This refers to significant narrowing of the arteries distal to the arch of the aorta (any arterial disease other than the coronary arteries or aorta). Critical limb ischaemia is the severe manifestation of the disease, defined as PAD leading to the presence of:
Ischaemic rest pain
Acute limb ischaemia refers to a sudden decrease in lower limb perfusion, related to thromboembolic disease.
The main pathophysiology process is atherosclerosis. This leads to narrowing of blood vessels and impairment of blood flow, most commonly in the lower limbs. The end result of this is impaired substrate delivery to these tissues (particularly oxygen). Claudication is a clear manifestation of this, as there is often a well defined level of activity (and hence oxygen utilisation) which leads to the symptoms, as utilisation outsrips supply.
Much PAD is asymptomatic. The most common symptom is intermittent claudication:
Pain in a muscle group on exercise
Fatigue, aching, cramping in nature
Rapid improvement with resting
Clarification of a specific ‘claudication distance’ can be useful.
Ischaemic rest pain occurs without exertion, and often worse at night. It may be relieved by hanging the limb out of bed.
Buttock claudication and erectile dysfunction may indicate aortoiliac disease - Leriche syndrome.
Ulcers or tissue changes may be present.
The Edinburgh Claudication Questionnaire can aid with detection.
The history should be investigated for the closely associated diseases: coronary artery disease, cerebrovascular disease, smoking related respiratory disease, diabetes and renal disease. Risk factors should also be explored.
Ulcers - punched out
Beurger’s Test Elevate the leg for a period of time, then lower it off the bed. If positive ( a sign of severe disease) it will go pale when elevated, then hyperaemic after lowering.
ABPI Ankle brachial pressure index. Measured using a doppler. The ratio is compared to that in the upper limb. 1 is normal <0.9 suggest arterial disease <0.8 moderate <0.5 severe This can be very useful for:
This may involve:
exploring the nature of the disease - imaging
Assessing for risk factors
U&E - renal dysfunction common
ECG - disease common Imaging
Broken down into:
Modification of lifestyle risk factors. Stopping smoking is the most important. Increasing exercise, can help develop collateral blood supply, achieved by careful pushing of the claudication distance. Supervised exercise classes can be useful.
Addition modification of risk factors is key factor here:
Additional factors include:
Antiplatelet therapy - clopidogrel shown to be more effective than aspirin (CAPRIE trial)
The goals of surgical intervention include:
Improve ischaemic rest pain
Aid tissue healing
Improve quality of life
Prevent limb loss
This may be broken down into:
Endovascular interventions often involves passing a wire along the artery past regions of stenosis. Dilation, sometimes with stent formation, restores patency. There are risks from the vessel puncture, as well as risks of distal thromboembolic complications, and of recurrent stenosis. Not all anatomy or disease characteristics are suitable for such an approach. There was no notable difference shown in the BASIL trial in outcomes in patients surviving up to 2 years, although patients with surgical intervention had better outcomes beyond this time frame. Centres with high numbers of endovascular procedures also did better.
Bypass surgery is a major operation. Regions of stenosis can be bypasses with synthetic or natural (e.g. vein) methods. Vein grafts are preferred in many cases as they demonstrate better 5 year patency rates. The key features that are considered with a bypass are for their to be an adequate supply (inflow), and adequate run-off (somewhere for the blood to go). Forms that this bypass surgery may take include:
The prevalence increases with age, with much disease probably being undiagnosed and asymptomatic. The long term prognosis of patients with this disease is poor, due to the number of overlapping risk factors for complications. The 5 year survival for patients with critical limb ischaemia is only 50-60%. Even those without have a 5 year mortality rate of 10-15%, and a 20% rate of non-fatal CVS events e.g. MI. This includes a high perioperative risk of mortality, as high as 17%.
As noted, these are high risk patients, and surgery for PAD is high risk in nature. These patients have a high risk of perioperative complications, particularly relating to CVS events and coronary artery disease. Surgical interventions can be required for acute ischaemic limbs (time critical) or urgent intervention for critical limb ischaemia, thus providing challenges on the ability for optimisation.
This should aim to establish the nature of the disease and associated diseases. Modification of risk factors should aim to be undertaken here. Investigations should include:
Functional assessment can be challenging because of the limitations that PVD can impose on activity. Dobutamine stress echo can be useful to assess for significant ischaemic heart disease, the main benefit being its high negative predictive value. Lee’s revised cardiac risk index tool can be useful for risk assessment.
Optimisation of the patient’s medical care should be undertaken where time allows. This is balanced against the risks of excessive delay in the case of significant ischaemia, and a period of 6 weeks is described as suitable for optimisation. The multiple risk factors described above should be optimised. Examples include:
There is no evidence strongly favouring one technique over another. Close attention to giving a ‘good anaesthetic’ is probably more important for outcome. This includes:
Minimising CVS disturbance
Optimising respiratory status
Appropriate fluid therapy
Regional anaesthesia has some theoretical advantages of effective analgesia and minimal respiratory impact, but may be limited in cases of anticoagulation. Patients may have a neuropathic component to their pain from chronic ischaemia.
Full AAGBI monitoring is essential. A 5 lead ECG configuration can help with increased sensitivity for cardiac ischaemia. Continuous arterial monitoring may be required in cases of major vascular work but in some smaller cases may not. Central venous access is often not needed unless there are specific other indications. Blood loss in longer operations can be steady and so may result in relatively large volumes. Cell salvage may have a role in more complex procedures (e.g. redos) to reduce the risk of requiring allogenic transfusion.
Postoperative MI is the most significant cause of death in these patients. Continuation of the intraoperative principles is an important component of minimising this risk. Higher risk patients may warrant a critical care environment to ensure that these features can be achieved. Cardiac medications should be continued throughout the operative period. Simple and opioid analgesia can provide appropriate analgesia for a good number of patients postop when combined with local anaesthesia at the end of the procedure.