Leg ischaemia (acute)

Definition

• Acute Lower Limb Ischaemia is defined as the sudden reduction in limb perfusion threatening the viability of the limb and requiring urgent evaluation and management 1 4 7
• To be considered acute, the timeline of the onset of symptoms must be less than two weeks; symptom onset greater than two weeks is considered to represent chronic limb ischaemia 7 8

History Considerations

• A good clinical history is important. A history of atrial fibrillation (AF) without anticoagulation will predispose towards embolic phenomena, whilst a history of peripheral arterial disease (PAD) or chronic limb threatening ischaemia (CLTI) may raise concern for an atheroembolic cause and may present with different symptoms as there will likely be more extensive collateralisation. 7
• As part of the history, some initial bedside investigations that can be done to assist in determining underlying cause and severity include an electrocardiogram (ECG) and an Ankle-Brachial Index (ABI):
  • ECG helps in identifying AF; if this is a new finding it may point more towards an embolic cause of acute lower limb ischaemia
  • ABI obtained via hand-held Doppler pulse can assist in differentiating between CLTI and ALI 7
• It is important to establish the chronology of symptom onset 2 See: Rutherford Criteria

Clinical Signs and Symptoms

• The 6 P’s - some, but not all, are usually present:
  • Pain
    • Usually of sudden onset. It is described as feeling like a cramp or claudication-like pain on movement. It will progress to rest pain as ischemic time increases.
  • Pallor
    • Typically, the limb appears white. As time progresses mottling with a blue/purple colour occurs. At this point it is still blanching; however, if left it will progress to a darker blue/purple colour that is non-blanching.
    • It is important to note that pallor is also present in chronic ischaemia
  • Pulse deficit
    • Absent pulses distal to embolus
    • It is important to note that pulses may also be absent in chronic ischaemia
  • Paralysis
    • The degree of muscle weakness varies depending upon viability of the limb (see Rutherford Criteria) with paralysis being the end result of long ischaemic times
  • Paraesthesia
    • Sensory deficit along with pain are the most common symptoms present in ALI. The extent of paraesthesia is related to the location of the embolus and ischaemia time
    • Paraesthesia usually starts at the most distal aspect (toes first), before progressing along the rest of limb
  • Poikilothermia (Temperature)
    • The limb tends to be cooler compared to the contralateral side. However, as time goes on the limb takes on the ambient temperature.
    • It is important to note that chronically ischaemic limbs also tend to be cool at baseline; as such, it is important to compare the temperature of the affected leg to the contralateral side. 3 7 9

