Diagnostic Testing For Patients With

The rational treatment of patients with chronic venous insufficiency (CVI) and its sequelae requires the use of noninvasive studies to determine the anatomic and hemodynamic characteristics of the patient's venous system. The treatment of lower extremity arterial insufficiency (AI) clearly is guided by the use of ankle/brachial index and Doppler waveform information to define the hemodynamic effect of anatomic lesions, which are clearly illustrated by artieriography. This information, in addition to the history and physical examination, allows the clinician to determine which patients require intervention, and the optimal choice of intervention when needed. In the treatment of CVI, this same information, the anatomic sites of venous dysfunction, and the hemodynamic importance of this dysfunction, are required to allow treatment plans to be formulated and optimal results to be achieved. Selecting surgical therapy without a knowledge of which vein segments are abnormal is essentially blind surgery and cannot result in optimal results.

Duplex Ultrasound

Imaging techniques using ultrasound combined with Doppler interrogation of the venous system have been validated as sensitive methods of diagnosis of deep venous thrombosis. Important information for patients with CVI that would be detected with this technique includes the presence or absence of venous obstruction or other changes typical of previous DVT. This information will help to determine whether the patient's CVI is due to obstruction, reflux, or both (pathophysiology). However, the assessment of reflux is limited to qualitative information. Valsalva maneuvers or manual compression may be performed with the patient supine to look for reflux in the common femoral vein or saphenous vein, but these are not reproducible, quantitative tests of venous reflux. However, the presence of outflow obstruction in the iliac veins and/or IVC often can be detected looking at flow patterns, phasicity, and respiratory variation in the common femoral vein. In addition to an examination of the deep and superficial systems, the perforator veins are carefully examined for evidence of incompetence.

Unfortunately, the accuracy of duplex at identifying incompetent perforator veins is somewhat controversial. Most authors agree that perforating veins demonstrated on duplex to allow flow in the reverse direction with manual augmentation maneuvers, from deep to superficial system, are incompetent. The hemodynamic significance of incompetent perforators is not well established, because most occur along with either deep or superficial reflux, and the contribution of each to venous insufficiency is not usually known. The vascular technician must be experienced in the typical anatomic location of perforators and expert in their imaging to allow a proper evaluation of perforator incompetence.

Second, venous reflux in the deep and superficial venous systems is evaluated with the patient in the standing position using duplex ultrasound and either manual compression or a rapid inflation/deflation system to elicit reflux. The measurement of valve closure times after release of distal compression is described in detail in Chapter 18. In studies of normal volunteers and patients with CVI, a normal valve closure time of <0.5 has been defined. Systematic interrogation of the common femoral, superficial femoral, popliteal, Greater Saphenous, and lesser saphenous veins is conducted, allowing an anatomic map of venous reflux in the limb to be constructed.

Using this information, the clinician can determine the etiology, anatomy, and pathophysiology of CVI for the patient. For example, the patient that has superficial and perforator disease may be differentiated from the patient with superficial and deep reflux, allowing alternate treatment plans to be selected. Although duplex evaluation provides detailed information on the anatomy of venous disease, it cannot define the importance of anatomic abnormalities in the venous function of the limb. Clearly, one patient with gross reflux in the saphenous vein will have no resultant symptoms, whereas another patient may have class 6 CVI with an active ulcer from saphenous reflux alone. The clinical assessment of the severity of CVI is often subjective, so testing that allows objective measurement of the hemody-namic performance of the lower extremity venous system would greatly assist with patient assessment and treatment decisions.

Photoplethysmography

Plethysmography is defined as the determination of changes in volume, and various techniques of plethysmog-raphy have been evaluated in the noninvasive examination of the venous system. Photoplethysmography (PPG) utilizes a transducer that emits infrared light from a light emitting diode into the dermis. The backscattered light is measured by an adjacent photodetector and displayed as a line tracing. The amount of backscattered light varies with the capillary red blood cell volume in the dermis. Using this technology and provocative limb maneuvers, an assessment of the venous system is obtained. A representative PPG tracing is reproduced in Figure 55.1 and illustrates the primary measure obtained, the refill or recovery time (VRT), which represents the time required for the PPG tracing to return to 90% of baseline after cessation of calf contraction. PPG does not produce a quantitative measure, but the refill time has been found to correlate closely with ambulatory venous pressure (AVP) measurements. The use of an above knee tourniquet inflated to 50 mm Hg has been described to differentiate the contribution of the deep and superficial venous systems to venous reflux.

