A study of the chemical compositon and potential hazards of an antifoam substance used in intracardiac surgery.

Silicone fluids have been extensively used in certain heart-lung machines in order to remove bubbles produced by the mechanical oxygenation of the blood. The antifoaming technique involves the passing of oxygenated blood over a filmed surface or through a mesh or sponge treated with antifoam material. This is done to prevent air emboli which might occur if bubbles were allowed to enter the circulation. The method of oxygenation used in the unit in which this work was done is the DeWall type of bubble oxygenator. A cursory examination of a proprietary antifoaming material originally used in this type of oxygenator in Johannesburg showed the presence of considerable amounts of particulate material consisting largely of finely divided amorphous silica (about 200 A in diameter). Apart from the possibility of these particles aggregating to form still larger particles which could result in capillary occlusion, it is considered that the toxic action of the finely divided silica constitutes a very real hazard. The phenomenon of "silica shock " caused by the intravenous injection of finely divided amorphous silica of particle diameter 200-500 A into experimental animals has been known since the work of Gye and Kettle in 1922, and has since been widely confirmed by many workers. Work done in this laboratory (Harington and Sutton, 1961; Harington, 1961) leaves little doubt that silica of this particle size can, even at low concentrations, produce rapid and serious physiological defects. In view of the above evidence, a detailed chemical analysis was made of the antifoaming material being used here, and a simple procedure is described by means of which particulate material in antifoam preparations can be removed.