2. inflow; 3. graft; 4. outflow; 5. technique.
Patient
All vascular interventions must be preceded by a risk, benefit analysis that is shared with the patient and his/her family, taking into account the patient’s expectations and overall prognosis, the difficulty, hazard and predicted success of the procedure and the long-term prospects.
The analysis should cover all treatment options, whether conservative or palliative, endovascular or ablative.
Prior to any intervention, all available means should be implemented to optimise the con- dition of both patient and limb.
Cardiorespiratory, nutritional and renal assessment should be undertaken and any deficits corrected as far as possible.
Oedema, dermatitis, superficial ulcer- ation and deep sepsis all impair tissue viability and prejudice outcome.
As far as is practicable, these factors should be corrected prior to intervention.
Bacterial culture and sensitivity testing is essential, and any deep collections of pus should undergo preliminary drainage.
Adjunctive minor amputations should usually be postponed until after revascularisation is achieved, since incisions into ischaemic tissue always induce some degree of trauma-related local necrosis.
When surgical reconstruction is required, consideration must be given to the mode of anaes- thesia, whether local, regional, neuraxial or general.
This choice will normally be made with the advice of an experienced anaesthetic colleague, but it is worth remembering that all in- frainguinal arterial bypass procedures can, if necessary, be performed using local anaesthesia only.21 Prilocaine 0.5% is a useful agent, because of its rapidity of action and its low toxicity.
The femoral exposure can be undertaken using local infiltration only, using a 25-gauge nee- dle.
When distal anaesthesia is required, blockade of the femoral nerve should be included, performed percutaneously or by direct infiltration of the nerve through the femoral wound.
Usually additional local infiltration is needed to numb the medial thigh above the knee in order to enter the popliteal fossa.
It is then a simple matter to locate the sciatic nerve, lying between the vascular bundle medially and the belly of biceps femoris muscle laterally.
About 15 ml
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of 0.5% prilocaine is injected directly into the sciatic nerve, which can be felt bulging as it lies between finger and thumb.
Within 1 min of this manoeuvre the onset of sciatic blockade should achieve complete anaesthesia of the remainder of the limb for at least 6 h.
The author has encountered no complications from this technique in well over 100 applications.
Adjunc- tive sedation can be employed to alleviate anxiety or positional discomfort but may produce disinhibition and confusion, and so should be used selectively.
Inflow Success with infrainguinal bypass depends on adequate inflow to the CFAs and profunda femoris arteries (PFAs).
Whenever there is doubt over the adequacy of the femoral pulse, angiographic or ultrasonic aorto-iliac assessment is required so that any stenoses can be cor- rected, preferably by endovascular means.
Questionable stenoses can be evaluated by biplanar imaging or intra-operatively by papaverine testing.22 CFA disease is common in diabetes, and so extended open endarterectomy from the external iliac to the PFAs is needed in 30, 50% of cases.
Plaque in the profunda is best removed by retrograde squeezing using finger and thumb, since this is less likely to leave loose flaps.
Iliac angioplasty, endarterectomy or bypass can be performed synchronously with infrain- guinal bypass.
Extensive iliac atheroma with sparing of the aorta is not uncommon; if an- gioplasty fails or is contraindicated, this problem can usually be corrected by pulsion iliac endarterectomy.
This entails exposing the iliac arteries from the aortic bifurcation through a small iliac extraperitoneal incision, then cracking and dissecting the plaque within the intact artery, beginning distally, by vigorous squeezing using finger and thumb.
Once loosened in this way, the core of atheroma can be extruded distally in sections through the CFA arteriotomy.
The resulting endarterectomised iliac segment makes a reliable autogenous conduit which ap- pears resistant to infection and re-stenosis.
Heavily calcified iliac arteries are unsuitable for this manoeuvre and aorto-femoral or ilio-femoral bypass will be required.
In special circumstances (need for local or regional anaesthesia; hostile abdomen), extra-anatomical inflow procedures, such as axillo-femoral or cross-femoral bypass, may be considered.
When inflow enhancement is required, distal disease is likely to be less extensive, and so sequential distal bypass should not need to extend below popliteal level.
