include data that would validate their categorisation and merely refer to the presence of rest pain or trophic change.
This has contributed to misconceptions over the differing roles of angioplasty and surgical reconstruction.
Factors that confound assessment include the effects of neuropathy and arthropathy on pain levels and of trauma, sepsis, neuropathy and venous disease in causing trophic change, particularly ulceration.
Ankle pressure measurement is fraught with the difficulties of interpreting sphygmomano- metric data in the presence of calcification of the leg arteries.
Sometimes, observation of the height that induces the reproducible disappearance of the pedal Doppler signal whilst slowly elevating the leg from the supine position may provide a more accurate measure (in cm H2 O) of perfusion pressure (provided this is below 50 mm Hg, otherwise the leg cannot be elevated sufficiently high to lose the signal).17 In future, it may be helpful to define a subgroup of patients with subcritical ischaemia in whom rest pain or trophic change is not associated with the expected two anatomical levels of arterial occlusion on imaging, or in whom toe pressure measurement exceeds 30 mm Hg.
In these patients, progression to limb loss in the absence of treatment is unlikely but vascular intervention, in combination with adjunctive measures, will improve symptoms and the prospects of healing.
Inspection of the affected limb should take into account swelling and pigmentation.
Sym- metrical woody swelling and pigmentation of both calves point to longstanding congestive heart failure, whereas when occurring unilaterally, deep venous incompetence should be sus- pected.
Uncomplicated superficial venous incompetence due to junctional or perforator reflux will give rise, on standing, to varicose veins (VVs) and purple telangiectases around the ankle.
Calf swelling and ankle ulceration seldom develop as a result of primary VVs and if present they warrant a search for additional contributing factors such as post-phlebitic incompetence of deep veins.
Buerger’s sign (ruddy hyperaemia of the foot in dependency, compared to deathly pallor and venous guttering on elevation) is a reliable pointer to the presence of CLI in non-diabetic patients.
It indicates loss of the normal sympathetically mediated vasomotor tone in an extrem- ity that has suffered prolonged hypoperfusion.
In people with diabetes, the onset of autonomic neuropathy may precede that of PAOD and this ‘autosympathectomy’ may mimic Buerger’s sign.
Similarly, combined motor and sensory neuropathy can predispose to the development of frictional, thermal or compression ulcers in feet that may not be suffering from ischaemia.
Portable (Continuous Wave) Doppler Ultrasound The usefulness of portable Doppler devices is not confined to sphygmomanometric measure- ment of ankle systolic pressures and the calculation of the ankle, brachial pressure index (ABPI).
Portable Doppler insonation of the ankle arteries with the patient seated upright and the legs dependent affords useful information on the distal vasculature, which, unlike pressure measurement, is not affected by arterial calcification.
Patency of the anterior tibial, posterior tibial and peroneal arteries can be estimated, and the subjective quality of the signal (damped, staccato or vigorous) in systole and diastole can be interpreted to provide a crude estimate of inflow and outflow.
If the deep plantar artery signal can be insonated (at the base of the first metatarsal space on the dorsum of the foot) then the effect on this plantar signal of manually occluding each of the ankle arteries in turn can be observed (peroneal artery compression is achieved by digital pressure postero-medial to the fibula, 5, 10 cm above the lateral malleolus).
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PRESENTATION AND EVALUATION OF PAOD IN DIABETES 253
The artery providing dominant perfusion to the foot is the one that, when occluded, produces disappearance or weakening of the plantar signal.18 Sometimes, failure to obliterate the plan- tar signal is observed whichever artery is compressed.
This may reflect good bidirectional perfusion, or possibly heavy arterial wall calcification making the arteries incompressible.
For all the above reasons, evaluating and weighing the contribution of PAOD when assessing trophic changes in the diabetic foot requires experience and judgement.
Therapeutic decision making will usually necessitate some form of arterial imaging.
However, if it has been es- tablished previously by non-invasive means that endovascular intervention is not practicable, or if circumstances demand urgent intervention, direct surgical exploration and reconstruc- tion can be undertaken on the basis of clinical and Doppler assessment only, with recourse to intra-operative on-table arteriography (OTA) as required.19
Duplex Ultrasonography Duplex ultrasound merges greyscale imaging and Doppler velocity analysis into a single probe, so that both anatomical images and haemodynamic information can be provided at whichever site is chosen, at low cost and with no hazard to the patient.
The only drawbacks are the expense and portability of the machines, both of which show steady improvement, and the training and expertise of the ultrasonographer, which are necessary to produce reliable and reproducible results.
In expert hands, duplex ultrasonography can provide comprehensive imaging and flow data throughout the peripheral vascular tree.
Vessel diameter, wall thickness, consistency and compliance can be assessed, as can the presence of luminal plaque, thrombus and venous valves.
In conjunction with this anatomical information, analysis of the Doppler spectrum enables calculation of the severity of stenoses and of the velocity and volume of blood flow.
Limitations on the quality of information obtained are imposed by intervening tissues or gas or the presence of heavy vascular calcification, and because the resolution of the equipment is insufficient for vessels less than 2-mm diameter.
However, in patients of normal build, it is possible to obtain diagnostic imaging and flow data from the aorta to the plantar arteries.
This should be sufficient for the planning of therapeutic interventions such as angioplasty or bypass reconstruction, so that this exercise can take place routinely in the outpatient clinic.
The need for contrast arteriography as a diagnostic tool has reduced further as a result of developments in computerised tomography and magnetic resonance imaging, and its main role now resides in therapeutic intervention.
Arteriography This topic is covered in the preceding chapter but mention should be made of the place of intra- operative OTA.20 In its simplest form, this consists of direct intra-arterial injection of contrast below a vascular clamp, with a sterile-wrapped X-ray plate placed under the site of interest.
Because of the temporary circulatory arrest produced by clamping, it is possible to flood the outflow bed with contrast so that good images can be obtained reliably, using simple portable equipment rather than image intensifiers.
A standard technique is to inject rapidly 50 ml of contrast into the proximally clamped common femoral artery (CFA) via a 19-gauge needle, and then wait for 5 s before making the X-ray exposure.
This technique almost invariably yields
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254 PERIPHERAL VASCULAR DISEASE AND RECONSTRUCTION
perfect detailed images, the exception being the acutely ischaemic white leg, when flow in the affected part of the limb may be too slow to admit sufficient contrast. The use of an image intensifier and a radiolucent remote-adjusting table in the operating theatre enables complex interventional manoeuvres such as stent deployment to be carried out through exposed arteries in a sterile environment, either alone or in combination with surgical reconstructive procedures.
SURGICAL RECONSTRUCTION When contemplating reconstructive arterial surgery, the mantra should be