Author: Michael A. Evans, MD – Ann & Robert H. Lurie Children’s Hospital of Chicago, Northwestern Feinberg School of Medicine


A 6-month-old infant with a history of perimembranous ventricular septal defect (VSD) undergoes VSD closure on cardiopulmonary bypass (CPB). After separating from CPB, additional residual muscular VSDs are demonstrated on transesophageal echocardiography (TEE).


In order to ascertain the hemodynamic significance of the residual VSDs, calculation of the ratio of pulmonary flow to systemic flow (Q_p:Q_s) is necessary. The table below demonstrates data from a venous and arterial blood gases. The surgeon also obtains pulmonary arterial blood from the field, which yields a saturation of 85% on blood gas analysis.





Assuming no pulmonary venous desaturation, which of the following BEST represents the Q_p:Q_s in this patient?