Effect Of Position On Varicose Geometry

For the following sections, refer to Figure 13.4.

Standing

For a standing patient with a superficial varicosity of 2 cm in diameter, the final concentration at a distance from the injection site of 10 cm (4 inches) is 30 times lower than the initial concentration. Doubling the initial concentration serves only to double the final concentration, which will still be 15 times weaker than the concentration in the syringe. In other words, if 1 cc of a 3% solution is injected, the final concentration at the endothelial surface is 1% at a distance of 1 cm from the injection point, 0.5% at a distance of 2 cm, 0.25% at a distance of 4 cm, and 0.2% at a distance of 5 cm (2 inches) from the injection point. As we shall see, this means that it is very difficult to achieve sclerosis of a large vessel by injecting detergent sclerosants with the patient in a standing position: if the highest available concentration is injected, the dilution factor may still drop the final concentration below the threshold of effectiveness within 1.5 inches from the injection site.

Supine

What about the supine position? Varicose vessels that bulge when the patient is standing may collapse when the patient is supine, but duplex ultrasound readily demonstrates that the veins are not empty of blood. Both varicose and normal vessels contain a significant volume of blood with the legs extended in the supine position. A bulging varicos-ity that has a diameter of 2 cm in the standing position may have a diameter of 1 cm in the supine position and of 0.5 cm or less when the legs are elevated as high as possible. With such a patient in the supine position, injection of 1 cc of a 3% solution leads to a final concentration of approximately

1.7% at a distance of 1 cm and a concentration of about 0.6% at a distance of 5 cm (2 inches). This supine technique limits dilution enough to allow successful sclerosis of large vessels using detergent solutions, as long as sufficient concentrations and volumes of sclerosants are injected. The only problem is that if an injection of sclerosant at a high initial concentration is made directly into a perforating vessel, so that sclerosant flows directly into the deep system, dilution within the deep vessel will still permit Zone 1 and Zone 2 endothelial injury for a short distance within the deep vein. This can lead to deep vein valve damage and chronic venous insufficiency, to deep vein thrombosis, and to life-threatening pulmonary embolism.

Legs Elevated

In contrast to the standing and supine positions, when a patient lies supine and the legs are raised vertically so that they are well above the central circulation, most superficial varices collapse to the point where they no longer contain any significant volume of blood. Repeating this calculation for a patient in this position, injection of 1 cc of a 3% solution leads to a final concentration of 2.5% at a distance of 1 cm from the injection, and a final concentration of 1.6% at a distance of 5 cm (2 inches). In fact, the final concentration will still be above 1% at a distance of 10 cm from the injection site. Because the superficial varicosity is collapsed, there is very little dilution with distance as long as the sclerosant stays within the floppy-walled varicosity.

With the increasing use of foamed preparations of sclerosants, another factor must be taken into consideration since the dilution of these medications is significantly reduced. Although all the preceding considerations still play an important role, the distance over which a foamed sclerosant remains at high concentration is markedly increased. Therefore, smaller volumes and/or lower original concentrations should be employed when using a foamed sclerosant.

What happens when sclerosant passes through into normal vessels? Although flow measurements reveal little or no spontaneous flow through varices and smaller superficial veins when the patient is in the leg-up position, a substantial intravenous volume and a substantial rate of flow still persists in the deep veins and in normal larger superficial veins, which have less collapsible walls. This difference in volumes and flow rates may be exploited to cause damage that is almost perfectly localized to superficial varices. If an elevated, empty varicose vessel is perfused with a concentration of sclerosant so low that it is just barely sufficient to cause endothelial injury, then any further dilution will reduce the concentration below the threshold of injury. Because larger superficial vessels and deep vessels continue to carry a volume of blood in the leg-up position, any sclerosant passing into these vessels will immediately be diluted to a safe and noninjurious concentration, sparing the endothelium of vessels that we wish to preserve. Injection of this threshold concentration directly into a perforating vein (or even directly into a deep vein) will not cause any deep vein injury.

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