Each doctor chooses the sclerotherapy solution that works best for him or her. I use 23.4% hypertonic saline (NaCl) for small spider veins that are actually in the surface of the skin and a chemical detergent called polidocanol for the larger reticular veins just under the skin that are the drivers of the spider veins.
The concentration of salt (NaCl) in the blood is only 0.9%, so 23..4% is really 'high test'.
Hypertonic saline disrupts the walls of the endothelial cells that line the veins by creating a big osmotic suction that causes the fluid in the cells to rush out.
The chemical detergent disrupts the endothelial cell walls chemically rather than osmotically.
I have found that for most patients it is necessary to treat both the spider veins and the feeding reticular veins.
Some doctors only use hypertonic saline for both and some only use a chemical detergent (there are several) in various dilutions.
What the doctor uses is less important than what the doctor knows.
