Sclerosant foam structure and stability is strongly influenced by liquid air fraction

Objectives To determine the effects of sclerosant foam preparation and composition on foam structure, the time course of liquid drainage, and foam coarsening. Methods Sodium tetradecyl sulphate (STS) and polidocanol (POL) foams were investigated in a range of concentrations (0.5-3%) and liquid-plus-air fractions (LAF; 1 + 2 to 1 + 8). Foam was injected into a vein simulation model (polyvinyl chloride tubing, inner diameter 3 mm, constant pressure 5-7 mmHg) filled with saline or blood. Liquid drainage, bubble count, and diameter were measured and documented by serial photography. Results Liquid drainage was faster in the vertical position than the horizontal one. In all variations, very small bubbles (diameter <30 μm) were generated initially that coarsened to form micro-foams (<250 μm). By 3 minutes mini-foams (>250 μm) and by 7.5 minutes macro-foams (>500 μm) were formed. Following injection, the upper regions of foam coarsened faster as liquid drained to the bottom of the vessel. Wet preparations produced significantly smaller bubbles. Low concentration POL foam produced significantly higher bubble counts and coarsened slower than STS. Conclusions Foam structure is strongly influenced by the LAF. Despite the initial formation of micro-bubbles in the syringe, mini- and macro-bubbles are formed in target vessels with time post-injection.