Safe limit of hemodilution in cardiopulmonary bypass -comparative analysis between cyanotic and acyanotic congenital heart disease.

A safe limit of hemodilution in cardiopulmonary bypass (CPB) for open heart surgery was investigated by analyzing of the perfusion results of 100 patients with tetralogy of Fallot (TOF) and ventricular septal defect (VSD). The higher perfusion flow was necessary to compensate for the reduced oxygen carrying capacity and to maintain adequate arterial pressure in proportion to the increase in hemodilution. Once the dilution ratio reached over 40% in TOF and 50% in VSD, however, adequate oxygen transfer and stable hemodynamic conditions could not be maintained. The former was due to inadequate oxygen delivery and the latter to an impaired venous return. In these cases, various complications caused by residual diluent in the body space despite of extensive diuretic therapy occurred immediately postop. The safe limit of hemodilution is 50%. However, that of cyanotic disease, even in the presence of remarkable polycythemia, must be limited to less than 40%.