Chronic wounds are a debilitating and costly medical condition that often affects patients with additional comorbid conditions, which have detrimental effects on their healing or preclude application of specific treatments. Formulation of treatment and management therefore includes identification of underlying pathophysiology, risk factors and accurate wound diagnosis.
Following the aforementioned steps is often easier said than done, even in economically developed countries with well-funded and organised healthcare systems. One comprehensive study conducted in the UK on the quality of wound care found that 40% of patients with leg ulcers were not given an Ankle-Brachial (pressure) Index (ABPI or ABI) assessment (or it was unclear whether a recording had been taken). Additionally, about 31% of patients with venous leg ulcers included in the study were not receiving compression therapy (a staple conservative treatment method for venous leg ulcers).
Knowing whether a patient with chronic wounds also has peripheral artery disease (PAD or lower-extremity artery disease, LEAD for short) is of the utmost importance to the wound care or compression therapy provider, not only from the perspective of increased confidence (that they are giving proper treatment), but from a purely legal viewpoint (malpractice). Underestimating the severity of PAD or misdiagnosing wounds (ulcers) may have serious consequences. This brings us to another benefit of ABI—differentiating between the different types of leg ulcers.
Venous leg ulcers caused by chronic venous insufficiency (CVI) are by far the most common type of ulcers and represent 72% of all cases of lower-extremity ulceration, followed by arterial insufficiency ulcers (ischaemic ulcers), which represent 10–30% of diagnosed ulcers, and neuropathic ulcers that compromise 15–25% of wounds. The list of chronic wounds also includes lymphatic and infectious ulcers although they represent only a very small percentage of all cases: an extensive study of 555 patients with chronic leg ulcers found that only 2.5% of them had lymphatic ulcers.
Some types of wounds (arterial insufficiency ulcers) are considerably more difficult and expensive to treat than others (venous ulcers). However, this is not of immediate concern to wound care/compression therapy providers who (may) have to consult with other specialists (cardiologist, diabetologist, etc.) in regard to a patient’s medical record. Some patients might have ulcers of mixed aetiology, complicating treatment. The ABI assessment is invaluable in this regard as it can help not only differentiate between arterial and venous ulcers, but can reveal the extent of PAD and consequent appropriateness of compression therapy (modified compression levels) or the need for other methods. However, certain patients might require a different type of PAD/wound assessment.
When performing TBI measurement in addition to ABI?
The utility of ABI goes beyond diagnosing PAD and wound type and extends to overall cardiovascular health: it is recognised as an important indicator for improving the accuracy of cardiovascular risk assessment in addition to the FRS (Framingham Risk Score). However, for all its benefits it has one single major disadvantage—it is unusable (for diagnosing PAD) in patients with incompressible arteries, although it has specific/limited diagnostic value even in those cases. Such patients are usually those with diabetes, renal insufficiency and rheumatoid arthritis. According to the guidelines, they should be given ABI assessment first and if result is >1,4 the clinician should continue with TBI measurement. When using MESI ABPI MD or MESI mTABLET ABI, both assessment tools will also warn the clinician about incompressible arteries with a special warning. This is provided by a state of the art PADsense™ algorithm that analyses the shape of pulse waveforms giving an accurate indication of incompressible arteries.
Fortunately, there are alternative methods for diagnosing PAD and wound assessment that are as convenient and time- and cost-effective as the ABI. We are talking about the Toe-Brachial Index (TBI). The TBI is a fairly similar diagnostic procedure, as it involves blood pressure measuring, but there are three key differences. The site of lower-extremity measurement is different (toe in lieu of ankle), the pressure cuff is considerably smaller (with the addition of a photoplethysmograph sensor) and the result has no mathematical correlation with ABI. Namely, in contrast to leg arteries, those in the toe are rarely affected by calcification (most common mechanism contributing to stiff arteries), making them suitable for taking blood pressure measurements.
The TBI may be used in place of ABI in patients with excruciating pain in the lower extremities (due to ulcers or other causes).
Having both ABI and TBI assessment tools at their disposal gives the wound care/compression therapy provider the option of assessing a wide variety of patients, making them another important piece in the mosaic of preventive screening for PAD (in addition to personal/general physicians, cardiologists, diabetologists, etc.). Even more so if they are using an electronic health record (EHR) system or diagnostic devices with integrated support for EHRs, enabling easy storage of diagnostic results and convenient data sharing. However, from their perspective, they should be mostly concerned with association of TBI (and included parameters) with wound diagnosis, healing rates and other pertinent criteria.
Studies have shown that absolute toe pressures (greater than 30 mmHg) are a clinically significant predictor of wound healing potential, while low toe pulse wave amplitude is associated with a greater risk of amputation and death in patients with skin lesions and arterial disease. In connection with that, the TBI assessment is recommended for diagnosis of critical limb ischaemia (CLI) in suspected patients and is even more accurate in this regard than ABI. Lastly, the TBI has diagnostic value outside the realm of PAD and chronic wounds: low TBI is associated with increased risk of recurrent CVD in patients with type 2 diabetes and progression of diabetic nephropathy in type 2 diabetics.
The ABI assessment is an invaluable and versatile tool in wound care, but may fall short when evaluating patients with incompressible arteries, requiring additional assessment in the form of a TBI measurement.