THEORETICAL OPTIMIZATION OF PULMONARY-TO-SYSTEMIC FLOW RATIO AFTER A BIDIRECTIONAL CAVOPULMONARY ANASTOMOSIS

A univentricle with parallel pulmonary and systemic circulations is in herently inefficient because mixing of pulmonary and systemic venous r eturn occurs. Thus a cavopulmonary anastomosis is used as a staged pal liative procedure to reduce volume overload in patients with cyanotic congenital heart disease. On the basis of oxygen uptake and consumptio n, an equation was derived that related cardiac output, pulmonary veno us oxygen saturation, upper body oxygen consumption, and superior-to-i nferior vena caval blood flow ratio (Q(SVC)/Q(IVC)) to oxygen delivery . The primary findings were as follows. 1) As Q(SVC)/Q(IVC) increases, total body oxygen delivery and arterial and superior vena caval oxyge n saturations increase. 2) As Q(SVC)/Q(IVC) increases, lower body oxyg en delivery and inferior vena caval oxygen saturation initially increa se, then peals, and then decrease, 3) As the percentage of lower body oxygen consumption increases, oxygen delivery and saturation decrease, 4) A cavopulmonary anastomosis decreases the required cardiac output for a given oxygen delivery. Thus we concluded that a high systemic ar terial oxygen saturation after cavopulmonary anastomosis requires a hi gh percentage of upper body oxygen consumption and a high Q(SVC)/Q(IVC ) and that the cavopulmonary anastomosis reduces the volume load on th e single ventricle.