Pro: The use of modified ultrafiltration during pediatric cardiac surgery is a benefit

Abstract

p EDIATRIC CARDIOPULMONARY BYPASS (CPB) often results in increased capillary permeability and accumulation of excess total-body water (TBW), which can lead to multiple organ system dysfunction. This morbidity is principally because of the hemodilution effects of CPB, as well as a systemic inflammatory response caused by the exposure of blood elements to the nonendothelialized surfaces of the CPB circuit. Organs most notably affected include the heart, lungs, and brain. Small children, long CPB times, hypothermia, and hemodihition are the greatest risk factors for the accumulation of excess water.1 Recently, modified ultrafiltration (MUF) has been used during pediatric cardiac surgery to limit the deleterious effects of CPB. The recognized benefits of MUF are multiple and include a reduction in the TBW accumulation seen after CPB; improvement of left ventricular (LV) function; an increase in hematocrit with a concomitant decrease in transfused blood products; an improvement in hemostasis, dynamic pulmonary compliance, and cerebral metabolic recovery after CPB with circulatory arrest; and modification of complement activation. Conventional ultrafiltration is a convective process in which substances with a molecular mass less than the membrane pore size are filtered because of a transmembrane gradient. This process, performed during the rewarming phase of CPB, is instituted in an attempt to decrease the excess TBW and edema seen in patients after CPB. The increase in TBW is believed to occur because of the relatively large volume of pump prime compared with the circulating blood volume, especially in small children. This increase in TBW is further aggravated by an increase in capillary permeability, which is believed to occur secondary to the inflammatory response initiated by exposure of the patient's blood elements to the foreign surface of the oxygenator and tubing. Theoretically, no fluid is transfused back to the patient to replace the volume removed by ultrafiltration. However, additional crystalloid or blood is often added to the circuit to maintain adequate volume in the reservoir and cardiopulmonary support while still on bypass. For these reasons, no consistent reduction in excess TBW or transfusion requirement has been shown with this method. MUF represents an alternative method of removing excess TBW, increasing the hematocrit, and improving vital organ function after CPB. MUF is performed after separation from