Possible underestimation of Shunt Fraction in the Hepatopulmonary Syndrome

Abstract

Estimating the right-to-left shunt fraction with standard equations can be useful for outpatient assessment and management of patients with the hepatopulmonary syndrome. However, because the patient's true arteriovenous oxygen content difference cannot be measured without invasive techniques, available equations for use in outpatient settings often assume a value of 5 mL/dL. This article examines the degree to which assuming a value of 5 mL/dL for the arteriovenous oxygen content difference causes calculated values of the percent shunt to underestimate true values. Such underestimation can be misleading in clinical conditions such as the hepatopulmonary syndrome, in which the hyperdynamic circulation may be associated with actual values of the arteriovenous oxygen content difference that are < 5 mL/dL.