1559 THE ROLES OF PATENT FORAMEN OVALE SHUNT AND PATENT DUCTUS ARTERIOSUS SHUNT IN THE PATHOGENESIS OP RDS

Abstract

In order to study the role of right to left (Rt to Lt) PFO shunt and Lt to Rt PDA shunt in the pathogenesis of RDS, contrast echocardiography was performed in 23 newborns (m GA 32.3 wks, m BW 1690 gms) with RDS requiring mechanical ventilation and FiO2 of >40%. Shunts were studied daily using realtime 2D ultrasound (HP 77020) with 5 MHZ transducer. Two ml of normal saline was injected through umbilical venous (UV) line (tip in inferior vena cava) and umbilical arterial (UA) catheter (tip at T6 level) to produce echo contrast for PFO and PDA studies respectively. Rt to lt PFO shunt was present in 23/23 patients (100%) who required FiO2 >40%. The frequency of shunt decreased while FiO2 requirement decreased; i.e. 55% for FiO2 between 30-39% O2 and 0% for FiO2 40% and 40% O2. No simultaneous shunt was found when PiO2 was <30%. This study systematically and chronologically demonstrates the evidence of Rt to Lt shunt at PFO level (which results in hypoxemia through venous mixing) and also evidence of Lt to Rt shunt through PDA (which leads to increased pulmonary flow and resultant pulmonary edema). Both of these shunts at different levels through different mechanisms contribute to the pathogenesis of RDS.