To the Editor.—In reference to the editorial comment by Dr Nathan Couch following the article on the Bentley blood filter (Arch Surg 112:222-225, 1977), a serious hazard of this filter, due to its foam, is retention of air in lower portions of this filter. If pressure is applied to the blood bag above the filter, an infusion of air from the filter into the patient is a great risk. There is no way to assure that all air from the filter has been replaced by either blood or a fluid primer. I have personally seen two times, in separate patients, sudden movement of quantities of air down the transfusions toward the patients. Each time, the filters had been primed according to instructions of the manufacturer, and had been running at a slow drip for several minutes before the pressure bag was inflated on the blood container.
Because of this