of a new bypass. Consideration needs to be given to the age of the graft, conduit availability, the duration and degree of ischemia, and the overall condition and comorbidities of the patient.

Absolute contraindications to thrombolysis are recent intracranial or retinal surgeries. The practitioner must be ready to abort thrombolysis in favor of open surgical revascularization if at any point thrombolysis is causing an unacceptable delay in revascularization. The decision to perform thrombolysis versus open surgical revascularization should be made by a surgeon familiar with both techniques in a center equipped to perform either procedure.