IN THE ABSENCE of pulmonary disease, reduced systemic arterial oxygen saturation is usually accepted as evidence of a right-to-left intracardiac shunt in patients with congenital heart disease. However, several authors1-4 have reported reduced arterial oxygen saturations in both systemic arterial and pulmonary venous samples in some patients with large left-to-right shunts. They suggested that this was caused by rapid flow through dilated pulmonary channels, impaired diffusion resulting from a high pulmonary flow, or a bypass of the alveoli through precapillary shunts in such patients.
With one exception4 these workers employed methods which measured only oxygen content and saturation in assessing the right-to-left intrapulmonary shunts. Because of the conflicting opinions regarding such shunts investigated by relatively insensitive techniques, it was felt worthwhile to reevaluate them with modern polarographic measurements of oxygen tension.
Due to the shape of the blood oxygen dissociation curve, the current polarographic method of direct measurement