Foam Microsclerotherapy
Foam
In order of increasing the efficacy and safety of sclerotherapy, techniques like tAir-block and foaming of the sclerosant vave been introduced. In recent years many different techniques of foam production have been proposed.
The definition of a sclerosing foam (SF) is a mixture of gas and liquid sclerosing solution (detergent type) with tensio-active properties. The gas must be well tolerated or physiologic and the bubble size less than 100 1-1. The behavior of sclerosing foam is different when in jected, compared to the action of a liquid solution.
The use of air and a sclerosing drug in combination was described in 1944 by Orbach: the air block technique. The sclerosing solution was added to air, simply shaking the syringe or the vial, with production of large bubbles which had a high air: liquid ratio and with increased efficacy only for smaller veins. The method was not suitable for larger veins where after the injection the air positioned itself along the upper side of the vein, impeding contact with endothelium.
Further advancement came then from subsequent innovations: Cabrera et al published an article about the production of a complex foam with CO2 and an unknown tensio-active agent; In 1997, Monfreux described the MUS method that generated a simple foam with air by means of a glass syringe; Mingo-Garcia developed a special device to produce foam with compressed air; in 1998 Benigni and Sadoun published a method to produce a very short-lasting foam in a plastic syringe and in 1999 Tessari presented an original method of foam production with two disposable syringes and a three-way tap.
In 2000 Frullini published a different method that generated foam in a vial of sclerosing solution, provided that the vial has a rubber cap. The method was derived from the ideas of Lorenzo Tessari, and it utilises the vortex effect that a disposable syringe and a relatively large connector can create into the vial with a fast push and pull action on the piston. With respect to the Monfreux method, Tessari's and Frullini's method may produce a foam with higher consistency, whereas the durability of the MUS foam is longer. Unfortunately long durability does not always mean good therapeutic effect because the latter is more correlated to high consistency for a minimum period of time in order to obtain optimal sclerosis.
The Monfreux Method
This method was initially reported by Monfreux in 1995, but he claims he has used it for many years. The foam is produced in a glass syringe filled with 0.3-0.5 ml of liquid. The tip of the syringe is then closed with a sterile plug and the operator must hold tension on the piston until 2-3 ml of foam are generated. A little training is required before using the technique to prepare a good quality foam. This SF is quite long lasting (even 3 h in vitro, probably up to 20 min in vivo) but it has a low consistency due to the relatively large diameter of the bubbles. Moreover, we demonstrated that the same technique and quantity of liquid can produce very different SF because it is very difficult to standardize this technique.
This technique has a higher rate of side effects. This is probably because of the large size of the bubbles which easily spread along the vessels. Patients sometimes experience dizziness or a confused state. These are self-limited side effects and they are of short duration. Even if the true nature of this symptom is still debatable (liquid drugs may generate similar symptoms), the best treatment is prophylaxis, asking the patient to lay on the office bed for about 5 min after the injection and avoiding excessive tension during foam generation in order to produce smaller bubbles. Another limitation with the Monfreux technique is the use of glass syringes, which may be a problem for doctors and patients and which require additional work for sterilization.
The Cabrera Method
In 1997 Juan Cabrera reported about his experience with a special foam prepared with POL or STS and an unknown tensio-active agent. The gas used was not air but CO2 (or a different physiologic gas). Cabrera recently published the details and results of his technique (up to 7 years follow-up with excellent results). The technology for developing this SF is der development in the UK and it will probably be available in the future.
The Tessari Method
In 1999Tessari described an original method that uses two disposable syringes and a three-way tap to produce a high-quality foam with purified sodium tetradecylsulfate (STS). By this method the SF was produced by means of disposable material; later a dedicated kit was produced, in order to provide a prefilled syringe with sterile air. This made it possible to avoid the problems of using "nonsterile air" for injections and to avoid using glass syringes. This foam is very compact and with a very small bubble diameter. Another advantage is the ability to reconstitute the foam if the treatment session takes time to be completed.
Results
The overall result of foam sclerotherapy has been very good with an immediate success rate of 93.3% with the Tessari method (clinical and instrumental follow-up at 20-180 days).