Conditions

• Aortic Dissection
  • This is a catastrophic vascular disorder characterized by a tear in the intimal layer of the aorta, leading to separation of aortic wall layers, creating a true and false lumen. It is important to delineate between Stanford Type A and B aortic dissections, as the management varies.
  • Type A requires immediate cardiothoracic surgery referral whilst Type B management is largely driven by signs or symptoms of end organ dysfunction. Type B can be managed either conservatively with medical management if the patient and the dissection are stable, or via surgical approach if there are signs of end organ dysfunction. Signs and symptoms of complications secondary to a Type B aortic dissection that will be encountered depend upon the extent of dissection. If there is concern for an aortic dissection then an ECG-gated CT Angiogram should be performed. 7 9
  • See: Aortic Dissection (Spontaneous, Suspected) pathway
• Aortic Occlusion
  • This is the obstruction of blood flow through the aorta due to either thrombosis or embolism. Although acute occlusion is quite rare (2-5 cases per million people per year) it is associated with high morbidity and mortality even with emergency surgery. The signs and symptoms depend on the location of the occlusion. In most cases acute thrombosis has been most significantly associated with atherosclerosis as the most common cause. Imaging should be performed via CT Angiogram (CTA) and the case referred to vascular surgeons. 10
• Visceral Emboli
  • Given that the majority of cases of acute lower limb ischaemia are secondary to embolus, some patients can also present with other complications of embolism, like visceral ischaemia
  • Presentation and management depend upon the organ that has been affected and the extent to which it has been affected (e.g. acute mesenteric ischaemia, liver/spleen infarct, kidney injury)
  • In the case of acute mesenteric ischaemia, patients are likely to require immediate intervention (laparotomy + resection, thrombectomy). However, in other scenarios (splenic or renal infarct), medical management may be appropriate.
  • If the patient is presenting with signs or symptoms that raise concern about a visceral embolus, CTA is recommended. The location of the embolus and patient status will play a role in ongoing management.
  • See Other imaging considerations for other recommendations for investigations to establish a cause of embolus 7
• Haemorrhage/Shock
  • Low cardiac output states are a rare cause of ischaemic lower limb and are usually seen in the presence of intra-arterial devices (extracorporeal membrane oxygenation, Intra-aortic balloon pump (IABP)) 7
• Thrombosed Popliteal Aneurysm
  • A popliteal aneurysm occurs when the popliteal artery undergoes focal dilatation and exceeds 50% of its normal range. Secondary to changes in blood flow dynamics within the aneurysm, thrombus formation can result.
  • Thrombosed aneurysm as the cause of ALI alters the treatment approach. Thrombolysis is usually the first line therapy as it is needed to help re-establish distal runoff for later bypass. As a result of chronic emboli from the popliteal aneurysm, the tibial vessels are usually occluded. Given that a bypass is the mainstay of long-term limb salvage, there needs to be a distal outflow target for the bypass to graft to.
  • If acutely thrombosed and imaging shows patent tibial arteries, then vascular surgery can consider bypass at time of presentation 7 9
• Spinal Cord Compression
  • This may mimic some of the symptoms of acute limb ischaemia such as pain, paralysis and paraesthesia
  • Usually, the nature of the pain in lower limb ALI is typically crampy or claudication-like pain, whereas the pain associated with nerve compression is more of a sharp, tingling pain
  • Additionally, spinal cord compression may have other symptoms not typical of ALI e.g. urinary incontinence
  • Usually the distribution of pain and paraesthesia will be different -
    • In lower limb ALI the distribution of pain is confined below the level of arterial occlusion, usually starting distally and progressing up the leg as time progresses
    • With nerve pathologies, the pain is more likely to be seen within the distribution of the nerve
    • Additionally, poikilothermic changes are only seen below the level of the occlusion
  • Spinal cord compression requires review by neurosurgical team who should also advise on the best imaging modality 10

Trauma

• In the trauma patient with lower limb ALI, it is important that if there is a known or suspected bony injury this should be reduced prior to doing a CT Angiogram (CTA) 6
• When scanning the lower limbs, imaging needs to include the aortic bifurcation as a minimum as well as both of the lower limbs, as this will help with surgical planning (i.e. endovascular vs. open)
• If there is a significant haematoma appreciated clinically then the CTA should include a delayed phase to assess for blush within the haematoma suggesting ongoing haemorrhage

Non-Traumatic 7

• Further management will largely be determined by the presence or absence of a femoral pulse
• If there is no femoral pulse present there is a need to consider and rule out aortic dissection, other aortic disease (e.g. aneurysm thromboembolism), or embolic causes See: Absent femoral pulse
• If a femoral pulse is palpable, assessment is required regarding the viability of the limb See: Rutherford Criteria

Imaging 7

• In a patient presenting with suspected ALI of the lower limb in the non-traumatic setting, imaging should include the aortic bifurcation and both limbs at a minimum, to allow optimal surgical planning when considering an endovascular vs. open approach
• Additionally, imaging above the bifurcation may also identify a cause of the lower limb ALI (e.g. Coral-reef atheroma, floating thrombus)
• To further assist in the surgical planning, there is a need to include a delayed phase in the runoff to assess for collaterals or slow perfusion
• It is also important to report on whether there is any filling of the main vessel via any collaterals whilst making comment on any aneurysmal or calcific disease within the iliacs, femorals and popliteals

