INTRODUCTION
Acute limb ischemia is a surgical emergency condition, which requires timely management or can be associated with high morbidity and mortality rates. Complete limb ischemia will lead to extensive tissue necrosis within six hours unless the limb is revascularized. Incomplete acute limb ischemia can also benefit from medical treatment (anticoagulation or thrombolysis).
The most common causes for nontraumatic acute limb ischemia include:
- Embolism from the heart
- Thrombosis over an existing arterial plaque/stenosis
- Thromboembolism from arterial aneurysm
- Acute bypass graft occlusion (Vein or synthetic graft).
It is most important to differentiate between embolic and thrombotic occlusions as the management as well as the prognosis is different for both (Table 1.1).
Presenting Symptoms and Signs of Acute Embolic Occlusion
The classic clinical manifestation is known by the 6 P’s
- Pain
- Pallor
- Pulse less limb
- Paresthesia: This may progress to anesthesia
- Paresis, which may develop into paralysis
- Perishing cold.
Sudden onset of pain in the upper or lower limb, usually a few hours duration only with rapid onset of muscle weakness or paresis of the toes/fingers and limb should immediately lead to suspicion of acute arterial occlusion.
An embolic arterial occlusion is usually sudden in onset and aggravates rapidly. However, a thrombotic occlusion is less dramatic and insidious in onset and shows relatively slow progression.
The limb becomes pale and cold, and later may show cyanosis (Fig. 1.1).
If further time passes without anticoagulation or immediate treatment, the ischemia aggravates further and patient will develop muscle paralysis or foot drop (Fig. 1.2). The presence of anesthesia with muscle paresis suggests the urgent requirement of revascularization.
Fig. 1.2: The patient is asked to dorsiflex her feet, but she has an ischemic foot drop on the left side
|
The onset of paralysis with cold foot, and fixed mottled appearance suggests irreversible ischemia (Fig. 1.3). There may be associated ischemic muscle swelling and compartment syndrome with a tight and tender calf or forearm.
The presence of acute aortic thrombus or saddle emboli (involving aortic bifurcation) may present as acute paraplegia due to spinal ischemia. The history of sudden onset pain followed by weakness and coldness of both feet as well as the absence of palpable femoral pulses points towards this uncommon clinical condition. Timely intervention may provide complete recovery. However, late diagnosis and treatment fails to improve the established irreversible neurologic deficit.
According to severity, acute limb ischemia can be classified in three grades (Table 1.2).
Factors Predisposing to Acute Thrombosis
There are certain predisposing factors for development of thrombosis in a normal or diseased artery, which are mentioned in Table 1.3.4
|
Diagnosis of Acute Limb Ischemia
A sudden painful limb with reduced temperature and absent pulses with presence of a cardiac etiology for embolism (Myocardial infarction or rheumatic valvular disease) is clinically an acute embolic limb ischemia and may not require further sophisticated investigative modalities as an early treatment is crucial for limb salvage.
Color Doppler Imaging
This is useful if performed without any delay. The absence of color filling or spectral flow in the arteries is suggestive of an embolic occlusion. The embolus is usually hypoechoic in the early stages. Emboli usually lodge at sites of arterial bifurcation, commonly the femoral bifurcation or rarely popliteal bifurcation.
If the lumen of the occluded artery appears hyperechoic, the thrombus is usually at least 24 hours old. Other features favoring thrombosis is the presence of collaterals with possible reformation of distal arteries.
Angiography
An angiography is usually not required for an embolic limb ischemia. But when in doubt and if time permits, it is performed to guide for further treatment. A perfusion catheter can also be positioned across the thrombosed arterial segment and thrombolysis performed. A repeat angiography 6–8 hours later (when most of the thrombus is dissolved) can identify the culprit lesion and thus further angioplasty or bypass can be performed as feasible.
Figure 1.4 shows angiography with luminal emboli within the superficial femoral artery. There is no occlusion of the artery and distal flow is maintained. In Figure 1.5 note convex margin of the thrombus with total occlusion of distal superficial femoral artery at the adductor hiatus. Also note the presence of collaterals arising from the artery proximal to the thrombotic occlusion.
Echocardiography
When a cardiac source of embolus is suspected, an echocardiography is performed to assess the presence of intramural clots or valvular vegetations. If a surface echo is normal, a trans-esophageal echo may detect the presence of clots.5
Immediate Treatment of Acute Limb Ischemia due to Embolic Occlusion
Immediate anticoagulation by intravenous heparinization.
