The technique of modified ultrafiltration is a more efficient application of the concept of ultrafiltration during cardiopulmonary bypass. It has been shown to be superior to the conventional method of ultrafiltration.
The method can save considerable quantities of donor blood by returning not only the red cells, but also the white cells, platelets, and clotting factors back to the patient, components which otherwise would be discarded. The elevation of the hematocrit made possible by this method after bypass will permit an “acceptable” hematocrit to be achieved when temperatures become normal after ultrafiltration. The return of platelets and clotting factors along with a high hematocrit will contribute towards significantly minimizing the postoperative loss of blood, and, consequently, the amount of blood requiring to be transfused. The possibility of elevation of the hematocrit allows for a lower hematocrit during bypass. This can achieve a considerable saving of donor blood, particularly in small children who invariably need blood added to the prime, making bloodless pediatric surgery a real possibility. The technique also minimizes the rise in total water in the body after cardiopulmonary bypass in children and promises favorably to alter the course of leaking capillaries as seen frequently in neonates and infants. It has been shown to improve hemodynamics at a crucial time when the patient has been weaned from cardiopulmonary bypass and needs optimum conditions for recovery. From the point of view of research, ultrafiltration offers a window to look at the inflammatory process induced by cardiopulmonary bypass.
It promises to be a valuable technique to investigate the elimination and possibly quantification of toxic metabolites produced during bypass. It also allows evaluation and assessment of different protocols for bypass, involving varying rates of flow and temperature, for their response to the production of these toxic metabolites, thus offering the potential to achieve a model of cardiopulmonary bypass which is as physiological as possible. With advances in the systems of perfusion, aided by computers, it should be possible to control the rate of ultrafiltration and precisely regulate the transfusion of the venous reservoir fluid with the aid of feedback loops from the venous and arterial pressures in the heart. This could make ultrafiltration an integral part of routine cardiopulmonary bypass.