Pulmonary blood flow during closed heart surgery. Use of a modified Qp/Qs ratio to assess adequacy of palliation of systemic-pulmonary artery shunts.

The ability to assess changes in pulmonary blood flow, using a modified Qp/Qs ratio (Qp/Qsmod), was evaluated in 12 infants with congenital heart disease and complete intracardiac mixing who underwent modified Blalock-Taussig shunt procedures. At the various measuring stages there were no major changes in mean arterial pressure or heart rate. Arterial oxygen tensions and saturation increased (P less than 0.01) and the arterial to end-tidal carbon dioxide difference (PaCO2-PE'CO2) was significantly reduced (P less than 0.001) after completion of the shunt procedure. There was a significant increase in mean Qp/Qsmod after chest closure (P less than 0.001), which was seen to correlate well with early clinical outcome. Two patients who did not demonstrate any increase in Qp/Qsmod over the course of the procedure had failed shunts. The limitations of use of the Qp/Qsmod are discussed. A modified Qp/Qs ratio of less than unity after surgery is strongly indicative of inadequate palliation.