Variability of right-sided cardiac oxygen saturations in adults with and without left-to-right intracardiac shunting

In many catheterization laboratories and intensive care units, oxygen saturation of single blood specimens is measured from the superior vena cava (SVC), right atrium (RA) and pulmonary artery (PA) during right-sided catheterization, but variability of such single measurements in adults with and without intracardiac left-to-right shunting has not been assessed. Oxygen saturation of SVC, RA and PA single blood samples were measured in 1,031 adults (524 men, 507 women, aged 50 ± 13 years [mean ± standard deviation SD]). In the 980 patients without shunting, differences in saturation between SVC and RA, RA and PA and SVC and PA were 3.9 ± 2.4%, 2.3 ± 1.7%, and 4.0 ± 2.5%, respectively, so that the normal limits of variability (mean ± 2 standard deviations) for these saturation differences were 8.7%, 5.7% and 9.0%, respectively. Of the 51 patients with left-to-right shunting, these limits of variability of oxygen saturation correctly identified 46 (90%), and the 5 with shunting whose saturation differences were below these limits had small shunts ( Qp Qs ratios of 1.9 or less). Thus, assessment of oxygen saturation from single blood specimens obtained from the SVC, RA and PA offers excellent sensitivity (more than 90%), specificity (94 to 95%) and predictive accuracy (94% or more) in identifying patients with and without intracardiac left-to-right shunting. The sensitivity of these limits is especially high in patients with large shunts ( Qp Qs of 2 or more).