The A-aDO2 Rather Than the Fick Principle Can Be Used to Estimate the Right-to-left Shunt Fraction in Pulmonary Arteriovenous Malformation

Introduction: The quantification of right-to-left shunts (RLSs) in patients with a pulmonary arteriovenous malformation (PAVM) is important with respect to diagnosis and follow-up evaluations. Recently, RLSs are measured by lung perfusion scintigraphy (LPS). Coil embolization is recommended for first-line treatment of PAVMs, during which arterial and mixed venous blood sampling is readily available. Therefore, RLSs can be calculated by means of the Fick principle. Aims: The aim of this study was to determine the association between arterial and mixed venous blood gas analysis, RLSs calculated using the Fick principle, and RLSs measured by LPS. Methods: Fifty-six patients (mean age, 50.9 ± 20.9 y; 12 males) with proven PAVMs underwent LPS for measurement of the RLS fraction and arterial and mixed venous blood gas analysis prior to PAVM coil embolization from 2016-2020. The relationships between the RLS fraction by LPS, the RLS fraction calculated using the Fick principle ([98-SaO2]/[98-SvO2]), the alveolar-arterial oxygen difference (A-aDO2), and the arterial and mixed venous blood gas analysis were evaluated. Results: The RLS fraction as determined by LPS and the Fick principle were 9.48±3.14% and 14.38±8.09%, respectively. The A-aDO2 was 22.70±11.03mmHg. No correlation existed between the RLS fraction based on LPS and the Fick principle (r=0.184, P=0.178). In contrast, the A-aDO2, PaO2, and PaCO2 had a significant correlation between the RLS fraction measured by LPS (r=0.521 and P<0.0001, r=-0.264 and P=0.049, and r=-0.488 and P=0.0001, respectively). Conclusions: The A-aDO2 and PaCO2 can be substituted for the measurement of the RLS fraction by LPS.