Ankle Brachial Indices

Doppler devices are used to determine ABIs or wrist brachial indices. Diagnostic accuracy has been reported to be as high as 95 percent, but sensitivity and specificity vary depending on whether the classification of abnormal is set at a ratio of 1.0 or 0.9. 1 H This test does not reliably detect nonocclusive arterial disease, such as intimal flaps and pseudoaneurysms. It can augment the clinical examination by objectively confirming the subjective impression of a diminished pulse in a patient under observation. To perform accurate ABIs, it is important to place the patient in supine position and measure the systolic blood pressure in all four extremities. To measure an ankle systolic pressure, a standard adult blood pressure cuff should be snugly wrapped around the ankle just above the malleoli. While using the Doppler flowmeter to monitor the signal from the posterior of the anterior tibial artery, distal to the cuff, inflate the cuff to a pressure approximately 30 mmHg above the systolic pressure to occlude flow temporarily. As the cuff is slowly deflated (2 to 5 mmHg/s), the pressure at which the Doppler flow signal is heard should be noted and recorded as the ankle systolic pressure. To assure accuracy, the upper extremity systolic blood pressure should be measured by using a Doppler flowmeter, as well. An ABI is then calculated by dividing the ankle systolic blood pressure by the greater of the two systolic upper extremity blood pressures. An ABI of greater than 1.0 is normal. An ABI of 0.5 to 0.9 is indicative of injury to a single arterial segment. An ABI of less than 0.5 is indicative of severe arterial injury or injury to multiple arterial segments. A difference of greater than 20 mmHg between the upper extremity blood pressures is indicative of upper extremity arterial injury. Underlying conditions, such as preexisting peripheral vascular disease or severe hypothermia, can also affect the accuracy of the ABI.

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