Discussion
Since the introduction of air block technique in sclerotherapy in 1944 its effectiveness has always been reported but reproducibitikty could not be attained. . Experimental experiences on animals in 1934 by Harkins and Harmon and in 1937 by Richardson et al. demonstrated the safety of a small amount of air injected in a relatively small period of time. In 1997 Henriet revised these experiences and analyzed the passage of air in the general circulation in different conditions as extracorporeal circulation or during the gas-echocardiography used to study septal defects. In this technique an embolus of 5-10 ml of air is injected to demonstrate interatrial or interventricular defects. In his experience in 3200 sessions with a sclerosing foam (Monfreux's method) for minor varicosities, Henriet reported only a few minor complications and six side effects, possibly related to the use of air (three transient visual disturbances, two headaches, and one vomiting).
Recent findings confirm that the use of an air sclerosing foam is as safe as liquid solution in terms of major complications (eg, pulmonary embolism, deep vein thrombosis, ischemic lesions, allergy, etc.), but it is our opinion that the total amount of foam injected per session should never exceed 3 ml, apart from very selective indications (ie, large saphenous stems, obese patients) and a minimum interval of 7 days between sessions should be respected. Future enhancements of the methods will allow the use of a larger amount of foam, and recent experiences of a few Australian colleagues (unpublished data) seem to favor large quantities of SF.
The advantages of sclerotherapy using SF are based on several theoretical and practical considerations. When the injection of a liquid sclerosant is performed, the concentration in the syringe is related to the dilution that will be obtained in the vein; it must be a high concentration because mixing with blood is unavoidable, leading to the action of a diluted drug on the endothelium. If the threshold level is reached, the sclerosing effect will start. This process is related to the concentration in the syringe, the volume of blood in which the drug will be diluted (which can be hardly judged from the diameter of the vessel), and the speed of injection.
When SF is injected the physics of the injection are completely different. The foam is made of tiny bubbles of gas covered by the tensio-active liquid. The latter is pure and the quantity of sclerosing drug in 1 ml of foam is related to the size of bubbles: with little bubbles, the foam will be highly active; large bubbles form poorly active foam. We should look at the sclerosis with foam as an active dynamic process; the interaction with endothelium forms links with cellular mem branes and the higher the dose of drug per ml of foam, the higher the number of links between the SF and en dothelium. Large bubbles of foam, even if it seems to last more in vitro, has a weaker effect because there is less sclerosing drug available for this linkage.
If we use SF, endothelial cells of large and minor veins should probably respond to the sclerosing agent at a given concentration in the same manner. The same concentration of sclerosing agent can be suitable for large and small veins (even saphenous stems of 6-10 mm have been successfully treated with low-concentration SF of purified STS) and this finding could change the decision-making process of sclerotherapy, due to the fact that lower concentrations and low doses of liquid could be used.
We can identify several peculiar properties of foam: adhesiveness, compactness, long lasting, echovisibility, enhancement of sclerosing power and reduction of drug doses and concentration. In fact, the SF adheres to the venous inner wall and with proper maneuvers it is possible to push the foam downward in collaterals and upward, close (not too close) to deep veins with low risk of propagation. The compactness is related to the size of the bubbles, and when this size is sufficiently small, no (or poor) mixing with blood occurs in the vein in the first moments after the injection; this results in a closer relationship between the injected dose and the final result.
The durability of the foam is related to bubble size, the tensio-activity of the liquid solution, and the conditions in which the SF is formed and kept. The air contained in the SF explains the echovisibility of the foam: in our opinion this is one of the biggest advan tages when performing duplex-guided sclerotherapy, because it gives an enhanced view of the process, bet ter identification of the injected flow, and the chance to push the SF in a safer way near the sapheno-popliteal or sapheno-femoral junction, or within the collaterals under direct visualization.
The increase in vein spasm generated by each injec tion is commonly reported by foam users and it may sometimes be dramatic. Another property of SF is the reduction of drug doses: 0.4-0.5 ml of liquid solution can be transformed in 2-2.5 ml of foam. Higher amounts of foam can be produced from the same quantity of liquid according to the volume of air used, but the best dilution with the Tessari method, in our experience, is 1 to 4 or 1 to 5.
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