Comments on ABPI article.

Invited comment from David Carser

In my opinion, measuring ankle pressure in patients with ulceration is extremely difficult. In many cases, patients cannot tolerate the cuff inflation and it becomes impossible to get an accurate pressure measurement. Indeed, we had a case a few weeks ago where a patient's family threatened litigation when a haematoma developed after an aborted attempt at pressure measurement. In this particular case, the cuff could not be inflated beyond 50 mmHg because the patient was in such distress. As such I would not advocate measuring pressure over an ulcer. Placing the cuff at mid thigh or just below the knee will very often result in artefact - a pressure reading which is not reflective of the pressure in the ankle vessels.

With regards to the article by Vowden and Vowden, I totally agree that the 0.8 borderline does not appear to be based on definitive scientific fact. It does indicate some degree of arterial disease in all patients, but it does not in itself indicate whether full compression is or is not possible. The standard Doppler test does not take into account the fact that blood pressure in the lower limbs will generally decrease during exercise if arterial disease is present. This then leads to the question of whether or not there should be separate guidelines according to the patient's mobility. For example, a patient with a high systemic pressure (e.g. 200 mmHg systolic) who has moderate to severe arterial disease (e.g. ABPI of 0.6) will have an ankle pressure of 120 mmHg. This is much greater than the 40 mmHg of pressure that full compression will exert. It is plausible to suggest that if this patient takes little or no exercise, then full compression may be carried out with no resultant tissue injury. If, on the other hand, the patient is very active, the ankle pressure may fall by as much as 70% during exercise. This would result in an ankle pressure of 36 mmHg (0.18) and significant tissue damage could be expected.

If I am asked to assess a patient with ulcers I generally perform waveform analysis only. If the waveform is biphasic or triphasic with an estimated velocity of 50 or 60 cm/s, then I would say that there is little or no arterial disease. For all other patients, the opinion of a vascular surgeon should be sought. Such an analysis is very difficult if the Doppler equipment does not display the waveform or print it out. Unfortunately, many community Dopplers fall into this category.

The Doppler test is very good for identifying patients with a normal or very abnormal arterial tree. For patients with mild/moderate arterial disease, however, things are less clear cut. An ABPI of 0.8 cannot be looked at in isolation and factors such as arrhythmias and large limbs affect the calculated index and make pressure measurement difficult; the amount of exercise the patient takes will also have an affect and should not be excluded.

In summary, I agree with the authors that an ABPI of 0.8 does not mean much on its own. Other than indicating some degree of arterial disease, it does not mean that patients with an index of less than 0.8 will have ulcers of an ischaemic aetiology. Thus, the Doppler test is very clear at the two extremes - either a normal arterial tree or a very abnormal one. For patients who lie in between, we need to determine at which point full compression is ruled out and when is it safe to use lighter compression. I fully accept that criteria need to be set down but, as all patients are different, it is difficult to see how those with mild/moderate arterial disease can be grouped for the purposes of prescribing a particular bandage. A patient's activity level should also be an important consideration.