Non-invasive methods of venous diagnostic
Non invasive diagnostic methods for venous disease were developed for screening, for quantifying lesions, and for hemodynamic studies. Both the general practitioner and the specialist must, at their different levels, know the significance of the various vascular tests, their indications and limitations, so they can avoid having to prescribe unnecessarily invasive and costly tests.
Because venous disease is is so manyfold it is somewhat more difficult to evaluate than arterial disease and requires experience and closer evaluation. This means venous tests are much more operator-dependent and require specific clinical skills, particularly in the evaluation of CVI. CVI can be the result of obstruction to venous outflow or reflux, or to a combination of the two. Clinical examination and diagnostic techniques therefore aim to establish which conditions are present. The anatomical location of the alterations must be found and the reflux and/or obstruction must be identified.
There are many simple, rapid and efficient tests available, with good cost-benefit ratios. The diagnostic procedures listed summarily below reflect those set out in the Procedure Operative for the Vein Clinic.
List of diagnostic procedures
Diagnostic
- Main investigational techniques Ultrasound
- Continuous-wave (CW) Doppler
- Duplex scan
- Echo(color) Doppler (ECD).
- Radiographic imaging
- angio-computed tomography (CT) scans
- angio-magnetic resonance (MR) scans.
- Plethysmography
- Quantitative photoplethysmography
- Phlebography (venography).
Diagnostic process
The aim of the investigation is to check whether there is venous reflux or superficial and/or deep venous thrombosis. Depending on the findings, the diagnostic pathways divide. The deep venous circulation should always be examined.
Evaluation of venous reflux
Reflux is usually assessed with the patient standing. The examiner holds the probe which is placed at the origin of the small or great saphena. The left hand makes swift compressing motions, releasing the vein distally. These maneuvers are essential, especially for CW Doppler, which does not visualize the vein being probed. Once the probe is centered on the vein the patient executes a prolonged standard Valsava maneuver during which reflux is assessed. The following are usually taken as normal and pathological limits (Table III).
Table III: Normal and pathological reflux.
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Normal saphenus veins: Dilated but competent saphenous vein: Saphenous valves incompetent: |
reflux up to 0.5 s reflux more than 0.5 s but less than 1 s reflux more than 1 s |
The vein can be followed distally, identifying the axis of the reflux and establishing whether the valves are incompetent throughout the vein or only in parts. This is important as a basis for establishing how far distally the saphena needs stripping.
ECD is easier to interpret than CW Doppler, and provides more information on the morphology of the long saphenous vein, such as its diameter, caliber and the competence of valves in the ostial collaterals and any accessory saphenous veins. It gives an excellent view of the ostial and preostial valve. When examining reflux in the short saphenous vein ECD is useful to study the vascular anatomy of the popliteal area, helping establish the exact origin of the popliteal vein, rather than a high start of the long saphenous vein from the superficial femoral vein; it also confirms competence of Giacomini's vein, and whether reflux comes from a popliteal perforating vein.
Briefly, therefore, the procedure is similar for ECD and CW Doppler examinations. Both provide the information needed, i.e. the duration of reflux, in seconds, during the Valsava maneuver, which should always be clear from the documentation supplied by these techniques. ECD provides morphological data, so one can "reconstruct" the vascular anatomy and establish the diameter of vessels, giving a useful preoperative hemodynamic map and serving to assess post-surgical or post-sclerotherapy recurrences. ECD shows accurately when reflux comes from an incompetent perforating vein, but CW Doppler cannot give this information clearly and should therefore not be used for this assessment.
Ultrasonography serves to study a single superficial or deep axis, identifying it on the basis of the anatomical location. The origin and axis of the reflux can be established completely. This examination also gives a repeatable, reliable quantitative finding (the duration of reflux during a standard Valsava maneuver). As ultrasonographyselectively evaluates one district at a time, it cannot be used for an overall functional investigation of damage due to a single venous reflux.
Venous plethysmography measures changes in venous blood volume in the legs, to evaluate overall venous function. Three plethysmography techniques are currently in use: photo-pulse-plethysmography/reflected light rheography (PPGIRLR), strain gauge plethysmography (SGP), and air plethysmography (APG).
