Automated ankle brachial pressure index measurement devices to detect peripheral arterial disease in people with leg ulcers
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2 The diagnostic tests
Clinical need and practice
The condition
2.1 Leg ulcers are slow-healing wounds that usually develop on the inside of the leg, just above the ankle. It is estimated that about 1 million or 2% of adults in the UK have a leg ulcer (Guest et al. 2020). Around 65% of leg ulcers are venous meaning they are caused by a problem in the blood flow in the veins. Treatment involves using compression such as bandages or stockings. Strong compression therapy can disturb the arterial blood supply in the leg, so it should not be offered to people with peripheral arterial disease.
2.2 People with peripheral arterial disease may not have any symptoms, but it can lead to serious complications such as chronic limb-threatening ischaemia. In this condition, loss of blood supply to the leg causes tissue to die and there is a significant risk of losing a limb and premature death.
Care pathway
2.3 The National Wound Care Strategy Programme (NWCSP) recommendations for lower limb ulcers advise using the ankle brachial pressure index (ABPI) to screen for peripheral arterial disease in people with leg ulcers alongside a full clinical assessment.
2.4 People with leg ulcers may present in primary care. NWCSP guidance recommends immediate care for ulcers should include cleaning, application of emollient and a simple low-adherent dressing. In the absence of any 'red flag symptoms' (such as infection, symptoms of sepsis, ischaemia, suspected deep vein thrombosis or skin cancer), mild graduated compression should be applied until full clinical assessment and ABPI measurement can take place. However, if there are not enough staff able to do manual Doppler assessment, delayed assessment may lead to longer periods without compression or sub-optimal compression. Clinical experts noted that in practice some practitioners are uncomfortable applying even mild compression without ABPI measurement. People should be offered a full clinical assessment within 14 days of initial presentation, but clinical experts noted this is a challenge and it can take substantially longer in some areas.
Potential value of the technologies
2.5 Automated ABPI measurement devices may be easier to use than manual devices. This may reduce the time needed to complete the assessment and make ABPI measurement more comfortable for people with leg ulcers. A further potential benefit could be a reduction in the time to assessment and consequently treatment for people with venous ulcers when there are not enough staff able to do manual Doppler assessment.
The interventions
2.6 Automated ABPI devices include Doppler-, oscillometry- and plethysmography-based devices. Doppler-based devices use a Doppler probe and provide Doppler waveform signals as an output. Oscillometry-based devices assess oscillations in the vessel wall and plethysmography-based devices assess blood volume changes. These devices either estimate blood pressure directly or use a pressure cuff to help with the measurement. Diabetes, rheumatoid arthritis, systemic vasculitis, atherosclerotic disease and advanced chronic renal failure can cause calcium build-up and hardening of the arteries which can make ABPI measurements appear misleadingly normal. Clinical experts highlighted the value of information provided by Doppler waveform signals in these situations. Devices that do not provide Doppler waveform signals may provide information about the quality of arterial circulation in the ankles. But there is uncertainty about whether these alternative outputs are comparable with Doppler waveform signals.
2.7 There are 7 automated devices for measuring ABPI and assessing arterial circulation (see Table 1).
Automated device | Technology | Component | Resting period needed | Cost (£ per unit) |
|---|---|---|---|---|
BlueDop Vascular Expert | Doppler | Hand-held Doppler device | No rest | 4,995 |
boso ABI-system 100 | Oscillometry | 2 arm cuffs 2 ankle cuffs | 5 minutes | 3,187 |
WatchBP Office ABI | Oscillometry | 2 cuffs | 5 minutes | 2,145 |
WatchBP Office Vascular | Oscillometry | 2 cuffs | 5 minutes | 2,445 |
MESI ABPI MD | Plethysmography Oscillometry | 3 cuffs | No rest | 2,499 |
MESI mTABLET ABI | Plethysmography Oscillometry | 4 wireless cuffs | 5 minutes | 2,847 |
Dopplex Ability | Plethysmography | 4 dual-chamber cuffs | No rest | 3,937 |
The comparators
2.8 Currently, ABPI is measured in people with leg ulcers during initial clinical assessment. Blood pressure is measured using a hand-held Doppler ultrasound probe and a sphygmomanometer with a manually inflated cuff. The ABPI is calculated manually. People with leg ulcers need to lie down before and throughout the test. The test takes up to 1 hour and may be painful and uncomfortable for people with leg ulcers.
2.9 ABPI measurement is typically done by district or community nurses at a person's home, care home or a leg ulcer clinic, or by practice nurses at GP practices. This is when they are trained in doing both the full clinical assessment and ABPI measurement. In some parts of the country, leg ulcer clinics are in use, or are being implemented. Some clinics may already do, or increasingly do in the future, initial ABPI assessment. In areas without enough practitioners trained to do manual Doppler measurements, people may have initial ulcer care and then be referred to specialist vascular services for the full clinical assessment.
2.10 The reference standard for detecting peripheral arterial disease is imaging such as duplex ultrasound, magnetic resonance angiography or CT angiography. However, these would not be used as part of the initial clinical assessment in practice.
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