Limbs affected with CVI typically have a much shorter VRT than normal limbs. As such, PPG can provide a relatively simple measure of whether venous insufficiency is

Photo Plethysmography Venous
FIGURE 55.1 Diagrammatic representation of hemodynamic values obtained from air plethysmography. VV = venous volume, VFI = venous filling index, EF = ejection fraction, RVF = residual volume fraction. Reprinted with permission from Cristopoulos et al, J Vasc Surg. 1987, 5:148-159.

present or not. However, the technique can vary depending on the site of photosensor placement and the small sample area obtained. Placement near the site of a varicose vein or perforating vein may affect results, and patient compliance with the maneuvers required can be problematic.

PPG measurements have not been proven to be a strong discriminator of the severity of CVI. Nicolaides and Miles reported that normal limbs were well identified by a PPG refill time of greater than 18 seconds with their protocol. Abnormal limbs with CVI consistently had a refill time of <18 seconds. However, in the abnormal group, PPG refill time could not differentiate between degrees of CVI, with similar PPG refill times obtained in patients with AVP measurements ranging from 45 to 100 mm Hg. Therefore, PPG is a poor test for assessing the results of venous corrective surgical procedures.

In summary, PPG is a reasonable measure of the presence or absence of CVI that is best used when no further information concerning the venous hemodynamic situation is desired. However, if information concerning the severity of CVI, or an evaluation of the improvement after venous surgery is required, a quantitative test will be more useful.

Air Plethysmography

Air plethysmography (APG) utilizes a technique to improve on the shortcomings of PPG and other types of plethysmography that have limited sampling areas. It employs a low-pressure air-filled cuff measuring 30 to 40 cm in length that is applied to the lower leg, allowing quantitative evaluation of volume changes of the entire lower leg from knee to ankle. The technique is fully described in

Chapter 5. Briefly, the patient lies supine initially with the leg elevated and supported at the heel allowing the cuff to be applied to the lower leg. The cuff is inflated to a pressure of 6 mm Hg to provide snug apposition to the limb without compressing the superficial veins. A baseline volume in the supine position is obtained with the patient resting. The patient then moves to a standing position supported by a walker to remove weight from the tested limb. The volume tracing gradually increases until a plateau is reached. The patient then performs one calf contraction/tiptoe maneuver followed by rest. A subsequent series of 10 tiptoe maneuvers completes the test procedure. The test protocol may be repeated with the use of a thigh tourniquet to isolate the deep venous system from the superficial system.

In Figure 55.1 the data calculated from the tracings obtained are illustrated. The venous volume (VV) is the difference in limb volumes obtained in the resting and standing positions. The venous filling index (VFI) is calculated by measuring 90% of the VV and dividing this volume by the time the limb requires to refill to 90% of the VV after moving to the standing position. Expressed in cc per second, VFI measures the average filling rate of the dependent leg and is slow in normal limbs. The volume of blood ejected with one tiptoe movement divided by the VV gives the ejection fraction (EF), and the limb volume remaining after 10 tiptoe movements divided by the VV gives the residual volume fraction (RVF).

In 1988, Christopoulos et al. described the use of APG for evaluation of normal limbs and those affected with CVI. A VFI <2 ml/second was associated with clinically normal limbs, and increasing levels of VFI were associated with more severe symptoms (see Table 55.1).1 The VFI is believed

TABLE 55.1 Prevalence of the Sequelae of Venous Disease in Relation to VFI in 134 Limbs with Venous Disease Studied with Air-Plethysmography

VFI, ml/sec

Swelling(%)

Skin Changes(%)

Ulceration (%)

<3

0 0

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