Acute Limb Ischaemia
Acute limb ischaemia represents the sudden blockage of the arterial flow in the interested limb. It’s a critical situation which needs rapid intervention because it leads to extensive tissue necrosis in a short time spam.
Etiology of Acute limb ischaemia
The most frequent causes of acute ischaemia are embolism and in situ thrombosis.
The starting points of embolism are the heart and the big arteries. Cardiac embolism can happen in various diseases, such as: atrial fibrillation, myocardial infarction, ventricular aneurysm, cardiomyopathy, infectious endocarditis, valvular prosthetics, atrial mixoma etc.
Extracardiac embolism usually originates from the ulcerated atheromatous plague on the walls of the vessel.
Embolism happen in 80% of the times, while thrombosis is the culprit just in 20% of the times.
thrombosis occurs in unstable atheroma plagues.
Other causes , but less common, can be trauma, Raynaud’s Syndrome , compartment syndrome ( insufficient blood supply to the muscles and nerves due to increased pressure in a closed space of the body; usually happens after trauma) or even congenital causes, for example aortic hypoplasia.
The severity of the ischaemia deeply depends on the importance of the occluded vessel and the presence of collateral supply. Without rapid treatment , ischaemia will lead to tissue necrosis very fast, in a matter of a few hours.
Nerves and muscles are the first ones to be affected before any visible changes- in a matter of 4 hours, then in 6 hours irreversible damage happens if complete occlusion of the vessel and no collateral circulation is available..
There are also many changes on the molecular level. Lactic acid, thromboxane and potassium will be produced and accumulated due to anaerobic metabolism. Along with these, myoglobin ( resulted from muscle fiber infarction) will lead to renal failure, myocardial depression and arrhythmias.
These effects are more present on reperfusion.
The simple 6 p’s that make up the ”image” of acute limb ischaemia are:
1. Pain – can be absent in complete ischaemia;
2. Pallor – also present in chronic ischaemia;
3. Pulselessness – present as well in chronic ischeamia;
4. Paraesthesia – leads to anaesthesia;
5. Paralysis – unable to shake toes or fingers;
6. Poikilothermia – inability to regulate core body temperature.
The presence of paralysis and anaesthesia indicates complete ischaemia and requires EMERGENCY surgical treatment.
How to differentiate embolus and thrombosis in situ
Following we’ll discuss the clinical features of both
severity: complete because there are no collaterals;
onset: second or minutes;
limb affected: leg 3:1 arm;
multiple sites: up to 15%;
embolic source: ( +) ( cardiac embolism);
previous claudication: ( – ) ;
palpation of artery: soft, tender;
contralateral leg pulses : (+);
treatment: embolectomy, warfarin.
Thrombosis in situ
severity: incomplete ( + collateral);
onset: hours or days;
limb affected: leg 10:1 arm;
multiple site: rare;
embolic source: (-);
previous claudication: ( +);
palpation of artery: hard, calcified;
contralateral leg pulses: ( +);
treatment: medical, bypass, thrombolysis;
Rutherford Classification of Acute Limb Ischaemia
Category I: Viable (no immediate threat)
Category IIA: Marginally threatened (salvageable if promptly treated)
Category IIB: Immediately Threatened (salvageable if immediately revascularised)
Category III: Irreversible (major tissue loss with permanent nerve injury)
Although the diagnose is most of the time evident clinically, complementary exams confirm the disease and show the exact level of the occlusion, its degree and the causal mechanism.
Doppler evaluation – shows the blood flow in smaller arteries, so it allows you to see the extend and degree of the ischaemia;
Duplex ultrasonography – It’s a medical ultrasonography composed of two elements
Grayscale ultrasound which shows you the layout of the body part; there’s no motion or blood flow evaluated; this way the plague is easily imaged in the blood vessel.
Color Doppler ultrasound evaluates flow and movement , mostly used for imaging blood flow within an artery;
– the speed of the blood through a narrowed region of the artery increases, indicating a region of resistance.
As the name implies, both elements are presented together on the same scree, greatly facilitating interpretation.
Another advantage is that is an inexpensive and non- invasive way to determine pathology.
It’s usually done before any invasive investigation or surgical procedure.
CTA vs MRI
I’ve previously discussed ( peripheral artery occlusive disease) the advantages/disadvantages of both.
In this case TIME is everything, and although CTA uses radiation is much quicker than MRI.
Compared to Duplex Ultrasound, they are used more often because are more precise in planning revascularisation.
Treatment of Acute limb ischaemia
First of all any life threatening medical conditions must be assessed;
Eventually will follow correction of fluid and electrolyte imbalance;
Start coagulation as soon as possible ( Heparin);
i.v analgesics – Opioids;
ECG ( AF, recent AMI) ;
blood test .
The role of Heparin anticoagulation
It is used Unfractioned Heparin in i.v infusion. The dose is adjusted to APTT ( 2-2,5X).
The standard contraindications apply when giving heparin. It’s not necessary to administer if intervention is planned soon ( less than 90 min) , otherwise is very important to give.
In case of EMBOLUS
conservative: anticoagulation only;
balloon catheter embolectomy ( Fogarty);
arterial bypass/ reconstruction;
In case of THROMBUS
conservative: anticoagulation only;
thrombolytic therapy : Streptokinase, Urokinase, rTPA;
- catheter thrombectomy.