The latest article in our Clinical Practice series reviews the evaluation of patients with acute limb ischemia, including assessment of temperature, appearance, and pulses, by palpation and Doppler. Strategies for treatment of viable limbs are reviewed.
Acute limb ischemia is defined as a sudden decrease in limb perfusion that threatens the viability of the limb. The incidence of this condition is approximately 1.5 cases per 10,000 persons per year. The clinical presentation is considered to be acute if it occurs within 2 weeks after symptom onset.
• What are the symptoms and findings on physical examination in acute limb ischemia?
Symptoms develop over a period of hours to days and range from new or worsening intermittent claudication to pain when the patient is at rest, paresthesias, muscle weakness, and paralysis of the affected limb. Physical findings may include an absence of pulses distal to the occlusion, cool and pale or mottled skin, reduced sensation, and decreased strength. These features of acute limb ischemia are often grouped into a mnemonic known as the six Ps: paresthesia, pain, pallor, pulselessness, poikilothermia (impaired regulation of body temperature, with the temperature of the limb usually cool, reflecting the ambient temperature), and paralysis.
• What is the appropriate initial evaluation of acute limb ischemia?
Acute limb ischemia should be distinguished from critical limb ischemia caused by chronic disorders in which the duration of ischemia exceeds 2 weeks and is usually much longer. A careful examination of the limbs is necessary to detect signs of ischemia, including decreased temperature and pallor or a mottled appearance of the affected limb. Sensation and muscle strength should be assessed. The vascular examination includes palpation of pulses in the femoral, popliteal, dorsalis pedis, and posterior tibial arteries in the legs and in the brachial, radial, and ulnar arteries in the arms. The presence of flow, particularly in the dorsalis pedis and posterior tibial arteries supplying the affected foot or radial and ulnar arteries of the symptomatic hand, is routinely assessed by means of Doppler imaging. If flow is audible, perfusion pressure to the ischemic limb can be measured with a sphygmomanometric cuff placed at the ankle or wrist just proximal to the Doppler probe; a perfusion pressure of less than 50 mm Hg indicates limb ischemia. Optimal management requires prompt administration of intravenous heparin to minimize thrombus propagation.
Morning Report Questions
Q: When should endovascular versus surgical intervention be used for treatment?
A: On the basis of several randomized trials and recent case series, catheter-directed thrombolysis has the best results in patients with a viable or marginally threatened limb, recent occlusion (no more than 2 weeks’ duration), thrombosis of a synthetic graft or an occluded stent, and at least one identifiable distal runoff vessel. Surgical revascularization is generally preferred for patients with an immediately threatened limb or with symptoms of occlusion for more than 2 weeks.
Q: What is reperfusion injury?
A: Reperfusion may result in injury to the target limb, including profound limb swelling with dramatic increases in compartmental pressures. Symptoms and signs include severe pain, hypoesthesia, and weakness of the affected limb; myoglobinuria and elevation of the creatine kinase level often occur. Since the anterior compartment of the leg is the most susceptible, assessment of peroneal-nerve function (motor function, dorsiflexion of foot; sensory function, dorsum of foot and first web space) should be performed after the revascularization procedure. The diagnosis is made primarily from the clinical findings but can be confirmed if the compartment pressure is more than 30 mm Hg or is within 30 mm Hg of diastolic pressure. If the compartment syndrome occurs, surgical fasciotomy is indicated to prevent irreversible neurologic and soft-tissue damage.