Ann Thorac Surg 2005;80:28
© 2005 The Society of Thoracic Surgeons
Original article: Cardiovascular
Invited commentary
Ko Bando, MD
Department of Cardiovascular Surgery, National Cardiovascular Center, 5-7-1 Fujishirodai, Suita, Osaka, 565-8565 Japan
(Email: kobando{at}hsp.ncvc.go.jp).
Cardiopulmonary bypass (CPB) in children is associated with the accumulation of water as a consequence of an inflammatory capillary leak. That increase in total body water is associated with tissue edema and subsequent organ dysfunction, particularly in the heart, lungs, and brain. Modified ultrafiltration (MUF) was designed to reduce these adverse effects of CPB. Previous studies have shown that MUF after CPB in children decreases body water, removes inflammatory mediators, and improves hemodynamics.
Rodriguez and associates investigated the effects of different blood flow rates during arteriovenous modified ultrafiltration on the cerebral hemodynamics of children with weights of more than and less than 10 kg. Their study indicates that high blood flow rates through the ultra-filter during arteriovenous MUF in small infants (< 10 kg) decrease cerebral blood flow velocities and transcranial mixed venous oxygen saturations compared with the use of lower blood flow rates in older children. They indicated that a possible explanation for these effects is that the MUF circuit produces an increased diastolic runoff from the aorta that steals flow from the cerebral circulation. The authors should be congratulated for bringing this important new observation to the literature.
This adverse effect may be one of the potential disadvantages of an arteriovenous MUF system. Other possible disadvantages of this system include: (1) the potential for air entrainment at the aortic cannulation site, (2) limitations of flow due to the aortic size, (3) significant arterial to venous shunts, and (4) difficulty in maintaining desired filling pressure, temperature, and blood oxygen saturation. Using a veno-venous MUF system, these potential disadvantages of arteriovenous MUF can be avoided.
As the authors have correctly pointed out, further study is necessary to determine what constitutes an adequate flow based on the patient’s body size. I would add that comparing the impact of veno-venous versus arteriovenous MUF on cerebral blood flow and cognitive function may also be important.