Graft Autogenous vein remains the best conduit for infrainguinal bypass reconstruction, exhibiting low thrombogenicity and infectivity, with optimal properties of flexibility and compliance.
It is a living graft, capable of repair and even, as shown when implanted in children, of growth.
The ipsilateral long saphenous vein (LSV) is the first choice when available, because it is conveniently located in the leg and offers more options of length and calibre.
It can be used in various configurations, either in situ (ISV), when valves and tributaries require extirpation,23 or as a fully mobilised conduit, when it can be implanted reversed (RV) or non-reversed (NRV).24 Randomised studies have shown no advantage for any particular configuration for vein grafts,25 and the technique with which the surgeon is most familiar should be selected.
When the LSV is partly or completely unavailable because of phlebitis, varicosity or previous excision, grafts can be constructed (in order of preference) from arm veins (cephalic, basilic, ulnar or linked
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256 PERIPHERAL VASCULAR DISEASE AND RECONSTRUCTION
configurations),26 the contralateral LSV or from the short saphenous veins (SSV) of either leg.
Conjoined lengths of vein make acceptable grafts and splicing together two or three lengths of good-quality vein is preferable to compromising by using narrow (<3 mm) or fibrosed phlebitic segments.
Venous valve extirpation is essential when using ISV or NRV configurations and is best performed after completion of the proximal arterial anastomosis.
The valvulotome (developed by Hall and by Cartier but now available in various disposable forms) is passed retrogradely through the free open end of the graft up to the proximal anastomosis and then slowly with- drawn, so that after the pulsatile column of blood has shut each valve in turn, the valvulotome can engage and tear each pair of cusps sequentially as it progresses distally.
One advantage of not reversing the LSV is that since the proximal to distal taper of the vein is more compatible with arterial anatomy, veins with diameters as small as 2.5 mm can be considered for grafting.
Consequently, vein utilisation is optimised.
Other advantages are that the graft can be tunnelled when pulsating, minimising the risk of kinking, and finally, should the graft undergo thrombosis at any stage, the absence of valves facilitates embolectomy.
Routing vein grafts through deep tunnels alongside the native arteries has the advantage of separating the grafts from skin wounds that, especially in diabetic patients, are susceptible to infection and breakdown.
Wound dehiscence can leave subcutaneous grafts exposed to the air, with disastrous consequences.
When the length of LSV required for bypass is less than the full length of the leg, it is preferable to harvest the proximal section, from groin down, in order both to take advantage of what is usually the largest and most healthy section of vein and also to minimise dissection in the distal part of the leg, where tissue viability is usually poor.
A careful search for vein, assisted in obese patients by duplex ultrasound scanning, will invariably reveal sufficient for infrainguinal bypass in patients presenting with limb ischaemia for the first time.
However, in some patients requiring secondary grafting, insufficient vein remains and alternative sources of graft must be considered if amputation is to be avoided.
In this situation, up-to-date and clear arterial imaging is important in strategic planning.
Com- bined endovascular and surgical options may still be feasible, and occasionally, total SFA endarterectomy may restore a useful conduit.
Unlike iliac endarterectomy, special instrumen- tation is required and late re-stenosis is problematic.27 Prosthetic grafts should be regarded as a last resort in infrainguinal bypass for limb salvage in the diabetic population.
When grafted to diseased arteries in the calf, the late results in term of patency and limb salvage are inferior28 and the addition of distal anastomotic cuffs29 or fistulae30 confers little or no benefit.
However, when used as the proximal component in a composite sequential femoral to popliteal to crural graft, in which the distal component is made of vein, prosthetic materials can yield satisfactory results.31
Outflow Optimal tissue viability is sustained by normotensive pulsatile arterial flow and unimpeded venous drainage.
Vascular reconstruction in diabetic PAOD should aim to restore this status.
This can be achieved only if the arteries perfusing the arteriolar bed of the foot remain patent and accessible.
When the obliterative process extends beyond the dorsalis pedis and plantar arteries into the pedal arch and the metatarsal and digital arteries, reconstruction is futile and healing of foot necrosis will not proceed, irrespective of the patency or otherwise of proximal bypass grafts.
The development of ischaemic necrosis in a diabetic foot despite the presence of a