Absent Femoral Pulse 5 7

• If there is no femoral pulse present, there is a need to consider and rule out aortic diseases including dissection, aneurysm thromboembolism and embolic causes See: Red flag conditions
• CT/MR are preferable over Doppler Ultrasonography (DUS) as DUS is suboptimal for obtaining diagnostic quality images of the supra-inguinal region. Additionally, in an acute context, the patient is unlikely to deal well with the pressure from the US probe. Furthermore, absence of fasting may further reduce image quality.
• Another benefit of using CT and MR is that they allow for more accurate assessment of any inguinal disease, which will help to assist with surgical planning
• In the setting where there is no CT/MR, chest X-ray to assess for mediastinal widening +/- pleural effusion can be used to help assess for aortic dissection. See: Aortic Dissection (Spontaneous, Suspected) pathway. In addition, plain Abdo XR and ultrasound of the abdomen may provide evidence of abdominal aortic aneurysm as a cause of embolus.
• There should be a low threshold for performing CT angiography (CTA) when there is absence of the femoral pulse in order to diagnose an intrathoracic or intra-abdominal cause. However, chronic limb ischaemia also needs to be considered.

Rutherford Criteria 8

• The Rutherford criteria were developed in 1997 as a revision of earlier standards for reports dealing with lower extremity ischemia
• A limb classified as viable is one that is not immediately threatened - there is no continuing ischaemic pain, no neurological deficit, adequate capillary circulation, and audible Doppler flow in a pedal artery
• Threatened limbs are those where there is reversible ischaemia in a limb that is salvageable without major amputation if arterial obstruction is resolved quickly. There are two levels within this -
  • Marginally threatened: may experience numbness and transient or minimal sensory loss; continuous pain is absent
  • Immediately threatened: persistent rest pain, detectable loss of sensation and/or any motor loss
• An irreversibly ischaemic limb is one that will predictably require major amputation or suffer significant permanent neuromuscular damage regardless of therapy. There is usually profound sensory loss and muscle paralysis with absent capillary refill or evidence of skin mottling. Neither arterial or venous signals are audible 8.

Magnetic resonance angiography (MRA) and Duplex Ultrasonography (DUS) can be used in the assessment of lower limb ALI:   5 7

• Magnetic resonance angiography (MRA) with contrast has been found to have a sensitivity and specificity of up to 97% and 96% respectively for detecting hemodynamically significant arterial stenosis, in comparison to digital subtraction angiography (DSA) 5
  • Benefits include: no artefact from calcium in small vessel walls; time-resolved sequences allowing visualisation of arterial and venous flows; allows for surgical planning
  • Main disadvantages: longer acquisition time and greater potential for artefact related degradation (motion and metal artefact) 5
• Duplex ultrasonography (DUS) can be used to help support the diagnosis for ALI. However, it is limited in its ability due to poor accessibility of vessels and shadowing from vascular calcifications. Hence, unless there is lack of other imaging modalities, there is no evidence to support its use as an initial imaging modality to diagnose ALI. 5
• Given morbidity and mortality associated with ALI, one of the most important aims of post-operative management is prevention of recurrent embolization. Given that the highest risk is from cardiac causes, investigations include -
  • ECG +/- Holter monitor
  • Transthoracic echocardiography (TTE)/Transoesophageal echocardiography (TOE)
  • CT Angiogram (CTA) of whole aorta if no intracardiac embolic source is identified 7

Medical Management of acute limb ischaemia 1 2 7

• As per established evidence, once there is suspicion of lower limb ALI patients should be commenced on a heparin infusion immediately, unless there are absolute contraindications
• The target therapeutic ranges for the heparin infusion can be guided by local protocols or vascular surgical team management

Surgical management of acute limb ischaemia

Surgical management is undertaken by vascular surgeons with urgency guided by Rutherford criteria. See: Rutherford Criteria The surgical method used is up to clinician preference of open thrombectomy vs. interventional therapies (catheter directed thrombolysis or mechanical thrombectomy). Imaging plus clinical findings will help the clinician make a decision as to the best path forward for the patient. 1 2 7