Page 144 - Libro 2

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PART 3 — PERIPHERAL ARTERIAL
AB
Figure 8-1 Correct transducer position for the insonation of pedal Doppler signals. A: Insonation of the posterior tibial artery. B: Insonation of the dorsalis pedis artery.
to body habitus. The same applies to the ankle level, where 10-cm cuffs are usually appropriate. For the measurement of an ankle–brachial index, cuffs are placed around the ankle level and around the upper arm. For a multilevel lower extremity examination, cuffs are also placed around the upper arm as well as at thigh, calf, and ankle levels. For upper extrem- ity evaluations, cuffs can be placed around the upper arm, forearm, and wrist levels.
The measurement of a systolic pressure begins with obtaining a Doppler signal distal to the cuff. Figure 8-1 illustrates the correct positioning for in- sonating pedal Doppler signals. Care must be ex- ercised not to compress the underlying artery with the Doppler transducer (Fig. 8-2), particularly at the posterior tibial, dorsalis pedis, and radial arteries because each courses just above an adjacent bone. While listening to the Doppler signal, the pressure in the cuff is inflated until the audible signal is no lon- ger heard. If the Doppler signal output is also being displayed on a monitor or a strip-chart recorder, this will be seen as a pulsatile waveform (when a Dop- pler signal is audible) and thus will change to a flat line (once the Doppler signal is no longer audible). The pressure should continue to be inflated 20 mm Hg above this point. The cuff is then slowly deflated
at a rate of approximately 3 mm Hg/s. The pressure at which the audible Doppler signal (or the pulsatile Doppler waveform) returns is the systolic pressure at the level of the cuff. An incorrect pressure measure- ment can be recorded when a patient is arrhythmic, whereupon several measurements should be made from which to calculate an average systolic pressure.
Figure 8-2 Inappropriate transducer pressure is applied to this pedal artery. Such pressure may compress the artery.