How to...Ten top tips for Doppler ABPI
21/11/11 | Assessment and diagnosis, Leg ulcers | Pauline Beldon
This practical guide offers tips on how to use a hand-held Doppler ultrasound for assessing peripheral arterial disease. Leg ulcers can have an extremely deleterious effect on a patient’s well being and quality of life. One part of a comprehensive assessment of a patient with a leg ulcer is to perform a Doppler ultrasound and examine the signals transmitted from the Doppler probe. However, this is a skilled procedure and forms only one part of the overall assessment.
Why doppler ABPI is useful
When employed by clinicians as part of a vascular assessment, the Doppler assessment system uses the direction and velocity of blood flow to ascertain whether the patient's arterial blood vessels are healthy or whether they have become diseased.
The brachial and ankle systolic pressures are measured by the clinician using a hand-held Doppler probe at the patient's brachial pulse, and the dorsalis pedis pulse on the dorsum of the foot. The ankle pressure is then divided by the brachial pressure to obtain the patient's ankle brachial pressure index (ABPI).
How to use Doppler ultrasound to measure ABPI
It must be stressed that a Doppler assessment alone does not constitute the entire assessment of a patient with a leg ulcer.
Preparation: The procedure should be performed by two nurses, if possible, one of whom should be a registered nurse trained in Doppler assessment.
Explaining the procedure: Before undertaking a Doppler assessment, the patient should receive a full explanation of the procedure so they are aware of what is involved.
Informing the patient: Patients should be told that they will need to lie as flat as possible, with one pillow under their head, for 10-20 minutes, because this removes the effect of gravity on blood flow [Fig 1]. Patients with breathing difficulties may not be able to lie entirely flat, in which case they should be asked to lie as low as is tolerable for them. Patients should be informed that they may experience some discomfort from the blood pressure cuff on the ankle and that they may stop the procedure at anytime if it is too painful.
Equipment needed: Clinicians must have access to the following:
- A Doppler ultrasound with an 8Mhz probe
- A sphygmomanometer (blood pressure meter) and the appropriate size blood pressure cuff for the shape and size of the patient's arms and ankles
- Cling film to cover the ulcer bed (this prevents the blood pressure cuff from rubbing against the ulcer bed directly, and prevents discomfort and contamination of the cuff)
- Ultrasound gel should be used as a contact medium between the patient and the Doppler probe.
The procedure: The blood pressure cuff should be applied to the arm above the patient's elbow [Fig 2]. The brachial artery is located (with the fingers), and then ultrasound gel applied. The Doppler probe is held between 45-70 degrees on the skin and moved around until the clearest signal is heard.
The blood pressure cuff should be inflated until the signal disappears, then the cuff slowly released while the nurse listens carefully for the signal to emerge. This is recorded as the brachial systolic pressure.This is then repeated on the other arm. The highest systolic pressure is used to compare against the ankle pressures.
Blood pressure: The patient's ulcer is then exposed and covered in cling film [Fig 3].
The nurse should then locate the patient's pedal (foot) pulse to assess the arteries [Fig 4].
Two of these four pedal pulses can be used:
- Anterior tibial artery
- Posterior tibial artery
- Peroneal artery
- Dorsalis pedis artery.
The two most common arteries used in the procedure are the dorsalis pedis and posterior tibial arteries, mainly because they are accessible when the blood pressure cuff is applied to the leg. The blood pressure cuff is then applied just above the patient's malleoli (ankle).
While the registered nurse applies the Doppler probe over the artery and listens for the signal, the other nurse slowly inflates the blood pressure cuff.
The registered nurse listens for the Doppler signal to disappear due to the artery's occlusion by the blood pressure cuff
The cuff is then slowly deflated and both nurses observe the pressure at which the Doppler signal reappears - this pressure is recorded for that artery. The registered nurse finds another pedal artery and the process is repeated. If the artery cannot be compressed by the blood pressure cuff, this indicates severe disease.
Blood pressure result: In theory, a patient's brachial blood pressure should be the same as the ankle.
Doppler ultrasound signals: In addition to recording the ABPI, the nurse should also be listening to the signals of the Doppler probe as these can impart useful information and are equally as valuable as the ABPI measurement.
This is represented by three sounds heard very quickly together (duh...duh...dum), as the blood runs through a healthy non-diseased artery.
This can be recognised as two sounds heard together (duh, dum ... duh, dum), this may be because the Doppler probe is not at the optimum angle. Again, it indicates a healthy artery.
A single, almost 'banging' sound (...dum! ...) indicates that the Doppler signal is unable to penetrate a diseased artery.
Diagnosis: In the absence of arterial disease, systolic pressure should be equal or exceed that in the arm (producing an ABPI of at least 1), whereas in arterial disease, the index will be below 1. An index of approximately 0.8 (or below) is considered a sign of significant arterial disease.
Leg ulcer assessment: The nurse performs a Doppler ultrasound as well as taking a comprehensive social and medical history.
1. Thomas S. Compression bandaging in the treatment of venous leg ulcers. World Wide Wounds 2010. Available at: http://www.worldwidewounds.com/1997/september/Thomas-Bandaging/bandage-paper.html (accessed 27 May, 2010).
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