PPG/RLR uses photo sensors attached to the skin to measure filling of the cutaneous vein network. SGP uses extensimetric sensors (elastic sensor straps) to measure changes in the circumference of the leg at the point where they are applied. The APG sensors are inflatable leg cuffs which measure changes in the total venous volume of the leg. By taking measurements in various positions and during various maneuvers it is possible to evaluate the following:
- venous outflow (slowed if there is occlusion);
- total venous reflux (degree of valvular incontinence);
- the efficiency of the muscle pump in the calf (venous drainage during exercise and the speed of refilling after exercise).
These measurements can be done in baseline conditions, or using a tourniquet to exclude the superficial veins, to give separate evaluations of the superficial and deep veins and forecast how removal of the saphena might affect venous return. A 3 cm cuff is recommended, inflated to 100 mmHg. PPG offers the advantage of a quantitative result, in seconds - indicating the venous refilling time - that gives an overall picture of the functional impairment of venous return due to reflux.
Quantitative Computerized PPG: procedure
For this quantitative investigation the baseline signal is automatically adjusted and a precise evaluation can be made of the parameters connected with refilling time after the muscle pump test, and with the signal amplitude. The probe is fixed about 8 cm above the internal malleolus, with a bi-adhesive ring. The patient sits comfortably with his feet firmly on the ground. There should be an angle of about 110° between the patient's trunk and his thighsllegs. The muscle pump test is the most widely used and involves 8 dorsal extensions of the tibio-tarsal joint in 16 seconds. At the end of the test the patient sits still for 30 seconds.
Modern equipment is programmed to emit sound signals for the dorsal extension of the foot and to mark the filling period. The venous refilling time (To) is expressed in seconds, and classified as follows (Table IV).
Table IV. - Venous refilling time.
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1) Normal 2) Pump inadequate grade 1, mild 3) Pump inadequate grade 2, moderate 4) Pump inadequate grade 3, severe |
more than 24 s between 24-20 s 19-10 s less than 10 s |
These computerized instruments also assess the power of the venous pump (Vo) but this findings is not yet sufficiently standardized for use in diagnosis.
Venous plethysmography has the following applications in clinical practice:
a) to measure and document the degree ofimpairment of the various venous functions (obstruction, reverse flow) and follow them over time;
b) to quantify the involvement of the superficial and deep veins and predict the hemodynamic effects of superficial vein surgery;
c) to study and document the hemodynamic effects of different surgical options and validate new technics.
One limitation of PPG is that it may be difficult to distinguish superficial and deep venous reflux, or reflux from incompetent perforating vessels.
Phlebography using injection into a vein of the foot is no longer used to assess venous reflex, as ECD is preferred. Phlebography should be kept for patients with a history of venous thrombosis, those who have undergone surgery, and have unexplained recurrences (surgical technic not known), and cases where ultrasonography gives unclear results. Some centers still use "varicography" to investigate recurrences after surgery or sclerotherapy, especially in the popliteal cavity or for incompetent veins, particularly if there are several.
Radiographic imaging is the second level requested by a specialist, and completes the ultrasonographic examination, helping establish the site and nature of the lesion, and evaluate the pathology, especially in cases involving the deep circulation. It is indicated for angiodysplasia, where angio- MR is preferred. It cannot yet replace phlebography.
The microcirculation is investigated using the following techniques:
- laser-Doppler;
- capillaroscopy;
- microlymphography;
- interstitial pressure;
- 02 and CO2 partial pressure.
Recommendations
Ultrasound examination is useful to demonstrate reflux, identify its origin and follow its axis cranio-caudally. Grade A
After clinical examination, the main screening method for CVI should be CW Doppler. Grade B
Echo- Doppler and echo color-Doppler should be used to establish the location and the morphology of the problem, and preoperatively. Grade A
Phlebography is only needed for a small number of patients who have anatomical anomalies or malformations, or when surgery or endovascular therapy on the deep venous system is indicated. Grade B Plethysmography should be considered as an additional quantitative test. Grade B Investigations of the microcirculation are only indicated in selected patients, mainly for research purposes. Grade C