Page 180 - Libro vascular I

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ANATOMY OF THE LOWER LIMB VENOUS SYSTEM AND ASSESSMENT OF VENOUS INSUFFICIENCY
giving a hard, ‘woody’ feel to the area. The develop- ment of an ulcer is sometimes initiated by a minor injury or abrasion that fails to heal. It is important to remember that some venous ulcers are also associ- ated with arterial disease, and patients with mixed venous and arterial ulceration pose a challenging diagnostic problem for the vascular laboratory. It is therefore routine practice to measure the ankle– brachial pressure index (ABPI) in all patients with venous ulceration to exclude a significant arterial component. However, in some situations it may be impossible to measure the ABPI due to pain, and a subjective assessment of the pedal Doppler signals will have to suffice. A layer of cling film is ideal for wrapping around areas of ulceration to protect the ulcer and to keep the pressure cuff clean.
Historically, it was thought that venous ulceration was primarily due to deep venous insufficiency fol- lowing valve failure, post-thrombotic syndrome or failure of the calf muscle pump, resulting in deep venous hypertension. However, more recent studies (Scriven et al 1997, Magnusson et al 2001) demon- strated that a significant number of patients with ulceration have superficial reflux alone, with the deep veins being competent. Therefore, ligation of the relevant superficial vein junction, with or with- out stripping of the superficial vein, results in the healing of the majority of ulcers due to the reduc- tion in venous hypertension. The role of perforator ligation remains controversial, but there is evidence that chronic venous insufficiency is associated with an increase in the number and diameter of medial calf perforators (Stuart et al 2000). Some vascular laboratories are asked to mark the position of incompetent perforators with the aid of the duplex scanner prior to surgery.
Varicose ulcers caused by significant deep venous insufficiency are not usually treated by the ligation or stripping of superficial varicose veins, as the underlying deep venous hypertension will not be corrected. Instead, the use of compression bandag- ing, which reduces edema and venous hypertension, has proved to be an effective method of healing ulcers. Different grades of compression bandaging can be used depending upon the clinical situation (Lambourne et al 1996). However, an ABPI 0.8 is required for the application of four-layer compres- sion dressings, in order to avoid arterial compromise in the tissues under the bandaging. This can be a
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serious complication and can lead to limb loss in extreme cases.
PRACTICAL CONSIDERATIONS FOR
DUPLEX SCANNING OF VARICOSE VEINS
The purpose of the scan is to assess the compe- tency of the superficial and deep veins and identify the cause of the varicose veins. At least half an hour should be allocated for a bilateral vein scan. Adopting a logical approach to the examination is useful, as this reduces the amount of time required for the assessment. The patient should be asked the fol- lowing questions before starting the examination:
● Have you had any previous varicose vein treatment, either by surgery or by injection sclerotherapy? It is not uncommon to find that the request card has omitted previous clinical details, and the patient may have undergone some form of treatment in the past. This may be evident on the duplex scan.
● Have you ever had a deep vein thrombosis or severe leg swelling? If the patient has had a deep vein thrombosis, there may be chronic damage of the deep venous system, causing deep venous insuf- ficiency or obstruction, which may be the cause of the current symptoms.
The sonographer should also visually examine the position and distribution of the varicose veins, as this can provide a clue to their supply. There is no prepa- ration required before the scan, but the legs should be accessible from the groin to the ankles. It is nec- essary to position the patient so that the feet are sub- stantially lower than the heart in order to generate sufficient hydrostatic pressure to assess the compe- tency of the venous valves. If the patient is lying completely flat, there is very little pressure differen- tial between the central venous system and the legs. Therefore, any reflux occurring after a distal calf squeeze may be of such low velocity that it is not detected. Common positions in which to assess a patient include the supine position on the examina- tion table with the whole table tilted feet down by an angle of at least 30° (reverse Trendelenburg posi- tion). Alternatively, the patient can sit on the edge of the examination table with the feet resting on a stool. Many units perform the examination with the patient in a standing position. The leg under investigation