Page 181 - Libro vascular I

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PERIPHERAL VASCULAR ULTRASOUND
should be non-weight-bearing, and the patient can use a hand rail, or suitable alternative, for support. It should be noted that it is not uncommon for patients to feel faint during the examination (especially younger patients). Let the patient lie down immedi- ately if he or she feels unwell, and, if necessary, appropriate medical advice should be sought.
AUGMENTATION MANEUVERS AND
VENOUS REFLUX
Before considering the practical techniques used for scanning the venous system, it is important to have an understanding of the methods most com- monly employed for assessing venous valve compe- tency. These are calf compression, to augment flow toward the heart, and the Valsalva maneuver for examining the competency of the veins in the groin. In addition, proximal compression can be used to assess flow in perforators.
Calf compression
To assess the competency of the valves, the flow in the veins toward the heart should be temporarily increased or augmented. The easiest way to produce flow augmentation is to place a hand around the back of the calf and give a firm squeeze that is then quickly released. In our experience flow augmenta- tion should be sufficiently strong to produce a tran- sient peak flow velocity of 30cm/s in the main superficial vein trunks so that valve closure should be rapid on the squeeze release (Fig. 12.11). However, this velocity can be difficult to achieve in very small veins. If an inadequate calf squeeze is per- formed, flow augmentation may be very poor, and this can be a source of conflicting results among dif- ferent sonographers. For this reason some units pre- fer to use a rapid cuff inflater to inflate cuffs placed around the calf or thigh. The system inflates the cuff to a preset pressure before rapid deflation to provide reproducible compression. The disadvantage of this method is that it can be time-consuming and cum- bersome to apply the cuffs.
Valsalva maneuver
The competency of the proximal deep veins and saphenofemoral junction can be assessed with a
Augmentation of flow in the LSV following calf compression. There is a short duration of
normal retrograde flow below the baseline (arrows) as the venous valves close.
END
The Valsalva maneuver demonstrates competency of the proximal superficial femoral vein. There is a cessation of normal phasic flow during the
Valsalva maneuver followed by a surge of flow during expiration (END).
Valsalva maneuver. The patient is told to inhale deeply and then to push out and expand the cheeks without breathing out, while at the same time bearing pressure down on the abdomen. This pro- duces an increase in intra-abdominal pressure, thus increasing the venous blood pressure in the iliac and femoral veins. It is usual to see the common femoral vein distending during a Valsalva maneu- ver. Provided that the venous valves are competent, there should be no reflux across the sapheno- femoral junction or proximal superficial femoral vein during Valsalva testing (Fig. 12.12). There should be a temporary cessation of the normal
Figure 12.11
START VALSALVA
Figure 12.12