Left-to-right shunt assessed by thermodilution during surgery for congenital heart disease

In nine children with congenital heart defects, left-to-right shunting was assessed during open-heart surgery by injecting cold 5% glucose solution through a left atrial line and detecting temperature change with a pulmonary arterial thermistor. The shunt was quantified by recording the temperature after injecting the same amount of cold glucose solution also through a central venous line. Oximetric determination of the left-to-right shunt was used as a reference. The result was expressed as shunt flow divided by pulmonary blood flow (Qshunt/Qp). The regression equation then obtained was Qshunt/Qp by thermodilution = 0.05 + 0.87 x Qshunt/Qp by oximetry. The residual standard deviation around the line of regression was 0.03. The thermodilution technique can be used for rapid assessment of the presence and magnitude of left-to-right shunting, provided that there is opportunity for the indicator to mix adequately in the main blood stream before shunting occurs.