Author: Sana Ullah, MB ChB, FRCA – Dallas, TX


An 8-month-old male infant is status post repair of a large perimembranous ventricular septal defect (VSD). After separation from cardiopulmonary bypass, the patient has the following vital signs: heart rate 130, blood pressure 80/45, and pulse oximetry 99% with a fractional inspired oxygen (FiO₂) of 0.25. The post-repair transesophageal echocardiogram (TEE) reveals a small residual VSD. In order to determine if the VSD is hemodynamically significant, the surgeon samples blood from the superior vena cava (SVC) and the main pulmonary artery (PA), resulting in oxygen saturations of 60% and 80% respectively. What is the Qp:Qs?