Light microscopic visualization of plasma intrusion into microporous hollow fibers

An immunohistochemical method has been developed to describe the pattern and extent of plasma intrusion into hydrophobic microporous membranes. Even though these membranes have very high calculated capillary intrusion pressures, they fill with plasma, sometimes during short-term use and routinely over the time spans characteristic of extracorporeal membrane oxygenation applications. It is not clear whether intrusion is widespread and caused by operating procedure or general properties of the membrane or localized and caused by defects in the membrane. The staining method reported here depends upon the fact that plasma proteins appear on pore walls only where the pores have been contacted by plasma. The selected plasma protein can be revealed, in sections viewed under the light microscope, by the immunospecific attachment of colloidal gold particles covered with an appropriate antibody. The particles are made visible by using them to nucleate precipitation of silver. Data are reported for Celanese polypropylene hollow fibers: 1) uniformly wetted with plasma; 2) locally intruded by centrifuging a plasma filled fiber covering a range of radii in a hematocrit centrifuge; and 3) locally intruded by wetting out the fiber with a "microdrop" of alcohol followed by saline, then plasma. In all instances, intruded and unintruded regions were distinguished clearly and unequivocally.