Urgent embolectomy via the femoral route (for lower limb) or brachial route (for upper limb).
This surgery can be performed under local anesthesia as an emergency.
The common femoral artery is exposed and slinged for control. The superficial femoral and profunda femoris arteries are also controlled. In case of the brachial artery, exposure at its bifurcation in elbow is recommended as the Fogarty catheter can be passed in the radial and ulnar arteries under vision.
In an embolic occlusion, the artery would be soft, noncalcified and filled with dark red clots (Fig. 1.6).
A transverse or longitudinal arteriotomy is made on the artery. Bulging of dark red clots from the arteriotomy can be noted in Figure 1.7.
A Fogarty catheter is passed proximally. After adequate balloon inflation, the catheter is withdrawn and the embolus comes out from the artery with restoration of pulsatile blood flow from the proximal artery (Fig. 1.8).6
The catheter should be passed repeatedly till two negative passes and adequate pulsatile flow is confirmed.
The catheter is also passed distally in both the branches and emboli extracted. A good distal flow may not be the only satisfactory sign of emboli clearance.7
Fig. 1.9: Cyanosed hand of patient with brachial embolic occlusion. The other hand is of a normal person for comparison
The length of Fogarty catheter passed distally should be noted and heparin-saline flushed distally.
The transverse arteriotomy is closed primarily with polypropylene sutures, whereas a longitudinal arteriotomy is sutured with a vein patch and polypropylene sutures to prevent arterial narrowing.
After a successful embolectomy, there is an immediate relief in pain and the limb becomes flushed in some time. Improvement in foot or hand temperature and resolution of cyanosis with return of finger or toe movements are signs of adequate perfusion (Figs 1.9 and 1.10).
Figure 1.11 shows the extracted emboli from the brachial artery. Note that these fresh clots are dark red in color and gelatinous in consistency as compared to the firm white clots found in organized arterial thrombus.
If there is no significant improvement in the clinical signs within a few hours of an embolectomy, distal embolic occlusion with poor distal run-off is the cause and a repeat embolectomy, possibly from a distal artery may be required.
Postoperatively, anticoagulation by heparin followed by long-term warfarin is recommended to reduce the risk of recurrent embolism.8
Fig. 1.11: Extracted clots (embolus) from the brachial artery with a Fogarty catheter. Note that the clots are dark red
Treatment of Acute Limb Ischemia due to Thrombotic Occlusion
Patients with thrombotic occlusion with good distal run-off can be offered direct surgical treatment or percutaneous thrombolysis with subsequent endovascular or surgical therapy.
Thrombolysis is suited for patients without critical limb ischemia (without anesthesia or paresis) as this procedure takes some time to provide relief in ischemia. In this procedure, after an angiography, a perfusion catheter is passed across the thrombotic segment and intra-arterial thrombolysis administered. Repeat angiography 6–12 hours later after dissolution of thrombus often demonstrates the original arterial culprit lesion which can be then treated accordingly.
A localized thrombotic occlusion can be treated surgically with a thrombo-embolectomy. The finding of organized thrombus with an underlying plaque is suggestive of a thrombotic occlusion (Fig. 1.12). Figure 1.13 shows the organized thrombi extracted from the popliteal artery.
A thromboembolectomy procedure alone may often not be sufficient to salvage the limb and occasionally an emergency limb bypass is required, depending on the level of the arterial occlusion and status of distally reformed artery.
In case of delay in time to revascularization, the patient may develop compartment syndrome which is manifest by severe pain, with tight and tender muscle compartment.
The compartment syndrome can increase after revascularization as the arterial circulation is re-established and venous return also increases. In these patients, a fasciotomy is performed to release the tight compartments. Figure 1.14 shows fasciotomy with viable healthy calf muscles. Figure 1.15 shows patient who has undergone brachial embolectomy with fasciotomy of the forearm muscles.
In patients with advanced ischemia and significant delay in treatment (more than 6–8 hours), the fasciotomy may reveal dusky or nonviable muscles (Fig. 1.16).9
These patients are at a high risk of myoglobinuria or crush syndrome and acidosis. The eventual requirement for amputation is also higher in these patients. Acute limb ischemia can lead to various loco-regional as well as systemic complications which are mentioned in Box 1.1.