In the treatment of acute to chronic injuries, wound care professionals have to perform a continuous clinical assessment to ensure the wounds they manage are healing satisfactorily. Among the most critical determinants of wound healing is tissue perfusion. An objective, yet non-invasive way of assessing blood flow to a wound site is the ankle-brachial index.
What Is an Ankle-Brachial Index (ABI)?
The ankle-brachial index is a test used to assess the patency of the blood vessels in the lower limbs. The test compares the blood pressure at a selected lower limb and an arm. Significant differences could be attributed to a pathological narrowing in the leg vessels typically due to peripheral vascular disease. The test may be done before or after an exercise involving the lower limbs to determine the extent of vessel obstruction.
Why Do an ABI?
Wound care experts may perform an ABI in patients with chronic wounds where there is a high suspicion of an underlying peripheral arterial disease. This category of persons might experience a slower rate of tissue repair compared to other persons who do not have any associated medical conditions.
What Category of Patients Require an ABI Assessment?
Wound care providers should do an ABI for patients with chronic wounds who also have a history of the following risk factors:
- Chronic cigarette smoking
- Persistently elevated blood pressure
- Elevated blood cholesterol
- Above 50 years of age
Components of an ABI
A standard ABI test consists of two components, quantitative and qualitative measurements. The quantitative aspect of the test assesses the ratio of the blood pressure in the arms and the ankles while the qualitative part is done using Doppler ultrasonography which analyses waveforms and the dynamics of blood flow. Wound care providers looking to optimize the healing outcomes in their patients will require both components to effectively guide individualized therapies.
Procedure for Conducting ABI
The procedure for conducting an ABI is straightforward, non-invasive, and painless. It also does not require any special preparation however it is advisable to wear comfortable loose-fitting clothes.
While the procedure itself will last for just a few minutes, the patient undergoing the test should ideally be asked to rest for at least 5 minutes. While lying on a flat couch, the blood pressure in both arms and ankles is measured and recorded using inflatable cuffs. An ultrasound device attached is also connected to the lower limbs being assessed providing images of the blood vessels in the area. The measurements obtained can subsequently be interpreted by a wound care physician.
Interpreting The ABI
The ABI is measured as the difference between the blood pressure readings gotten from the arms and the value recorded from cuffs placed at the ankles. Depending on the calculated number, wound care professionals can categorize their patients into different groups.
- Patients who have an ABI between 1 and 4 are considered unlikely to have a peripheral arterial disease that might affect the rate of their wound healing
- An ankle-brachial index between 0.91 and 0.99 is considered a borderline score. Patients who fall in this category may experience intermittent pain worsened by exercise and relieved by rest. This category of individuals requires further assessment using an exercise ABI.
- Calculated ABI values below 0.9 are abnormal and confirm a diagnosis of peripheral arterial disease. Patients with confirmed peripheral arterial disease are more likely to develop slow-healing, chronic wounds with poor outcomes. This group of persons should have further radiological assessments such as ultrasonography and angiography done to determine appropriate treatments.
Ankle-Brachial Index Testing: The Role of Vascular Testing Devices
Ankle-brachial index testing has been around for a while and the technology used in assessing this important determinant of limb perfusion has developed significantly. Vascular testing equipment incorporates ultrasonography, blood pressure cuffs, and sensor probes to accurately analyze blood vessel patency.
Apart from standard ABI testing features, vascular study devices also measure the velocity of blood flow, skin perfusion pressures, and transcutaneous oxygen levels.
Important Information for Wound Care Professionals
While the ankle-brachial index test provides an effective management tool for wound care managers seeking to optimize their patient outcomes, the limitations and contraindications must be understood.
Contraindications to ABI
In some cases, performing an ABI should be avoided entirely. Contraindications to the test include:
- Severe, debilitating pain in the legs
- Confirmed or suspected deep venous thrombosis (higher risk of clot dislodgement and embolism
- Painful, slow healing wounds or ulcers on the lower limbs
Limitations to ABI Testing
The ABI is prone to some inaccuracies as it often can’t pinpoint the exact location of narrowing within a blood vessel. Hence, using the ABI alone is not enough to accurately guide therapies in patients with chronic wounds.
Apart from peripheral arterial disease, several other conditions can also cause an elevated ABI. Rheumatoid arthritis, diabetes, and kidney disease can cause a high ABI. Consequently, wound care providers must do a careful clinical assessment in addition to an ankle-brachial index to guide wound management.