Need for intervention
Limb not threatened; elective intervention
No sensorimotor deficits
Limb threatened; urgent intervention
Mild sensory loss at most; no motor signs
Limb threatened; emergent intervention
Sensory loss, possible rest pain. Mild weakness
Limb irreversibly damaged
Profound sensorimotor loss
Once a diagnosis of ALI has been formulated, further characterization of arterial anatomy and status is best evaluated through diagnostic imaging. The predominating imaging modalities utilized in this assessment are computed tomographic angiography (CTA) and traditional contrast angiography with some limited role for duplex ultrasound:
CTA is being increasingly used as the preferred initial imaging exam for ALI due to several attributes. Due to systemic delivery of contrast, CTA can effectively delineate entire limb arterial anatomy simultaneously. This is useful for identifying the extent of thrombosis as well as proximal and distal vessel targets for intervention. Sluggish flow particularly within the tibial vessels and distally can limit the delivery of contrast and therefore reduce the amount of information provided by the exam. Additional information readily available via CTA includes vessel calcification, vessel diameter, collateralization, and presence of previous stents or bypass grafts. CTA is, however, a static study providing very little information about flow dynamics. Disadvantages include the need for radiation and potentially nephrotoxic contrast.
Contrast angiography is considered by many to be the gold-standard imaging modality for ALI. Angiography has the indisputable advantage of being both diagnostic and potentially therapeutic. It also provides information regarding flow characteristics. Angiography, however, only provides information available through opacification of the vessel lumen and therefore does not provide any extralumenal assessment. Collateral pathways can be quite variable in ALI and the ability to opacify vessels distal to the affected region requires catheter selection of the appropriate supplying collateral pathway as well as adequate timing to allow for contrast to be delivered. Angiography, like CTA, also uses radiation and potentially nephrotoxic contrast; however, contrast volumes are often less than CTA. Additional risks are associated with arterial cannulation and intralumenal manipulation but are relatively minimal.
Duplex ultrasound (US), although not frequently used for ALI, can provide some valuable information expeditiously, especially if readily performed by the provider. In cases of strongly suspected arterial embolism, the location of embolus can be quickly confirmed via US. Also potential access points for arterial cannulation can be quickly assessed for feasibility. Lastly, availability of venous conduit for arterial reconstruction can be ascertained.
Once a diagnosis of ALI has been established, appropriate further management should be expeditiously applied. Treatment strategies can be divided into two arms: anticoagulation and revascularization. Early anticoagulation via systemic heparinization is the initial management maneuver in cases of ALI as long as no contraindication to anticoagulation exists (Table 2.2). Revascularization strategies consist of endovascular techniques, open surgical revascularization, and hybrid procedures. All of the different treatment modalities for ALI are not intended to be competitive but rather complimentary. The astute clinician should be proficient with all and be prepared to apply them to the specific scenario on hand:
Contraindication to thrombolysis.
Systolic BP > 180 mmHg; diastolic BP > 110 mmHg
Recent major surgery, including eye surgery
Trauma within 10 days
GI bleeding within 10 days
Intracranial or spinal surgery within 3 months
Head injury within 3 months
Stroke within 6 months
Management of Rutherford Class I ischemia with anticoagulation alone is appropriate, allowing time for more thorough evaluation and possibly elective revascularization.
For Class IIa and IIb ischemia, anticoagulation alone is not sufficient and prompt revascularization is warranted to prevent further ischemic damage.
Class III ischemia implies irreversible damage requiring some level of amputation; however, treatment may be incorporated to lower the level of amputation.
Anticoagulation through systemic heparinization serves several purposes. Most importantly, risk of further clot propagation is decreased especially in small distal runoff vessels where flow can become quite static. Second, in the cases of embolism, risk of recurrent embolism can be reduced. Lastly, through antiinflammatory and microcirculation properties, heparin may improve symptomatology and even restore some perfusion such that more time for further evaluation is allowed. Low molecular-weight heparin serves no role in the initial management of ALI.