The Role of Vascular Testing In Amputation Prevention
While there are several causes of lower extremity amputation, one of the most prevalent is Peripheral Artery Disease (PAD). PAD is a circulatory condition that results from the narrowing of the arteries and subsequent reduced blood flow to the limbs. If left untreated, it can lead to limb loss. So, how important is vascular testing to limb salvage and prevention of unnecessary amputations?
What is Vascular Testing?
Vascular testing is a systematic, non-invasive approach that checks the blood flow in the arteries and veins using ultrasound and other emerging technologies. Methods for vascular assessment of limbs include the Ankle-Brachial Index (ABI) test, duplex arterial ultrasound, transcutaneous oximetry, magnetic resonance angiography (MRA), and spatial frequency domain imaging (SFDI).
Exercise testing using lower extremity exercise has been the “gold standard” for screening for arterial diseases. However, many patients with PAD and those who have had prior amputation have difficulty in doing this type of exercise. In such a case, arm exercise ergometer is a safe and effective alternative for the detection of artery diseases.
Ankle-Brachial Index (ABI) Test
Also called toe pressure test, or toe-brachial index (TBI). An ABI test is performed to determine the level of tissue perfusion in a limb by comparing the difference in systolic blood pressure at the brachium of the ankle.
It uses inflatable cuffs placed on the legs at different levels to gauge circulation and measure blood pressure in the arteries. A low ABI is an indication of reduced circulation to the lower limbs because of blocked or constricted blood vessels.
Transcutaneous Oximetry (TcO2)
This vascular test measures the oxygen content of a limb to assess perfusion. It’s especially essential in determining the severity of blood flow deprivation due to advanced PAD. To perform the procedure, a vascular specialist first removes any wound dressings, cleans the site with alcohol, and applies an electrically-conductive gel onto the limb.
The electrodes in the gel warm the subcutaneous layer of the skin to improve oxygen flow for a more accurate reading. A sensory apparatus is used to measure the number of oxygen molecules present, while a radiometer offers a visual aid for transcutaneous oxygen measurement.
Clinicians can use it to assess circulation, monitor treatment, and evaluate outcomes. TcO2 causes minimal discomfort to the patient and the test can be done within 15 minutes.
Duplex Arterial Ultrasound
This test uses high-frequency ultrasound to assess the circulation and structure of arteries in the affected limbs. The Doppler ultrasound creates a color map of blood flow through the vessels while B-mode ultrasound creates a 2D representation of the artery structure.
A clinician uses a small handheld probe (transducer) that generates ultrasound waves which reflect off bones and tissues and are converted into electrical signals displayed on a monitor. The transducer is pressed against the patient’s skin while in a prone position.
Magnetic Resonance Angiography (MRA)
An MRA test is an advanced imaging study for detecting PAD with a high level of specificity. This non-invasive approach uses modern computerized image processing techniques to create 3-dimensional imaging of the arterial structure of the limbs.
Spatial Frequency Domain Imaging
Spatial frequency domain imaging (SFDI) is a modern technique for the assessment of arterial insufficiency that is becoming popular over the last decade. This vascular test is based on the principle that beamed light reflected off arterial structures and tissues provides information about their state.
SFDI estimates levels of tissue perfusion by analyzing absorption, scattering, and fluorescence. It measures tissue hemoglobin and tissue oxygen saturation to assess the degree of circulation in the lower extremity to a high degree of accuracy.
The Importance of Vascular Testing
A diagnostic test is the only sure way to establish whether an arterial disease is treatable or manageable. Unfortunately, many decisions to perform a limb amputation rest on the judgment of clinicians and are not necessarily an outcome of a thorough vascular assessment.
Tests such as simple checks for pulses can help determine poor blood circulation, but such a test isn’t enough to offer a clear diagnosis. Vascular testing fills the gap and goes a long way in limb salvage.
A case study conducted in a group of patients with PAD found that about 18.2% did not receive a vascular diagnosis before amputation, pointing to the underuse of health services. Further, in one-third of these patients, major amputation probably could have been avoided.
Such a statistic shows how crucial a vascular test can be in amputation prevention. If these patients had gone through vascular testing, there’s no doubt that some of the limbs could have been saved by alternative treatment methods such as angioplasty and atherectomy.
If you are a member of a group that is at risk of vascular disease, you should always consult with your doctor to know whether vascular testing is an option for you. This includes diabetics, PAD patients, people over 50 years, obese people, and those with a history of high blood pressure.
The approach to be used in vascular testing depends on several factors. For instance, many diabetics have falsely elevated segmental pressures (ABI) that may mask an ischemic foot. In such a case, measurement of the toe/brachial index might be useful. Overall, vascular testing shouldn’t be a one-off approach, but should be done on an ongoing basis.