How ultrasound guided foam sclerotherapy (UGFS) works
Sclerotherapy works by injecting a sclerosant liquid into a vein which kills the vein wall. Foam sclerotherapy is a modification of this liquid sclerotherapy. The reason for this modification is explained below.
For sclerotherapy to be effective, there are many more issues than just simply injecting a sclerosant liquid into the vein. In the first instance, the right substance needs to be injected in the right concentration. If it is too weak, it will not kill the vein. If it is too strong, it runs the risk of damaging tissue outside of the vein. Therefore the correct strength of sclerosant solution must be chosen and this will vary on the size of the vein.
When we are looking at the size of the vein, the most important measurement is the vein diameter. Actually what we would really like to know is the thickness of the vein wall as this will tell us how many cells have to be killed by the sclerosant if we are to destroy the vein. A thicker vein wall needs a stronger sclerosant solution to penetrate it, whereas a thinner vein wall has fewer cells and therefore will be killed by a weaker sclerosant solution. Unfortunately, the ultrasound machines that are currently available are not able to quickly and easily measure the thickness of each vein wall accurately. But by measuring the diameter of the vein, which can be measured quickly and easily on ultrasound, we can estimate the thickness of the vein wall.
A very small vein, perhaps half a millimetre in diameter, will only have a couple of cells in the whole of the vein wall and will be very thin. A small vein perhaps 1 to 2 mm diameter will have a thicker wall perhaps getting to some 5 or 10 cells thick. As the vein gets bigger in diameter, the vein wall also gets thicker and therefore the distance any sclerosant has to penetrate increases.
Because of this, it is not surprising that when research has been performed on the very best techniques of sclerotherapy or foam sclerotherapy, veins less than 3 mm in diameter do very well with the correct sclerotherapy technique. Veins greater than 6 mm do very badly and are rarely successfully closed in the long-term.
Once we have understood that it is the vein wall thickness that is important in sclerotherapy, and it is the diameter of the vein on ultrasound that can indicate this to us, the understanding of sclerotherapy becomes easier.
To get the best treatment for sclerotherapy, the vein needs to be completely filled with the sclerotherapy solution, allowing maximum contact and penetration of the sclerotherapy substance into the vein wall. In very small veins, liquid sclerotherapy can be injected as this will push the blood out of the way leaving the vein full of only a sclerotherapy solution.
Unfortunately when veins get larger than roughly 1 mm in diameter, the amount of sclerotherapy solution that needs to be injected to push all of the blood out becomes too great, and could result in too much sclerosant being injected into the patient. However the result of injecting too little of the sclerosant is that it just mixes with the blood rather than pushing it out of the vein. As blood is a living tissue, the blood cells get killed by the sclerosant forming a clot also known as thrombus or, if caused by sclerotherapy, “sclerothrombus”.
The fact that the sclerosant effect was wasted on the blood means that it is impossible that the vein wall has had a maximum effect from the injected sclerotherapy solution. Therefore the vein will be inadequately treated and will be full of a sclerothrombus that causes inflammation, often being seen as a hard tender lump in the leg, which often causes a discolouration – initially red and then brown, which might be permanent.
In the past, doctors have tried to reduce this by elevating the leg when injecting the veins to try and empty the blood away from the vein being injected. Others have put tight bandages on the veins before injecting them to try to get the same result. Other techniques have also included injecting air first to push the blood out of the vein and then liquid sclerotherapy to follow. None of these techniques are particularly successful.
In 1935 a technique of mixing a sclerosant solution with air was developed to make a ‘foam’. When this was injected into veins, the foam pushed the blood out of the vein, allowing the sclerosant in the bubble walls to have a full effect on the vein wall itself. Unfortunately this technique was lost to be “reinvented” in 1985.
Since 1985, there has been a lot of interest in research in developing foam sclerotherapy to treat veins. The principle remains the same – the foam is made and injected into the target vein under ultrasound control. The foam pushes the blood out of the vein and has its full effect on the vein wall, killing the cells of the vein wall. The foam lasts between 1 and 2 minutes after which the foam bubbles pop and blood can come back into the vein. This of course would be a disaster as blood in a dead vein would clot causing a thrombus. This would lead to painful inflammation and discolouration just like a sclerothrombus above. Therefore to prevent this happening, as soon as the foam sclerotherapy is injected into the vein, the leg is bound with a tight bandage keeping the blood out of the vein and then a graduated support stocking. Once in place, these are not removed for 14 days and nights as this is the length of time it takes for the vein wall to die and scar to be permanently closed.
Finally, it is of course dangerous to inject air into the bloodstream. Air is 80% nitrogen and nitrogen does not dissolve easily in the blood. If air is injected into the bloodstream as part of the foam, the nitrogen can travel to the heart and, in one in four people, passes into the left side of the heart and from there can go to the eye or brain. Therefore experts making foam sclerotherapy do not use air when they make foam, but rather use carbon dioxide or combinations of carbon dioxide and oxygen. Carbon dioxide is the fastest dissolving gas and therefore causes the least problems when injected into the blood stream and oxygen is metabolised by the body and therefore is taken away safely.